Spawn (biology)
Encyclopedia
Spawn refers to the egg
s and sperm released or deposited, usually into water, by aquatic animal
s. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning. Most aquatic animals, apart from aquatic mammal
s, reproduce through a process of spawning.
Spawn consists of the reproductive cells (gamete
s) of aquatic animals, some of which will become fertilized and produce offspring. The process of spawning typically involves females releasing ova
(unfertilized eggs) into the water, often in large quantities, while males simultaneously or sequentially release spermatozoa (milt
) to fertilize the eggs.
Most fish reproduce by spawning, and so do most other aquatic animals, including crustacean
s such as crabs and shrimps, molluscs such as oysters and squid, echinoderm
s such as sea urchins and sea cucumbers, amphibious animals such as frogs and turtles, aquatic insects such as mayflies and mosquitoes, and coral
s (which are small aquatic animals and not plants). Fungi, such as mushrooms, are also said to "spawn" a white fibrous matter that forms the matrix from which they grow.
There are many variations in the way spawning occurs, depending on sexual differences in anatomy, on how the sexes relate to each other, on where and how the spawn is released, and on whether or how the spawn is subsequently guarded.
Marine animals, and particularly bony fish, commonly reproduce by broadcast spawning. This is an external method of reproduction where the female releases many unfertilised eggs into the water. At the same time, a male or many males release a lot of sperm into the water which fertilises some of these eggs. The eggs contain a drop of nutrient oil to sustain the embryo as it develops inside the egg case. The oil also provides buoyancy, so the eggs float and drift with the current. The strategy for survival of broadcast spawning is to disperse the fertilised eggs, preferably away from the coast into the relative safety of the open ocean. There the larvae
develop as they consume their fat stores, and eventually hatch from the egg capsule into miniature versions of their parents.
To survive, they must then become miniature predators themselves, feeding on plankton. Fish eventually encounter others of their own kind (conspecifics), where they form aggregations and learn to school.
Internally, the sexes of most marine animals can be determined by looking at the gonad
s. For example, male testes of spawning fish are smooth and white and account for up to 12% of the mass of the fish, while female ovaries
are granular and orange or yellow, accounting for up to 70% of the fish's mass. Male lampreys, hagfish and salmon discharge their sperm into the body cavity where it is expelled through pores in the abdomen. Male shark
s and rays
can pass sperm along a duct into a seminal vesicle
, where they store it for a while before it is expelled, while teleosts usually employ separate sperm ducts.
Externally, many marine animals, even when spawning, show little sexual dimorphism
(difference in body shape or size) or little difference in colouration
. Where species are dimorphic, such as sharks or guppies
, the males often have penis-like intromittent organ
s in the form of a modified fin.
A species is semelparous if its individuals spawn only once in their lifetime, and iteroparous if its individuals spawn more than once. The term semelparity comes from the Latin
semel, once, and pario, to beget, while iteroparity comes from itero, to repeat, and pario, to beget.
Semelparity is sometimes called "big bang" reproduction, since the single reproductive event of semelparous organisms is usually large and fatal to the spawners. The classic example of a semelparous animal is the Pacific salmon, which lives for many years in the ocean before swimming to the freshwater stream of its birth, spawning, and then dying. Other spawning animals which are semelparous include mayflies
, squid
, octopus
, smelt, capelin
and some amphibians. Semelparity is often associated with r-strategists
. However, most fish and other spawning animals are iteroparous.
When the internal ovaries
or egg masses of fish and certain marine animals are ripe for spawning they are called roe
. Roe from certain species, such as shrimp
, scallop
, crab
and sea urchin
s, are sought as human delicacies in many parts of the world. Caviar
is a name for the processed, salted roe of non-fertilized sturgeon
. The term soft roe or white roe denotes fish milt
. Lobster roe is called coral because it turns bright red when cooked. Roe (reproductive organs) are usually eaten either raw or briefly cooked.
"The reproductive behaviour of fishes is remarkably diversified: they may be oviparous (lay eggs), ovoviparous (retain the eggs in the body until they hatch), or viviparous (have a direct tissue connection with the developing embryos and give birth to live young). All cartilaginous fishes—the elasmobranches (e.g., sharks, rays, and skates)—employ internal fertilization and usually lay large, heavy-shelled eggs or give birth to live young. The most characteristic features of the more primitive bony fishes is the assemblage of polyandrous (many males) breeding aggregations in open water and the absence of parental care..."
There are two main reproduction methods in fish. The first method is by laying eggs and the second by live-bearing (producing their young alive).
Monogamy occurs when one male mates with one female exclusively. This is also called pair spawning. Most fish are not monogamous, and when they are, they often alternate with non-monogamous behaviours. Monogamy can occur when feeding and breeding grounds are small, when it is difficult for fish to find partners, or when both sexes look after the young. Many tropical cichlid
s, which rear their young together in locations where they must fiercely defend against competitors and predators are monogamous. "In some pipefish
es and seahorse
s, development of eggs takes a long time before the female can place them in the brood pouch of a male, where they are fertilized. While the male is pregnant, the female starts a new batch of eggs, which are ready at about the same time that the male gives birth to the young from the previous mating. This close timing of development promotes monogamy, especially if the likelihood of encountering another potential mate is low.
Polygyny
occurs when one male gets exclusive mating rights with multiple females. In polygyny a large conspicuous male usually defends females from other males or defends a breeding site. The females choose large males that are successfully defending prime breeding sites which the females find attractive. For example, sculpin
males defend "caves" underneath rocks which are suitable for the incubation of embryos.
Another way males get to mate with several females is through the use of leks. Leks are places where many fish come together, and the males display to each another. Based on these displays, each female then selects the male they want to be their mate. For example, among the cichlid Cyrtocara eucinostomus in Lake Malawi
, up to 50,000 large and colourful males display together on a lek four kilometres long. The females, which are mouth brooders, choose which male they want to fertilize their eggs.
Polyandry occurs when one female gets exclusive mating rights with multiple males. This is not common, but it does happen among fish like clownfish
that change their sex. It can also happen when males do the brooding but can cannot handle all the eggs the female produce, such as with some pipefish
.
The males in some deep sea anglerfish
es are much smaller than the females. When they find a female they bite into her skin, releasing an enzyme
that digests the skin of their mouth and her body and fusing the pair down to the blood-vessel level. The male then slowly atrophies
, losing first his digestive organs, then his brain, heart, and eyes, ending as nothing more than a pair of gonads, which release sperm
in response to hormones in the female's bloodstream indicating egg
release. This extreme sexual dimorphism
ensures that, when the female is ready to spawn, she has a mate immediately available. A single anglerfish female can "mate" with many males in this manner.
Polygynandry
occurs when multiple males mate indiscriminately with multiple females. This mutual promiscuity is the approach most commonly used by spawning animals, and is perhaps the "original fish mating system." Common examples are forage fish
, such as herring
s, which form huge mating shoals
in shallow water. The water becomes milky with sperm and the bottom is draped with millions of fertilized eggs.
Alternate male strategies which allow small males to engage in cuckoldry can develop in species where spawning is dominated by large and aggressive males. Cuckoldry is a variant of polyandry, and can occur with sneak spawners (sometimes called streak spawners). A sneak spawner is a male that rushes in to join the spawning rush of a spawning pair. A spawning rush occurs when a fish makes a burst of speed, usually on a near vertical incline, releasing gametes at the apex, followed by a rapid return to the lake or sea floor or fish aggregation. Sneaking males do not take part in courtship. In salmon and trout, for example, jack males are common. These are small silvery males that migrate upstream along with the standard, large, hook-nosed males and that spawn by sneaking into redds to release sperm simultaneously with a mated pair. This behaviour is an evolutionarily stable strategy
for reproduction, because it is favoured by natural selection just like the "standard" strategy of large males.
Cuckoldry occurs in many fish species, including parrotfish
es and wrasses on tropical reefs and the bluegill
sunfish in fresh water. Sneaker males that becomes too large to hide effectively become satellite males. With bluegill sunfish, satellite males mimic the behaviour and colouration of the females. They hover over a nest containing a pair of courting sunfish, and gradually descend to reach the pair just as they spawn. "Both sneaker and satellite males are usually badly chewed up by irate parental males by the end of the spawning season, but their strategy is nevertheless a successful one (giving them high fitness). Because these smaller males do not have to spend any energy on parental care, they can spawn at a much younger age than the parental males. Parental males may be 6 or 7 years old before they are large enough to compete successfully for the best nest sites, but the sneaker and satellite males may be only 2 or 3 years old."
, where each individual in a species is either male or female, and remains that way throughout their lives. Most fish are gonochorists, but hermaphroditism is known to occur in 14 families of teleost fishes. "Hermaphrodites can be either synchronous, in which individuals possess both ovarian and testicular tissue, or sequential, in which individuals change sex. Synchronous hermaphrodites are uncommon. Among the best studied is the black hamlet
, a species in which individuals take turns releasing sperm and eggs during spawning. Because such egg trading is advantageous to both individuals, hamlets are typically monogamous for short periods of time–an unusual situation in fishes. The most common pattern, known as Synchronous hermaphroditism, is for a female to change into a male (protogyny). This often happens when a large, dominant male controlling a harem of females is removed by a predator. Within a few days, the largest female in the harem becomes a dominant male and takes over the missing male's function. This pattern is common in coral reef fishes, such as parrotfish
es, wrasses, and grouper
s. Less common than protogyny is protandry, in which a male converts to a female."
The sex of many fishes is not fixed, but can change with physical and social changes to the environment where the fish lives. "Sex change
occurs mainly in fishes in which one sex had higher survival and reproductive rates, usually as the result of larger size. In such situations it may pay for an individual of the smaller sex to change to the larger sex when the opportunity arises. For example anemone fishes live as monogamous pairs in single anemone
s, protected from predators by the stings of the anemone. Female anemone fish are typically larger than males, because a male does not have to vigorously compete for mates once he has paired with a female. If the female dies, however, a juvenile anemone fish quickly moves in; such fish are always male. The resident male then turns into a female and reproductive advantages of the large female–small male combination continue. In some fishes, sex change is reversible, depending on the social situation. Thus some gobbies
will switch sex when kept in what initially were single sex groups of either sex."
, a minnow found in several river basins in Portugal and Spain, appears to be an all-male species. The existence of this species illustrates the potential complexity of mating systems in fish. The species originated as a hybrid between two species, and is diploid, but not hermaphroditic. It can have triploid and tetraploid forms, including all-female forms that reproduce mainly through hybridogenesis.
It is rare to find true parthenogenesis
in fishes, where females produce female offspring with no input from males. All-female species include the Texas silverside
, Menidia clarkhubbsi as well as a complex of Mexican mollies
. Parthenogenesis has been recently observed in hammerhead shark
s and blacktip shark
s. It is also known to occur in crayfish and amphibians.
. This classification is based on how the eggs are fertilized (internal or external spawners), where the eggs are deposited (pelagic or benthic spawners), and whether and how the parents look after the eggs after spawning (bearers, guarders and nonguarders).
without complex courtship rituals, and males outnumber females.
s build nests out of piles of stones rather than dig holes. The minnow males have tubercle
s on their head and body which they use to help them defend the nest site.
Bitterling
s have a remarkable reproduction strategy where parents transfer responsibility for the care of their young to mussel
s. The female extends her ovipositor
into the mantle cavity of the mussel and deposits her eggs between the gill filaments. The male then ejects his sperm into the mussel's inhalant water current and fertilization takes place within the gills of the host. The same female may use a number of mussels, and she deposits only one or two yellow, oval eggs into each. Early developmental stages are protected from predation within the body of the mussel. After 3 to 4 weeks larvae swim away from the host to continue life on their own.
Territorial behaviour is generally necessary for guarders, and the embryos are almost always guarded by males (apart from cichlids). There is a need to be territorial because looking after embryos usually includes defending the site where they are being looked after. It also often means there is competition for the best egg-laying sites. Elaborate courtship behaviour is usual among guarders.
Guarding males keep the embryos safe from predators, keep oxygen levels high by fanning water currents, and keep the area free from dead embryos and debris. They protect the embryos until they hatch, and often look after the larval stages as well. The time spent guarding can range from a few days to several months.
es (Centrarchidae
) construct nests of this sort, often in colonies. The males defend the embryos and the young until the young become too active to be kept in the nest. In some cichlids eggs are laid and incubated in one nest depression, but the young are tended (by both parents) in one or more additional depressions that are constructed nearby."
"A few species construct nests on sandy bottoms. Either the eggs and embryos in such nests have special adaptations (e.g., semibuoyancy) to reduce the possibility of being smothered, or the parent fish must spend considerable time handling them."
"In areas where bottoms are muddy, nest-building fish commonly build nests of plant material. Usually plant-nesting fishes construct loose aggregations of material in which the eggs are laid. One special type of plant-nest builder uses a kidney secretion to glue the pieces of plant together to form a tight nest. The main examples of this type of nesting are the stickleback
s in which the male builds a tube which is usually attached to rooted plants or is placed in a small pit. By means of a complicated courtship ritual, a female is enticed into a nest, where she deposits some eggs after being nudged by the male. After the eggs are laid, he chases the female out and fertilizes them. This process is repeated several times, until enough embryos are in the nest and the male begins to incubate them by fanning currents of water across them. After the embryos hatch, the male guards the young for several days, first in the nest, and then in a shoal outside the nest."
"Perhaps the most common type of nests among fishes are those in caves, cavities, or burrows. These nests are characteristic of fish that live in active habitats, such as rocky intertidal zone or streams. For stream-dwelling fishes, the typical cave nest is the underside of a flat rock in midstream, which has plenty of current to keep the water well oxygenated. Sculpin
s and many darter
s deposit their eggs in clusters on the roofs of such shelters and then guard the embryos until they hatch. In quieter water, minnows, such as the fathead minnow
, lay their eggs on the underside of a log or a board in an area that has been cleaned off by the male. Spawning males develop a thick horny pad on their head, which is used for rubbing algae and other materials of the spawning surface. Many large catfish
es lay their eggs in cavities ranging from hollow logs to old muskrat burrows to oil drums, where the embryoes are guarded by the males. These catfish also guard schools of young for one or more weeks after they emerge from the nest."
es and seahorse
s. In this family, only the males do the brooding. After the eggs are fertilized, the female places the embryos on the male. Herald (1950) notes a continuum of forms in the Syngnathidae
, starting with skin-brooding pipefishes and ending with seahorses, which have closed pouches with only one opening. In seahorses, after an extended courtship period, the female deposits eggs in the pouch (marsupium
) of the male by means of a penis-like oviduct
. The eggs are fertilized as they enter the marsupium, and 25 to 100 embryos are provided with nutrients, oxygen and protection (Jones and Avise 1997). After hatching, the free embryos are carried in the pouch until they are capable of fairly active swimming, at which time they are expelled by the brooding male."
"Another way of internally carrying young that are spawned externally is found in mouth brooders. This method is found in families as diverse as sea catfishes
, cichlid
s, cardinal fishes and bonytongues. Mouthbrooders carry the large, yolky embryos until they hatch, and these brooders typically carry the free embryos about as well. Even after the young become active, they are usually closely associated with the parent fish for a period of time and may flee back into the mouth cavity when threatened. In chchilids, both sexes may participate in some species, but the female usually carries the embryos, which she picks up quickly after spawning."
Mouth brooders
- carry eggs or larvae in their mouth. Mouth brooders can be ovophile
s or larvophiles. Ovophile or egg-loving mouth-brooders lay their eggs in a pit, which are sucked up into the mouth of the female. The small number of large eggs hatch in the mother's mouth, and the fry remain there for a period of time. Fertilization often occurs with the help of egg-spots, which are colorful spots on the anal fin of the male. When the female sees these spots, she tries to pick up the egg-spots, but instead gets a mouthful of sperm, fertilizing the eggs in her mouth. Many cichlids and some labyrinth fish are ovophile mouthbrooders. Larvophile or larvae-loving mouth-brooders lay their eggs on a substrate and guard them until the eggs hatch. After hatching, the female picks up the fry and keeps them in her mouth. When the fry can fend for themselves, they are released. Some eartheaters are larvophile mouthbrooders.
and a few bony fish. There seems to be no strong correlation between internal bearing families and the elaborateness of courtship behaviour. In guppies, mosquitofish
and other livebearing poeciliids. the most important trait of the courtship behaviour of males that successfully copulate with females seems to be persistence (although subtle interactions among competing males and other courtship-related behaviour do exist). In contrast, some surfperches have fairly elaborate courtship behaviour, with males establishing breeding territories to attract passing females."
Facultative internal bearers: The beginning of the evolutionary process of livebearing starts with facultative
(optional) internal bearing. The process occurs in several species of oviparous (egg-laying) killifish
es which spawn in the normal way on the substrate, but in the process accidentally fertilize eggs which the female retains and does not spawn. These eggs are spawned later, usually without allowing much time for embryonic development.
Obligate internal bearers: The next step in the evolution of livebearing is obligate
(by necessity) internal bearing, where the female retains all the embryos. "The only source of nutrition for these embryos, however, is the egg yolk, as in externally spawned eggs. This situation, also referred to as ovoviviparity
, is characteristic of marine rock fishes and the Lake Baikal sculpin
s. This strategy allows these fish to have fecundities approaching those of pelagic fish with external fertilization, but it also enables them to protect the young during their most vulnerable stage of development. By contrast, sharks and rays using this strategy produce a relatively small number of embryos and retain them for a few weeks to 16 months or longer. The shorter times spans are characteristic of species that eventually deposit their embryos in the environment, surrounded by a horny capsule; whereas the longer periods are characteristic of sharks that retain the embryos until they are ready to emerge as actively swimming young."
Viviparous fish: "Given the advantages of retaining the embryos internally, it is not surprising that a number of fishes have developed means to provide additional nutrition for their young while the female is carrying them and then give birth to large, active young (viviparity). Viviparous fishes provide nutrition for their young in various ways. The greatest variety is found in the sharks, but the teleosts also show a considerable range of methods. In the superperches, the young develop in the mother's ovary and obtain nutrients through the close contact of the extra-large fins with the ovarian wall. Many poeciliid embryos have highly vascular pericardial tissue that loops around the neck and is in close contact with the ovarian wall of the mother, through which nutrients are exchanged."
However, some fish do not fit these categories. The livebearing largespring gambusia
(Gambusia geiseri) was thought to be ovoviviparous until it was shown in 2001 that the embryos received nutrients from the mother.
Spawning grounds are the areas of water where aquatic animals spawn, or produce their eggs. After spawning, the spawn may or may not drift to new grounds which become their nursery grounds. Many species undertake migrations
each year, and sometimes great migrations, to reach their spawning grounds. For example, lakes and river watersheds can be major spawning grounds for anadromous fish such as salmon
. These days, it is often necessary to construct fish ladder
s and other bypass systems so salmon can navigate their way past hydroelectric dams on their way to spawning grounds. Coastal fish
often use mangrove
s and estuaries as spawning grounds, while reef fish
can find adjacent seagrass meadows that make good spawning grounds. Short-finned eel
s can travel anything up to three or four thousand kilometres to their spawning ground in deep water somewhere in the Coral Sea
.
Forage fish
often make great migrations between their spawning, feeding and nursery grounds. Schools of a particular stock usually travel in a triangle between these grounds. For example, one stock of herrings have their spawning ground in southern Norway
, their feeding ground in Iceland
, and their nursery ground in northern Norway. Wide triangular journeys such as these may be important because forage fish, when feeding, cannot distinguish their own offspring.
Capelin
are a forage fish of the smelt family found in the Atlantic
and Arctic
oceans. In summer, they graze on dense swarms of plankton
at the edge of the ice shelf. Larger capelin also eat krill
and other crustacean
s. The capelin move inshore in large schools to spawn and migrate in spring and summer to feed in plankton rich areas between Iceland
, Greenland
, and Jan Mayen
. The migration is affected by ocean current
s. Around Iceland maturing capelin make large northward feeding migrations in spring and summer. The return migration takes place in September to November. The spawning migration starts north of Iceland in December or January.
The diagram on the right shows the main spawning grounds and larval drift routes. Capelin on the way to feeding grounds is coloured green, capelin on the way back is blue, and the breeding grounds are red. In a paper published in 2009, researchers from Iceland recount their application of an interacting particle model to the capelin stock around Iceland, successfully predicting the spawning migration route for 2008.
Referred to as "the greatest shoal
on earth", the sardine run
occurs when millions of sardine
s migrate from their spawning grounds south of the southern tip of Africa northward along the Eastern Cape coastline. Chinook salmon
make the longest freshwater migration of any salmon, over 3000 kilometres (1,864.1 mi) up the Yukon River
to spawning grounds upstream of Whitehorse
, Yukon. Some green sea turtle
s swim more than 2600 kilometres (1,615.6 mi) to reach their spawning grounds.
Goldfish
Goldfish
, like all cyprinid
s, are egg-layers. They usually start breeding after a significant temperature change, often in spring. Males chase females, prompting them to release their eggs by bumping and nudging them. As the female goldfish spawns her eggs, the male goldfish stays close behind fertilizing them. Their eggs are adhesive and attach to aquatic vegetation. The eggs hatch within 48 to 72 hours. Within a week or so, the fry begins to assume its final shape, although a year may pass before they develop a mature goldfish colour; until then they are a metallic brown like their wild ancestors. In their first weeks of life, the fry grow quickly—an adaptation born of the high risk of getting devoured by the adult goldfish.
Carp
A member of the Cyprinidae family, carp spawn in times between April and August, largely dependant upon the climate and conditions they live in. Oxygen levels of the water, availability of food, size of each fish, age, number of times the fish has spawned before and water temperature are all factors known to effect when and how many eggs each carp will spawn at any one time.
Siamese fighting fish
Prior to spawning, male Siamese fighting fish
build bubble nest
s of varying sizes at the surface of the water. When a male becomes interested in a female, he will flare his gills, twist his body, and spread his fins. The female darkens in colour and curves her body back and forth. The act of spawning takes place in a "nuptial embrace" where the male wraps his body around the female, each embrace resulting in the release of 10-40 eggs until the female is exhausted of eggs. The male, from his side, releases milt
into the water and fertilization takes place externally. During and after spawning, the male uses his mouth to retrieve sinking eggs and deposit them in the bubble nest (during mating the female sometimes assists her partner, but more often she will simply devour all the eggs that she manages to catch). Once the female has released all of her eggs, she is chased away from the male's territory, as it is likely that she'll eat the eggs due to hunger. The eggs then remain in the male's care. He keeps them in the bubble nest, making sure none fall to the bottom and repairing the nest as needed. Incubation lasts for 24–36 hours, and the newly hatched larvae remain in the nest for the next 2–3 days, until their yolk sacs are fully absorbed. Afterwards the fry leave the nest and the free-swimming stage begins.
Copepods
Copepod
s are tiny crustacean
s which usually reproduce either by broadcast spawning or by sac spawning. Broadcasting copepods scatter their eggs into the water, but sac spawners lay their eggs into an ovigerous sac. Sac spawners spawn few but relatively large eggs that develop slowly. By contrast, broadcast spawners spawn numerous small eggs that develop rapidly. However, the shorter hatch times that result from broadcasting are not short enough to compensate for the higher mortality compared to sac spawners. To produce a given number of hatched eggs, broadcasters must spawn more eggs than sac spawners.
Spiny lobsters
After mating, the fertilized eggs of the California spiny lobster
are carried on the female's pleopods until they hatch, with between 120,000 and 680,000 carried by a single female. The eggs begin coral red, but darken as they develop to a deep maroon. When she is carrying the eggs, the female is said to be "berried". The eggs are ready to hatch after 10 weeks, and spawning takes place from May to August,> The larva
e that hatch (called phyllosoma
larvae) do not resemble the adults. Instead, they are flat, transparent
animals around 14 mm (0.551181102362205 in) long, but as thin as a sheet of paper. The larvae feed on plankton
, and grow through ten molts
into ten further larval stages, the last of which is around 30 millimetre long. The full series of larval molts takes around 7 months, and when the last stage molts, it metamorphoses
into the puerulus state, which is a juvenile
form of the adult, though still transparent. The puerulus larvae settle to the sea floor when the water is near its maximum temperature, which in Baja California is in the fall.
Egg-bearing female lobster
s migrate inshore from deeper waters to hatch their eggs, though they do not have specific spawning grounds. These lobster migrations can occur in close single-file formation "lobster trains".
Oysters are broadcast spawners, that is, eggs and sperm are released into open water where fertilisation occurs. They are protandric; during their first year they spawn as males by releasing sperm
into the water. As they grow over the next two or three years and develop greater energy reserves, they spawn as females by releasing eggs
. Bay oysters usually spawn by the end of June. An increase in water temperature prompts a few oysters to spawn. This triggers spawning in the rest, clouding the water with millions of eggs and sperm. A single female oyster can produce up to 100 million eggs annually. The eggs become fertilized in the water and develop rapidly into planktonic larva
e. which eventually find suitable sites, such as another oyster's shell, on which to settle. Attached oyster larvae are called spat. Spat are oysters less than 25 millimetre (0.984251968503937 in) long.
The Pacific oyster
usually has separate sexes. Their sex can be determined by examining the gonad
s, and it can change from year to year, normally during the winter months. In certain environmental conditions, one sex is favoured over the other. Protandry
is favoured in areas of high food abundance and protogyny occurs in areas of low food abundance. In habitats with a high food supply, the sex ratio
in the adult population tends to favour females, and areas with low food abundances tend to have a larger proportion of male adults. Spawning in the Pacific oyster occurs at 20 °C (68 °F). This species is very fecund
, with females releasing about 50–200 million eggs in regular intervals (at a rate of 5–10 times a minute) in a single spawning. Once released from the gonad
s, the eggs move through the suprabranchial chambers (gill
s), are then pushed through the gill
ostia into the mantle chamber, and are finally released in the water, forming a small cloud. In males, the sperm is released at the opposite end of the oyster, along with the normal exhalent stream of water. A rise in water temperature is thought to be the main cue in the initiation of spawning, as the onset of higher water temperatures in the summer results in earlier spawning in the Pacific oyster.
The larvae
of the Pacific oyster are planktotrophic
, and are about 70 µm at the prodissoconch
1 stage. The larvae
move through the water column via the use of a larval foot to find suitable settlement locations. They can spend several weeks at this phase, which is dependent on water temperature, salinity and food supply. Over these weeks, larvae
can disperse great distances by water currents before they metamorphose
and settle as small spat
. Similar to other oyster species
, once the Pacific oyster larvae
find a suitable habitat
, they attach to it permanently using cement secreted from a gland in their foot. After settlement, the larvae metamorphose into juvenile spat. The growth rate is very rapid in optimum environmental conditions, and market size can be achieved in 18 to 30 months.
Cephalopods
Cephalopod
s, such as squid and octopuses, have prominent heads and a set of arms (tentacle
s) modified from the primitive foot of molluscs. All cephalopods are sexually dimorphic
. However, they lack external sexual characteristics, so they use colour communication. A courting male approaches a likely looking mate flashing his brightest colours, often in rippling displays. If the other cephalopod is female and receptive, her skin will change colour to become pale, and mating will occur. If the other cephalopod remains brightly coloured, it is taken as a warning.
All cephalopods reproduce by spawning egg
s. Most cephalopods use semi-internal fertilization where the male places his gametes inside the female's mantle cavity to fertilize the ova
in the female's single ovary
. The "penis" in most male cephalopods is a long and muscular end of the gonoduct used to transfer spermatophores to a modified sperm-carrying arm called a hectocotylus
. That in turn is used to transfer the spermatophores to the female. In species where the hectocotylus is missing, the "penis" is long and able to extend beyond the mantle cavity and transfers the spermatophores directly to the female. In many cephalopods, mating occurs head to head and the male may simply transfer sperm to the female. Others may detach the sperm-carrying arm and leave it attached to the female. Deep water squid have the greatest known penis length relative to body size of all mobile animals, second in the entire animal kingdom only to certain sessile barnacle
s. Penis elongation in the greater hooked squid
may result in a penis that is as long as the mantle, head and arms combined.
Some species brood their fertilized eggs: female paper nautilus construct shelters for the young, while Gonatiid squid carry a larva-laden membrane from the hooks on their arms. Other cephalopods deposit their young under rocks and aerate them with their tentacles hatching. Mostly the eggs are left to their own devices; many squid lay sausage-like bunches of eggs in crevices or occasionally on the sea floor. Cuttlefish
lay eggs separately in cases and attach them to coral or algal fronds. Like Pacific salmon, cephalopods are mostly semelparous, spawning many small eggs in one batch and then dying. Cephalopods usually live fast and die young. Most of the energy extracted from their food is used for growing, and they mature rapidly to their adult size. Some gain as much as 12% of their body mass each day. Most live for one to two years, reproducing and then dying shortly thereafter.
Echinoderm
s are marine animals, widespread in all oceans, but not found in fresh water. Just below their skin is an endoskeleton
composed of calcareous
plates or ossicles.
Sea urchins
Sea urchin
s are spiky echinoderms with spherical bodies which usually contain five gonad
s. They move slowly, feed mostly on seaweed
, and are important for the diet of sea otter
s. Sea urchins are dioecious
, having separate male and female sexes, although there is generally no easy way to distinguish the two. The gonads are lined with muscles underneath the peritoneum
, and these allow the animal to squeeze its gamete
s through the duct and into the surrounding sea water, where fertilization takes place. Their roe
(male and female gonads) is soft and melting, with a colour ranging from orange to pale yellow, and is sought after as a human delicacy in many parts of the world.
Sea cucumbers
Sea cucumber
s are leathery echinoderms with elongated bodies which contain a single, branched gonad. They are found on the sea floor worldwide, and occur in great numbers on the deep sea floor where they often make up the majority of the animal biomass
. They feed on plankton
and decaying organic debris found at the sea bottom, catching food that flows by with their open tentacles or sifting through bottom sediment
s. Like sea urchins, most sea cucumbers reproduce by releasing sperm
and ova
into the ocean water. Depending on conditions, one organism can produce thousands of gamete
s.
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Sea cucumbers are typically dioecious
, with separate male and female individuals. The reproductive system consists of a single gonad
, consisting of a cluster of tubules emptying into a single duct that opens on the upper surface of the animal, close to the tentacles. Many species fertilise their eggs internally. The fertilised egg develops in a pouch on the adult's body and eventually hatches as a juvenile sea cucumber. A few species brood their young inside the body cavity, giving birth through a small rupture in the body wall close to the anus. The remaining species develop their eggs into a free-swimming larva
, usually after about three days of development. This larva swims by means of a long band of cilia wrapped around its body. As the larva grows it transforms into a barrel-shaped body with three to five separate rings of cilia. The tentacles are usually the first adult features to appear, before the regular tube feet.
Amphibian
s are found in and around fresh water lakes and ponds, but not in marine environments. Examples are frogs and toads, salamander
s, newt
s and caecilian
s (which resemble snakes). They are cold-blooded animals that metamorphose
from a juvenile water-breathing form, usually to an adult air-breathing form, though mudpuppies retain juvenile gills in adulthood.
Frogs and toads
Female frogs and toads usually spawn gelatinous egg masses containing thousands of eggs in water. Different species lay eggs in distinctive and identifiable ways. For example, the American toad
lays long strings of eggs. The eggs are highly vulnerable to predation
, so frogs have evolved many techniques to ensure the survival of the next generation. In colder areas the embryo is black to absorb more heat from the sun, which speeds up development. Most commonly, this involves synchronous reproduction. Many individuals will breed at the same time, overwhelming the actions of predators; the majority of the offspring will still die due to predation, but there is a greater chance some will survive. Another way in which some species avoid predators and the pathogens eggs are exposed to in ponds is to lay eggs on leaves above the pond, with a gelatinous coating designed to retain moisture. In these species the tadpoles drop into the water upon hatching. The eggs of some species laid out of water can detect vibrations of nearby predatory wasps or snakes, and will hatch early to avoid being eaten.
While the length of the egg stage depends on the species and environmental conditions, aquatic eggs generally hatch within one week. Unlike salamanders and newts, frogs and toads never become sexually mature while still in their larval stage. The hatched eggs continue life as tadpole
s, which typically have oval bodies and long, vertically flattened tails. As a general rule, free living larvae are fully aquatic. They lack eyelids and have a cartilaginous skeleton, a lateral line system, gills for respiration (external gills at first, internal gills later) and tails with dorsal and ventral folds of skin for swimming. They quickly develop a gill pouch that covers the gills and the front legs; the lungs are also developed at an early stage as an accessory breathing organ. Some species which go through the metamorphosis inside the egg and hatch to small frogs never develop gills; instead there are specialised areas of skin that take care of respiration. Tadpoles also lack true teeth, but the jaws in most species usually have two elongate, parallel rows of small keratin
ized structures called keradonts in the upper jaw while the lower jaw has three rows of keradonts, surrounded by a horny
beak, but the number of rows can be lower (sometimes zero), or much higher. Tadpoles feed on algae, including diatom
s filtered from the water through the gill
s. Some species are carnivorous at the tadpole stage, eating insects, smaller tadpoles, and fish. Cannibalism
has been observed among tadpoles. Early developers who gain legs may be eaten by the others, so the late bloomers survive longer.
Sea turtles
Sea turtle
s are amphibious reptiles, but they are not amphibian
s. Reptiles belong to the class Reptilia while amphibians belong to the class Amphibia. These are two distinct taxonomic groups. Reptiles have scales and leathery skins, while the skins of amphibians are smooth and porous. Unlike frogs, sea turtle eggs have tough, leathery shells which allow them to survive on land without drying out.
Some sea turtles migrate long distances between feeding and spawning grounds. Green turtles have feeding grounds along the Brazilian coast. Each year, thousands of these turtles migrate about 2300 kilometres (1,429.2 mi) to their spawning ground, Ascension Island
in the Atlantic, an island only 11 kilometres (6.8 mi) across. Each year the returning turtles dig between 6,000 and 15,000 nests, often returning to the same beach from where they hatched. Females usually mate every two to four years. Males on the other hand visit the breeding areas every year, attempting to mate. Green sea turtles' mating is similar to other marine turtles. Female turtles control the process. A few populations practice polyandry
, although this does not seem to benefit hatchlings. After mating in the water, the female moves above the beach's high tide line where she digs a hole with her hind flippers and deposits her eggs. Litter size depends on the age of the female and species, but green turtle clutches range between 100 to 200. She then covers the nest with sand and returns to the sea.
At around 45 to 75 days, the eggs hatch during the night and the hatchlings instinct
ively head directly into the water. This is the most dangerous time in a turtle's life. As they walk, predators such as gull
s and crab
s grab them. A significant percentage never make it to the ocean. Little is known of the initial life history of newly hatched sea turtles. Juveniles spend three to five years in the open ocean before they settle as still-immature juveniles into their permanent shallow-water lifestyle. It is speculated that they take twenty to fifty years to reach sexual maturity
. Individuals live up to eighty years in the wild. They are among the larger sea turtles, many more than a meter long and weighing up to 300 kilograms (661.4 lb).
"are famed for their short adult life. Some species have under an hour to mate and lay their eggs before they die. Their pre-adult stage, known as the subimago, may be even shorter - perhaps lasting just a few minutes before they moult into their adult form. Therefore a mayfly spends most of its life as a nymph, hidden from view under the water."
Corals can be both gonochoristic
(unisexual) and hermaphroditic, each of which can reproduce sexually and asexually. Reproduction also allows corals to settle new areas.
Corals predominantly reproduce sexually
. 25% of hermatypic coral
s (stony corals) form single sex (gonochoristic) colonies, while the rest are hermaphroditic. About 75% of all hermatypic corals "broadcast spawn" by releasing gamete
s—eggs
and sperm
—into the water to spread offspring. The gametes fuse during fertilization to form a microscopic larva
called a planula
, typically pink and elliptical in shape. A typical coral colony form several thousand larvae per year to overcome the odds against formation of a new colony.
Planulae exhibit positive phototaxis
, swimming towards light to reach surface waters where they drift and grow before descending to seek a hard surface to which they can attach and establish a new colony. They also exhibit positive sonotaxis, moving towards sounds that emanate from the reef and away from open water. High failure rates afflict many stages of this process, and even though millions of gametes are released by each colony very few new colonies form. The time from spawning to settling is usually 2–3 days, but can be up to 2 months. The larva grows into a polyp and eventually becomes a coral head by asexual budding and growth.
Synchronous spawning
is very typical on the coral reef and often, even when multiple species
are present, all corals spawn on the same night. This synchrony is essential so that male and female gametes can meet. Corals must rely on environmental cues, varying from species to species, to determine the proper time to release gametes into the water. The cues involve lunar changes, sunset time, and possibly chemical signalling. Synchronous spawning may form hybrids and is perhaps involved in coral speciation
. In some places the spawn can be visually dramatic, clouding the usually clear water with gametes, typically at night.
Corals use two methods for sexual reproduction, which differ in whether the female gametes are released:
Fungi
are not plants, and require different conditions for optimal growth. Plants develop through photosynthesis
, a process that converts atmospheric carbon dioxide
into carbohydrate
s, especially cellulose
. While sunlight provides an energy source for plants, mushrooms derive all of their energy and growth materials from their growth medium
, through biochemical decomposition
processes. This does not mean that light is an unnecessary requirement, since some fungi use light as a signal to induce fruiting. However, all the materials for growth must already be present in the growth medium. Instead of seeds, mushrooms reproduce sexually during underground growth, and asexually through spore
s. Either of these can be contaminated with airborne microorganisms, which will interfere with mushroom growth and prevent a healthy crop. Mycelium
, or actively growing mushroom culture, is placed on growth substrate to seed or introduce mushrooms to grow on a substrate
. This is also known as inoculation, spawning or adding spawn. Its main advantages are to reduce chances of contamination while giving mushrooms a firm beginning.
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
s and sperm released or deposited, usually into water, by aquatic animal
Aquatic animal
An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. It may breathe air or extract its oxygen from that dissolved in water through specialised organs called gills, or directly through its skin. Natural environments and the animals that...
s. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning. Most aquatic animals, apart from aquatic mammal
Aquatic mammal
Aquatic and semi-aquatic mammals are a diverse group of mammals that dwell partly or entirely in bodies of water. They include the various marine mammals who dwell in oceans, as well as various freshwater species, such as the Platypus and the European Otter.-Groups:* Order Sirenia: Sirenians**...
s, reproduce through a process of spawning.
Spawn consists of the reproductive cells (gamete
Gamete
A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
s) of aquatic animals, some of which will become fertilized and produce offspring. The process of spawning typically involves females releasing ova
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
(unfertilized eggs) into the water, often in large quantities, while males simultaneously or sequentially release spermatozoa (milt
Milt
Milt is the seminal fluid of fish, mollusks, and certain other water-dwelling animals who reproduce by spraying this fluid, which contains the sperm, onto roe .-Milt as food:...
) to fertilize the eggs.
Most fish reproduce by spawning, and so do most other aquatic animals, including crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s such as crabs and shrimps, molluscs such as oysters and squid, echinoderm
Echinoderm
Echinoderms are a phylum of marine animals. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone....
s such as sea urchins and sea cucumbers, amphibious animals such as frogs and turtles, aquatic insects such as mayflies and mosquitoes, and coral
Coral
Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...
s (which are small aquatic animals and not plants). Fungi, such as mushrooms, are also said to "spawn" a white fibrous matter that forms the matrix from which they grow.
There are many variations in the way spawning occurs, depending on sexual differences in anatomy, on how the sexes relate to each other, on where and how the spawn is released, and on whether or how the spawn is subsequently guarded.
Overview
Larvae
In Roman mythology, lemures were shades or spirits of the restless or malignant dead, and are probably cognate with an extended sense of larvae as disturbing or frightening...
develop as they consume their fat stores, and eventually hatch from the egg capsule into miniature versions of their parents.
To survive, they must then become miniature predators themselves, feeding on plankton. Fish eventually encounter others of their own kind (conspecifics), where they form aggregations and learn to school.
Internally, the sexes of most marine animals can be determined by looking at the gonad
Gonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s. For example, male testes of spawning fish are smooth and white and account for up to 12% of the mass of the fish, while female ovaries
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
are granular and orange or yellow, accounting for up to 70% of the fish's mass. Male lampreys, hagfish and salmon discharge their sperm into the body cavity where it is expelled through pores in the abdomen. Male shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s and rays
Batoidea
Batoidea is a superorder of cartilaginous fish commonly known as rays and skates, containing more than 500 described species in thirteen families...
can pass sperm along a duct into a seminal vesicle
Seminal vesicle
The seminal vesicles or vesicular glands are a pair of simple tubular glands posteroinferior to the urinary bladder of male mammals...
, where they store it for a while before it is expelled, while teleosts usually employ separate sperm ducts.
Externally, many marine animals, even when spawning, show little sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
(difference in body shape or size) or little difference in colouration
Animal colouration
Animal coloration is the general appearance of an animal resulting from the reflection or emission of light from its surfaces. The mechanisms for colour production in animals include pigments, chromatophores, structural coloration, and bioluminescence....
. Where species are dimorphic, such as sharks or guppies
Guppy
The guppy , also known as the millionfish, is one of the most popular freshwater aquarium fish species in the world. It is a small member of the Poeciliidae family [females long, males long] and like all other members of the family, is live-bearing....
, the males often have penis-like intromittent organ
Intromittent organ
An intromittent organ is a general term for an external organ of a male organism that is specialized to deliver sperm during copulation. Intromittent organs are found most often in terrestrial species, as most aquatic species fertilize their eggs externally, although there are...
s in the form of a modified fin.
A species is semelparous if its individuals spawn only once in their lifetime, and iteroparous if its individuals spawn more than once. The term semelparity comes from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
semel, once, and pario, to beget, while iteroparity comes from itero, to repeat, and pario, to beget.
Semelparity is sometimes called "big bang" reproduction, since the single reproductive event of semelparous organisms is usually large and fatal to the spawners. The classic example of a semelparous animal is the Pacific salmon, which lives for many years in the ocean before swimming to the freshwater stream of its birth, spawning, and then dying. Other spawning animals which are semelparous include mayflies
Mayfly
Mayflies are insects which belong to the Order Ephemeroptera . They have been placed into an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies...
, squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
, octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...
, smelt, capelin
Capelin
The capelin or caplin, Mallotus villosus, is a small forage fish of the smelt family found in the Atlantic and Arctic oceans. In summer, it grazes on dense swarms of plankton at the edge of the ice shelf. Larger capelin also eat a great deal of krill and other crustaceans...
and some amphibians. Semelparity is often associated with r-strategists
R/K selection theory
In ecology, r/K selection theory relates to the selection of combinations of traits in an organism that trade off between quantity or quality of offspring...
. However, most fish and other spawning animals are iteroparous.
When the internal ovaries
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
or egg masses of fish and certain marine animals are ripe for spawning they are called roe
Roe
Roe or hard roe is the fully ripe internal egg masses in the ovaries, or the released external egg masses of fish and certain marine animals, such as shrimp, scallop and sea urchins...
. Roe from certain species, such as shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
, scallop
Scallop
A scallop is a marine bivalve mollusk of the family Pectinidae. Scallops are a cosmopolitan family, found in all of the world's oceans. Many scallops are highly prized as a food source...
, crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
and sea urchin
Sea urchin
Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull...
s, are sought as human delicacies in many parts of the world. Caviar
Caviar
Caviar, sometimes called black caviar, is a luxury delicacy, consisting of processed, salted, non-fertilized sturgeon roe. The roe can be "fresh" or pasteurized, the latter having much less culinary and economic value....
is a name for the processed, salted roe of non-fertilized sturgeon
Sturgeon
Sturgeon is the common name used for some 26 species of fish in the family Acipenseridae, including the genera Acipenser, Huso, Scaphirhynchus and Pseudoscaphirhynchus. The term includes over 20 species commonly referred to as sturgeon and several closely related species that have distinct common...
. The term soft roe or white roe denotes fish milt
Milt
Milt is the seminal fluid of fish, mollusks, and certain other water-dwelling animals who reproduce by spraying this fluid, which contains the sperm, onto roe .-Milt as food:...
. Lobster roe is called coral because it turns bright red when cooked. Roe (reproductive organs) are usually eaten either raw or briefly cooked.
"The reproductive behaviour of fishes is remarkably diversified: they may be oviparous (lay eggs), ovoviparous (retain the eggs in the body until they hatch), or viviparous (have a direct tissue connection with the developing embryos and give birth to live young). All cartilaginous fishes—the elasmobranches (e.g., sharks, rays, and skates)—employ internal fertilization and usually lay large, heavy-shelled eggs or give birth to live young. The most characteristic features of the more primitive bony fishes is the assemblage of polyandrous (many males) breeding aggregations in open water and the absence of parental care..."
There are two main reproduction methods in fish. The first method is by laying eggs and the second by live-bearing (producing their young alive).
- In the first method, the female fish lays eggs either on the sea floor or on the leaves of an aquatic plant. A male fish fertilizes the eggs, and both then work together to protect the eggs/babies from danger until they can defend themselves.
- In the second method, the male fish uses its anal fin to transmit sperm into the female fish and fertilize the fish eggs. Later, the female gives live birth to her fry.
Basic strategies
| The four basic mating systems | ||
|---|---|---|
| Single female | Multiple females | |
| Single male | Monogamy | Polygyny Polygyny threshold model The polygyny threshold model is an explanation of polygyny, the mating of one male of a species with multiple females. The model shows how females may gain a higher level of biological fitness by mating with a male who already has a mate... |
| Multiple males | Polyandry | Polygynandry Polygynandry Polygynandry occurs when two or more males have an exclusive relationship with two or more females. The numbers of males and females need not be equal, and in vertebrate species studied so far, the number of males is usually lower.-In Bonobos:... |
Cichlid
Cichlids are fishes from the family Cichlidae in the order Perciformes. Cichlids are members of a group known as the Labroidei along with the wrasses , damselfish , and surfperches . This family is both large and diverse. At least 1,300 species have been scientifically described, making it one of...
s, which rear their young together in locations where they must fiercely defend against competitors and predators are monogamous. "In some pipefish
Pipefish
Pipefishes or pipe-fishes are a subfamily of small fishes, which, together with the seahorses, form the family Syngnathidae.-Anatomy:...
es and seahorse
Seahorse
Seahorses compose the fish genus Hippocampus within the family Syngnathidae, in order Syngnathiformes. Syngnathidae also includes the pipefishes. "Hippocampus" comes from the Ancient Greek hippos meaning "horse" and kampos meaning “sea monster”.There are nearly 50 species of seahorse...
s, development of eggs takes a long time before the female can place them in the brood pouch of a male, where they are fertilized. While the male is pregnant, the female starts a new batch of eggs, which are ready at about the same time that the male gives birth to the young from the previous mating. This close timing of development promotes monogamy, especially if the likelihood of encountering another potential mate is low.
Polygyny
Polygyny threshold model
The polygyny threshold model is an explanation of polygyny, the mating of one male of a species with multiple females. The model shows how females may gain a higher level of biological fitness by mating with a male who already has a mate...
occurs when one male gets exclusive mating rights with multiple females. In polygyny a large conspicuous male usually defends females from other males or defends a breeding site. The females choose large males that are successfully defending prime breeding sites which the females find attractive. For example, sculpin
Sculpin
A Sculpin is a fish that belongs to the order Scorpaeniformes, suborder Cottoidei and superfamily Cottoidea, that contains 11 families, 149 genera, and 756 species...
males defend "caves" underneath rocks which are suitable for the incubation of embryos.
Another way males get to mate with several females is through the use of leks. Leks are places where many fish come together, and the males display to each another. Based on these displays, each female then selects the male they want to be their mate. For example, among the cichlid Cyrtocara eucinostomus in Lake Malawi
Lake Malawi
Lake Malawi , is an African Great Lake and the southernmost lake in the Great Rift Valley system of East Africa. This lake, the third largest in Africa and the eighth largest lake in the world, is located between Malawi, Mozambique, and Tanzania...
, up to 50,000 large and colourful males display together on a lek four kilometres long. The females, which are mouth brooders, choose which male they want to fertilize their eggs.
Polyandry occurs when one female gets exclusive mating rights with multiple males. This is not common, but it does happen among fish like clownfish
Clownfish
Clownfish or anemonefish are fishes from the subfamily Amphiprioninae in the family Pomacentridae. Twenty-eight species are recognized, one in the genus Premnas, while the remaining are in the genus Amphiprion. In the wild they all form symbiotic mutualisms with sea anemones...
that change their sex. It can also happen when males do the brooding but can cannot handle all the eggs the female produce, such as with some pipefish
Pipefish
Pipefishes or pipe-fishes are a subfamily of small fishes, which, together with the seahorses, form the family Syngnathidae.-Anatomy:...
.
The males in some deep sea anglerfish
Anglerfish
Anglerfishes are members of the teleost order Lophiiformes . They are bony fishes named for their characteristic mode of predation, wherein a fleshy growth from the fish's head acts as a lure; this is considered analogous to angling.Some anglerfishes are pelagic , while others are benthic...
es are much smaller than the females. When they find a female they bite into her skin, releasing an enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
that digests the skin of their mouth and her body and fusing the pair down to the blood-vessel level. The male then slowly atrophies
Atrophy
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations , poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, disuse or lack of exercise or disease intrinsic to the tissue itself...
, losing first his digestive organs, then his brain, heart, and eyes, ending as nothing more than a pair of gonads, which release sperm
Spermatozoon
A spermatozoon is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote...
in response to hormones in the female's bloodstream indicating egg
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
release. This extreme sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
ensures that, when the female is ready to spawn, she has a mate immediately available. A single anglerfish female can "mate" with many males in this manner.
Polygynandry
Polygynandry
Polygynandry occurs when two or more males have an exclusive relationship with two or more females. The numbers of males and females need not be equal, and in vertebrate species studied so far, the number of males is usually lower.-In Bonobos:...
occurs when multiple males mate indiscriminately with multiple females. This mutual promiscuity is the approach most commonly used by spawning animals, and is perhaps the "original fish mating system." Common examples are forage fish
Forage fish
Forage fish, also called prey fish or bait fish, are small fish which are preyed on by larger predators for food. Predators include other larger fish, seabirds and marine mammals. Typical ocean forage fish feed near the base of the food chain on plankton, often by filter feeding...
, such as herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
s, which form huge mating shoals
Shoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
in shallow water. The water becomes milky with sperm and the bottom is draped with millions of fertilized eggs.
Cuckoldry
Evolutionarily stable strategy
In game theory and behavioural ecology, an evolutionarily stable strategy , which is sometimes also called an evolutionary stable strategy, is a strategy which, if adopted by a population of players, cannot be invaded by any alternative strategy that is initially rare. An ESS is an equilibrium...
for reproduction, because it is favoured by natural selection just like the "standard" strategy of large males.
Cuckoldry occurs in many fish species, including parrotfish
Parrotfish
Parrotfishes are a group of fishes that traditionally had been considered a family , but now often are considered a subfamily of the wrasses. They are found in relatively shallow tropical and subtropical oceans throughout the world, but with the largest species richness in the Indo-Pacific...
es and wrasses on tropical reefs and the bluegill
Bluegill
The Bluegill is a species of freshwater fish sometimes referred to as bream, brim, or copper nose. It is a member of the sunfish family Centrarchidae of the order Perciformes.-Range and distribution:...
sunfish in fresh water. Sneaker males that becomes too large to hide effectively become satellite males. With bluegill sunfish, satellite males mimic the behaviour and colouration of the females. They hover over a nest containing a pair of courting sunfish, and gradually descend to reach the pair just as they spawn. "Both sneaker and satellite males are usually badly chewed up by irate parental males by the end of the spawning season, but their strategy is nevertheless a successful one (giving them high fitness). Because these smaller males do not have to spend any energy on parental care, they can spawn at a much younger age than the parental males. Parental males may be 6 or 7 years old before they are large enough to compete successfully for the best nest sites, but the sneaker and satellite males may be only 2 or 3 years old."
Hermaphroditism
Hermaphroditism occurs when a given individual in a species possesses both male and female reproductive organs, or can alternate between possessing first one, and then the other. Hermaphroditism is common in invertebrates but rare in vertebrates. It can contrasted with gonochorismGonochorism
In biology, gonochorism or unisexualism describes sexually reproducing species in which individuals have just one of at least two distinct sexes. The term is most often used with animals . The sex of an individual may change during its lifetime, this can for example be found in parrotfish...
, where each individual in a species is either male or female, and remains that way throughout their lives. Most fish are gonochorists, but hermaphroditism is known to occur in 14 families of teleost fishes. "Hermaphrodites can be either synchronous, in which individuals possess both ovarian and testicular tissue, or sequential, in which individuals change sex. Synchronous hermaphrodites are uncommon. Among the best studied is the black hamlet
Hypoplectrus nigricans
Hypoplectrus nigricans is a hamlet from the Western Atlantic. It occasionally makes its way into the aquarium trade. It grows to a size of 15 cm in length....
, a species in which individuals take turns releasing sperm and eggs during spawning. Because such egg trading is advantageous to both individuals, hamlets are typically monogamous for short periods of time–an unusual situation in fishes. The most common pattern, known as Synchronous hermaphroditism, is for a female to change into a male (protogyny). This often happens when a large, dominant male controlling a harem of females is removed by a predator. Within a few days, the largest female in the harem becomes a dominant male and takes over the missing male's function. This pattern is common in coral reef fishes, such as parrotfish
Parrotfish
Parrotfishes are a group of fishes that traditionally had been considered a family , but now often are considered a subfamily of the wrasses. They are found in relatively shallow tropical and subtropical oceans throughout the world, but with the largest species richness in the Indo-Pacific...
es, wrasses, and grouper
Grouper
Groupers are fish of any of a number of genera in the subfamily Epinephelinae of the family Serranidae, in the order Perciformes.Not all serranids are called groupers; the family also includes the sea basses. The common name grouper is usually given to fish in one of two large genera: Epinephelus...
s. Less common than protogyny is protandry, in which a male converts to a female."
- Example: Most wrasseWrasseThe wrasses are a family, Labridae, of marine fish, many of which are brightly colored. The family is large and diverse, with over 600 species in 82 genera, which are divided into nine subgroups or tribes....
s are protogynous hermaphrodites within a haremic mating system. Hermaphroditism allows for complex mating systems. Wrasses exhibit three different mating systems: polygynous, lek-like, and promiscuous mating systems. Group spawning and pair spawning occur within mating systems. The type of spawning that occurs depends on male body size. Labroids typically exhibit broadcast spawning, releasing high amounts of planktonic eggs, which are broadcast by tidal currents; adult wrasses have no interaction with offspring. Wrasse of a particular subgroup of the Labridae family Labrini do not exhibit broadcast spawning. - homogamyHomogamy-In sociology:Homogamy is marriage between individuals who are, in some culturally important way, similar to each other. Homogamy may be based on socio-economic status, class, gender, ethnicity, or religion...
versus dichogamyDichogamySequential hermaphroditism is a type of hermaphroditism that occurs in many fish, gastropods and plants. Here, the individual is born one sex and changes sex at some point in their life. They can change from a male to female , or from female to male...
: Dichogamy, also known as sequential hermaphrodism, is the separation in time of gender expression in a hermaphroditicHermaphroditeIn biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...
organism, a characteristic of some fishes, gastropods, crustaceans. This is the opposite of simultaneous hermaphrodites, or homogamy. - "Hermaphrodites have both male and female sex organs, either throughout their lives (homgamy) or that develop and mature at different points in their life cycle (dichogamy). Homogamy is the maturation in hermaphroditic animals of the ova and sperm at different times so as to preclude self-fertilization. It is the condition in which an organism changes sex during its lifetime."
The sex of many fishes is not fixed, but can change with physical and social changes to the environment where the fish lives. "Sex change
Sex change
Sex change is a term often used for gender reassignment therapy, that is, all medical procedures transgendered people can have, or specifically to sexual reassignment surgery, which usually refers to genitalia surgery only...
occurs mainly in fishes in which one sex had higher survival and reproductive rates, usually as the result of larger size. In such situations it may pay for an individual of the smaller sex to change to the larger sex when the opportunity arises. For example anemone fishes live as monogamous pairs in single anemone
Anemone
Anemone , is a genus of about 120 species of flowering plants in the buttercup family Ranunculaceae in the north and south temperate zones...
s, protected from predators by the stings of the anemone. Female anemone fish are typically larger than males, because a male does not have to vigorously compete for mates once he has paired with a female. If the female dies, however, a juvenile anemone fish quickly moves in; such fish are always male. The resident male then turns into a female and reproductive advantages of the large female–small male combination continue. In some fishes, sex change is reversible, depending on the social situation. Thus some gobbies
Gobby
Gobby is a free software collaborative real-time editor available on Windows and Unix-like platforms. It was initially released in June 2005 by the 0x539 dev group....
will switch sex when kept in what initially were single sex groups of either sex."
Unisexuality
Unisexuality occurs when a species is all-male or all-female. Unisexuality is not uncommon among fish species, and can take complex forms. Squalius alburnoidesSqualius alburnoides
Tropidophoxinellus alburnoides is a species of fish in the family Cyprinidae. It is found in Portugal and Spain. Its natural habitats are rivers and intermittent rivers. It may be threatened by habitat loss....
, a minnow found in several river basins in Portugal and Spain, appears to be an all-male species. The existence of this species illustrates the potential complexity of mating systems in fish. The species originated as a hybrid between two species, and is diploid, but not hermaphroditic. It can have triploid and tetraploid forms, including all-female forms that reproduce mainly through hybridogenesis.
It is rare to find true parthenogenesis
Parthenogenesis
Parthenogenesis is a form of asexual reproduction found in females, where growth and development of embryos occur without fertilization by a male...
in fishes, where females produce female offspring with no input from males. All-female species include the Texas silverside
Silverside
Silverside may refer to:* Silverside , a cut of beef* Silverside , a type of fish; see also Neotropical silversides* Brycinus longipinnis, a species of African fish also known as Silversides...
, Menidia clarkhubbsi as well as a complex of Mexican mollies
Molly
"Molly" may refer to:* Molly , a female given name* Mollies or Poecilia, a family of fish* Molly Smitten-Downes, singer/songwriter of pop/dance/folk* Molly , a Swedish band mixing ska and Irish folk music...
. Parthenogenesis has been recently observed in hammerhead shark
Hammerhead shark
The hammerhead sharks are a group of sharks in the family Sphyrnidae, so named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a "hammer" shape called a "cephalofoil". Most hammerhead species are placed in the genus Sphyrna while the...
s and blacktip shark
Blacktip shark
The blacktip shark is a species of requiem shark, family Carcharhinidae. It is common to coastal tropical and subtropical waters around the world, including brackish habitats. Genetic analyses have revealed substantial variation within this species, with populations from the western Atlantic Ocean...
s. It is also known to occur in crayfish and amphibians.
Spawning strategies
This section is patterned after a classification of the spawning behaviours of fish by Balon (1975, 1984) into reproductive guildsGuild (ecology)
A guild is any group of species that exploit the same resources, often in related ways. As can be seen from the list of examples below, it does not follow that the species within a guild occupy the same, or even similar, ecological niches...
. This classification is based on how the eggs are fertilized (internal or external spawners), where the eggs are deposited (pelagic or benthic spawners), and whether and how the parents look after the eggs after spawning (bearers, guarders and nonguarders).
Open substrate spawners
Open substrate spawners scatter their eggs in the environment. They usually spawn in shoalsShoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
without complex courtship rituals, and males outnumber females.
- Broadcast spawners: release their gametes (sperm and eggs) into open water for external fertilisation. There is no subsequent parental care. About 75% of coral species are broadcasters, the majority of which are hermatypic, or reef-building corals.
- Pelagic spawners: a kind of broadcast spawners, spawn in the open sea, mostly near the surface. They are usually pelagic fishPelagic fishPelagic fish live near the surface or in the water column of coastal, ocean and lake waters, but not on the bottom of the sea or the lake. They can be contrasted with demersal fish, which do live on or near the bottom, and reef fish which are associated with coral reefs.The marine pelagic...
such as tunaTunaTuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...
and sardineSardineSardines, or pilchards, are several types of small, oily fish related to herrings, family Clupeidae. Sardines are named after the Mediterranean island of Sardinia, around which they were once abundant....
s. Some demersal fish leave the bottom to spawn pelagically, particularly coral reef fish such as parrotfishParrotfishParrotfishes are a group of fishes that traditionally had been considered a family , but now often are considered a subfamily of the wrasses. They are found in relatively shallow tropical and subtropical oceans throughout the world, but with the largest species richness in the Indo-Pacific...
and wrasses. Pelagic spawning means water currents widely disperse the young. The eggs, embryos and larvae of pelagic spawners contain oil globules or have a high water content. As a result, they are buoyant and are widely dispersed by currents. The downside is that mortalityFish mortalityFish mortality is a term widely used in fisheries science that denotes the loss of fish from a stock through death. The term is also commonly used in British English as a synonym for fish kill. Fish mortality can be divided into two types:...
is high, because they can be eaten so easily by pelagic predators or they can drift into unsuitable areas. Females compensate by spawning large numbers of eggs and extending their spawning periods. Pelagic spawners who live in or around coral reefCoral reefCoral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
s can spawn a small number of eggs almost daily over a period of months. These fishes have complex breeding behaviours including sex changeSex changeSex change is a term often used for gender reassignment therapy, that is, all medical procedures transgendered people can have, or specifically to sexual reassignment surgery, which usually refers to genitalia surgery only...
s, haremsHarem (zoology)The term harem is used in zoology to describe the social organization of certain herbivore species, such as those in the Hominidae and Equidae families, into groups of females and young surrounding a single dominant male...
, leks and territoriality. See also: Coral reef fish.
- Pelagic spawners: a kind of broadcast spawners, spawn in the open sea, mostly near the surface. They are usually pelagic fish
- Benthic spawners: deposit their spawn on or near the bottom of the sea (or lake). They are usually demersal fish such as codCodCod is the common name for genus Gadus, belonging to the family Gadidae, and is also used in the common name for various other fishes. Cod is a popular food with a mild flavor, low fat content and a dense, flaky white flesh. Cod livers are processed to make cod liver oil, an important source of...
and flatfishFlatfishThe flatfish are an order of ray-finned fish, also called the Heterosomata, sometimes classified as a suborder of Perciformes. In many species, both eyes lie on one side of the head, one or the other migrating through and around the head during development...
. These species typically spawn without ceremony; they do not engage in elaborate courtship rituals. Each female is usually followed by several males who fertilize the eggs as they are released. Various strategies ensure the eggs and embryos remain in place, and do not drift with the current. The eggs can adhere to other eggs or to whatever they are deposited on, or the eggs can be laid in long strings which are wrapped around plants or rocks. Some eggs take on water after they are released, so they can be dropped into cracks where they swell and wedge themselves in place. "The free embryos and larvae of these fishes may be either pelagic or benthic. Those that are pelagic (eg, those of smelt) become active or buoyant immediately after "hatching", whereas those that are benthic stay close to the spawning area until they can swim freely. In lakes or shallow ocean waters, plants are often important substrates for the adhesive embryos of benthic spawners. Some fishes always spawn on such plants. For example, common carpCommon carpThe Common carp is a widespread freshwater fish of eutrophic waters in lakes and large rivers in Europe and Asia. The wild populations are considered vulnerable to extinction, but the species has also been domesticated and introduced into environments worldwide, and is often considered an invasive...
s and pikesEsoxEsox is a genus of freshwater fish, the only living genus in the family Esocidae — the esocids which were endemic to North America, Europe and Eurasia during the Paleogene through present.The type species is E. lucius, the northern pike...
generally spawn only on vegetation that is flooded by high water in the spring. If such material is not available, spawning either does not take place or is much less successful. Once the embryos hatch, the young remain among the plants; some of them have adhesive organs on their heads, with which they can stick to the stems of the plants."- Egg scatterers: scatter adhesive or non-adhesive eggs to fall to the substrate, into plants, or float to the surface. These species do not look after their brood and even eat their own eggs. These are often schooling fishShoaling and schoolingIn biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
which spawn in groups or pairs, often laying a large number of small eggs. The fry hatch quickly. - Egg depositers: deposit eggs on a substrate (tank glass, wood, rocks, plants). Egg depositors usually lay less eggs than egg-scatterers, although the eggs are larger. Egg-depositors fall into two groups: those that care for their eggs, and those that do not. Among eggs depositors that care for their eggs are cichlidCichlidCichlids are fishes from the family Cichlidae in the order Perciformes. Cichlids are members of a group known as the Labroidei along with the wrasses , damselfish , and surfperches . This family is both large and diverse. At least 1,300 species have been scientifically described, making it one of...
s and some catfish. Egg-depositors that care for their young can be divided into two groups: cavity spawners and open spawners. - Cavity spawners: lay eggs in a cave or cavity. These fish form pairs and have advanced brood care where the eggs are defended and cleaned. The eggs take a few days to hatch, and the fry are often guarded by the parents. Various catfishCatfishCatfishes are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores...
, Cyprinidae, and killifishKillifishA killifish is any of various oviparous cyprinodontiform fish . Altogether, there are some 1270 different species of killifish, the biggest family being Rivulidae, containing more than 320 species...
make up the majority. Cavity spawners can be contrasted with open (shelter) spawners, which lay their eggs on an open surface.
- Egg scatterers: scatter adhesive or non-adhesive eggs to fall to the substrate, into plants, or float to the surface. These species do not look after their brood and even eat their own eggs. These are often schooling fish
Brood hiders
Brood hiders hide their eggs but do not give parental care after they have hidden them. Brood hiders are mostly benthic spawners that bury the fertilized eggs. For example, among salmon and trout the female digs a nest with her tail in gravel. These nests are called redds. The female then lays her eggs while the male fertilizes them, while both fish defend the redd if necessary from other members of the same species. Then the female buries the nest, and the nest site is abandoned. In North America, some minnowMinnow
Minnow is a general term used to refer to small freshwater and saltwater fish, especially those used as bait fish or for fishing bait. More specifically, it refers to small freshwater fish of the carp family.-True minnows:...
s build nests out of piles of stones rather than dig holes. The minnow males have tubercle
Tubercle
A tubercle is generally a wart-like projection, but it has slightly different meaning depending on which family of plants or animals it is used to refer to....
s on their head and body which they use to help them defend the nest site.
- Egg buriers - can inhabit waters that dry up at some time of the year. An example are annual killifishKillifishA killifish is any of various oviparous cyprinodontiform fish . Altogether, there are some 1270 different species of killifish, the biggest family being Rivulidae, containing more than 320 species...
which lay their eggs in mud. The parents mature quickly and lay their eggs before dying when the water dries up. The eggs remain in a dormant stage until rains stimulate hatching.
Bitterling
Bitterling
The Amur Bitterling, Rhodeus sericeus, is a small fish of the carp family. It is sometimes just called "bitterling", but this is wrong: for one thing, it dates back to the time when the European Bitterling was still considered conspecific with R. sericeus, for another, "bitterling" properly refers...
s have a remarkable reproduction strategy where parents transfer responsibility for the care of their young to mussel
Mussel
The common name mussel is used for members of several families of clams or bivalvia mollusca, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which are often more or less rounded or oval.The...
s. The female extends her ovipositor
Ovipositor
The ovipositor is an organ used by some animals for oviposition, i.e., the laying of eggs. It consists of a maximum of three pairs of appendages formed to transmit the egg, to prepare a place for it, and to place it properly...
into the mantle cavity of the mussel and deposits her eggs between the gill filaments. The male then ejects his sperm into the mussel's inhalant water current and fertilization takes place within the gills of the host. The same female may use a number of mussels, and she deposits only one or two yellow, oval eggs into each. Early developmental stages are protected from predation within the body of the mussel. After 3 to 4 weeks larvae swim away from the host to continue life on their own.
Guarders
Guarders protect their eggs and offspring after spawning by practicing parental care (also called brood care). Parental care is an "investment by parents in offspring that increases the offsprings' chances of surviving (and hence reproducing). In fish, parental care can take a variety of forms including guarding, nest building, fanning, splashing, removal of dead eggs, retrieval of straying fry, external egg carrying, egg burying, moving eggs or young, ectodermal feeding, oral brooding, internal gestation, brood-pouch egg carrying, etc."Territorial behaviour is generally necessary for guarders, and the embryos are almost always guarded by males (apart from cichlids). There is a need to be territorial because looking after embryos usually includes defending the site where they are being looked after. It also often means there is competition for the best egg-laying sites. Elaborate courtship behaviour is usual among guarders.
Guarding males keep the embryos safe from predators, keep oxygen levels high by fanning water currents, and keep the area free from dead embryos and debris. They protect the embryos until they hatch, and often look after the larval stages as well. The time spent guarding can range from a few days to several months.
Substrate spawners
Some guarders build nests (nest spawners) and some do not (substrate spawners), though the difference between the two groups can be small. Substrate spawners clean off a suitable area of surface suitable for egg laying, and look after the area, but they do not actively build a nest.Nest spawners
Nest spawners construct "some sort of structure, cavity, or pit in which the eggs are laid and fertilized and the embryos are defended. The young are often defended in a nest as well, and in some species, the parents even herd schools of young around for a period of time. Pit nests can be made of a wide variety of material, but the most common are nests of gravel and rocks. Such nests are typically shallow depressions that are carefully constructed and tended by territorial males. Most sunfishes and black bassBlack bass
Micropterus , is a genus of freshwater fish in the sunfish family of order Perciformes. The type species is M. dolomieu, the smallmouth bass...
es (Centrarchidae
Centrarchidae
The sunfishes are a family of freshwater ray-finned fish belonging to the order Perciformes. The type genus is Centrarchus . The family's 27 species includes many fishes familiar to North Americans, including the rock bass, largemouth bass, bluegill, pumpkinseed, and crappies...
) construct nests of this sort, often in colonies. The males defend the embryos and the young until the young become too active to be kept in the nest. In some cichlids eggs are laid and incubated in one nest depression, but the young are tended (by both parents) in one or more additional depressions that are constructed nearby."
"A few species construct nests on sandy bottoms. Either the eggs and embryos in such nests have special adaptations (e.g., semibuoyancy) to reduce the possibility of being smothered, or the parent fish must spend considerable time handling them."
"In areas where bottoms are muddy, nest-building fish commonly build nests of plant material. Usually plant-nesting fishes construct loose aggregations of material in which the eggs are laid. One special type of plant-nest builder uses a kidney secretion to glue the pieces of plant together to form a tight nest. The main examples of this type of nesting are the stickleback
Stickleback
The Gasterosteidae are a family of fish including the sticklebacks. FishBase currently recognises sixteen species in the family, grouped in five genera. However several of the species have a number of recognised subspecies, and the taxonomy of the family is thought to be in need of revision...
s in which the male builds a tube which is usually attached to rooted plants or is placed in a small pit. By means of a complicated courtship ritual, a female is enticed into a nest, where she deposits some eggs after being nudged by the male. After the eggs are laid, he chases the female out and fertilizes them. This process is repeated several times, until enough embryos are in the nest and the male begins to incubate them by fanning currents of water across them. After the embryos hatch, the male guards the young for several days, first in the nest, and then in a shoal outside the nest."
"Perhaps the most common type of nests among fishes are those in caves, cavities, or burrows. These nests are characteristic of fish that live in active habitats, such as rocky intertidal zone or streams. For stream-dwelling fishes, the typical cave nest is the underside of a flat rock in midstream, which has plenty of current to keep the water well oxygenated. Sculpin
Sculpin
A Sculpin is a fish that belongs to the order Scorpaeniformes, suborder Cottoidei and superfamily Cottoidea, that contains 11 families, 149 genera, and 756 species...
s and many darter
Darter
The darters or snakebirds are mainly tropical waterbirds in the family Anhingidae. There are four living species, three of which are very common and widespread while the fourth is rarer and classified as near-threatened by the IUCN. The term "snakebird" is usually used without any additions to...
s deposit their eggs in clusters on the roofs of such shelters and then guard the embryos until they hatch. In quieter water, minnows, such as the fathead minnow
Fathead minnow
The fathead minnow , is a species of temperate freshwater fish belonging to the Pimephales genus of the cyprinid family. The natural geographic range extends throughout much of North America, from central Canada south along the Rockies to Texas, and east to Virginia and the Northeastern United...
, lay their eggs on the underside of a log or a board in an area that has been cleaned off by the male. Spawning males develop a thick horny pad on their head, which is used for rubbing algae and other materials of the spawning surface. Many large catfish
Catfish
Catfishes are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores...
es lay their eggs in cavities ranging from hollow logs to old muskrat burrows to oil drums, where the embryoes are guarded by the males. These catfish also guard schools of young for one or more weeks after they emerge from the nest."
Bearers
Bearers are fish that carry their embryos (and sometimes their young) around with them, either externally or internally.External bearers
"Fishes that carry their embryos externally have developed a wide variety of ways for doing so, ranging from the short-term attachment of embryos to the adult until a suitable place is found to put them (transfer brooders) to the carrying of embryos and young in special pouches. Good examples of various kinds of bearers can be found amongst pipefishPipefish
Pipefishes or pipe-fishes are a subfamily of small fishes, which, together with the seahorses, form the family Syngnathidae.-Anatomy:...
es and seahorse
Seahorse
Seahorses compose the fish genus Hippocampus within the family Syngnathidae, in order Syngnathiformes. Syngnathidae also includes the pipefishes. "Hippocampus" comes from the Ancient Greek hippos meaning "horse" and kampos meaning “sea monster”.There are nearly 50 species of seahorse...
s. In this family, only the males do the brooding. After the eggs are fertilized, the female places the embryos on the male. Herald (1950) notes a continuum of forms in the Syngnathidae
Syngnathidae
Syngnathidae is a family of fish which includes the seahorses, the pipefishes, and the weedy and leafy sea dragons. The name is derived from Greek, meaning "fused jaw" - syn meaning fused or together, and gnathus meaning jaws. This fused jaw trait is something the entire family has in common...
, starting with skin-brooding pipefishes and ending with seahorses, which have closed pouches with only one opening. In seahorses, after an extended courtship period, the female deposits eggs in the pouch (marsupium
Marsupium
Marsupium is the Latin word for a pouch in several animal groups:* Pouch , in marsupials* Brood pouch , in peracarid crustaceans* Brood pouch , in syngnathids such as sea horses...
) of the male by means of a penis-like oviduct
Oviduct
In non-mammalian vertebrates, the passageway from the ovaries to the outside of the body is known as the oviduct. The eggs travel along the oviduct. These eggs will either be fertilized by sperm to become a zygote, or will degenerate in the body...
. The eggs are fertilized as they enter the marsupium, and 25 to 100 embryos are provided with nutrients, oxygen and protection (Jones and Avise 1997). After hatching, the free embryos are carried in the pouch until they are capable of fairly active swimming, at which time they are expelled by the brooding male."
"Another way of internally carrying young that are spawned externally is found in mouth brooders. This method is found in families as diverse as sea catfishes
Ariidae
The Ariidae or ariid catfish are a family of catfish that mainly live in marine waters with many freshwater and brackish water species. They are found worldwide in tropical to warm temperate zones.-Taxonomy:...
, cichlid
Cichlid
Cichlids are fishes from the family Cichlidae in the order Perciformes. Cichlids are members of a group known as the Labroidei along with the wrasses , damselfish , and surfperches . This family is both large and diverse. At least 1,300 species have been scientifically described, making it one of...
s, cardinal fishes and bonytongues. Mouthbrooders carry the large, yolky embryos until they hatch, and these brooders typically carry the free embryos about as well. Even after the young become active, they are usually closely associated with the parent fish for a period of time and may flee back into the mouth cavity when threatened. In chchilids, both sexes may participate in some species, but the female usually carries the embryos, which she picks up quickly after spawning."
Mouth brooders
Mouthbrooder
Mouthbrooding, also known as oral incubation and buccal incubation, is the care given by some groups of animals to their offspring by holding them in the mouth of the parent for extended periods of time. Although mouthbrooding is performed by a variety of different animals, most notably Darwin's...
- carry eggs or larvae in their mouth. Mouth brooders can be ovophile
Ovophile
Ovophiles are mouthbrooding members of the Cichlidae family of fish . Ovophiles dig pits or holes in which the female lays eggs. The female lays eggs in this pit and then immediately takes the eggs into her mouth. The male then fertilizes the eggs in the female's mouth...
s or larvophiles. Ovophile or egg-loving mouth-brooders lay their eggs in a pit, which are sucked up into the mouth of the female. The small number of large eggs hatch in the mother's mouth, and the fry remain there for a period of time. Fertilization often occurs with the help of egg-spots, which are colorful spots on the anal fin of the male. When the female sees these spots, she tries to pick up the egg-spots, but instead gets a mouthful of sperm, fertilizing the eggs in her mouth. Many cichlids and some labyrinth fish are ovophile mouthbrooders. Larvophile or larvae-loving mouth-brooders lay their eggs on a substrate and guard them until the eggs hatch. After hatching, the female picks up the fry and keeps them in her mouth. When the fry can fend for themselves, they are released. Some eartheaters are larvophile mouthbrooders.
Internal bearers
"Internal bearers may have similarities to pouch brooders, although fertilization is internal and females always carry the embryos and/or young. Internal bearers typically produce only a small number of large, active young, which is a strategy characteristic of all sharks and raysBatoidea
Batoidea is a superorder of cartilaginous fish commonly known as rays and skates, containing more than 500 described species in thirteen families...
and a few bony fish. There seems to be no strong correlation between internal bearing families and the elaborateness of courtship behaviour. In guppies, mosquitofish
Mosquitofish
The mosquitofish is a species of freshwater fish, also commonly, if ambiguously, known by its generic name, gambusia. It is sometimes called the western mosquitofish, to distinguish it from the eastern mosquitofish . It is a member of the family Poeciliidae of order Cyprinodontiformes...
and other livebearing poeciliids. the most important trait of the courtship behaviour of males that successfully copulate with females seems to be persistence (although subtle interactions among competing males and other courtship-related behaviour do exist). In contrast, some surfperches have fairly elaborate courtship behaviour, with males establishing breeding territories to attract passing females."
Facultative internal bearers: The beginning of the evolutionary process of livebearing starts with facultative
Facultative
Facultative means "optional" or "discretionary" , used mainly in biology in phrases such as:* Facultative anaerobe, an organism that can use oxygen but also has anaerobic methods of energy production...
(optional) internal bearing. The process occurs in several species of oviparous (egg-laying) killifish
Killifish
A killifish is any of various oviparous cyprinodontiform fish . Altogether, there are some 1270 different species of killifish, the biggest family being Rivulidae, containing more than 320 species...
es which spawn in the normal way on the substrate, but in the process accidentally fertilize eggs which the female retains and does not spawn. These eggs are spawned later, usually without allowing much time for embryonic development.
Obligate internal bearers: The next step in the evolution of livebearing is obligate
Obligate
Obligate means "by necessity" and is used mainly in biology in phrases such as:* Obligate aerobe, an organism that cannot survive without oxygen* Obligate anaerobe, an organism that cannot survive in the presence of oxygen...
(by necessity) internal bearing, where the female retains all the embryos. "The only source of nutrition for these embryos, however, is the egg yolk, as in externally spawned eggs. This situation, also referred to as ovoviviparity
Ovoviviparity
Ovoviviparity, ovovivipary, or ovivipary, is a mode of reproduction in animals in which embryos develop inside eggs that are retained within the mother's body until they are ready to hatch...
, is characteristic of marine rock fishes and the Lake Baikal sculpin
Sculpin
A Sculpin is a fish that belongs to the order Scorpaeniformes, suborder Cottoidei and superfamily Cottoidea, that contains 11 families, 149 genera, and 756 species...
s. This strategy allows these fish to have fecundities approaching those of pelagic fish with external fertilization, but it also enables them to protect the young during their most vulnerable stage of development. By contrast, sharks and rays using this strategy produce a relatively small number of embryos and retain them for a few weeks to 16 months or longer. The shorter times spans are characteristic of species that eventually deposit their embryos in the environment, surrounded by a horny capsule; whereas the longer periods are characteristic of sharks that retain the embryos until they are ready to emerge as actively swimming young."
Viviparous fish: "Given the advantages of retaining the embryos internally, it is not surprising that a number of fishes have developed means to provide additional nutrition for their young while the female is carrying them and then give birth to large, active young (viviparity). Viviparous fishes provide nutrition for their young in various ways. The greatest variety is found in the sharks, but the teleosts also show a considerable range of methods. In the superperches, the young develop in the mother's ovary and obtain nutrients through the close contact of the extra-large fins with the ovarian wall. Many poeciliid embryos have highly vascular pericardial tissue that loops around the neck and is in close contact with the ovarian wall of the mother, through which nutrients are exchanged."
However, some fish do not fit these categories. The livebearing largespring gambusia
Gambusia
Gambusia is a large genus of fish in family Poeciliidae . Gambusia contains over 40 species, most of which are principally found in freshwater habitats, though some species may also be found in brackish or saltwater habitats. The type species is the Cuban gambusia, Gambusia punctata)...
(Gambusia geiseri) was thought to be ovoviviparous until it was shown in 2001 that the embryos received nutrients from the mother.
Spawning grounds
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
each year, and sometimes great migrations, to reach their spawning grounds. For example, lakes and river watersheds can be major spawning grounds for anadromous fish such as salmon
Salmon
Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...
. These days, it is often necessary to construct fish ladder
Fish ladder
A fish ladder, also known as a fishway, fish pass or fish steps, is a structure on or around artificial barriers to facilitate diadromous fishes' natural migration. Most fishways enable fish to pass around the barriers by swimming and leaping up a series of relatively low steps into the waters on...
s and other bypass systems so salmon can navigate their way past hydroelectric dams on their way to spawning grounds. Coastal fish
Coastal fish
Coastal fish, also called offshore fish or neritic fish, are fish that inhabit the sea between the shoreline and the edge of the continental shelf. Since the continental shelf is usually less than 200 metres deep, it follows that pelagic coastal fish are generally epipelagic fish, inhabiting the...
often use mangrove
Mangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
s and estuaries as spawning grounds, while reef fish
Reef fish
Coral reef fish are fish which live amongst or in close relation to coral reefs. Coral reefs form complex ecosystems with tremendous biodiversity. Among the myriad inhabitants, the fish stand out as particularly colourful and interesting to watch. Hundreds of species can exist in a small area of a...
can find adjacent seagrass meadows that make good spawning grounds. Short-finned eel
Short-finned eel
The short-finned eel, Anguilla australis, is one of the 15 species of eel in the family Anguillidae. It is native to the lakes, dams and coastal rivers of south-eastern Australia, New Zealand, and much of the South Pacific, including New Caledonia, Norfolk Island, Lord Howe Island, Tahiti, and...
s can travel anything up to three or four thousand kilometres to their spawning ground in deep water somewhere in the Coral Sea
Coral Sea
The Coral Sea is a marginal sea off the northeast coast of Australia. It is bounded in the west by the east coast of Queensland, thereby including the Great Barrier Reef, in the east by Vanuatu and by New Caledonia, and in the north approximately by the southern extremity of the Solomon Islands...
.
Forage fish
Forage fish
Forage fish, also called prey fish or bait fish, are small fish which are preyed on by larger predators for food. Predators include other larger fish, seabirds and marine mammals. Typical ocean forage fish feed near the base of the food chain on plankton, often by filter feeding...
often make great migrations between their spawning, feeding and nursery grounds. Schools of a particular stock usually travel in a triangle between these grounds. For example, one stock of herrings have their spawning ground in southern Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
, their feeding ground in Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
, and their nursery ground in northern Norway. Wide triangular journeys such as these may be important because forage fish, when feeding, cannot distinguish their own offspring.
Capelin
Capelin
The capelin or caplin, Mallotus villosus, is a small forage fish of the smelt family found in the Atlantic and Arctic oceans. In summer, it grazes on dense swarms of plankton at the edge of the ice shelf. Larger capelin also eat a great deal of krill and other crustaceans...
are a forage fish of the smelt family found in the Atlantic
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
and Arctic
Arctic Ocean
The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region, is the smallest and shallowest of the world's five major oceanic divisions...
oceans. In summer, they graze on dense swarms of plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
at the edge of the ice shelf. Larger capelin also eat krill
Krill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
and other crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s. The capelin move inshore in large schools to spawn and migrate in spring and summer to feed in plankton rich areas between Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
, Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
, and Jan Mayen
Jan Mayen
Jan Mayen Island is a volcanic island in the Arctic Ocean and part of the Kingdom of Norway. It is long and 373 km2 in area, partly covered by glaciers . It has two parts: larger northeast Nord-Jan and smaller Sør-Jan, linked by an isthmus wide...
. The migration is affected by ocean current
Ocean current
An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as breaking waves, wind, Coriolis effect, cabbeling, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun...
s. Around Iceland maturing capelin make large northward feeding migrations in spring and summer. The return migration takes place in September to November. The spawning migration starts north of Iceland in December or January.
The diagram on the right shows the main spawning grounds and larval drift routes. Capelin on the way to feeding grounds is coloured green, capelin on the way back is blue, and the breeding grounds are red. In a paper published in 2009, researchers from Iceland recount their application of an interacting particle model to the capelin stock around Iceland, successfully predicting the spawning migration route for 2008.
Referred to as "the greatest shoal
Shoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
on earth", the sardine run
Sardine run
The sardine run of southern Africa occurs from May through July when billions of sardines – or more specifically the Southern African pilchard Sardinops sagax – spawn in the cool waters of the Agulhas Bank and move northward along the east coast of South Africa...
occurs when millions of sardine
Sardine
Sardines, or pilchards, are several types of small, oily fish related to herrings, family Clupeidae. Sardines are named after the Mediterranean island of Sardinia, around which they were once abundant....
s migrate from their spawning grounds south of the southern tip of Africa northward along the Eastern Cape coastline. Chinook salmon
Chinook salmon
The Chinook salmon, Oncorhynchus tshawytscha, is the largest species in the pacific salmon family. Other commonly used names for the species include King salmon, Quinnat salmon, Spring salmon and Tyee salmon...
make the longest freshwater migration of any salmon, over 3000 kilometres (1,864.1 mi) up the Yukon River
Yukon River
The Yukon River is a major watercourse of northwestern North America. The source of the river is located in British Columbia, Canada. The next portion lies in, and gives its name to Yukon Territory. The lower half of the river lies in the U.S. state of Alaska. The river is long and empties into...
to spawning grounds upstream of Whitehorse
Whitehorse, Yukon
Whitehorse is Yukon's capital and largest city . It was incorporated in 1950 and is located at kilometre 1476 on the Alaska Highway in southern Yukon. Whitehorse's downtown and Riverdale areas occupy both shores of the Yukon River, which originates in British Columbia and meets the Bering Sea in...
, Yukon. Some green sea turtle
Green Sea Turtle
The Green sea turtle or green turtle is a large sea turtle of the family Cheloniidae. It is the only species in the genus Chelonia. Its range extends throughout tropical and subtropical seas around the world, with two distinct populations in the Atlantic and Pacific Oceans...
s swim more than 2600 kilometres (1,615.6 mi) to reach their spawning grounds.
Fish
Goldfish
Goldfish
The goldfish is a freshwater fish in the family Cyprinidae of order Cypriniformes. It was one of the earliest fish to be domesticated, and is one of the most commonly kept aquarium fish....
, like all cyprinid
Cyprinid
The family Cyprinidae, from the Ancient Greek kyprînos , consists of the carps, the true minnows, and their relatives . Commonly called the carp family or the minnow family, its members are also known as cyprinids...
s, are egg-layers. They usually start breeding after a significant temperature change, often in spring. Males chase females, prompting them to release their eggs by bumping and nudging them. As the female goldfish spawns her eggs, the male goldfish stays close behind fertilizing them. Their eggs are adhesive and attach to aquatic vegetation. The eggs hatch within 48 to 72 hours. Within a week or so, the fry begins to assume its final shape, although a year may pass before they develop a mature goldfish colour; until then they are a metallic brown like their wild ancestors. In their first weeks of life, the fry grow quickly—an adaptation born of the high risk of getting devoured by the adult goldfish.
Carp
A member of the Cyprinidae family, carp spawn in times between April and August, largely dependant upon the climate and conditions they live in. Oxygen levels of the water, availability of food, size of each fish, age, number of times the fish has spawned before and water temperature are all factors known to effect when and how many eggs each carp will spawn at any one time.
Siamese fighting fish
Prior to spawning, male Siamese fighting fish
Siamese fighting fish
The Siamese fighting fish , also known as the betta , is a popular species of freshwater aquarium fish. The name of the genus is derived from ikan bettah, taken from a local dialect of Malay...
build bubble nest
Bubble nest
Bubblenests, also spelled bubble nests or bubble-nests, created by some fish species, are floating masses of bubbles blown with an oral secretion, saliva bubbles, and occasionally aquatic plants, or an area for egg deposit attached at the bottom. Fish that build and guard bubble nests are known as...
s of varying sizes at the surface of the water. When a male becomes interested in a female, he will flare his gills, twist his body, and spread his fins. The female darkens in colour and curves her body back and forth. The act of spawning takes place in a "nuptial embrace" where the male wraps his body around the female, each embrace resulting in the release of 10-40 eggs until the female is exhausted of eggs. The male, from his side, releases milt
Milt
Milt is the seminal fluid of fish, mollusks, and certain other water-dwelling animals who reproduce by spraying this fluid, which contains the sperm, onto roe .-Milt as food:...
into the water and fertilization takes place externally. During and after spawning, the male uses his mouth to retrieve sinking eggs and deposit them in the bubble nest (during mating the female sometimes assists her partner, but more often she will simply devour all the eggs that she manages to catch). Once the female has released all of her eggs, she is chased away from the male's territory, as it is likely that she'll eat the eggs due to hunger. The eggs then remain in the male's care. He keeps them in the bubble nest, making sure none fall to the bottom and repairing the nest as needed. Incubation lasts for 24–36 hours, and the newly hatched larvae remain in the nest for the next 2–3 days, until their yolk sacs are fully absorbed. Afterwards the fry leave the nest and the free-swimming stage begins.
Crustaceans
Copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
s are tiny crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s which usually reproduce either by broadcast spawning or by sac spawning. Broadcasting copepods scatter their eggs into the water, but sac spawners lay their eggs into an ovigerous sac. Sac spawners spawn few but relatively large eggs that develop slowly. By contrast, broadcast spawners spawn numerous small eggs that develop rapidly. However, the shorter hatch times that result from broadcasting are not short enough to compensate for the higher mortality compared to sac spawners. To produce a given number of hatched eggs, broadcasters must spawn more eggs than sac spawners.
Spiny lobsters
After mating, the fertilized eggs of the California spiny lobster
California spiny lobster
The California spiny lobster, Panulirus interruptus, is a species of spiny lobster found in the eastern Pacific Ocean from Monterey Bay, California to the Gulf of Tehuantepec, Mexico. It typically grows to a length of and is a reddish-brown color with stripes along the legs, and has a pair of...
are carried on the female's pleopods until they hatch, with between 120,000 and 680,000 carried by a single female. The eggs begin coral red, but darken as they develop to a deep maroon. When she is carrying the eggs, the female is said to be "berried". The eggs are ready to hatch after 10 weeks, and spawning takes place from May to August,> The larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e that hatch (called phyllosoma
Phyllosoma
The phyllosoma is the larval stage of spiny, slipper and coral lobsters , and represents one of the most significant characteristics that unify them into the taxon Achelata...
larvae) do not resemble the adults. Instead, they are flat, transparent
Transparency and translucency
In the field of optics, transparency is the physical property of allowing light to pass through a material; translucency only allows light to pass through diffusely. The opposite property is opacity...
animals around 14 mm (0.551181102362205 in) long, but as thin as a sheet of paper. The larvae feed on plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
, and grow through ten molts
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
into ten further larval stages, the last of which is around 30 millimetre long. The full series of larval molts takes around 7 months, and when the last stage molts, it metamorphoses
Metamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
into the puerulus state, which is a juvenile
Juvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
form of the adult, though still transparent. The puerulus larvae settle to the sea floor when the water is near its maximum temperature, which in Baja California is in the fall.
Egg-bearing female lobster
Lobster
Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...
s migrate inshore from deeper waters to hatch their eggs, though they do not have specific spawning grounds. These lobster migrations can occur in close single-file formation "lobster trains".
Molluscs
Pacific oystersOysters are broadcast spawners, that is, eggs and sperm are released into open water where fertilisation occurs. They are protandric; during their first year they spawn as males by releasing sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
into the water. As they grow over the next two or three years and develop greater energy reserves, they spawn as females by releasing eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
. Bay oysters usually spawn by the end of June. An increase in water temperature prompts a few oysters to spawn. This triggers spawning in the rest, clouding the water with millions of eggs and sperm. A single female oyster can produce up to 100 million eggs annually. The eggs become fertilized in the water and develop rapidly into planktonic larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e. which eventually find suitable sites, such as another oyster's shell, on which to settle. Attached oyster larvae are called spat. Spat are oysters less than 25 millimetre (0.984251968503937 in) long.
The Pacific oyster
Pacific oyster
The Pacific oyster, Japanese oyster or Miyagi oyster , is an oyster native to the Pacific coast of Asia. It has become an introduced species in North America, Australia, Europe, and New Zealand.- Etymology :...
usually has separate sexes. Their sex can be determined by examining the gonad
Gonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s, and it can change from year to year, normally during the winter months. In certain environmental conditions, one sex is favoured over the other. Protandry
Dichogamy
Sequential hermaphroditism is a type of hermaphroditism that occurs in many fish, gastropods and plants. Here, the individual is born one sex and changes sex at some point in their life. They can change from a male to female , or from female to male...
is favoured in areas of high food abundance and protogyny occurs in areas of low food abundance. In habitats with a high food supply, the sex ratio
Sex ratio
Sex ratio is the ratio of males to females in a population. The primary sex ratio is the ratio at the time of conception, secondary sex ratio is the ratio at time of birth, and tertiary sex ratio is the ratio of mature organisms....
in the adult population tends to favour females, and areas with low food abundances tend to have a larger proportion of male adults. Spawning in the Pacific oyster occurs at 20 °C (68 °F). This species is very fecund
Fecundity
Fecundity, derived from the word fecund, generally refers to the ability to reproduce. In demography, fecundity is the potential reproductive capacity of an individual or population. In biology, the definition is more equivalent to fertility, or the actual reproductive rate of an organism or...
, with females releasing about 50–200 million eggs in regular intervals (at a rate of 5–10 times a minute) in a single spawning. Once released from the gonad
Gonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s, the eggs move through the suprabranchial chambers (gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s), are then pushed through the gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
ostia into the mantle chamber, and are finally released in the water, forming a small cloud. In males, the sperm is released at the opposite end of the oyster, along with the normal exhalent stream of water. A rise in water temperature is thought to be the main cue in the initiation of spawning, as the onset of higher water temperatures in the summer results in earlier spawning in the Pacific oyster.
The larvae
Larvae
In Roman mythology, lemures were shades or spirits of the restless or malignant dead, and are probably cognate with an extended sense of larvae as disturbing or frightening...
of the Pacific oyster are planktotrophic
Marine larval ecology
Marine larval ecology is the study of the factors influencing the dispersing larval stage exhibited by many marine invertebrates and fishes. Marine organisms with a larval stage usually release large numbers of larvae into the water column, where these larvae develop and grow for a certain period...
, and are about 70 µm at the prodissoconch
Apex (mollusc)
Apex is an anatomical term for the tip of the mollusc shell of a gastropod, scaphopod, or cephalopod mollusc.-Gastropods:The word "apex" is most often used to mean the tip of the spire of the shell of a gastropod...
1 stage. The larvae
Larvae
In Roman mythology, lemures were shades or spirits of the restless or malignant dead, and are probably cognate with an extended sense of larvae as disturbing or frightening...
move through the water column via the use of a larval foot to find suitable settlement locations. They can spend several weeks at this phase, which is dependent on water temperature, salinity and food supply. Over these weeks, larvae
Larvae
In Roman mythology, lemures were shades or spirits of the restless or malignant dead, and are probably cognate with an extended sense of larvae as disturbing or frightening...
can disperse great distances by water currents before they metamorphose
Metamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
and settle as small spat
Oyster
The word oyster is used as a common name for a number of distinct groups of bivalve molluscs which live in marine or brackish habitats. The valves are highly calcified....
. Similar to other oyster species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
, once the Pacific oyster larvae
Larvae
In Roman mythology, lemures were shades or spirits of the restless or malignant dead, and are probably cognate with an extended sense of larvae as disturbing or frightening...
find a suitable habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
, they attach to it permanently using cement secreted from a gland in their foot. After settlement, the larvae metamorphose into juvenile spat. The growth rate is very rapid in optimum environmental conditions, and market size can be achieved in 18 to 30 months.
Cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s, such as squid and octopuses, have prominent heads and a set of arms (tentacle
Tentacle
A tentacle or bothrium is one of usually two or more elongated flexible organs present in animals, especially invertebrates. The term may also refer to the hairs of the leaves of some insectivorous plants. Usually, tentacles are used for feeding, feeling and grasping. Anatomically, they work like...
s) modified from the primitive foot of molluscs. All cephalopods are sexually dimorphic
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
. However, they lack external sexual characteristics, so they use colour communication. A courting male approaches a likely looking mate flashing his brightest colours, often in rippling displays. If the other cephalopod is female and receptive, her skin will change colour to become pale, and mating will occur. If the other cephalopod remains brightly coloured, it is taken as a warning.
All cephalopods reproduce by spawning egg
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
s. Most cephalopods use semi-internal fertilization where the male places his gametes inside the female's mantle cavity to fertilize the ova
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
in the female's single ovary
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
. The "penis" in most male cephalopods is a long and muscular end of the gonoduct used to transfer spermatophores to a modified sperm-carrying arm called a hectocotylus
Hectocotylus
A hectocotylus is one of the arms of the male of most kinds of cephalopods that is modified in various ways to effect the fertilization of the female's eggs. It is a specialized, extended muscular hydrostat used to store spermatophores, the male gametophore...
. That in turn is used to transfer the spermatophores to the female. In species where the hectocotylus is missing, the "penis" is long and able to extend beyond the mantle cavity and transfers the spermatophores directly to the female. In many cephalopods, mating occurs head to head and the male may simply transfer sperm to the female. Others may detach the sperm-carrying arm and leave it attached to the female. Deep water squid have the greatest known penis length relative to body size of all mobile animals, second in the entire animal kingdom only to certain sessile barnacle
Barnacle
A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are sessile suspension feeders, and have...
s. Penis elongation in the greater hooked squid
Greater Hooked Squid
The Greater Hooked Squid is a species of squid in the family Onychoteuthidae. It occurs worldwide in subantartic oceans.Although O...
may result in a penis that is as long as the mantle, head and arms combined.
Some species brood their fertilized eggs: female paper nautilus construct shelters for the young, while Gonatiid squid carry a larva-laden membrane from the hooks on their arms. Other cephalopods deposit their young under rocks and aerate them with their tentacles hatching. Mostly the eggs are left to their own devices; many squid lay sausage-like bunches of eggs in crevices or occasionally on the sea floor. Cuttlefish
Cuttlefish
Cuttlefish are marine animals of the order Sepiida. They belong to the class Cephalopoda . Despite their name, cuttlefish are not fish but molluscs....
lay eggs separately in cases and attach them to coral or algal fronds. Like Pacific salmon, cephalopods are mostly semelparous, spawning many small eggs in one batch and then dying. Cephalopods usually live fast and die young. Most of the energy extracted from their food is used for growing, and they mature rapidly to their adult size. Some gain as much as 12% of their body mass each day. Most live for one to two years, reproducing and then dying shortly thereafter.
Echinoderms
Echinoderm
Echinoderms are a phylum of marine animals. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone....
s are marine animals, widespread in all oceans, but not found in fresh water. Just below their skin is an endoskeleton
Endoskeleton
An endoskeleton is an internal support structure of an animal, composed of mineralized tissue. Endoskeleton develops within the skin or in the deeper body tissues. The vertebrate is basically an endoskeleton made up of two types of tissues . During early embryonic development the endoskeleton is...
composed of calcareous
Calcareous
Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...
plates or ossicles.
Sea urchins
Sea urchin
Sea urchin
Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull...
s are spiky echinoderms with spherical bodies which usually contain five gonad
Gonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s. They move slowly, feed mostly on seaweed
Seaweed
Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...
, and are important for the diet of sea otter
Sea Otter
The sea otter is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between 14 and 45 kg , making them the heaviest members of the weasel family, but among the smallest marine mammals...
s. Sea urchins are dioecious
Dioecious
Dioecy is the property of a group of biological organisms that have males and females, but not members that have organs of both sexes at the same time. I.e., those whose individual members can usually produce only one type of gamete; each individual organism is thus distinctly female or male...
, having separate male and female sexes, although there is generally no easy way to distinguish the two. The gonads are lined with muscles underneath the peritoneum
Peritoneum
The peritoneum is the serous membrane that forms the lining of the abdominal cavity or the coelom — it covers most of the intra-abdominal organs — in amniotes and some invertebrates...
, and these allow the animal to squeeze its gamete
Gamete
A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
s through the duct and into the surrounding sea water, where fertilization takes place. Their roe
Roe
Roe or hard roe is the fully ripe internal egg masses in the ovaries, or the released external egg masses of fish and certain marine animals, such as shrimp, scallop and sea urchins...
(male and female gonads) is soft and melting, with a colour ranging from orange to pale yellow, and is sought after as a human delicacy in many parts of the world.
Sea cucumbers
Sea cucumber
Sea cucumber
Sea cucumbers are echinoderms from the class Holothuroidea.They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. There are a number of holothurian species and genera, many of which are targeted...
s are leathery echinoderms with elongated bodies which contain a single, branched gonad. They are found on the sea floor worldwide, and occur in great numbers on the deep sea floor where they often make up the majority of the animal biomass
Biomass (ecology)
Biomass, in ecology, is the mass of living biological organisms in a given area or ecosystem at a given time. Biomass can refer to species biomass, which is the mass of one or more species, or to community biomass, which is the mass of all species in the community. It can include microorganisms,...
. They feed on plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
and decaying organic debris found at the sea bottom, catching food that flows by with their open tentacles or sifting through bottom sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
s. Like sea urchins, most sea cucumbers reproduce by releasing sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
and ova
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
into the ocean water. Depending on conditions, one organism can produce thousands of gamete
Gamete
A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
s.
Dioecious
Dioecy is the property of a group of biological organisms that have males and females, but not members that have organs of both sexes at the same time. I.e., those whose individual members can usually produce only one type of gamete; each individual organism is thus distinctly female or male...
, with separate male and female individuals. The reproductive system consists of a single gonad
Gonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
, consisting of a cluster of tubules emptying into a single duct that opens on the upper surface of the animal, close to the tentacles. Many species fertilise their eggs internally. The fertilised egg develops in a pouch on the adult's body and eventually hatches as a juvenile sea cucumber. A few species brood their young inside the body cavity, giving birth through a small rupture in the body wall close to the anus. The remaining species develop their eggs into a free-swimming larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
, usually after about three days of development. This larva swims by means of a long band of cilia wrapped around its body. As the larva grows it transforms into a barrel-shaped body with three to five separate rings of cilia. The tentacles are usually the first adult features to appear, before the regular tube feet.
Amphibious animals
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s are found in and around fresh water lakes and ponds, but not in marine environments. Examples are frogs and toads, salamander
Salamander
Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...
s, newt
Newt
A newt is an aquatic amphibian of the family Salamandridae, although not all aquatic salamanders are considered newts. Newts are classified in the subfamily Pleurodelinae of the family Salamandridae, and are found in North America, Europe and Asia...
s and caecilian
Caecilian
The caecilians are an order of amphibians that superficially resemble earthworms or snakes. They mostly live hidden in the ground, making them the least familiar order of amphibians. All extant caecilians and their closest fossil relatives are grouped as the clade Apoda. They are mostly...
s (which resemble snakes). They are cold-blooded animals that metamorphose
Metamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
from a juvenile water-breathing form, usually to an adult air-breathing form, though mudpuppies retain juvenile gills in adulthood.
Frogs and toads
Female frogs and toads usually spawn gelatinous egg masses containing thousands of eggs in water. Different species lay eggs in distinctive and identifiable ways. For example, the American toad
American toad
The American Toad is a common species of toad found throughout the eastern United States and Canada. It is divided into three subspecies—the Eastern American Toad , the Dwarf American Toad , and the rare Hudson Bay Toad...
lays long strings of eggs. The eggs are highly vulnerable to predation
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
, so frogs have evolved many techniques to ensure the survival of the next generation. In colder areas the embryo is black to absorb more heat from the sun, which speeds up development. Most commonly, this involves synchronous reproduction. Many individuals will breed at the same time, overwhelming the actions of predators; the majority of the offspring will still die due to predation, but there is a greater chance some will survive. Another way in which some species avoid predators and the pathogens eggs are exposed to in ponds is to lay eggs on leaves above the pond, with a gelatinous coating designed to retain moisture. In these species the tadpoles drop into the water upon hatching. The eggs of some species laid out of water can detect vibrations of nearby predatory wasps or snakes, and will hatch early to avoid being eaten.
While the length of the egg stage depends on the species and environmental conditions, aquatic eggs generally hatch within one week. Unlike salamanders and newts, frogs and toads never become sexually mature while still in their larval stage. The hatched eggs continue life as tadpole
Tadpole
A tadpole or polliwog is the wholly aquatic larval stage in the life cycle of an amphibian, particularly that of a frog or toad.- Appellation :...
s, which typically have oval bodies and long, vertically flattened tails. As a general rule, free living larvae are fully aquatic. They lack eyelids and have a cartilaginous skeleton, a lateral line system, gills for respiration (external gills at first, internal gills later) and tails with dorsal and ventral folds of skin for swimming. They quickly develop a gill pouch that covers the gills and the front legs; the lungs are also developed at an early stage as an accessory breathing organ. Some species which go through the metamorphosis inside the egg and hatch to small frogs never develop gills; instead there are specialised areas of skin that take care of respiration. Tadpoles also lack true teeth, but the jaws in most species usually have two elongate, parallel rows of small keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
ized structures called keradonts in the upper jaw while the lower jaw has three rows of keradonts, surrounded by a horny
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
beak, but the number of rows can be lower (sometimes zero), or much higher. Tadpoles feed on algae, including diatom
Diatom
Diatoms are a major group of algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons , fans , zigzags , or stellate colonies . Diatoms are producers within the food chain...
s filtered from the water through the gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s. Some species are carnivorous at the tadpole stage, eating insects, smaller tadpoles, and fish. Cannibalism
Cannibalism
Cannibalism is the act or practice of humans eating the flesh of other human beings. It is also called anthropophagy...
has been observed among tadpoles. Early developers who gain legs may be eaten by the others, so the late bloomers survive longer.
Sea turtles
Sea turtle
Sea turtle
Sea turtles are marine reptiles that inhabit all of the world's oceans except the Arctic.-Distribution:...
s are amphibious reptiles, but they are not amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s. Reptiles belong to the class Reptilia while amphibians belong to the class Amphibia. These are two distinct taxonomic groups. Reptiles have scales and leathery skins, while the skins of amphibians are smooth and porous. Unlike frogs, sea turtle eggs have tough, leathery shells which allow them to survive on land without drying out.
Some sea turtles migrate long distances between feeding and spawning grounds. Green turtles have feeding grounds along the Brazilian coast. Each year, thousands of these turtles migrate about 2300 kilometres (1,429.2 mi) to their spawning ground, Ascension Island
Ascension Island
Ascension Island is an isolated volcanic island in the equatorial waters of the South Atlantic Ocean, around from the coast of Africa and from the coast of South America, which is roughly midway between the horn of South America and Africa...
in the Atlantic, an island only 11 kilometres (6.8 mi) across. Each year the returning turtles dig between 6,000 and 15,000 nests, often returning to the same beach from where they hatched. Females usually mate every two to four years. Males on the other hand visit the breeding areas every year, attempting to mate. Green sea turtles' mating is similar to other marine turtles. Female turtles control the process. A few populations practice polyandry
Polyandry
Polyandry refers to a form of marriage in which a woman has two or more husbands at the same time. The form of polyandry in which a woman is married to two or more brothers is known as "fraternal polyandry", and it is believed by many anthropologists to be the most frequently encountered...
, although this does not seem to benefit hatchlings. After mating in the water, the female moves above the beach's high tide line where she digs a hole with her hind flippers and deposits her eggs. Litter size depends on the age of the female and species, but green turtle clutches range between 100 to 200. She then covers the nest with sand and returns to the sea.
Instinct
Instinct or innate behavior is the inherent inclination of a living organism toward a particular behavior.The simplest example of an instinctive behavior is a fixed action pattern, in which a very short to medium length sequence of actions, without variation, are carried out in response to a...
ively head directly into the water. This is the most dangerous time in a turtle's life. As they walk, predators such as gull
Gull
Gulls are birds in the family Laridae. They are most closely related to the terns and only distantly related to auks, skimmers, and more distantly to the waders...
s and crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s grab them. A significant percentage never make it to the ocean. Little is known of the initial life history of newly hatched sea turtles. Juveniles spend three to five years in the open ocean before they settle as still-immature juveniles into their permanent shallow-water lifestyle. It is speculated that they take twenty to fifty years to reach sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
. Individuals live up to eighty years in the wild. They are among the larger sea turtles, many more than a meter long and weighing up to 300 kilograms (661.4 lb).
Aquatic insects
Aquatic insects also spawn. MayfliesMayfly
Mayflies are insects which belong to the Order Ephemeroptera . They have been placed into an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies...
"are famed for their short adult life. Some species have under an hour to mate and lay their eggs before they die. Their pre-adult stage, known as the subimago, may be even shorter - perhaps lasting just a few minutes before they moult into their adult form. Therefore a mayfly spends most of its life as a nymph, hidden from view under the water."
Corals
Gonochorism
In biology, gonochorism or unisexualism describes sexually reproducing species in which individuals have just one of at least two distinct sexes. The term is most often used with animals . The sex of an individual may change during its lifetime, this can for example be found in parrotfish...
(unisexual) and hermaphroditic, each of which can reproduce sexually and asexually. Reproduction also allows corals to settle new areas.
Corals predominantly reproduce sexually
Sexual reproduction
Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...
. 25% of hermatypic coral
Hermatypic coral
Hermatypic corals or "stony corals" are reef-building corals, while corals that do not deposit aragonite structures and contribute to coral reef development are referred to as ahermatypic species....
s (stony corals) form single sex (gonochoristic) colonies, while the rest are hermaphroditic. About 75% of all hermatypic corals "broadcast spawn" by releasing gamete
Gamete
A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
s—eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
and sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
—into the water to spread offspring. The gametes fuse during fertilization to form a microscopic larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
called a planula
Planula
A planula is the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species. The planula forms from the fertilized egg of a medusa, as the case in scyphozoans and some hydrozoans, or from a polyp, as in the case of anthozoans...
, typically pink and elliptical in shape. A typical coral colony form several thousand larvae per year to overcome the odds against formation of a new colony.
Planulae exhibit positive phototaxis
Phototaxis
Phototaxis is a kind of taxis, or locomotory movement, that occurs when a whole organism moves in response to the stimulus of light. This is advantageous for phototrophic organisms as they can orient themselves most efficiently to receive light for photosynthesis...
, swimming towards light to reach surface waters where they drift and grow before descending to seek a hard surface to which they can attach and establish a new colony. They also exhibit positive sonotaxis, moving towards sounds that emanate from the reef and away from open water. High failure rates afflict many stages of this process, and even though millions of gametes are released by each colony very few new colonies form. The time from spawning to settling is usually 2–3 days, but can be up to 2 months. The larva grows into a polyp and eventually becomes a coral head by asexual budding and growth.
Reproductive synchrony
Reproductive synchrony is a term used in evolutionary biology and behavioural ecology. Reproductive synchrony — sometimes termed 'ovulatory synchrony' — may manifest itself as 'breeding seasonality'...
is very typical on the coral reef and often, even when multiple species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
are present, all corals spawn on the same night. This synchrony is essential so that male and female gametes can meet. Corals must rely on environmental cues, varying from species to species, to determine the proper time to release gametes into the water. The cues involve lunar changes, sunset time, and possibly chemical signalling. Synchronous spawning may form hybrids and is perhaps involved in coral speciation
Speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
. In some places the spawn can be visually dramatic, clouding the usually clear water with gametes, typically at night.
Corals use two methods for sexual reproduction, which differ in whether the female gametes are released:
- Broadcasters, the majority of which mass spawn, rely heavily on environmental cues, because they release both sperm and eggs into the water. The corals use long-term cues such as day lengthDay lengthDay length, or length of day, or length of daytime, refers to the time each day from the moment the upper limb of the sun's disk appears above the horizon during sunrise to the moment when the upper limb disappears below the horizon during sunset...
, water temperature, and/or rate of temperature change. The short-term cue is most often the lunar cycleLunar phaseA lunar phase or phase of the moon is the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. The lunar phases change cyclically as the Moon orbits the Earth, according to the changing relative positions of the Earth, Moon, and Sun...
, with sunset cuing the release. About 75% of coral species are broadcasters, the majority of which are hermatypic, or reef-building corals. The positively buoyant gametes float towards the surface where fertilization produces planulaPlanulaA planula is the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species. The planula forms from the fertilized egg of a medusa, as the case in scyphozoans and some hydrozoans, or from a polyp, as in the case of anthozoans...
larvae. The larvae swim towards the surface light to enter into currents, where they usually remain for two days, but sometimes up to three weeks, and in one known case two months, after which they settle and metamorphose into polyps and form colonies. - Brooders are most often ahermatypic (non-reef building) in areas of high current or wave action. Brooders release only sperm, which is negatively buoyant, and can harbor unfertilized eggs for weeks, lowering the need for mass synchronous spawning events, which do sometimes occur. After fertilization the corals release planulaPlanulaA planula is the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species. The planula forms from the fertilized egg of a medusa, as the case in scyphozoans and some hydrozoans, or from a polyp, as in the case of anthozoans...
larvae which are ready to settle.
Fungi
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
are not plants, and require different conditions for optimal growth. Plants develop through photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
, a process that converts atmospheric carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
into carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
s, especially cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
. While sunlight provides an energy source for plants, mushrooms derive all of their energy and growth materials from their growth medium
Growth medium
A growth medium or culture medium is a liquid or gel designed to support the growth of microorganisms or cells, or small plants like the moss Physcomitrella patens.There are different types of media for growing different types of cells....
, through biochemical decomposition
Decomposition
Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...
processes. This does not mean that light is an unnecessary requirement, since some fungi use light as a signal to induce fruiting. However, all the materials for growth must already be present in the growth medium. Instead of seeds, mushrooms reproduce sexually during underground growth, and asexually through spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s. Either of these can be contaminated with airborne microorganisms, which will interfere with mushroom growth and prevent a healthy crop. Mycelium
Mycelium
thumb|right|Fungal myceliaMycelium is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae. The mass of hyphae is sometimes called shiro, especially within the fairy ring fungi. Fungal colonies composed of mycelia are found in soil and on or within many other...
, or actively growing mushroom culture, is placed on growth substrate to seed or introduce mushrooms to grow on a substrate
Substrate (biology)
In biology a substrate is the surface a plant or animal lives upon and grows on. A substrate can include biotic or abiotic materials and animals. For example, encrusting algae that lives on a rock can be substrate for another animal that lives on top of the algae. See also substrate .-External...
. This is also known as inoculation, spawning or adding spawn. Its main advantages are to reduce chances of contamination while giving mushrooms a firm beginning.
See also
- Anadromous
- Egg case
- Federal Inventory of Amphibian Spawning AreasFederal Inventory of Amphibian Spawning AreasThe Federal Inventory of Amphibian Spawning Areas is part of a 2001 Ordinance of the Swiss Federal Council implementing the Federal Law on the Protection of Nature and Cultural Heritage. The inventory includes spawning areas of amphibians of national importance in Switzerland...
- IchthyoplanktonIchthyoplanktonIchthyoplankton are the eggs and larvae of fish. They are usually found in the sunlit zone of the water column, less than 200 metres deep, which is sometimes called the epipelagic or photic zone...
- MiltMiltMilt is the seminal fluid of fish, mollusks, and certain other water-dwelling animals who reproduce by spraying this fluid, which contains the sperm, onto roe .-Milt as food:...
- MouthbrooderMouthbrooderMouthbrooding, also known as oral incubation and buccal incubation, is the care given by some groups of animals to their offspring by holding them in the mouth of the parent for extended periods of time. Although mouthbrooding is performed by a variety of different animals, most notably Darwin's...
- Reproduction
- Salmon runSalmon runThe salmon run is the time at which salmon swim back up the rivers in which they were born to spawn. All Pacific salmon die after spawning. While most Atlantic salmon die after their first spawn, about 5-10% return to the sea to feed between spawnings. The annual run is a major event for sport...
- Spawning bedSpawning bedA spawning bed is an underwater solid surface on which fish spawn to reproduce themselves.In fishery management, a spawning bed is an artificial bed constructed by wildlife professionals in order to improve the ability of desired game fish to reproduce...
- Spawning triggersSpawning triggersSpawning triggers are environmental cues that cause fish to breed. Most commonly they involve sudden changes in the environment, such as changes in temperature, salinity, and the abundance of food. Catfish of the genus Corydoras, for example, spawn immediately after heavy rain, the specific cues...
- Stream poolStream poolA stream pool, in hydrology, is a stretch of a river or stream in which the water depth is above average and the water velocity is quite below average.-Formation:...
External links
- Reproduction FAOFãoFão is a town in Esposende Municipality in Portugal....
, Rome.