Paranephrops
Encyclopedia
Paranephrops is a genus of freshwater
crayfish
species endemic to New Zealand
. They are known as in New Zealand, derived from the Māori language
. The two species are divided by the Southern Alps
of New Zealand's South Island
.
, but also in Marlborough
, Nelson
and the West Coast
of the South Island
. They reach lengths of about 70 millimetres (2.8 in).
, and on Stewart Island/Rakiura
. They reach lengths of about 80 millimetres (3.1 in). Koura occupy freshwater streams, lakes, rivers and swamps. Koura use their 4 pairs of walking legs to move through their environment and when alarmed can flick their tail forwards violently to propel themselves backwards at speed in order to avoid any threat. The koura's first pair of legs (chelae) are pincers that are used for scavenging, food and warding off predators or other koura.
their exoskeleton
s in order to increase in size. During moulting the carapace
becomes soft with calcium
being resorbed and the remaining outer shell shed. The new carapace forms underneath where it takes a number of days to harden. Calcium for this new outer shell comes from gastrolith
s that line the stomach wall of the koura and these produce around 10%–20% of the calcium needs for exoskeleton production. The gastroliths drop into the koura's foregut where they are broken down to allow the adsorption of calcium. Post moulting the demand for calcium in order to harden the exoskeleton is high and this demand is met in part by the koura eating its discarded exoskeleton. The remaining calcium required to completely harden the exoskeleton is achieved by absorption from the water. Lower limits of 5 mg/L of calcium
(Ca) in water for temperate species of koura have been suggested as sufficient to support exoskeleton hardening.
Water temperature and calcium concentrations are thought to be the key variables determining koura growth rates.
P. zealandicus have high survivability (>80%) rates below 16 °C (60.8 °F) but temperatures above this correlate with lower rates of survivability. Higher death rates are thought to be associated with increased activity of koura at higher temperatures. Greater activity by koura increases cannibalistic behaviour and increased activity may also impact on water quality with the greater production of ammonia
as a waste product. Survival of koura also increases with higher calcium concentrations in the water and this is thought to be in part due to a lower incidence of moulting related deaths and decreased risk from predation. A calcium concentration value of 20–30 mg/L Ca in water is thought to be ideal for maintaining koura growth and survivability in aquaculture setups.
, chironomids
, and mayflies
are the predominant food sources in the koura diet. Juvenile koura require higher amounts of protein
in their diet than adults due to greater growth rate demands with invertebrates forming the bulk of their diet. Koura in lakes have been shown to feed predominantly in the littoral zone where food availability is greatest. Feeding in the littoral zone may reflect diel movement with koura moving to deeper and darker parts of lakes to avoid predation during daylight hours and moving to the littoral zone at night in order to feed.
In lakes the type of habitat that koura occupy is largely influenced by light levels, with koura moving into shallower areas of the water column during periods of darkness and deeper parts of the water column during daylight hours. During daytime koura find shelter under rocks, debris such as cans and bottles, and vegetation. In soft sediments koura may also excavate fan shaped depressions with this commonly occurring at depths of 12–30 m (39.4–98.4 ) in some lakes. In streams koura take cover on the bottom beneath fallen leaf litter, fallen logs, and tree roots and undercut banks. Tree fern roots that project into the stream are thought to provide excellent cover for juvenile koura.
, perch
, catfish
and trout
are the major aquatic predators of koura. Other terrestrial predators include rat
s, kingfishers
, shags
, scaup
, stoat
s and kiwi
. Shag populations from the Te Arawa
lakes district in the North Island of New Zealand have been shown to feed on koura as the bulk of their diet. Predation on koura by trout is thought to be restricted to larger adult trout. Streams and lakes with established populations of trout have been shown to affect koura abundance. Cannibalism
in koura is most likely to occur when koura are sick or moulting. Cannibalism can be a greater problem in high density situations where competition
for shelter and territory is greatest. Juvenile koura can be consumed whole by larger koura and this presents problems for aquaculture
in ensuring continuity of intergenerational growth. Koura use their chelae for both attack and defence and when one limb is lost the koura will divert energy for overall growth to restoring the lost limb. The only disease known to seriously affect koura is "white tail disease" and this is caused by the microsporidian parasite Thelohania contejeani. This parasite causes degeneration of striated muscle in the tail area and this turns the tail a pale white colour and correspondingly leads to death soon after.
under the side flaps of her abdomen whereby they take 3–4 months to hatch. Over this time male sperm production corresponds with females' reproductivity. Once hatched juvenile koura cling to their mother’s abdomen using their pincers to attach until they have reached a length of 4–10 mm (0.15748031496063–0.393700787401575 ). At this stage they resemble adult koura in appearance. In Lake Rotoiti in the central North Island of New Zealand the main breeding period occurs between April–July (autumn–winter) with a second breeding period occurring from October–January (spring–summer). The total breeding length time from peak egg laying to the release of juveniles is estimated to be 28 weeks for the autumn–winter period and 19–20 weeks in spring–summer breeding groups. This difference is attributed to warmer temperatures speeding up the egg development process. In stream populations this growth period has been shown to take around 25–26 weeks in P. planifrons, and up to 60 weeks for P. zealandicus in Otago streams.
dish. Koura are harvestable once larger than 100 mm (3.9 in) in total length which can take between 2-5 years in P. planifrons. Sweet Koura Enterprises Ltd located in Central Otago, within the South Island of New Zealand, farm P. zealandicus in artificial ponds of approximately 200 square metres (239.2 sq yd) in size. These ponds attempt to replicate the natural environment that P. zealandicus grow in. Water supplied to the growing ponds is sourced from an aquifer
and is artificially aerated. The temperature of the water is controlled to reflect the seasonal temperature variations that would be expected in the natural environment. The optimum temperature for growth in these ponds is achieved at between 15–18 °C (59–64.4 F) with P. zealandicus sensitive to rapid temperature changes. The natural biological life in a pond can support 3–4 koura per square metre. Additional feed in the form of fish based pallets are supplied to koura to support growth and this feed has been altered to reflect the lower protein, higher calcium nutritional requirements of koura. Overstocking of crayfish can lead to higher rates of mortality which is associated with higher rates of cannibalism and increased competition for shelter and food.
New Zealand Clearwater Crayfish Ltd farm the northern koura species P. planifrons using a gravity fed system with pond culture and raceways for farming koura. A key step in this koura farm is the depuration of koura in clean running water without food for up to 2 days in order to purge the gut cavity. This enables the tail to be presented as an appealing white flesh to the consumer.
In order to breed koura in aquaculture a ratio of 1 male to 5 females is suggested during the mating periods with koura removed and placed in separate tanks depending of the life stage once hatched. The creation of artificial habitat in ponds may support koura survival. The use of plastic containers, tyres, plastic piping and bottles are all possible habits for koura to occupy when being grown in ponds. The suggested depth for ponds used to farm P. zealandicus are 1.3 metre deep.
A number of environmental challenges exist to koura farmers in ensuring optimum growth and survivability of stock. Environmental contamination of freshwater supplied to ponds from other land use activities such as livestock farming can affect Koura survivability. Other risks come from the introduction into the ponds of predators such as carp, eels and birds however these can be controlled by steps such as netting across pond surfaces. Algal bloom
s creating anoxic conditions and cannibalism caused by high density stocking of ponds is also a challenge to koura farmers.
The outlook for the growth of koura aquaculture in the New Zealand domestic setting may exist with the potential for increasing demand in the restaurant and tourism fields. Export of koura to the international market may offer less potential due to competition from other established freshwater crayfish species such as the red swamp crayfish Procambarus clarkii
of which the United States and China annually consume 34,000 tonnes and 88,000 tonnes respectively.
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
crayfish
Crayfish
Crayfish, crawfish, or crawdads – members of the superfamilies Astacoidea and Parastacoidea – are freshwater crustaceans resembling small lobsters, to which they are related...
species endemic to New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
. They are known as in New Zealand, derived from the Māori language
Maori language
Māori or te reo Māori , commonly te reo , is the language of the indigenous population of New Zealand, the Māori. It has the status of an official language in New Zealand...
. The two species are divided by the Southern Alps
Southern Alps
The Southern Alps is a mountain range extending along much of the length of New Zealand's South Island, reaching its greatest elevations near the island's western side...
of New Zealand's South Island
South Island
The South Island is the larger of the two major islands of New Zealand, the other being the more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman Sea, to the south and east by the Pacific Ocean...
.
Northern koura
The Northern koura, Paranephrops planifrons, is found mainly in the North IslandNorth Island
The North Island is one of the two main islands of New Zealand, separated from the much less populous South Island by Cook Strait. The island is in area, making it the world's 14th-largest island...
, but also in Marlborough
Marlborough, New Zealand
Marlborough is one of the regions of New Zealand, located in the northeast of the South Island. Marlborough is a unitary authority, both a region and a district, and its council is located at Blenheim. Marlborough is known for its dry climate, the picturesque Marlborough Sounds, and sauvignon blanc...
, Nelson
Nelson, New Zealand
Nelson is a city on the eastern shores of Tasman Bay, and is the economic and cultural centre of the Nelson-Tasman region. Established in 1841, it is the second oldest settled city in New Zealand and the oldest in the South Island....
and the West Coast
West Coast, New Zealand
The West Coast is one of the administrative regions of New Zealand, located on the west coast of the South Island, and is one of the more remote and most sparsely populated areas of the country. It is made up of three districts: Buller, Grey and Westland...
of the South Island
South Island
The South Island is the larger of the two major islands of New Zealand, the other being the more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman Sea, to the south and east by the Pacific Ocean...
. They reach lengths of about 70 millimetres (2.8 in).
Southern koura
The Southern koura, Paranephrops zealandicus, is found only in the east and south of the South IslandSouth Island
The South Island is the larger of the two major islands of New Zealand, the other being the more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman Sea, to the south and east by the Pacific Ocean...
, and on Stewart Island/Rakiura
Stewart Island/Rakiura
Stewart Island/Rakiura is the third-largest island of New Zealand. It lies south of the South Island, across Foveaux Strait. Its permanent population is slightly over 400 people, most of whom live in the settlement of Oban.- History and naming :...
. They reach lengths of about 80 millimetres (3.1 in). Koura occupy freshwater streams, lakes, rivers and swamps. Koura use their 4 pairs of walking legs to move through their environment and when alarmed can flick their tail forwards violently to propel themselves backwards at speed in order to avoid any threat. The koura's first pair of legs (chelae) are pincers that are used for scavenging, food and warding off predators or other koura.
Growth
Koura like all crustaceans moultEcdysis
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...
their exoskeleton
Exoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
s in order to increase in size. During moulting the carapace
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
becomes soft with calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
being resorbed and the remaining outer shell shed. The new carapace forms underneath where it takes a number of days to harden. Calcium for this new outer shell comes from gastrolith
Gastrolith
A gastrolith, also called a stomach stone or gizzard stones, is a rock held inside a gastrointestinal tract. Gastroliths are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. The grain size depends upon the size of the animal and the gastrolith's...
s that line the stomach wall of the koura and these produce around 10%–20% of the calcium needs for exoskeleton production. The gastroliths drop into the koura's foregut where they are broken down to allow the adsorption of calcium. Post moulting the demand for calcium in order to harden the exoskeleton is high and this demand is met in part by the koura eating its discarded exoskeleton. The remaining calcium required to completely harden the exoskeleton is achieved by absorption from the water. Lower limits of 5 mg/L of calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
(Ca) in water for temperate species of koura have been suggested as sufficient to support exoskeleton hardening.
Water temperature and calcium concentrations are thought to be the key variables determining koura growth rates.
P. zealandicus have high survivability (>80%) rates below 16 °C (60.8 °F) but temperatures above this correlate with lower rates of survivability. Higher death rates are thought to be associated with increased activity of koura at higher temperatures. Greater activity by koura increases cannibalistic behaviour and increased activity may also impact on water quality with the greater production of ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
as a waste product. Survival of koura also increases with higher calcium concentrations in the water and this is thought to be in part due to a lower incidence of moulting related deaths and decreased risk from predation. A calcium concentration value of 20–30 mg/L Ca in water is thought to be ideal for maintaining koura growth and survivability in aquaculture setups.
Diet
Koura in natural populations consume a variety of foods with animal protein contributing the most to growth. Invertebrates including aquatic snailsFreshwater snail
A freshwater snail is one kind of freshwater mollusc, the other kind being freshwater clams and mussels, i.e. freshwater bivalves. Specifically a freshwater snail is a gastropod that lives in a watery non-marine habitat. The majority of freshwater gastropods have a shell, with very few exceptions....
, chironomids
Chironomidae
Chironomidae are a family of nematoceran flies with a global distribution. They are closely related to the Ceratopogonidae, Simuliidae, and Thaumaleidae...
, and 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...
are the predominant food sources in the koura diet. Juvenile koura require higher amounts of protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
in their diet than adults due to greater growth rate demands with invertebrates forming the bulk of their diet. Koura in lakes have been shown to feed predominantly in the littoral zone where food availability is greatest. Feeding in the littoral zone may reflect diel movement with koura moving to deeper and darker parts of lakes to avoid predation during daylight hours and moving to the littoral zone at night in order to feed.
Habitat
Predators, cannibalism and disease
EelsNew Zealand longfin eel
The New Zealand Longfin eel is one of three freshwater eels found in New Zealand. The other two species of eel are the Shortfin eel which is also found in south-eastern Australia and the recently arrived Australian Longfin eel .The easiest method for identification of the New Zealand Longfin eel...
, perch
European perch
The European perch, Perca fluviatilis, is a predatory species of perch found in Europe and Asia. In some areas it is known as the redfin perch or English perch, and it is often known simply as perch. The species is a popular quarry for anglers and has been widely introduced beyond its native area,...
, catfish
Brown bullhead
The brown bullhead, Ameiurus nebulosus, is a fish of the Ictaluridae family that is widely distributed in North America. It is a species of bullhead catfish and is similar to the black bullhead and yellow bullhead...
and trout
Trout
Trout is the name for a number of species of freshwater and saltwater fish belonging to the Salmoninae subfamily of the family Salmonidae. Salmon belong to the same family as trout. Most salmon species spend almost all their lives in salt water...
are the major aquatic predators of koura. Other terrestrial predators include rat
Rat
Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...
s, kingfishers
Sacred Kingfisher
The Sacred Kingfisher is primarily a woodland kingfisher that occurs in mangroves, woodlands, forests, and river valleys of Australia, Lord Howe Is., Norfolk Is., New Guinea, N...
, shags
Cormorant
The bird family Phalacrocoracidae is represented by some 40 species of cormorants and shags. Several different classifications of the family have been proposed recently, and the number of genera is disputed.- Names :...
, scaup
New Zealand Scaup
The New Zealand Scaup commonly known as a Black teal, is a diving duck species of the genus Aythya. It is endemic to New Zealand. In Maori commonly known as papango, also matapouri, titiporangi, raipo .-Description:...
, stoat
Stoat
The stoat , also known as the ermine or short-tailed weasel, is a species of Mustelid native to Eurasia and North America, distinguished from the least weasel by its larger size and longer tail with a prominent black tip...
s and kiwi
Kiwi
Kiwi are flightless birds endemic to New Zealand, in the genus Apteryx and family Apterygidae.At around the size of a domestic chicken, kiwi are by far the smallest living ratites and lay the largest egg in relation to their body size of any species of bird in the world...
. Shag populations from the Te Arawa
Te Arawa
Te Arawa is a confederation of Māori iwi and hapu based in the Rotorua and Bay of Plenty areas of New Zealand, with a population of around 40,000.The history of the Te Arawa people is inextricably linked to the Arawa canoe...
lakes district in the North Island of New Zealand have been shown to feed on koura as the bulk of their diet. Predation on koura by trout is thought to be restricted to larger adult trout. Streams and lakes with established populations of trout have been shown to affect koura abundance. Cannibalism
Cannibalism
Cannibalism is the act or practice of humans eating the flesh of other human beings. It is also called anthropophagy...
in koura is most likely to occur when koura are sick or moulting. Cannibalism can be a greater problem in high density situations where competition
Competition
Competition is a contest between individuals, groups, animals, etc. for territory, a niche, or a location of resources. It arises whenever two and only two strive for a goal which cannot be shared. Competition occurs naturally between living organisms which co-exist in the same environment. For...
for shelter and territory is greatest. Juvenile koura can be consumed whole by larger koura and this presents problems for aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
in ensuring continuity of intergenerational growth. Koura use their chelae for both attack and defence and when one limb is lost the koura will divert energy for overall growth to restoring the lost limb. The only disease known to seriously affect koura is "white tail disease" and this is caused by the microsporidian parasite Thelohania contejeani. This parasite causes degeneration of striated muscle in the tail area and this turns the tail a pale white colour and correspondingly leads to death soon after.
Reproduction
The female carries between 20–200 eggsEgg (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...
under the side flaps of her abdomen whereby they take 3–4 months to hatch. Over this time male sperm production corresponds with females' reproductivity. Once hatched juvenile koura cling to their mother’s abdomen using their pincers to attach until they have reached a length of 4–10 mm (0.15748031496063–0.393700787401575 ). At this stage they resemble adult koura in appearance. In Lake Rotoiti in the central North Island of New Zealand the main breeding period occurs between April–July (autumn–winter) with a second breeding period occurring from October–January (spring–summer). The total breeding length time from peak egg laying to the release of juveniles is estimated to be 28 weeks for the autumn–winter period and 19–20 weeks in spring–summer breeding groups. This difference is attributed to warmer temperatures speeding up the egg development process. In stream populations this growth period has been shown to take around 25–26 weeks in P. planifrons, and up to 60 weeks for P. zealandicus in Otago streams.
Aquaculture
Farming of koura is currently undertaken by a small number of companies within New Zealand. Sweet Koura Enterprises Ltd and New Zealand Clearwater Crayfish Ltd are two such operators. Koura is sold solely to the high end restaurant trade where they are commonly eaten as an entréeEntrée
An entrée is a dish served before the main course, or between two principal courses of a meal.The disappearance in the early 20th century of a large communal main course such as a roast as a standard part of the meal in the English-speaking world has led to the term being used to describe the main...
dish. Koura are harvestable once larger than 100 mm (3.9 in) in total length which can take between 2-5 years in P. planifrons. Sweet Koura Enterprises Ltd located in Central Otago, within the South Island of New Zealand, farm P. zealandicus in artificial ponds of approximately 200 square metres (239.2 sq yd) in size. These ponds attempt to replicate the natural environment that P. zealandicus grow in. Water supplied to the growing ponds is sourced from an aquifer
Aquifer
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...
and is artificially aerated. The temperature of the water is controlled to reflect the seasonal temperature variations that would be expected in the natural environment. The optimum temperature for growth in these ponds is achieved at between 15–18 °C (59–64.4 F) with P. zealandicus sensitive to rapid temperature changes. The natural biological life in a pond can support 3–4 koura per square metre. Additional feed in the form of fish based pallets are supplied to koura to support growth and this feed has been altered to reflect the lower protein, higher calcium nutritional requirements of koura. Overstocking of crayfish can lead to higher rates of mortality which is associated with higher rates of cannibalism and increased competition for shelter and food.
New Zealand Clearwater Crayfish Ltd farm the northern koura species P. planifrons using a gravity fed system with pond culture and raceways for farming koura. A key step in this koura farm is the depuration of koura in clean running water without food for up to 2 days in order to purge the gut cavity. This enables the tail to be presented as an appealing white flesh to the consumer.
In order to breed koura in aquaculture a ratio of 1 male to 5 females is suggested during the mating periods with koura removed and placed in separate tanks depending of the life stage once hatched. The creation of artificial habitat in ponds may support koura survival. The use of plastic containers, tyres, plastic piping and bottles are all possible habits for koura to occupy when being grown in ponds. The suggested depth for ponds used to farm P. zealandicus are 1.3 metre deep.
A number of environmental challenges exist to koura farmers in ensuring optimum growth and survivability of stock. Environmental contamination of freshwater supplied to ponds from other land use activities such as livestock farming can affect Koura survivability. Other risks come from the introduction into the ponds of predators such as carp, eels and birds however these can be controlled by steps such as netting across pond surfaces. Algal bloom
Algal bloom
An algal bloom is a rapid increase or accumulation in the population of algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton species are involved, and some blooms may be recognized by discoloration...
s creating anoxic conditions and cannibalism caused by high density stocking of ponds is also a challenge to koura farmers.
The outlook for the growth of koura aquaculture in the New Zealand domestic setting may exist with the potential for increasing demand in the restaurant and tourism fields. Export of koura to the international market may offer less potential due to competition from other established freshwater crayfish species such as the red swamp crayfish Procambarus clarkii
Procambarus clarkii
Procambarus clarkii is a freshwater crayfish species, native to the Southeastern United States, but found also on other continents, where it is often an invasive pest. It is known variously as the red swamp crawfish, red swamp crayfish, Louisiana crawfish, Louisiana crayfish or mudbug.-Range and...
of which the United States and China annually consume 34,000 tonnes and 88,000 tonnes respectively.