Lernaeocera branchialis
Encyclopedia
Lernaeocera branchialis, sometimes called cod worm, is a parasite of marine fish, found mainly in the North Atlantic. It is a marine copepod
which starts life as a small pelagic crustacean larvae
. It is among the largest of copepods, ranging in size from 2–3 millimetres when it matures as a copepodid larva to more than 40 millimetres (1.6 in) as an adult.
Lernaeocera branchialis is ectoparasitic, which means it is a parasite that lives primarily on the surface of its hosts. It has many life stages, some of which are motile and some of which are sessile
. It goes through two parasitic stages, one where it parasites as a secondary host a flounder
or lumpsucker
, and another stage where it parasites as a primary host a cod
or other fishes of the cod family (gadoids). It is a pathogen
that negatively impacts the commercial fishing
and mariculture
of cod-like fish.
The cycle begins with the females laying eggs which hatch into a nauplius, the usual early larval stage of crustaceans. This nauplius moults about 10 minutes after hatching to produce nauplius II, and 48 hours later, nauplius II moults to a copepodid stage. At this point the copepodid is pelagic and free-swimming with an average length of about 0.5 mm.
The next stage is finding a secondary or intermediate host
, a demersal fish like a flounder
or lumpfish which is often stationary and therefore easy to catch. The copepodid have only a day to find such a fish and attach themselves to its gills.
When they locate such a fish, they capture it with grasping hooks at the front of their body. They penetrate the fish with a thin filament which they use to suck its blood. The nourished cod worms then progress via four moults from the naupliar stage to the mature chalimus stage. At this point the males transfer sperm to the females. Both sexes develop swimming seta
e, detach from the flounder or lumpfish and again swim freely as pelagic organisms.
The female worm still resembles a copepod and is 2 to 3 mm long. She now undergoes another pelagic quest, searching this time for a definitive or primary host. With her fertilised eggs, she looks for a cod
or a fish belonging to the same family as cod, such as a haddock
or whiting
.
When she locates one the worm enters the gill
chamber. There she clings to the gills and metamorphoses into a plump, sinusoidal, wormlike body, with a coiled mass of egg strings at her rear. These bodies are mostly about 20 mm long, but can measure up to 50 mm. The front part of the worm's body penetrates the body of the cod until it enters the rear bulb of the host's heart
. There, firmly rooted in the cod's circulatory system, the front part of the parasite develops in the shape of antlers or branches on a tree, reaching into the main artery
. In this way, while safely tucked beneath the cod's gill cover, the worm feeds from one end on cod blood while it pumps new offspring out the other end.
s, and follows physical clues in the water column such as those provided by halocline
s and thermocline
s.
. However, L. branchialis is probably the most serious parasitic crustacean among cod. Infestation reduces the efficiency with which food can be utilised, delaying the development of the gonad
s. Up to 30% loss in weight can occur, with increases in mortality because of open lesions with loss of blood, and possibly occlusion of vessels or aorta. These can have commercial impacts on wild fisheries, making cod-like fishes more expensive to market. Gadoids, particularly cod, are emerging marine aquaculture species in some North Atlantic countries. L. branchialis present potential problems for their successful mariculture
.
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,...
which starts life as a small pelagic crustacean larvae
Crustacean larvae
Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow...
. It is among the largest of copepods, ranging in size from 2–3 millimetres when it matures as a copepodid larva to more than 40 millimetres (1.6 in) as an adult.
Lernaeocera branchialis is ectoparasitic, which means it is a parasite that lives primarily on the surface of its hosts. It has many life stages, some of which are motile and some of which are sessile
Sessility (zoology)
In zoology, sessility is a characteristic of animals which are not able to move about. They are usually permanently attached to a solid substrate of some kind, such as a part of a plant or dead tree trunk, a rock, or the hull of a ship in the case of barnacles. Corals lay down their own...
. It goes through two parasitic stages, one where it parasites as a secondary host a flounder
Flounder
The flounder is an ocean-dwelling flatfish species that is found in coastal lagoons and estuaries of the Northern Atlantic and Pacific Oceans.-Taxonomy:There are a number of geographical and taxonomical species to which flounder belong.*Western Atlantic...
or lumpsucker
Lumpsucker
Lumpsuckers or lumpfish are mostly small scorpaeniform marine fish of the family Cyclopteridae. They are found in the cold waters of the Arctic, North Atlantic, and North Pacific oceans...
, and another stage where it parasites as a primary host a cod
Cod
Cod 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...
or other fishes of the cod family (gadoids). It is a pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
that negatively impacts the commercial fishing
Commercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
and mariculture
Mariculture
Mariculture is a specialized branch of aquaculture involving the cultivation of marine organisms for food and other products in the open ocean, an enclosed section of the ocean, or in tanks, ponds or raceways which are filled with seawater. An example of the latter is the farming of marine fish,...
of cod-like fish.
Life stages
The life-cycle of a cod worm involves a complex progression of life stages, including two successive hosts. It comprises "two free-swimming nauplius stages, one infective copepodid stage, four chalimus stages and the adult copepod, each separated by a moult".The cycle begins with the females laying eggs which hatch into a nauplius, the usual early larval stage of crustaceans. This nauplius moults about 10 minutes after hatching to produce nauplius II, and 48 hours later, nauplius II moults to a copepodid stage. At this point the copepodid is pelagic and free-swimming with an average length of about 0.5 mm.
The next stage is finding a secondary or intermediate host
Intermediate host
A secondary host or intermediate host is a host that harbors the parasite only for a short transition period, during which some developmental stage is completed. For trypanosomes, the cause of sleeping sickness, humans are the primary host, while the tsetse fly is the secondary host...
, a demersal fish like a flounder
Flounder
The flounder is an ocean-dwelling flatfish species that is found in coastal lagoons and estuaries of the Northern Atlantic and Pacific Oceans.-Taxonomy:There are a number of geographical and taxonomical species to which flounder belong.*Western Atlantic...
or lumpfish which is often stationary and therefore easy to catch. The copepodid have only a day to find such a fish and attach themselves to its gills.
When they locate such a fish, they capture it with grasping hooks at the front of their body. They penetrate the fish with a thin filament which they use to suck its blood. The nourished cod worms then progress via four moults from the naupliar stage to the mature chalimus stage. At this point the males transfer sperm to the females. Both sexes develop swimming seta
Seta
Seta is a biological term derived from the Latin word for "bristle". It refers to a number of different bristle- or hair-like structures on living organisms.-Animal setae:In zoology, most "setae" occur in invertebrates....
e, detach from the flounder or lumpfish and again swim freely as pelagic organisms.
The female worm still resembles a copepod and is 2 to 3 mm long. She now undergoes another pelagic quest, searching this time for a definitive or primary host. With her fertilised eggs, she looks for a cod
Cod
Cod 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...
or a fish belonging to the same family as cod, such as a haddock
Haddock
The haddock , also known as the offshore hake, is a marine fish distributed on both sides of the North Atlantic. Haddock is a popular food fish and is widely fished commercially....
or whiting
Merlangius merlangus
Merlangius merlangus, commonly known as whiting is an important food fish in the eastern North Atlantic, northern Mediterranean, western Baltic, and Black Sea...
.
When she locates one the worm enters 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...
chamber. There she clings to the gills and metamorphoses into a plump, sinusoidal, wormlike body, with a coiled mass of egg strings at her rear. These bodies are mostly about 20 mm long, but can measure up to 50 mm. The front part of the worm's body penetrates the body of the cod until it enters the rear bulb of the host's heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
. There, firmly rooted in the cod's circulatory system, the front part of the parasite develops in the shape of antlers or branches on a tree, reaching into the main artery
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
. In this way, while safely tucked beneath the cod's gill cover, the worm feeds from one end on cod blood while it pumps new offspring out the other end.
Behaviour
It is not known how L. branchialis searches for its fish hosts, but it probably uses chemoreceptors and mechanoreceptorMechanoreceptor
A mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion. There are four main types in the glabrous skin of humans: Pacinian corpuscles, Meissner's corpuscles, Merkel's discs, and Ruffini corpuscles...
s, and follows physical clues in the water column such as those provided by halocline
Halocline
In oceanography, a halocline is a subtype of chemocline caused by a strong, vertical salinity gradient within a body of water. Because salinity affects the density of seawater, it can play a role in its vertical stratification...
s and thermocline
Thermocline
A thermocline is a thin but distinct layer in a large body of fluid , in which temperature changes more rapidly with depth than it does in the layers above or below...
s.
Effects on fisheries
The most serious parasitic crustaceans among fish in general are sea liceSea lice
The sea louse is a copepod within the order Siphonostomatoida, family Caligidae. There are 36 genera within this family which include approximately 42 Lepeophtheirus and 300 Caligus species...
. However, L. branchialis is probably the most serious parasitic crustacean among cod. Infestation reduces the efficiency with which food can be utilised, delaying the development of 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. Up to 30% loss in weight can occur, with increases in mortality because of open lesions with loss of blood, and possibly occlusion of vessels or aorta. These can have commercial impacts on wild fisheries, making cod-like fishes more expensive to market. Gadoids, particularly cod, are emerging marine aquaculture species in some North Atlantic countries. L. branchialis present potential problems for their successful mariculture
Mariculture
Mariculture is a specialized branch of aquaculture involving the cultivation of marine organisms for food and other products in the open ocean, an enclosed section of the ocean, or in tanks, ponds or raceways which are filled with seawater. An example of the latter is the farming of marine fish,...
.