Lernaeocera branchialis is an ectoparasitic crustacean of cod and haddock found mainly in the North Atlantic.
Biogeographic Regions: atlantic ocean (Native )
Lernaeocera branchialis is among the largest of copepods. It ranges in size from 2-3 mm as a chalimus (a specialized copepodid larva) to more than 40 mm as an adult. Lernaeocera branchialis is highly evolved as an adult, having lost all semblance of crustacean heritage, and is therefore identified by its larval stages. As an adult, it appears S-shaped with 2 pairs of antennae on its head. This ectoparasite also has 2 pairs of maxillae used for piercing gill flesh, 1 pair of mandibles, and reduced antennules. Although the division between its head and trunk is not clearly defined, its posterior body segmentation in its larval stages is distinguishably crustacean. As a female adult, it appears as a mass of egg strings with a large egg sac. On a host, these parts of L. branchialis are seen external to the fish's body, and its egg sac is connected to other parts that lie internal to the fish host. These parts consist of a complex of antlers used for piercing, sucking, and maintaining feeding position. Respiration in L. branchialis is achieved through gills, and sometimes through its body surface.
Range length: 40 (high) mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Lernaeocera branchialis is strictly aquatic, being pelagic and in the upper 200 m of open ocean.
Habitat Regions: temperate ; saltwater or marine
Aquatic Biomes: pelagic
Lernaeocera branchialis parasitizes cod and haddock. It feeds on blood though root-like attachment organs, which invade throughout host tissue. Like other species of the Pennellidae family, it has a characteristic anterior site of growth and feeding. Lernaeocera branchialis attaches to the host fish in the branchial area. The parasite's cephalothorax grows into and through the ventral aorta, which is accomplished with its grotesque antler complex. The parasite inserts its antlers into the host's fleshy gill cavity by 3 branched processes, aided by strong antennae and maxillae for piercing into the wall of the bulbus arteriosus.
Animal Foods: body fluids
Primary Diet: carnivore (Eats body fluids)
Lernaeocera branchialis parasitizes cod and haddock.
Ecosystem Impact: parasite
Species Used as Host:
- cod and haddock, Gadidae
Larval mortality is high as few individuals make it to the suitable host. This species may be preyed on by fish.
Life History and Behavior
Crustaceans have various sensory resceptors, mainly setae over the body. Photoreceptors are also generally present.
Communication Channels: tactile ; chemical
Perception Channels: tactile ; chemical
The development of L. branchialis consists of several stages, begining when the animal hatches from an egg as a non-parasitic, free-swimming nauplius (the early larval stage of crustaceans). Three pairs of appendages (antennules, antennae, and mandibles) are used mainly for locomotion. Lernaeocera branchialis develops into a copepodid, which attaches to an intermediate host, such as a lumpfish (e.g. Cyclopterus lumpus), sculpin (Cottidae), or flounder (Pleuronectidae). After development into a chalimus, it copulates with another chalimus of the opposite sex and detaches. Lernaeocera branchialis is only 2 to 3 mm long at this point and is still resembles a copepod. It then undergoes a pelagic stage and searches for a definitive host. Once attached to the gill area of a cod or haddock, it undergoes profound metamorphosis and develops an egg sac and antlers. Any recognizable external segmentation is lost, and it grows more than 40 mm, excluding egg strings. In its final stages, L. branchialis appears reddish and worm-like, with its head (connected by a neck to a soft body) buried in gills. As a feeding adult, it is reduced to body parts needed for reproduction, feeding, and holding its position within the cod or haddock.
In comparison to other pennelids, its larval stage is almost indistinguishable from the larva of its free-living adult relatives. Although the biological role of L. branchialis larvae is unchanged, its adult form has adopted parasitism.
Development - Life Cycle: metamorphosis
Lernaeocera branchialis develops into a copepodid, which attaches to an intermediate host, such as a lumpfish (e.g. Cyclopterus lumpus), sculpin (Cottidae), or flounder (Pleuronectidae). After development into a chalimus, it copulates with another chalimus of the opposite sex and detaches. Lernaeocera branchialis is only 2 to 3 mm long at this point and is still resembles a copepod. It then undergoes a pelagic stage and searches for a definitive host. Once attached to the gill area of a cod or haddock, it undergoes profound metamorphosis and develops an egg sac and antlers. Any recognizable external segmentation is lost, and it grows more than 40 mm, excluding egg strings.
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); sexual
Parental Investment: pre-fertilization (Provisioning)
US Federal List: no special status
CITES: no special status
Relevance to Humans and Ecosystems
Lernaeocera branchialis causes severe damage by invasively feeding on blood. Death of the fish may occur from open lesions, too much blood loss, or possible formations of clots and occlusions of the aorta or blood vessels. Lernaeocera branchialis also causes a 20-30% loss of weight and liver fat in fish from the effects of growth retardation. It also has profound effects on reproduction by delaying gonad development and sexual maturity, and its presence influences fish behavior and reduces its resistance to other stresses. Lernaeocera branchialis is also known to be one of the most serious agents of trypanosomal parasites in Gadus mordua (cod). Overall, the parasite's changes on fish body weight loss and increased mortality affects commercial fisheries by making it more expensive to market cod, haddock, and flounder.
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 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, 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 setae, 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.
It is not known how L. branchialis searches for its fish hosts, but it probably uses chemoreceptors and mechanoreceptors, and follows physical clues in the water column such as those provided by haloclines and thermoclines.
Effects on fisheries
The most serious parasitic crustaceans among fish in general are sea lice. 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 gonads. 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.
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