| Lernaeocera branchialis | |
|---|---|
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| The gills of awhiting infested by two blood-suckingLernaeocera branchialis | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Copepoda |
| Order: | Siphonostomatoida |
| Family: | Pennellidae |
| Genus: | Lernaeocera |
| Species: | L. branchialis |
| Binomial name | |
| Lernaeocera branchialis | |
| Synonyms[1] | |
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Lernaeocera branchialis, sometimes calledcod worm, is aparasite of marine fish, found mainly in theNorth Atlantic.[2] It is a marinecopepod which starts life as a smallpelagiccrustacean larva. It is among the largest of copepods, ranging in size from 2 to 3 millimetres (3⁄32 to1⁄8 inch) when it matures as acopepodid larva to more than40 mm (1+1⁄2 in) as a sessile adult.
Lernaeocera branchialis isectoparasitic, which means it is a parasite that lives primarily on the surface of its hosts. It has many life stages, some of which aremotile and some of which aresessile. It goes through two parasitic stages, one where it parasitizes as a secondary host aflounder orlumpsucker, and another stage where it parasitizes as a primary host acod or other fishes of the cod family (gadoids). It negatively impacts thecommercial fishing andmariculture 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-swimmingnauplius stages, one infectivecopepodid stage, fourchalimus stages and the adult copepod, each separated by amoult".[3]
The cycle begins with the females laying eggs which hatch into anauplius, the usual earlylarval stage of crustaceans.[4] This nauplius I moults about 10 minutes after hatching to produce nauplius II, and 48 hours later, nauplius II moults to acopepodid stage. At this point the copepodid is pelagic and free-swimming with an average length of about 0.5 mm.[3]
The next stage is finding a secondary orintermediate host, ademersal fish like aflounder orlumpfish which is often stationary and therefore easy to catch. The copepodid has only a day to find such a fish and attach itself to the fish's gills.[4]
When they locate such a fish, they capture it with grasping hooks at the front of their body. They penetrate the fish with a thinfilament 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 swimmingsetae, detach from the flounder or lumpfish and again swim freely as pelagic organisms.[4][5]
The female cod worm still resembles a copepod and is 2 to 3 mm long. Females undergo another pelagic quest, searching this time for a definitive orprimary host. With her fertilised eggs, she looks for acod or a fish belonging to the same family as cod, such as ahaddock orwhiting.[4]
When a suitable definite host is located, females enter thegill chamber. There, while attached to a gill, the female develops a plump, sinusoidal, worm-like body, with a coiled mass of egg strings at the posterior end.[4] Females now measure about 20 mm long, but can grow up to 50 mm.[6] The oral end of the female copepod penetrates the body of the cod until it enters the rear bulb of the host'sheart. 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 mainartery. In this way, while safely tucked beneath the cod's gill cover, the female's deeply embedded oral end can feed on blood while eggs develop and are released into the water column from the posterior end.[4][5]
It is not known howL. branchialis searches for its fish hosts, but it probably useschemoreceptors andmechanoreceptors, and follows physical clues in thewater column such as those provided byhaloclines andthermoclines.[3]
The most serious parasitic crustaceans among fish in general aresea lice.[7] 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 thegonads. 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.[7] These can have commercial impacts onwild fisheries, making cod-like fishes more expensive to market.[7][8]Gadoids, particularly cod, are emerging marine aquaculture species in some North Atlantic countries.L. branchialis present potential problems for their successfulmariculture.[9]
