#cod worm

The Haddock have parasites, called cod worms, that latch on to them, for a parasitic relationship. A female worm with fertilized eggs, clings to the gills while it metamorphoses into a wormlike body, with a coiled mass of egg strings at the rear. The front part of the worm's body penetrates the body of the cod until it enters the host's heart. There, firmly rooted in the cod's circulatory system, the front part of the parasite develops like the branches of a tree, reaching into the main artery.

Cod Worm (Lernaeocera branchialis)

Taxonomy: Animalia, Arthropoda, Crustacea, Maxillopoda, Copepoda, Siphonostomatoida, Pennellidae, Lernaeocera, L. branchialis

Description & Lifestyle: L. branchiallis begins life as a naupilus (curstacean larvae), which then molts and becomes a copepodid, which is a 0.5mm long, free swiming larval stage (shown on the right). The copepod then has 24 hours to locate an intermediate host, which is usually a benthic fish species. They use hook-like appendages to attach themselves to the gills of a fish, where they feed on the blood of the fish with a filamentous structure and males pass sperm to the females. After four more molts, L. branchialis now enters the chalimus stage, gaining setae and becoming free swimming. The female (2-3mm long) then searches for a fish of the family Gadidae (its primary host), which it enters the gill slits of and attaches itself to. Here, the female enters its final life stage, becoming a sac-like organism with a characteristic string of eggs at its posterior. At the anterior end, the organism branches itself into an antler-like structure, connected to the main artery of the fish. In this way, it takes in blood from one end and releases eggs from the other.