cod or seal worm

The Cod or Seal Worm (Pseudoterranova decipiens) is a parasitic roundworm in the family Anisakidae whose complex life cycle interconnects marine food webs across the North Atlantic and North Pacific. Adults inhabit the stomachs of pinnipeds—primarily grey seals (Halichoerus grypus) and harbour seals (Phoca vitulina)—as their definitive hosts. Eggs are shed into the sea with seal faeces, hatch into free-swimming larvae, and are consumed by crustacean intermediate hosts, which in turn are eaten by fish, particularly gadoid species such as Atlantic Cod (Gadus morhua), haddock, and redfish. Encysted third-stage larvae accumulate in fish flesh, rendering heavily parasitised fillets unacceptable for sale in fisheries markets—a significant economic concern for the fishing industry. When humans consume raw or insufficiently cooked infected fish, larvae can cause anisakiasis, a painful gastrointestinal condition. The parasite is prevalent across the North Atlantic, with particularly high prevalence in cod populations associated with high seal densities in waters off Norway, Iceland, Canada, and the British Isles. The genus Pseudoterranova encompasses several morphologically similar sibling species now distinguished through molecular analysis. No conservation assessment applies to this parasite species.