Abstract
Atlantic cod Gadus morhua L. is host to more than 120 parasite species. Background abun- dance of these parasite species on adjacent wild hosts determines the infection pressure on cod farmed in open pens. In 2006, 2007 and 2008, 343 cod were col- lected from 4 locations along the coast of Norway: Oks- fjord, Kvaroy, Bronnoysund and Alesund. Freshly killed wild local cod, wild migratory cod, hatchery-reared farmed cod and wild-caught farmed cod were given a complete autopsy according to a standardized protocol. A total of 343 cod were examined, from which 48 para - site taxa, including 37 named species, were recorded. Wild local cod had the most diverse parasite fauna. Wild-caught farmed cod had a more diverse parasite fauna than the wild migratory cod, and the latter had 2 more parasite taxa than the hatchery-reared cod. The most common parasites in hatchery-reared cod were the digenean Cryptocotyle lingua, the monogenean Gyrodactylus marinus and the protozoans Spironucleus torosa and Trichodina spp. Other parasites occurring frequently in hatchery-reared cod were the para - sitic copepod Cresseyus confusus, the myxosporean Zschokkella hildae and the nematode Hystero thy la - cium aduncum. The nematode and digenean fauna of the hatchery-reared fish was sparse compared to wild cod and the wild-caught farmed cod. Caligid copepods were very rare on the hatchery-reared cod. These results support the hypothesis that food-borne para - sites, such as nematodes and mature stages of di - geneans, are most unlikely to become a health problem for farmed cod, and that parasites with simple life cycles and pelagic transmission stages, such as mono- geneans and trichodinids, may dominate the parasite fauna of farmed cod in the future
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