Alimentary tract parasites of haddock (Melanogrammus aeglefinus L.) on the Scotian Shelf

Abstract

Nineteen species of alimentary tract (including gall and swim bladders) parasites were found in haddock (Melanogrammus aeglefinus) on the Scotian Shelf, of which eight species were new Canadian records for haddock. Prevalence ranged up to 82.3% for Hysterothylacium aduncum and 70.9% for Echinorhynchus gadi, the most abundant parasites, with Lepidapedon rachion and Echinorhynchus gadi showing highest intensities (14.9 and 76.5, respectively). Prevalence decreased from summer to winter, was not related to sex of host, but showed geographical variation characterizing different geographical areas. The Bay of Fundy showed higher nematode and lower trematode abundance than the offshore Scotian Shelf which showed general clines in abundance of several species from southwest to northeast. There was no evidence of growth-related change in parasite prevalence in adult fish, but the parasite complex of young-of-the-year haddock indicated planktonic feeding, in contrast with benthic feeding in the adult. Site specificity within the alimentary tract was shown by several species. Echinorhynchus gadi changed its site seasonally. Lepidapedon rachion showed size differentiation in the gut, smaller trematodes occupying more anterior sites than larger. Only two parasite species offer prospects as biological tags, L. rachion and Myxidium bergense, but all may provide evidence of ecological, behavioral, seasonal and developmental changes in the host.