Trophically transmitted parasites in wild Atlantic salmon post‐smolts from Norwegian fjords
Abstract:The community structure of trophically transmitted intestinal helminths of Atlantic salmon Salmo salar post‐smolts was highly variable among four fjords in Norway. There were no severely pathogenic parasite species. Post‐smolts from the southernmost Trondheimsfjord had a higher diversity of freshwater parasite species compared to the three northern fjords (Tanafjord, Altafjord and Malangen). In contrast, the highest diversity and proportion of marine species was found in the three northern fjords. Post‐smolts were generally more infected with marine parasites in the outer rather than inner parts of all of the fjords. The prevalence of the acanthocephalan Echinorynchus gadi(range: 13–42%) and marine trematodes (range: 14–47%) was higher in post‐smolts in outer zones of the northern fjords than in fish from Trondheimsfjord (0 and 6%, respectively). The within‐fjord variability and north‐south geographical gradient in parasite infection patterns reflected differences in marine feeding of the post‐smolts on potential intermediate hosts such as amphipods (E. gadi) and fish larvae (trematodes), which were higher in the northern fjords (range: 27–28 and 67–85%, respectively) than in Trondheimsfjord (5 and 19%, respectively). High intensities of marine parasites suggest that some post‐smolts from northern fjords may have a prolonged fjord‐feeding compared to those from Trondheimsfjord. Parasites of both freshwater and marine origin appear to be suitable as bio‐indicators of feeding and migratory pattern of Atlantic salmon post‐smolts and preadults during their seaward migration.
Document Type: Regular Paper
Affiliations: 1: Norwegian College of Fishery Science, University of Tromsø, N-9037 Tromsø, Norway, 2: Norwegian Institute for Nature Research, N-9296 Tromsø, Norway, 3: Fisheries and Oceans Canada, P. O. Box 5667, St John’s, Newfoundland & Labrador, A1C 5X1, Canada, 4: Norwegian Institute of Fisheries and Aquaculture, N-9291 Tromsø, Norway, 5: Norwegian Institute for Nature Research, Tungasletta 2, N-7485 Trondheim, Norway and 6: Institute of Marine Research, Box 1870, N-5817 Bergen, Norway
Publication date: March 1, 2005