The helminth fauna of brown trout (Salmo trutta) from a sub-alpine lake revisited after 40 years with introduced European minnow (Phoxinus phoxinus)

The helminth fauna of brown trout (Salmo trutta) in the Norwegian subalpine lake, Øvre Heimdalsvatn was studied by examination gills, eyes, body cavity, kidney, stomach, pyloric region and intestine a total 112 randomly sampled June, July, September 2011. Ten species, Discocotyle sagittata, Phyllodistomum umblae, Crepidostomum farionis, C. metoecus, Diplostomum sp., Proteocephalus Cyathocephalus truncatus, Dibothriocephalus ditremus, D. dendriticus, Capillaria sp. were identified. These data compared to from period 1969 1972, just after first record European minnow (Phoxinus phoxinus) 1969. All ten except also present 1969–72. However, few major changes infection intensities have occurred. cestode ditremus trematode both with piscivorous birds as final hosts, had markedly higher relative densities (abundance) 2011 1969–72, while two species showed substantial decline densities. We suggest that these may be indirectly related establishment subsequent population increase lake. abundance minnows increased food basis for birds, primarily mergansers black-throated diver now regularly forage In addition, there been littoral invertebrate community, including serving intermediate hosts some parasites.