Ecology of helminth infections in salmonid fish
The ecology of helminth infections has been investigated in Scottish salmonid fish populations. Examination of 240 brown trout and 49 rainbow trout from 21 locations in Central Scotland indicated that Crepidostomum farionis (Digenea) was the most widely distributed helminth species, followed by Eubothrium crassum (Cestoda), Diphyllobothrium dendriticum and Diphyllobothrium ditremum (Cestoda), Neoechinorhynchus rutili (Acanthocephala), Echinorhynchus truttae (Acanthocephala), Eustrongylides sp (Nematoda), Capillaria salvenlini (Nematoda), Cyathocephalus truncatus (Cestoda), Raphidascaris acus (Nematoda) and cystidicola farionis (Nematoda) in that order. The wide distribution of Crepidostomum farionis may be explained through the variable habits of the definitive host species and possibly interactions with human and avian factors. The frequency distribution of numbers of worms per fish was observed to be overdispersed. Autogenic species were generally the dominant form and responsible for the most of the similarity in patterns of infection within and between localities. No evidence was found to indicate host morbidity due to the helminth infections. An analysis of pairs of associations between species of helminths revealed a significantly positive association between N. rutili and C. farionis. This may be because one species improves either the establishment or survival of the other. In contrast, there was no clear evidence of competition between helminth species. The results of this study were discussed in terms of observed patterns in the helminth communities in fresh water fish host. The endoparasitic helminth fauna was examined from three sympatric morphs of Arctic charr, Salvelinus alpinus, (small-headed benthic, large-headed benthic and pelagic) from Loch Rannoch, Scotland. Six species of endoparastic helminth were recovered from the fish and the morphs had different patterns of infection. Overall, infections in pelagic charr were heavier than in the large-headed benthic morph, which in turn was heavier than in small-headed benthic even though the benthic morph lives longer than the pelagic.