Abstract
The parasites of 484 brown trout, Salmo trutta, were studied between 2004 and 2007. An indicator value (IndVal) method was used for analysis, which combines measures of fidelity and specificity. Because of its resilience to detect changes in abundance, IndVal is an effective ecological bio-indicator. The IndVal method demonstrated that altitude, hydrographic network and season could influence the occurrence of parasite species in brown trout. A randomization test identified three parasite species as having a significant indicator value for altitude (the trematode Nicolla wisniewskii, and the nematodes Spinitectus gordoni and Rhabdochona gnedini); five parasite species for hydrographic network (the trematodes Nicolla testiobliquum, N. wisniewskii, Plagioporus stefanskii, and the nematodes S. gordoni and R. gnedini) and two parasite species for season (the nematodes S. gordoni, and R. gnedini). Data for species composition and infection levels should help to improve the monitoring and management of parasitism in salmonid populations.