Patterns and dynamics of infection of Triaenophorus crassus forel in lake whitefish (Coregonus clupeaformis) and cisco (C. artedi) in lakes of the James Bay Region, Quebec

Presence of Triaenophorus crassus Forel in the flesh of lake whitefish (Coregonus clupeaformis (Mitchill)) and cisco (C. artedi Lesueur) can be an important economic problem for commercial coregonine fisheries. This study was initiated during the development of native fisheries in northern Quebec. Coregonine populations from 6 lakes of the Nottaway watershed were sampled to determine infection patterns of T. crassus in relation to age and size of fish, and to document interlake differences in prevalence and number of T. crassus. Interspecific and interlake differences in the infection dynamics of T. crassus were described in relation to capsule types, sizes and plerocercoid conditions. Infection dynamics were also investigated with age of fish. All coregonine populations were infected with T. crassus, and cisco more so than lake whitefish where the two species co-occurred. Prevalence and number of T. crassus were independent of fish age and size in most lake whitefish populations. Number of T. crassus increased with fish age and size in all cisco populations, but prevalence increased only in the populations from the largest lakes. Interlake differences in prevalence and number of T. crassus were detected for both coregonine species, and were related to feeding behaviour of the fish and lake biophysical characteristics. Heavy infections in one lake whitefish population were mainly associated with piscivory. Interspecific and interlake differences in the infection dynamics of T. crassus were also observed. Differences in the proportions of capsule types, sizes, and plerocercoid conditions suggest that population turnover of T. crassus in cisco is faster than in lake whitefish. In contrast to previous studies, plerocercoid condition was found to be independent of capsule size. Coregonine populations, which did not differ in prevalence and number of T. crassus, showed some differences in the proportions of capsule types, sizes and plerocercoid conditions, suggestin