The parasite fauna of brook trout, Salvelinus fontinalis (Mitchill), in relation to lake morphometrics and the introduction of creek chub, Semotilus atromaculatus (Mitchill)

Creek chub, Semotilus atromaculatus (Mitchill), has been introduced in several brook trout, Salvelinus fontinalis (Mitchill), lakes of the Laurentian Shield, Quebec, Canada. The objectives of this study were to determine (i) if creek chub parasites colonized the lakes of the Laurentian Shield, (ii) if parasites were exchanged between the two fish species, (iii) the effect of the diet shift of brook trout in the presence of creek chub on its parasite fauna, and (iv) the importance of lake mean depth as a factor responsible for parasite community structure in brook trout. Eleven parasite species were identified from creek chub and fourteen from brook trout. Eight of the eleven parasite species found in creek chub colonized the lakes with creek chub. Two creek chub parasite species were exchanged with brook trout and two brook trout parasite species were exchanged with creek chub. The mean number of brook trout parasites acquired by feeding on benthic intermediate hosts was significantly higher in allopatric brook trout populations than in sympatric creek chub and brook trout populations. Larval stages of most parasite species occurred in low abundance or were absent from brook trout found in deep lakes, indicating that bird and mammal definitive hosts were not common in those lakes. A cluster analysis also showed that lakes with similar fish communities tended to clump together, suggesting that fish community structure clearly influences parasite community structure in brook trout. Brook trout parasite community structure was affected by parasite exchange, by diet shift of brook trout when living in sympatry with creek chub and by inter-lake variation due to depth and other factors.