The parasite communities of two populations of walleye (Sander vitreus) from Black Bay and Circle Lake, Ontario, Canada

Abstract

The parasite communities of fishes can provide important information on certain aspects of host biology such as where they have been, what they are eating, and what’s eating them. Unfortunately, fish parasite studies in the Laurentian Great Lakes have been considerably neglected in recent years—with this being especially true for Lake Superior. Black Bay once harboured the most economically important walleye (Sander vitreus) population on Lake Superior; however, historically it has been subject to a wide array of anthropogenic influences that ultimately contributed to a population collapse. Recently, this population has shown signs of recovery. This in turn presents a unique opportunity to investigate its parasite community and gain insight on the biology of the host. In the absence of historical parasite data within Black Bay, walleye parasite communities were compared to that of Circle Lake instead. Circle Lake is considerably different in both abiotic and biotic composition; however it is close in geographic proximity and resides in a watershed that drains into Black Bay. Thus, available parasite species were predicted to be similar. Quantitative parasite data were gathered from 43 walleye from Black Bay, and 46 walleye from Circle Lake. In total, 7 parasite species were found infecting Black Bay walleye (Ergasilus caeruleus, Urocleidus aculeatus, Bothriocephalus cuspidatus, Azygia angusticauda, Prosorhynchoides pusilla, Diplostomum sp., Echinorhynchus sp.) and 14 were found infecting Circle Lake walleye (Ergasilus caeruleus, Urocleidus aculeatus, Clinostomum complanatum, Glochidia, Bothriocephalus cuspidatus, Prosorhynchoides sp., Triaenophorus nodulosus, Azygia angusticauda, Sanguinicola occidentalis, Diplostomum sp., Prosorhynchoides pusilla, Neascus sp., Camallanus oxycephalus, Raphidascaris sp.). The relationship between host attributes and parasite abundance and intensity was variable across both sample locations. There was no relationship between host attributes and species richness or diversity. In 2 of 6 co-occurring species, prevalence was significantly higher in Circle Lake walleye. There was no statistically significant difference in the intensity of shared parasite species. Circle Lake walleye had significantly higher mean infracommunity richness and diversity. Nestedness analysis was used to determine if walleye parasite communities from either sample location were structured. All groupings exhibited a significant nested structure for both sample locations. Despite differences in richness, the order in which species are added as communities assemble showed a similar pattern across sample locations—that is, directly transmitted parasites are acquired first, followed by those using copepods/invertebrates as an intermediate host, and lastly those using forage fish as intermediate hosts. The information gathered in this study reveals that the parasite communities of Black Bay and Circle Lake, although markedly different, perhaps have similar processes contributing to their assembly.