Parasite community structure in slimy sculpin (Cottus cognatus) and longnose dace (Rhinichthys cataractae) from tributaries experiencing different levels of oil sands development

Parasite community species richness and structure were assessed in slimy sculpin ( Cottus cognatus ) and longnose dace ( Rhinichthys cataractae ) from the Steepbank and Firebag rivers, two tributaries of the Athabasca River (Alberta, Canada) experiencing differing degrees of oil sands development. Fish were collected from three locations on each tributary, and their parasite community species richness and Bray-Curtis similarity were examined in relation to factors (host species, tributary, location on tributary) and environmental variables (water chemistry, sediment characteristics, sediment contaminant levels). Mean parasite infracommunity species richness differed significantly between sculpin (S = 1.7 ± 0.9) and dace (2.7 ± 0.8), but not between rivers, nor among sites within individual rivers. Sculpin and dace differed in the composition of their parasite communities as well (mean Bray-Curtis dissimilarity 99.3%). Multivariate Analysis of Similarity detected significant among-site differences in parasite community structure for both sculpin and dace; notably, parasite community structure changed gradually from upstream to downstream for both species on both tributaries, suggesting a river continuum may be in effect. However, in slimy sculpin, parasite infracommunity species richness displayed inverse upstream-downstream gradients between the two tributaries, suggesting a disruption of the typical river continuum effect in the Firebag River. However, modified mantel tests failed to find any significant correlation between these changes and contaminant levels in either water or sediment; the only subset of environmental data that was significantly correlated to parasite community structure was concentrations of dissolved organic and inorganic carbon and sulfate ions in surface water, possibly reflecting some unmeasured anthropogenic input.