Ontogenetic dietary shifts of Silver Shiner (Notropis photogenis) in a Canadian watershed

Ontogenetic dietary shifts are common in freshwater fishes, typically occurring due to growth and gape widening that allow for an increasing breadth of dietary options. Identifying when changes occur can help quantify energetic and resource demands between life stages, and is particularly important for at-risk fishes by identifying the timing and extent of dietary shifts. Silver shiner (Notropis photogenis (Cope, 1865)), a Threatened species in Canada, has limited available ontogenetic dietary information. Here, stable isotope and gut content analyses were used to investigate the species' size-specific dietary shifts in Sixteen Mile Creek, one of five occupied watersheds in Canada. We hypothesized that ontogenetic niche shifts would be related to age/size and reflected in differing stable isotope values and gut contents. Ontogenetic dietary shifts occurring by size-classes were found, with trophic compression suggesting increased feeding specialization at the smallest and largest size-classes. The greatest dietary overlap and similarity were observed among intermediate size-classes and were lowest at both ends of the size range. The trophic shift observed in the larger size classes emphasizes the importance of maintaining sufficient terrestrial food resources for this species in Canada.