Trophic polymorphism in bluegill sunfish (Lepomis macrochirus) introduced into Lake Biwa: evidence from stable isotope analysis

Trophic polymorphism was recently reported in introduced bluegill (Lepomis macrochirus) in Lake Biwa, Japan, where three morphs are specialized in benthic invertebrates (benthivorous type), submerged aquatic plants (herbivorous type), and zooplankton (planktivorous type). We evaluated the long-term effects of food resource utilization by these trophic morphs using stable isotope ratios, δ^sup 15^N and δ^sup 13^C. A significant difference in δ^sup 15^N was found between the benthivorous and planktivorous types. The planktivorous type had the higher δ^sup 15^N value, which corresponded with the value expected from its prey, zooplankton. The lower δ^sup 15^N value of the benthivorous type would be derived from the lower δ^sup 15^N values of benthic prey organisms compared to zooplankton. These results support previous findings that the benthivorous and planktivorous types have different food resource utilization. In contrast, the δ^sup 15^N and δ^sup 13^C values of the herbivorous type were distinctly different from the expected values, indicating that this type was unlikely to utilize aquatic plants substantially, contradicting the results of the dietary analysis.[PUBLICATION ABSTRACT]