Stable isotope analysis reveals fish juveniles as a temporal main resource consumed by invasive pumpkinseed (Lepomis gibbosus)

The pumpkinseed Lepomis gibbosus (Linnaeus, 1758) is a small centrarchid fish species from North America that has invaded most European basins, with pronounced expected impacts. Analyses of pumpkinseed diet in its invasive range using gut content analysis (GCA) show macrozoobenthos as the most common dietary item, suggesting a competitive effect on native fish communities. Our study uses a combination of GCA and stable isotope analysis (SIA) to document pumpkinseed diet at two sites in its invaded range and relates pumpkinseed diet preferences with parasitic load. SIA revealed juvenile fish as a major prey item at one of the sites (63 and 50% of the diet of small and the large fish), while GCA showed pumpkinseed preying mostly on macroinvertebrates (chironomids, gastropods, Ephemeroptera, and Zygoptera larvae) at both sites. While infrequent infection by trophically transmitted parasitic nematodes could be related to low consumption of zooplankton, substantial infection by metacercariae of Posthodiplostomum centrarchi Hoffman1958 appears to reflect relatively high consumption rates of its intermediate host, physid snails. Using SIA allowed to demonstrate that pumpkinseed feeding in its non-native range can be based on piscivory, emphasising the need for combining multiple methods when studying the impact of non-native species on food webs.