Efficiency of pulsed gastric lavage for evaluating fingerling Walleye Sander vitreus diets
Pulsed gastric lavage (PGL) is a common nonlethal method for sampling fish stomach contents. However, the effectiveness of this method has not been assessed for fingerling Walleye. Our objective was to assess the efficiency of PGL on fingerling Walleye. Stomach contents were extracted from 57 Walleye with PGL. After PGL, Walleye were euthanized and stomachs were removed to check for remaining contents. Stomach contents were preserved in ethanol and identified. PGL recovered an average of 92% of prey items, but failed to remove all stomach contents in 14 of 57 (24%) instances. Recovery rate of fish (78%) was lower than benthic invertebrates (99%) and zooplankton (97%). For stomachs containing fish, PGL removed all portions of consumed fish 67% of the time, whereas scales remained in the stomach 30% of the time, and whole fish remained in the stomach 2% of the time. Total number of prey items removed from individual stomachs was not related to recovery rates for each prey item (e.g., fish, benthic invertebrates, or zooplankton) and Walleye total length was not related to proportion of remaining prey. These results suggest that PGL is an effective nonlethal technique for recovering stomach contents of advanced fingerling Walleye.