Evaluating the Efficiency of Pulsed Gastric Lavage for Age‐0 Walleyes

Abstract

AbstractAssessing fish diets through stomach content analysis leads to advances in the understanding of trophic dynamics, predation rates, and prey availability for fish populations. Although pulsed gastric lavage (PGL) is an effective nonlethal technique for sampling stomach contents of adult fishes, variable effectiveness has been reported for age‐0 fishes. Our objective was to assess the efficiency of PGL on age‐0 Walleyes Sander vitreus. Stomach contents were extracted from 49 age‐0 Walleyes with PGL using three 140‐mL syringes filled with purified water. After PGL, age‐0 Walleyes were euthanized and returned to the laboratory, and stomachs were removed and rinsed with water to check for remaining stomach contents. No injuries or deaths were observed during the PGL process. Only 4 of 49 age‐0 Walleye stomachs (8.2%) contained no prey items after PGL and dissection and therefore were not included in analysis. Of the 45 stomachs containing prey, only three stomachs (6.7%) still contained prey items after PGL; thus, PGL successfully removed all prey in 93.3% of stomachs containing prey items. Of the 45 stomachs containing prey items, 71.1% contained fish, 44.4% contained benthic invertebrates, and 48.9% contained zooplankton. Individual age‐0 Walleyes consumed an average of one fish (SD = 1), three benthic invertebrates (SD = 7), and four zooplankton (SD = 7). Pulsed gastric lavage recovered an average of 98.7% (SD = 6.4%) of total prey by number from age‐0 Walleyes. Mean percent recovery was 97.3% (95% CI = 4.2) for fish, 100% (95% CI = 0) for benthic invertebrates, and 99.5% (95% CI = 0.9) for zooplankton. Removal efficiency of PGL was not strongly correlated to the total number of consumed prey items per individual for fish, benthic invertebrates, or zooplankton nor to age‐0 Walleye TL. Combined, these results suggest that PGL is an effective nonlethal technique for recovering stomach contents of age‐0 Walleyes.