Lethal Stomach Content Collection Methods Reduce Detection of Zooplankton Prey of Juvenile Largemouth Bass Compared with Nonlethal Methods

The study of fish diets is an integral part of many fisheries research and management programs. Several studies have evaluated the effectiveness of nonlethal stomach content collection methods but none have considered the effectiveness of lethal methods that may also be biased by continued prey digestion. We compared one nonlethal and two lethal methods of stomach content collection and preservation for juvenile Largemouth Bass Micropterus salmoides ranging in size from 51–68 mm TL. Macroinvertebrates and zooplankton from stomachs of juvenile Largemouth Bass were collected using three methods, including gastric lavage (stomach contents immediately preserved), removing and preserving stomachs from fresh fish (whole stomach preserved after 3 h on ice), and removing and preserving stomachs after the fish had been frozen whole (stomach preserved after whole fish was frozen for 3 weeks at −20°C in a freezer). There were significant differences in total biomass of zooplankton and the total number of individual diet items for zooplankton among the three methods. Both cladocerans and copepods significantly differed among methods for total numbers and total biomass. In contrast, there were no differences between the different diet collection methods for any of the macroinvertebrate groups we were able to analyze (Ephemeroptera, Odonata, Diptera, and Coleoptera). These results suggest that prey in stomachs of fish continues to be digested after collection and that prey size and prey type are important factors. Our results suggest that gastric lavage yielded more accurate results of diet of juvenile Largemouth Bass than lethal methods.