Effect of Predator Size and Prey Characteristics on Piscivory of Juvenile Largemouth Bass

Abstract: Largemouth Bass Micropterus salmoides undergo a diet shift to fish prey during the juvenile stage, but mechanisms influencing piscivorous behavior are largely unknown. In laboratory experiments, we examined ontogenetic effects of predator and prey size on piscivory of juvenile Largemouth Bass. Prey size preferences were determined in aquaria experiments by introducing multiple size ranges of either Bluegill Lepomis macrochirus, Gizzard Shad Dorosoma cepedianum, or Fathead Minnow Pimephales promelas with a Largemouth Bass from one of three length-classes (30, 50, and 75 mm TL). For Gizzard Shad, Largemouth Bass most often selected larger sizes (33–65% of Largemouth Bass length) than in experiments with either Fathead Minnow or Bluegill (25–48%). Although an optimal foraging model (handling time/prey dry mass) predicted most prey sizes chosen, Largemouth Bass, with their large gape, chose slightly larger prey than predicted for all three prey species. Using optimal-sized prey, we further investigated differential prey vulnerability and development of foraging behavior of juvenile Largemouth Bass (30–75 mm) in experiments conducted in a 750-L tank. Prey increased schooling and distance maintained from predators as they grew, but all sizes of Largemouth Bass foraged similarly, suggesting differences in predation success were due to prey morphology and species-specific behavioral responses of prey. Results of our study can provide better predictions for prey consumption patterns of piscivorous juvenile Largemouth Bass in field settings.