Variation in Fast-Start Performance within a Population of Polyphenic Bluegill (Lepomis macrochirus)

Bluegill sunfish Lepomis macrochirus exhibit intraspecific variation in their morphology and swimming performance based on habitat. The pelagic form has a relatively streamlined, fusiform body shape associated with greater steady-state swimming speed and energy economy. In contrast, littoral bluegill have deeper bodies with fins located farther from their center of mass to enhance maneuverability among littoral vegetation. Deeper body shapes have been associated with increased fast-start performance to escape predators or capture prey. We hypothesized that littoral bluegill, which have a deeper body shape, would exhibit greater fast-start performance than pelagic bluegill. A total of 29 bluegill (16 littoral, 13 pelagic) were caught by hook and line, and their fast-start performance was analyzed from high-speed video recordings. Body shape appears to be a poor predictor of fast-start performance. Contrary to our expectations, pelagic bluegill had a significantly higher peak velocity, peak acceleration, and angular velocity compared to littoral bluegill. Pelagic bluegill living among larger predators and foraging on mobile prey may be exposed to selection pressures that favor increased fast-start performance. Integrated studies of internal morphology and physiology are needed to fully understand the relationship between morphology and performance in this population.