Swimming at the Edge: Testing the Endurance-Exhaustion Hypothesis in Shiner Perch (Cymatogaster aggregata)

Abstract

Fish escape responses are a type of fast start used by fish to avoid predation. Better escape performance leads to increased fitness due to increased ability to avoid predation. However, predators of fish can employ a number of behaviors and tools to increase their ability to catch prey fishes. One behavior employed by predators is prolonged chasing, which should exhaust fishes when they are forced into an oxygen debt while swimming at speeds that require burst swimming and the use of anaerobic muscles. It is hypothesized that more exhausted fishes will be worse at escaping from predators. In this study we aim to determine if exhaustion level effects escape performance. Shiner perch, (Cymatogaster aggreagata), a labriform swimming shore fish from the Pacific coast of North America, was used to test this hypothesis. We used critical swimming speed tests to determine gait transition (Up-c) and critical swimming speed (Ucrit). We then rested the fish overnight and transferred the fish to a large flume and tested their escape response while swimming for 20 minutes at 1 BL/s, Up-c, and Ucrit. Mean Up-c was reached at 4.24 ± 0.45 BL/s and mean Ucrit was reached at 4.92 ± 0.51 BL/s (mean ± standard deviation). Mean aerobic scope was 682 ± 174 mgO2/kg/h with most variation occurring in maximum metabolic rate (MMR). Shiner perch optimal swimming speed was 3.21 BL/s. Responsiveness to escape response stimulus increased with exhaustion, but not significantly. Onset of escape response was significantly longer at Up-c and Ucrit speeds compared to 1 BL/s, turning angle did not significantly differ among the levels of exhaustion. Our results indicate that escape performance may not be substantially altered while swimming at different levels of exhaustion.