Swimming Ability and Ecological Performance of Cultured and Wild European Sea Bass (Dicentrarchus labrax) in Coastal Tidal Ponds

Locomotor performance is commonly used to predict ecological performance of animals and is often considered a proxy for Darwinian fitness. In fish, swimming performance is often measured in the laboratory, but its contribution to individual success in the field is rarely evaluated. We assessed maximal swimming velocity of wild and cultured juvenile Dicentrarchus labrax (European sea bass) in a sprint performance chamber and found substantial variation among individuals within a cohort and differences between wild and cultured fish. Moreover, individual sprint swimming performance was found to be repeatable on a daily basis, making this test potentially useful for studies of individual fitness. Some animals were also tested for endurance performance with a modified critical swimming speed (U-crit) test that we had previously reported to be variable among individuals and significantly repeatable over 6 mo. To test whether these different swimming abilities might contribute to differential ecological success in sea bass, cultured juveniles of known sprint and endurance performance were released into experimental estuaries, where they foraged on natural prey under high densities without predation. A second experiment exposed both cultured and wild juveniles of known sprinting ability to natural forage but this time with reduced densities and natural avian predation. Ecological performance was assessed as survival and growth rate. Neither swimming performance was a direct predictor of ecological performance for cultured fish at high densities. Survival under these conditions was significantly predicted by prior growth rate and condition factor. When exposed to natural avian predators, the better-sprinting wild fish outperformed cultured fish (35% vs. 0% survival), and there was some evidence for sprinting ability contributing to survival within wild fish. Measuring sprint performance in mesocosm survivors revealed a significant inverse relationship between rapid growth and sprinting ability of cultured juvenile sea bass.