Reduced swimming and metabolic fitness of aquaculture-reared California Yellowtail (Seriola dorsalis) in comparison to wild-caught conspecifics

Aspects of swimming and metabolic physiology were measured in aquaculture-reared California Yellowtail (Seriola dorsalis) in comparison to wild-caught individuals in order to examine potential differences in health and fitness associated with captive rearing, and to help identify areas for targeted improvement in Seriola aquaculture. Incremental swimming velocity trials using a swim tunnel respirometer on small yellowtail (mean body length = 18.9 cm, mass = 80.1 g) showed that aquaculture-reared fish had a significantly slower mean maximum sustainable swimming speed (Ucrit) (4.16 ± 0.62 BL s−1) in comparison to that of wild-caught fish (4.80 ± 0.52 BL s−1). In addition, oxygen consumption (ṀO2) measurements at varying swimming speeds allowed for estimation of standard metabolic rate, which was significantly higher in aquaculture-reared yellowtail (7.31 ± 2.32 vs. 3.94 ± 1.60 mg O2 kg−1 min−1 at 18 °C). Aquaculture fish also had a lower aerobic scope (9.20 ± 3.44 mg O2 kg−1 min−1) in comparison to wild-caught yellowtail (15.80 ± 5.78 mg O2 kg−1 min−1), which likely contributed to their reduced capacity for fast sustainable swimming. Reduced physical fitness is commonplace in aquaculture-reared fishes, and the examination of wild-caught yellowtail in this study provides baseline metrics that can be used to gauge the health and fitness of future S. dorsalis production. In particular, the lower standard metabolic rate and higher aerobic scope of wild-caught fish represent desirable metabolic characteristics that if achievable in aquaculture through better-rearing practices could allow for increased feed conversion efficiencies and potentially faster growth. At a minimum, a 35-40% reduction in metabolic costs at low swimming speeds (to those observed for wild-caught yellowtail) should result in substantial cost savings for feed in aquaculture operations.