Growth of juvenile cobia, Rachycentron canadum, at three different densities in a recirculating aquaculture system

Cobia (Rachycentron canadum) is an excellent aquaculture candidate and culture of this species continues to develop worldwide. Current culture practices generally include larviculture and production of early juveniles on land with final growout occurring in ocean cages. Data indicate that production and/or growout of juveniles in land based recirculating systems may be hampered by growth depression in fish held at even relatively low densities. The current study investigated the responses of early cobia juveniles cultured at three different stocking densities (0.04, 0.22, and 0.44 g of fish/L) over a 10-week period in a recirculating aquaculture system. Water temperature was maintained at 27 ± 1 C and salinity was 32.0 ± 3.0 ppt. Fluorescent light banks were used to maintain a light/dark cycle of 14 h light/10 h dark. Early juveniles used in this trial had an average initial weight of 6.7 ± 0.2 g and were stocked at 3, 10, or 20 per tank in order to reach target stocking densities. Fish were fed to satiation twice daily with a commercial diet and the amount fed was measured to determine feed efficiency. Fish from each tank were counted and weighed collectively each week until the end of the trial to monitor growth and survival. In addition, fish from the control (0.04 g/L) tanks were individually marked via clipping of the pectoral fins and weighed individually each week. Survival was high (≥ 96% in all treatments) and there were no significant differences among treatments. Growth was also not significantly different among treatments with weight gains between 2523 and 2747% of initial weight (SGR ranging from 5.18 to 5.29). Feed efficiency of the control (0.96 ± 0.02) was significantly lower than that of the 0.22 g/L treatment (1.04 ± 0.03).