EFFECTS OF STOCKING DENSITY AND FEED RATE ON THE GROWTH OF HATCHERY-REARED JUVENILE SPOTTED SEATROUT, Cynoscion nebulosus
The spotted seatrout, Cynoscion nebulosus, is a highly sought after recreational fish in the Gulf of Mexico. Fisheries managers in Texas use stock enhancement as one of the management tools to protect the fishery. Hatchery production of juvenile spotted seatrout has been successful in Texas; however, to increase post-release survival it is thought that the size of fish upon release should be increased from 35 mm to > 40 mm total length. To address this question, a baseline study on the effects of stocking density and feed rate on juvenile fish was investigated. Spotted seatrout were stocked into indoor 44-L aquaria at 10, 20, and 30 fish/tank (equivalent to 0.226, 0.453, and 0.680 fish/L) and fed at rates of 3, 6, or 10% biomass per day. In order to evaluate variation in population performance, two trials were conducted (Trials 1 and 2). Mean initial wet weights of fish in treatments for Trial 1 were 0.91±0.13 g (stocking density of 0.020 kg/m3) and 0.82±0.12 g (stocking density of 0.019 kg/m3) for Trial 2. Mean final weight was 5.51±1.43 g for Trial 1 (30 day duration) and 4.952±1.386 g for Trial 2 (27 day duration).
Survival of fish at the highest stocking density significantly (P<0.05) increased with increased feed rate. Fish at the lowest stocking density showed significantly (P<0.05) higher whole-body protein content when fed the high feed rate. Fish fed at higher feeding rates had significantly (P<0.05) higher specific growth rate and, Fulton's condition factor (K), as well as whole-body energy, but reduced whole-body ash content. Treatment combinations of low stocking density and high feed rate resulted in highest survival and weight gain. The results of this study show that there is potential to rear spotted seatrout to larger sizes (> 40 mm) under hatchery conditions.