The Effects of Stocking Density on Survival, Growth, Condition, and Feed Efficiency of Bluegill Juveniles

Juvenile bluegills Lepomis macrochirus were reared at four densities in indoor aquaria to evaluate the effects of stocking density on growth, survival, condition, and feed efficiency. Fish (mean weight, 1.76 g) were stocked into 100-L aquaria containing 60 L of water at rates of 10, 20, 30, and 40 fish per aquarium (167, 334, 500, and 667 fish/m3, respectively). The growth trial was conducted over an 11-week period during which the fish were offered a 45%-protein commercial ration in slight excess. At the termination of the study, the mean weights as well as the lengths and weights of individual fish in each tank were recorded. Size was inversely related to stocking density. The final weights of the fish decreased significantly as density increased, with fish stocked at a density of 167/m3 having a mean weight of 10.7 g and those stocked at 667/m3 a mean weight of 7.3 g. The percent weight gain and feed efficiency also decreased as stocking density increased. No significant differences in relative condition were found among treatments. The results of this study suggest that density-dependent, nonaggressive competition resulted in reduced growth and feed utilization.