Effect of stocking density on growth and oxidative stress in juveniles of Paralichthys orbignyanus sole
Stocking density is considered an important variable in aquaculture as it affects fish growth and welfare. The Brazilian flounder Paralichthys orbignyanus is a species with a high commercial value and potential for marine fish culture. Given the demersal behavior of flounder, stocking density for these fish is to be studied considering area occupancy. Therefore, the objective of the presente study was to evaluate the effect of different stocking densities on growth and oxidative stress in juvenile flounder, considering the percentage of covered area (PCA) by fish. Juvenile Brazilian flounder (1.58 g) were distributed in 16 tanks (50 L each), connected to recirculating aquaculture systems and exposed to four stocking densities: 50, 100, 150, and 200% PCA for 45 days, with four replicates each one. Fish were measured and weighed at the beginning and end of the experiment. Samples of brain, gills, liver and muscle were collected at the end of the experiment for oxidative stress analyzes. Growth performance was hampered by increasing stocking density. The final weight in the 200% PCA treatment was significantly lower (P<0.05) than in other groups, flounder reared at 50% PCA reached 8.36 ± 0.41 g, while those reared at 200% PCA grew up to 6.13 ± 0.2 g. Similarly, increasing stocking density induced alterations which compromised the antioxidant system (reduced ACAP and GST activity) and enhanced oxidative damage in lipids. Increases in GST activity and PSH contents were also demonstrated. In conclusion, when the stocking density reached 150% PCA, growth performance and oxidative stress responses were adversely affected. Therefore, in order to enhance growth and minimize free radical production that could damage the antioxidant defense system, stocking density of juvenile Brazilian flounder should be limited to 100% PCA.