Effect of Stocking Density on Culture Efficiency and Physiological Indicators of Largemouth Bass (Micropterus salmoides) under Recirculating Water Conditions in Land-Based Round Ponds

Abstract

To identify the optimal stocking rate of Micropterus salmoides culture in a land-based round pond recirculating aquaculture system, five stocking densities were tested, i.e., D1–D5 with 60, 70, 80, 90, and 100 fish/m2, respectively. The water temperature of the experimental pond was 20.0–26.5°C. The effects of stocking density on culture productivity and physiological indexes of M. salmoides (initial body weight 50.83 ± 7.28 g) were examined. The D1 and D5 treatments exhibited significantly improved growth performance. The population weight gain in the D5 treatment was the highest, which increased by 63.73%, 52.82%, 60.93%, and 45.08%, compared with groups D1–D4 ( $P<0.05$ , each), and the feed conversion ratio was the lowest, which was decreased by 5.65%, 12.03%, 26.42%, and 21.48% compared with groups D1–D4. The levels of crude protein, essential amino acids, and total free amino acids in muscle tissue of group D3 were higher than those in the other groups. Stocking density did not differ significantly on muscle fatty acid composition $\left(P>0.05\right.$ , each). The activities of serum AKP and LZM and liver SOD, AKP, and LZM in group D5 were significantly higher than those in the other groups. Thus, 100 fish/m2 was the optimal stocking density of M. salmoides at a size stage of 50.83∼130.13 g in the circulating water of land-based round ponds.