To clarify the optimal stocking density and density stress mechanism of Micropterus salmoides juveniles of different sizes, two size classes of M. salmoides (size 1: 8.0 ± 0.5 g, size 2: 50 ± 3.2 g) were selected as the research objects. Five stocking density gradients (0.25, 0.75, 1.25, 1.75 and 2.25 kg·m−3) were set up. After 30 days of culture, the growth performance, feeding and swimming behaviors, oxidative stress, and water quality indices were determined. The results showed that the survival rates of 0.25, 0.75 and 1.25 kg·m−3 groups had no significant difference and were significantly higher than those of high-density groups. The optimal stocking density of size 1 M. salmoides was 0.75–1.25 kg·m−3, which could balance optimal growth and high survival; beyond this range, the growth performance decreased significantly. High stocking density led to intensified feeding competition, increased stress-induced swimming activity, aggravated oxidative damage and water quality deterioration. In addition, size 2 M. salmoides was more sensitive to high-density stress, with a significantly narrower optimal density window, and its optimal stocking density was identified as 0.75 kg·m−3. Density stress exerted its effects through the pathway of spatial competition → behavioral abnormalities → oxidative damage → growth inhibition, and formed a negative feedback loop with water quality deterioration. This study provides a scientific basis for the precision regulation of stocking density in intensive culture of M. salmoides.
Zhang et al. (Fri,) studied this question.