Effects of stocking density in pond cages on the growth performance, physiological health and muscle nutritional quality of Pelteobagrus vachelli

Stocking density is a key factor influencing production efficiency, physiological condition, and product quality in intensive pond-cage aquaculture. This study evaluated the effects of stocking density on the growth performance, physiological health, and muscle nutritional quality of juvenile Pelteobagrus vachelli and aimed to determine an appropriate density for pond-cage culture. Fish weighing (2.50 ± 0.02) g at purchase were acclimated for two weeks, and their body weight at the start of the formal experiment was (2.57 ± 0.27) g. They were then cultured for 120 days at three densities: low-density group LDG: initial (0.30 ± 0.01) kg/m³, final (2.81 ± 0.08) kg/m³, medium-density group MDG: initial (0.50 ± 0.01) kg/m³, final (5.27 ± 0.11) kg/m³, and high-density group HDG: initial (0.70 ± 0.01) kg/m³, final (6.39 ± 0.11) kg/m³. The MDG showed the highest weight gain rate and survival rate. Its feed conversion ratio was significantly lower and feeding rate significantly higher than those of the HDG, while hepatosomatic and viscerosomatic indices remained relatively low. Serum biochemical analysis showed that aspartate aminotransferase activity in the MDG was slightly higher than that in the LDG, whereas alanine aminotransferase and alkaline phosphatase activities showed no significant differences, suggesting no apparent impairment of liver function. In the intestine, malondialdehyde content in the MDG was significantly lower than that in the HDG, while total superoxide dismutase, catalase, and glutathione peroxidase activities remained relatively high. The MDG also showed higher muscle fiber density and favorable hardness and chewiness. Moreover, total essential amino acids, total umami amino acids, and the essential amino acid index were significantly higher in the MDG than in the HDG, and muscle protein quality met FAO/WHO recommendations. Overall, for juvenile P. vachelli with an initial experimental body weight of (2.57 ± 0.27) g, an initial stocking density of (0.50 ± 0.01) kg/m³ provided the best overall performance among the tested densities by promoting growth, improving feed utilization, maintaining physiological health, and enhancing muscle nutritional quality. These findings provide a practical basis for optimizing stocking density in intensive pond-cage culture of juvenile P. vachelli.