Effects of High-Density Aquaculture on Grass Carp, Leopard Coral Grouper, and Turbot: Growth Performance and Transcriptome Analysis of Lateral Line

The lateral line is a highly differentiated skin sensory organ in fish, but few studies have explored the relationship between stocking density and the physiological responses of the lateral line in different species. In this study, grass carp, turbot and leopard coral grouper were cultured at different stocking densities for 6, 8 or 10 weeks. The results indicate that high stocking densities reduced weight gain and feed efficiency, increased serum cortisol, malondialdehyde contents, and superoxide dismutase activity, and caused oxidative damage in juvenile grass carp (2.04 kg/m3) and turbot (12.61 kg/m3), but did not affect these indicators in juvenile leopard coral grouper (2.33 kg/m3). Meanwhile, high stocking densities did not affect the survival rate and feed intake of the fish, but decreased the viscerosomatic index in all three fish species. In the lateral line skin, high stocking densities upregulated the expression of genes related to glucocorticoid secretion, hypoxia, and oxidative stress in grass carp and turbot, and altered circadian rhythm-related gene expression in leopard coral grouper. The study shows that growth, cortisol level, and oxidative damage can serve as effective indicators for monitoring fish in high-density cultures, and demonstrates that optimal stocking density should be determined based on the farming system, fish species, and developmental stage.