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

## TL;DR

The study examines how high fish stocking density affects growth and stress in three species, finding that it harms grass carp and turbot but not leopard coral grouper.

## Contribution

The study introduces new insights into how stocking density affects lateral line gene expression and stress indicators in three different fish species.

## Key findings

- High stocking density caused oxidative damage and increased stress markers in grass carp and turbot but not in leopard coral grouper.
- Stocking density altered stress-related gene expression in the lateral line skin of all three species.
- Growth and cortisol levels can serve as indicators for monitoring fish health in high-density aquaculture.

## Abstract

Stocking density is a critical environmental factor in aquaculture, directly influencing water quality, fish health, yield per unit area and economic returns. However, the effects of stocking density on the physiological responses of the lateral line in different fish species remain unclear. In this study, grass carp, turbot and leopard coral grouper were farmed at different stocking densities. The results indicate that high stocking densities decreased growth and feed efficiency and caused oxidative damage, increasing serum cortisol, malondialdehyde contents, and superoxide dismutase activity 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 decreased the viscerosomatic index and altered the expression of stress-related genes in the lateral line skin across all three species, but did not affect the survival rate and feed intake of the three fish species. This study provides valuable insights for assessing fish health, welfare, and management strategies in intensive aquaculture.

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.