Gamma (γ)-aminobutyric acid (GABA) improves feeding, growth rate, and growth hormone of the sea cucumber Apostichopus japonicus at high stocking density

Gamma (γ)-aminobutyric acid (GABA) is a critical neuromodulator in behavioral and growth regulation of organisms. The present study showed that feeding behavior significantly reduced when individuals were cultured in a high-density stocking environment, and that dietary GABA significantly ameliorated the effect of high density on feeding behavior. We further found that high density significantly reduced the protease activity and defecation rate of sea cucumbers, indicating a suppressed digestion. No significant difference was found in the protease activity and defecation rate between individuals fed with dietary GABA and those fed without dietary GABA at high density, suggesting that dietary GABA did not improve digestion. Additionally, cortisol level significantly increased when the density of stocking increased, and dietary GABA did not relieve the elevated cortisol level. The growth rate directly affects the efficiency of sea cucumber aquaculture. The specific growth rate (SGR) and the level of growth hormone significantly reduced, while the coefficient of variation (CV) increased significantly at high density. These results revealed the inhibited growth performance at high density was potentially linked to reduced growth hormone level. We further found that dietary GABA improved the SGR and the level of growth hormone, but had no significant effect on individual growth difference of sea cucumbers cultured in high density. In conclusion, this study demonstrates that dietary GABA enhances growth rate by increasing feeding behavior and growth hormone level, but not by improving digestive capacity and stress hormone level. We suggest GABA serve as a feed supplement to partially mitigate growth suppression in high-density aquaculture of sea cucumbers. • Growth hormone is inhibited in A. japonicus at high density. • Dietary GABA improves feeding behavior in A. japonicus at high density. • Dietary GABA improves SGR and growth hormone in A. japonicus at high density.