Objective This experiment was conducted to research the effects of feeding frequency, water temperature and breeding density on growth performance, intestinal structure and hepatic GH and IGF-1 gene expression levels of largemouth bass in an indoor recirculating aquaculture system so as to determine the appropriate feeding frequency, water temperature and breeding density of largemouth bass.

Method The experiment consisted of 8 treatments (Ⅰ - Ⅷ). After 8 weeks of breeding, the growth performance indicators such as specific growth rate (SGR), feeding rate (FR), feed coefficient (FCR) and survival rate, the intestinal villus height, villus width and muscle thickness, and the expression of hepatic growth factor GH and IGF-1 genes of largemouth bass were evaluated.

Result Only the main effects of breeding density on FR and feeding frequency on condition factor (CF) were significant, while the interaction effects had a significant effect on CF. The one-way ANOVA results showed that, the growth performance of treatment Ⅴ was significantly better than that of other treatments, and the SGR was significantly higher than that of treatments Ⅱ, Ⅳ, Ⅵ and Ⅷ, increasing by 10.16%, 10.61%, 9.27% and 8.4%, respectively; the FR was significantly higher than that of treatments Ⅰ, Ⅱ, Ⅳ and Ⅵ, increased by 10.94%, 27.02%, 26.45% and 17.38%, respectively; the FCR was significantly lower than that of treatments Ⅳ, Ⅷ and Ⅷ, decreasing by 7.87%, 8.89% and 8.89%, respectively. Compared with the treatmentⅤ, the FR of treatment I was significantly lower than that of treatmentⅤ, but there were no significant differences in SGR and FCR. The main effect and the interaction effect on intestinal villus height, villus width, muscle thickness and hepatic GH and IGF-1 gene expression levels were not significant. The intestinal villus height of treatment Ⅴ was significantly higher than that of treatments Ⅳ, Ⅵ and Ⅶ, villus width of treatments Ⅰ and Ⅴ was significantly higher than that of treatments Ⅲ, the intestinal muscle thickness of treatments Ⅰ and Ⅲ was thicker than that of treatment Ⅷ, and there was no significant difference in other treatments. The hepatic GH and IGF-1 gene expression levels of treatments Ⅰ and Ⅴ were significantly higher than those of other treatments.

Conclusion The optimal feeding frequency for largemouth bass was 2-3 times/d, the water temperature was 25 ℃, and the breeding density was 25 fish per tank (150 L).