Effect of different stocking densities on growth performance and gut villi histology of endemic ornamental fish (Betta rubra) in the biofloc technology

The endemic ornamental fish Betta rubra, known locally as serban malem, is a high-value non-consumptive fishery product. This study aims to evaluate the growth performance and histological structure of gut villi of B. rubra fish maintained in a biofloc system with different stocking densities. This study used a completely randomized design with four treatments: 1 fish/liter (control, no biofloc system), 1 fish/liter (biofloc system), 2 fish/liter (biofloc system), and 4 fish/liter (biofloc system). Treatments showing significant differences were further evaluated using Duncan's test. The results showed that the survival rate, length increase, and feed conversion ratio in the biofloc systems were significantly different from those of the control (P<0.05). In contrast, daily growth rate and weight gain were not significantly different between treatments. Fish intestinal villi in the biofloc system were significantly different compared to those in the control. In conclusion, the optimal rearing density of B. rubra is 2 fish/liter in the biofloc system (P2).