STOCKING DENSITIES ON GROWTH, ANTIOXIDANT ENZYME ACTIVITIES AND INTESTINAL MICROBIOTA OF HYBRID OF CULTER ALBURNUS (♀)×MEGALOBRAMA TERMINALIS (♂) IN IPRA SYSTEM

This experiment was conducted to evaluate the appropriate stocking density of a new hybrid strain of (♀Culter alburnus) × (♂Megalobrama terminalis) initial body weight of (5.58±0.45) g for in-pond raceway aquaculture (IPRA) system. The new hybrid strains were farmed in three stocking densities of 0.5 (SD1), 1.0 (SD2) and 1.5 kg/m³ (SD3). The growth and antioxidant enzyme activities were analyzed on 90, 120, 150 and 180 days while the intestinal microbiota composition was analysed when the experiment finished. Growth results showed that the body weight and specific growth rate (SGR) decreased significantly when stocking density was above 1.0 kg/m³ on 120 days (P＜0.05). In the day of 150—180, indices of SGR and body weight decreased significantly with the increasing of rearing density (P＜0.05). Antioxidant enzyme activities in serum increased with the increasing of stocking density on 90 days, and fish farmed at SD3 had significantly higher antioxidant enzyme activities than group of SD1 (P＜0.05). In contrast, antioxidant enzyme activities in serum decreased with the increasing of stocking density in the day of 150—180, and the activities of catalase (CAT) and total antioxidant capacity (T-AOC) were significant lower in the group of SD3 than group of SD1 (P＜0.05). Antioxidant enzyme activities in liver increased with increasing stocking density in the day of 150—180, and values of GSH-Px decreased significantly with the increasing of stocking density (P＜0.05). MDA level decreased with increasing stocking density before the day of 120, whereas fish farmed at SD2 and SD3 groups had significant higher MDA values than the SD1 group on 180 days. The intestinal microbiota results demonstrated that microbiota community changed in genus level obviously, and the relative abundances of pathogenic genus such as Aeromonas, Pseudomonas and Acinetobacter increased while Shannon diversity indices decreased significantly in group of SD3 (P＜0.05). In conclusion, when culturing days below 120, the stocking density of SD2 had no great effect on the growth and antioxidant capacity, and the suitable stocking density is suggested below 1.0 kg/m³. When culturing time extends to 150 days, the stocking density of SD1 would inhibit growth and increase the relative abundances of pathogenic genus and decrease the Shannon diversity index of intestine microbiota, therefore 0.5 kg/m³ is suggested as an appropriate density.