Growth Performance of Critically Endangered Hypselobarbus pulchellus in Biofloc Systems with Various C/N Ratios

Background: Biofloc technology relies on adding a carbon source to maintain optimal carbon to nitrogen ratio for transforming the waste into microbial biomass that aquatic animals can use. In the present study, the growth performance of the critically endangered Hypselobarbus pulchellus in biofloc-based seed rearing with different Carbon to Nitrogen ratio was studied. Methods: Healthy early fry (0.01 g) was randomly stocked into 15 circular FRP tanks (1000 L) at a density of 100 individuals/m(3) and reared for 90 days. The carbon to nitrogen ratios of 5:1(CN5), 10:1(CN10), 15:1(CN15) and 20:1(CN20) were maintained using jaggery without considering carbon content derived from the feed and the control group received no additional source of carbon. Result: The results indicated that H. pulchellus had better growth performance in biofloc systems having higher C/N ratios. The highest weight gain (0.48 +/- 0.01 g) and weight gain percentage (3931.15 +/- 120.68%) and specific growth rate (4.11 +/- 0.03% per day) were found in the CN10 group (P<0.05), followed by CN15 and CN20, while the control group values were lowest. In terms of survival, all treatments had high survival rates ranging from 92% to 94.67%, with no significant variations ( P>0.05). The CN10, CN15 and CN20 treatments had significantly higher amylase, protease and lipase activities than control (P<0.05). Moreover, the immunological and antioxidant activity increased with CN ratios. The CN10, CN15 and CN20 groups had significantly lower total ammonia nitrogen, nitrite and nitrate levels than control group (P<0.05). Overall, this study suggests that C/N ratios of 10:1 to 20:1 are optimal for rearing H. pulchellus fingerlings from early fry, with 10:1 presenting the best growth results.