Evaluation of different stocking densities and carbon:nitrogen ratios on growth, body composition and production performance of Labeo rohita (Hamilton, 1822) spawn in biofloc based-nursery system

Biofloc technology (BFT) is an intensive sustainable farming technique that increases the carrying capacity of the culture system by controlling the C/N ratio. The present study aims to assess the potentiality of BFT for intensive nursery production of Labeo rohita spawn (6-8.5 mm). The assessment was done at different stocking densities, that is, 1 (D1), 2 (D2), 3 (D3), 4 (D4) and 5 (D5) spawn/L (study I) and at different C/N ratios, that is, 10:1, 15:1 and 20:1 (study II), by evaluating survival, growth, feed utilization and biochemical composition of spawn in biofloc culture system. The cultures reached at the end of 20 days showed a higher mean survival rate, that is, 89%, 91.38% and 80.4% in D1, D2 and D3 respectively. Moreover, these BFT groups exhibited spearheading growth in terms of final length, final weight and specific growth rate. The coefficient of variation and food conversion ratio was lowest in D2, but the highest production was achieved in D3. In study II, the biofloc culture (at 2 spawn/L density) with C/N ratio >15:1 effectively reduced the total ammoniacal and nitrite nitrogen and produced in situ live food adequately. In addition, the C/N ratio showed an interactive effect on the growth performance of fish by the substantial increase in final length, weight gain percentage, specific growth rate and feed utilization in C/N 20 and 15 groups than that in C/N 10 group. The crude protein and lipid level of biofloc in C/N 20 and 15 treatments was notably higher than in other treatments. The findings suggest that the BFT can be effectively applied to enhance the nursery production of L. rohita, preferably at 2-3 spawn/L stocking density and 15:1C/N ratio.