Effect of Carbon-to-Nitrogen Ratios Using Millet as a Carbon Source on Growth Performance, Water Quality, and Microbial Dynamics in a Biofloc System for Catla catla

Abstract

A 30-day experiment was conducted to optimize the Carbon-to-Nitrogen (C:N) ratio using millet as a carbon source for the rearing of Catla catla fry. The study utilized a Completely Randomized Design (CRD) with three treatments in triplicate: C:N 10:1 (T1), C:N 15:1 (T2), and C:N 20:1 (T3). Catla catla fry (initial weight 0.88 ± 0.03 g) were stocked at a density of 1.5 g/L (approx. 500 fish/tank) in 300 L tanks. Water quality, microbial floc volume, and growth parameters were monitored weekly. Results indicated significant differences (p < 0.05) in growth performance among treatments. Fish reared in T3 (C:N 20:1) achieved the highest final body weight (2.68 ± 0.10 g) and survival rate (85%), compared to T1 (1.69 ± 0.04 g; 66%). Water quality parameters in T3 were maintained within optimal ranges, with significantly lower Total Ammonia Nitrogen (TAN) (0.52 ± 0.09 ppm) compared to T1 (0.62 ± 0.14 ppm). Floc volume was highest in T3 (20.9 ± 1.23 mL/L), indicating robust microbial proliferation. These findings suggest that a C:N ratio of 20:1 using millet flour significantly enhances growth performance and water quality for Catla catla fry in biofloc systems.