Effect of Carbon-to-Nitrogen(C/N) Ratio Manipulation on the Growth Performance, Nutrient Utilization and Body Composition of Clarias gariepinus in a Wheat Bran Based Biofloc System

Abstract

Biofloc Technology (BFT) can be effectively implemented using a range of organic carbon sources; however, carbohydrate-based inputs are generally regarded as most suitable. The selection of an appropriate carbon source depends on several factors, including cost-effectiveness, biodegradability, local availability, and the efficiency of bacterial assimilation. A 10-week outdoor culture experiment was conducted to evaluate the effects of varying carbon-to-nitrogen (C/N) ratios on growth performance, nutrient utilisation, and body composition of African catfish (Clarias gariepinus) reared in a biofloc system. Biofloc-based treatments were established at three C/N ratios (10, 15, and 20) through the addition of wheat bran, while a freshwater system with regular water exchange and no supplementary carbon source served as the control (C). The experimental design comprised 12 plastic tanks (100 L capacity), with each treatment conducted in triplicate. Each tank was stocked with 20 fingerlings and the fish were fed a commercial diet containing 40% crude protein throughout the study period. The water quality parameters (EC, pH, temperature, total ammonia nitrogen, nitrite nitrogen, dissolved oxygen, and total dissolved solids) were monitored throughout the experiment. There was no significant (p > 0.05) difference among the treatments in the case of EC, TDS and temperature. The pH, total ammonia nitrogen, and DO showed significant differences. Survival rate improved with increasing C:N ratio up to 15:1 (83.33 ± 1.22%), followed by a slight decline at 20:1 (80.00 ± 2.89%). Final mean weight (FMW) and mean weight gain (MWG) increased significantly (p < 0.05) from 41.80 ± 0.69 g (control) to 52.73 ± 1.15 g at C:N 15, but declined slightly at C:N 20 (43.80 ± 0.64 g). Feed conversion ratio (FCR) improved markedly from 2.08 ± 0.05 (control) to 1.26 ± 0.12 at C:N 15, demonstrating better feed utilization due to microbial protein supplementation and nutrient recycling. Protein efficiency ratio (PER) and protein productive value (PPV) were also significantly affected by C:N ratio, peaking at C:N 15 (PER = 17.65 ± 1.15; PPV = 33.85 ± 1.35%). Crude protein increased significantly from 18.45 ± 1.23 % in the control to 27.60 ± 1.22 % at C:N 20. Fat content followed a similar pattern, rising from 3.24 ± 0.06 % (control) to 6.14 ± 0.44 % at C:N 20. All data collected were subjected to one-way ANOVA. However, the growth production and feed utilization results indicate that a C:N ratio of 15:1 in wheat bran–based biofloc systems provides the best performance thereby it is recommended for fish farmers. The proximate profiles reveal that moderate to high C:N ratios enhance nutrient deposition and metabolic efficiency in C. gariepinus.