Environmental parameters and stocking density influence growth, feed utilization and economics of butter catfish, Ompok bimaculatus (Bloch, 1794) production in floating net cages in a large tropical reservoir, India

An experiment was conducted to study the influence of environmental parameters and stocking density on growth, survival, feed utilization, and economic feasibility of a high value butter catfish, Ompok bimaculatus in floating cages in a large tropical reservoir of India for 180 days. The fingerlings (11.44 ± 1.33 cm; 8.05 ± 3.27 g) were stocked at three stocking densities, viz., 15, 25 and 35 fingerlings m⁻³ in GI cages (32m³) in triplicates. Commercial floating pellets were fed to fish at 5–3% of fish biomass. The results indicated that the fishes at the lowest stocking density of 15 fingerlings m⁻³ had significantly higher (p < 0.05) growth in relation to weight gain percentage (717.67 ± 39.10) and specific growth rate (1.14 ± 0.05). Survival percentage was also significantly higher (p < 0.01) at lower stocking densities compared with 35 fingerlings m⁻³. Similarly, the feed conversion efficiency (0.423 ± 0.025), protein efficiency ratio (1.37 ± 0.15) and feed conversion ratio (FCR) (2.37 ± 0.16) were significantly better at density of 15 fingerlings m⁻³. The fish growth and feed utilization efficiency did not vary significantly (p > 0.05) between stocking densities of 15 fingerlings m⁻³ and 25 fingerlings m⁻³. The condition factor was insignificantly higher at lower densities and its values close to 1 indicated congeniality of reservoir ecosystem for cage culture of the species. The coefficient of variation of weight was significantly higher (24.19 ± 1.20) at 35 fingerlings m⁻³. The highest economic gains in terms of benefit cost ratio (1.77) were achieved at the lowest stocking density. The present study indicated better growth and economic returns at lower stocking densities of 15–25 fingerlings m⁻³. The nutrient load and plankton abundance were higher at culture site, however, did not vary significantly from reference sites throughout the culture period. Although most of the environmental parameters showed significant seasonal variations, dissolved oxygen showed significant positive relation (r = 0.86) with the growth of the fish. This is the first study reporting feasibility of cage culture of this highly renumerative species in open waters. The cage culture of this species will not only ensure better economic returns to the marginal cage farmers but will aid in the conservation of this species in natural ecosystem. Being a low volume high value species, the impact on environment will be less compared with high volume low value species. This study will serve as baseline for standardization of its grow-out protocol in cages and will be a step towards much needed species diversification for sustainable small scale cage farming in tropical reservoirs of Asia.