Agricultural Horizons: Research, Technology and Sustainable Development Vol. 1

Stocking density is an important management factor in intensive aquaculture because it influences growth, feed utilisation, survival, physiological condition and resource-use efficiency. The present study evaluated the effects of five stocking densities on the production performance, physiological responses and resource utilisation of the Indian spiny loach, Lepidocephalichthys thermalis, during a 90-day outdoor tank-culture experiment. Fish were stocked at 500, 750, 1000, 1250 and 1500 fish per 0.2 m³, with three replicate tanks per treatment. Stocking density significantly affected growth, feed utilisation, survival, physiological stress, antioxidant defence, digestive enzyme activity, body composition, energy allocation and water productivity (P<0.05). The lowest density (500 fish/0.2 m³) produced the highest final body weight (0.40 ± 0.004 g), weight gain (0.262 ± 0.0049 g), weight gain percentage (187.5 ± 3.535%), specific growth rate (1.27 ± 0.012% day⁻¹), feed conversion efficiency (70.6 ± 0.353%) and protein efficiency ratio (1.945 ± 0.0356), together with the highest survival (98.90 ± 0.141%) and antioxidant and digestive enzyme activities. In contrast, increasing stocking density progressively reduced individual growth and feed efficiency while increasing cortisol concentration from 41.07 ± 0.063 to 73.56 ± 0.678 ng/mL. Final biomass increased with density, reaching 353.9 ± 2.757 g at 1500 fish/0.2 m³, while water-use productivity also increased. However, energy allocation to growth declined from 48.4 ± 0.636% to 29.1 ± 0.353% across the density gradient. Overall, 500 fish/0.2 m³ provided the best balance of individual growth, survival, feed efficiency and physiological condition, whereas higher densities increased biomass and water-use productivity at the expense of individual performance and physiological condition.