Effects of stocking density on growth, survival, and economic viability of Chocolate Mahseer larval rearing

ABSTRACT Objective The Chocolate Mahseer Neolissochilus hexagonolepis is an ecologically and economically significant species native to South and Southeast Asia. However, there is limited research on optimal rearing conditions for the larvae. This study aimed to investigate the effects of varying densities on growth, survival, water quality, and economic viability during larval rearing. Methods The 30-d experiment, conducted in a controlled laboratory, tested larval stocking densities of 5, 10, 15, and 20 larvae/L at 24 ± 1°C, with an initial larval weight (mean ± SE) of 5.2 ± 0.3 mg. Larvae were fed brine shrimp Artemia nauplii and commercial powdered feed. The study evaluated growth performance, survival rates, water quality (focusing on ammonia levels), and economic outcomes, including benefit–cost ratio and net return. Results All tested densities significantly influenced growth performance, survival rates, and water quality. The 10-larvae/L treatment achieved the highest specific growth rate (SGR; mean ± SE = 8.12 ± 0.24%/d) and weight gain (452.3 ± 15.7 mg), while the 5-larvae/L treatment had the highest survival rate (92.5 ± 2.1%). The 15-larvae/L treatment exhibited intermediate performance (SGR = 7.68 ± 0.21%/d; survival = 79.1 ± 4.5%), and the 20-larvae/L treatment showed the lowest values for both variables (SGR = 7.41 ± 0.20%/d; survival = 68.7 ± 5.8%). Water quality deteriorated with increased stocking density, especially with respect to ammonia levels. Economically, the 10-larvae/L treatment provided the highest benefit–cost ratio (1.68) and net return. Conclusions A stocking density of 10 larvae/L was found to offer the best balance between biological performance and economic viability for rearing Chocolate Mahseer larvae. These findings contribute valuable insights for developing efficient aquaculture practices for this species and supporting conservation efforts while also addressing economic considerations.