Optimizing stocking density of Catla (Catla catla) fingerlings for sustainable yield in Bandagiriya reservoir

Abstract

Inland fisheries play a significant role in the food security and livelihoods of Sri Lanka, especially the culture-based fisheries (CBF) systems in Sri Lankan reservoirs that rely on regular stocking. Stocked exotic fish species such as Catla (Catla catla) have become one of the most popular low cost protein sources in rural areas of Sri Lanka. Therefore, enhanced management practices are needed to maximize yields by fully harnessing the natural productivity of seasonal reservoirs. This study aimed to estimate the optimal stocking density of Catla in Bandagiriya reservoir to achieve maximum sustainable yield while ensuring the long-term sustainability of CBF. The potential yield of the reservoir was estimated using the widely established yield predictive model, the morpho-edaphic index (MEI), which predicts the fish yield based on water conductivity (µScm-1) and depth (m). A strong positive correlation (r= 0.93, p < 0.001) between MEI and fish yield was observed. Based on this relationship, the optimum potential yield of Bandagiriya reservoir was predicted to be 439.94 kg ha-1. The optimum number of fingerlings to be stocked was calculated using Cowx equation to determine the optimum stocking density in seasonal reservoirs. The estimated optimum stocking density of Catla fingerlings in Bandagiriya reservoir was 1795 fingerlings ha-1, which is above the previously reported highest stocking density of 700 fingerlings ha-1, suggesting that stocking density can be increased to enhance the CBF production in Bandagiriya reservoir. Based on these findings, we propose a foundational approach to optimize stocking densities for maximizing production in culture-based fisheries in Sri Lankan reservoirs, using Bandagiriya as a model system.