The effect of stocking density on profitability of African catfish (Clarias gariepinus) culture in extensive pond systems

摘要

Stocking density is a major factor determining fish production and farm profitability because it directly affects fish survival, growth, behavior, health, water quality, and feeding. The effects of stocking density on water quality, production, body composition and farming profitability of Clarias gariepinus fed a practical marine fish viscera-diet in earthen ponds were studied. Fish (initial weight: 13.0 +/- 0.2 g) were stocked in triplicate at densities of 5, 7 or 10 fish m(-2) in earthen ponds (3 x 10 x 1 m, each) and hand-fed to apparent satiation twice daily with a diet (43% crude protein, 20 kJ g(-1)) formulated by mixing 30% of marine fish viscera meal with locally available ingredients, for a period of 90 days. Results indicated strong dependence of water quality parameters on stocking density, with water transparency, dissolved oxygen and zooplankton abundance significantly decreasing with increased stocking density. Similarly, production performance as measured by final weight, specific growth rate, daily weight gain and weight gain were affected by stocking density, and peaked at a stocked density of 7 fish m(-2) (p 0.05). Conversely, total fish yield and annual production increased significantly with increasing stocking density and reached a maximum yield (186.6 +/- 3.2 kg are(-1)) and annual production (756.6 +/- 10.7 kg(-1)are(-1) year(-1)) at the highest density. Profitability analysis indicated that the profitability index (net return per total production cost) was high for all treatments and varied between 2.13 and 2.46, with significant differences between treatments. The highest profitability index was obtained at a density of 7 fish m(-2); however, the highest net return was realised at the highest stocking density, but came at the expense of decreased production efficiency and an increased environmental cost, thereby demonstrating the potential trade-offs between maximising shorter term on-farm profits vs. ensuring long term sustainability. The results are useful to guide extensive, pond-based aquaculture practices in Benin, and the work can be expanded in future through synergy-and-trade-off analysis to quantify potential impacts of stocking density on the wider smallholder aquaculture sector in Benin.