Optimizing Stocking Density under Semi-Movable Paddlewheel Aeration to Improve Water Quality, Growth Performance and Production of Nile Tilapia Reared in Concrete Ponds

This study evaluated the effects of increasing stocking density under a fixed aeration capacity on water quality, growth performance, and economic efficiency of Nile tilapia (Oreochromis niloticus) cultured in concrete ponds equipped with a semi-movable paddlewheel aeration configuration. Three stocking densities (80, 120, and 160 fish m(-3)) were tested over a 90-day production cycle using a completely randomized design with triplicate ponds per treatment (each 99 m(3)). The aerators were operated continuously (1.5 hp, 24 h day(-1)), and aeration power was kept constant across treatments. Water quality showed a clear density-dependent deterioration: dissolved oxygen (DO) decreased from 5.0 +/- 0.17 mg L-1 at 80 fish m(-3) to 3.3 +/- 0.17 mg L-1 at 160 fish m(-3) (p < 0.05), while unionized ammonia (UIA) increased from 0.028 +/- 0.01 mg L-1 to 0.056 +/- 0.01 mg L-1. In line with this, the growth performance decreased as density increased: the final body weight decreased from 304.3 +/- 0.882 g to 272.7 +/- 5.903 g, and the feed conversion ratio increased to 1.68. Survival rate showed a moderate decline to 93.2%. Whereas the highest density had the highest total biomass (3,969 kg) and gross revenue (US$8,972), the intermediate density (120 fish m(-3)) had the most balanced result between growth performance, survival, and profitability (benefit-cost ratio = 1.49). The highest stocking density was associated with lower DO, increased nitrogen loading, and reduced size uniformity, suggesting that production efficiency was mainly constrained by oxygen availability and overall biomass loading rather than by acute ammonia toxicity. These results imply that, when the aeration capacity in concrete pond systems is held constant, moderate stocking density can be best suited to a trade-off between biological performance and economic payoff and can be useful in the context of intensive Nile Tilapia production in situations with limited aeration capacity.