This study determined the effects of stocking density of Oreochromis niloticus on the economic benefits in a small-scale aquaponics system. Three larval stocking densities (150 fish m-3, 300 fish m-3 and 450 fish m-3) were tested. The treatments were replicated five times. After 8 weeks of the study, it was established that the total fish yield ranged from 6.0 kg per tank at a stocking density of 150 fish m-3 to a high value of 10.33 kg per tank at a stocking density of 450 fish m-3. The total yield of fish increased with increasing stocking density. The lettuce yields ranged from 1.66 kg at a stocking density of 150 fish m-3 to the highest value of 3.04 kg at a stocking density of 450 fish m-3. The break-even prices for variable costs could cover the fish cost in the local market, as they were below the sale price of KES 324 ($3.24) per case that the farm could receive in the market. A discount rate of 18% was used to calculate the NPV. It was observed that sales of fish and lettuce at a stocking density of 150 fish m-3 were not profitable, but profitability began to increase as density increased.
Keywords: Aquaponics, Nile tilapia, lettuce, stocking density, yield, profitability