The integration of fish farming and vegetable farming is a promising approach for utilizing fish farm effluents, which are rich in nitrogen, phosphorus, and potassium, while diversifying food production in agroaquaculture systems in West Africa. This study evaluated the effect of three stocking densities of Nile tilapia (Oreochromis niloticus) fingerlings, namely D1 (40 fingerlings m⁻³), D2 (60 fingerlings m⁻³), and D3 (80 fingerlings m⁻³), each tested with three replicates, on the zootechnical performance of the fish after 75 days of rearing, on the physicochemical quality of the effluent, and on the agronomic performance of lettuce (Lactuca sativa, 56 days) and tomato (Solanum lycopersicum, 70 days) grown in an integrated system. The results show that the average final weight, average daily gain, survival rate, and specific growth rate of the fish decreased significantly in D3 compared to D1 and D2 (p < 0.05), while the feed conversion ratio increased, reflecting a decline in feed efficiency at high stocking densities. At the same time, the concentrations of non-ionized ammonia, nitrite, nitrate, and potassium in the effluent increased significantly and almost linearly with stocking density (r = 1.00 for nitrate), without any notable change in temperature, pH, or dissolved oxygen. From an agronomic perspective, lettuce yield did not vary significantly across stocking densities (p > 0.05) but reached its maximum at D2. For tomato, the number of fruits, average fruit weight, total weight harvested per plant, and plant height were significantly higher at D2 than at D1 (p < 0.05). Density D2 (60 fingerlings m⁻³) thus appears to be the optimal compromise between fish production and vegetable production, ensuring sufficient enrichment of the effluent with assimilable nutrients without compromising fish growth or survival. These results provide a scientific basis for optimizing integrated systems in tropical regions and for the circular utilization of fish farm effluent in vegetable farming.
