Saidou et al. J. Appl. Biosci. 2014. Effet de l'urée et du NPK perlés et super granulés sur la productivité des variétés de riz IR841 et NERICA-L14 au Sud-Bénin 6575 Effet de l'urée et du NPK 15-15-15 perlés et super granulés sur la productivité des variétés de riz IR841 et NERICA-L14 en zone de bas-fond au Sud-Bénin

Nitrogen (N) and phosphorus (P) wastes produced by Nile tilapia Oreochromis niloticus L. fed Azolla, an aquatic atmospheric nitrogen fixing fern, was evaluated for 90 days in pond experiment. Six isonitrogenous (29.2% crude protein) and isoenergetic (16.9 Kj·g -1 ) diets A 0 , A 10 , A 20 , A 30 , A 40 and A 50 , containing 0%, 10%, 20%, 30%, 40% and 50% of Azolla meal (AM) respectively, as partial fishmeal (FM) substitutes, was provided to experimental fish. The Azolla-free diet A 0 served as a control. Fish specific growth rate (SGR) was higher with the control diet, the lower values being obtained in A 50 -fed fish (P < 0.05). Crude protein and P content in experimental fish showed similar values. Evaluation of the nutrient wasted show identical values (84.8% -87.8% of supplied) for total P (TP); while total N (TN) discharged into ponds by fish increased significantly when AM level greater than 30% in diets (P < 0.05), amounting 63.9% -74.2% of that supplied. From these findings, the fern Azolla could be used in diet to sustain Nile tilapia growth and as "environmentally-friendly" ingredient to limit P loss, while providing N to the field, beneficially in tropical marshland pond where this nutrient is already limiting.