NITROGEN AND MINERAL BUDGET OF NILE TILAPIA FRY FED RECYCLED FOOD WASTES MATERIALS SUPPLEMENTED WITH LYSINE AND METHIONINE IN A CLOSED RECIRCULATING FISH CULTURE SYSTEM

Abstract

The study evaluated nitrogen and mineral budgets of Nile tilapia Oreochromis niloticus in a closedrecirculation system for 11 weeks, during which no water renewal was carried out. Fish (mean weight 1.2 ± 0.11 g) were fed with different levels of recycled waste materials supplemented with lysine (lys) and methionine (met), designated as D1 (0% FIW+SSW), D2 (57.90 % FIW+SSW + lys and met) and D3 (54.84% FIW+SSW only). The result showed that fish fed D2 diet produced higher (P<0.05) growth performance and feed efficiency than those fed the other diets. The biofilter used in the recirculation system effectively converted ammonia to nitrate, as such toxic ammonia and nitrite were negligible. However inorganic phosphorus was similar among the treatments. Phosphorus retention was significantly higher (P<0.05) in fish fed the D2 diet, while nitrogen retention did not differ significantly among fish fed the experimental diets. No significant difference was recorded in nitrogen loading among the treatments, but phosphorus loading was lower in D2 and was significantly (P<0.05) different from other treatments. There was no considerable variation in the solid wastes generated among all treatments; however, mineral composition confirmed that the solid wastes were composed of phosphorus, calcium, iron, zinc, manganese and copper; while nitrogen, magnesium, sodium and potassium were noted in the rearing water. The results of this study revealed that diet D2 made the least negative impact on the environment.