Effect of Different Doses of Inorganic Fertilizer on Water Quality, Primary Productivity and Production of Nile Tilapia (Oreochromis niloticus) in Earthen Ponds
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Earthen ponds (surface area 155 m2 each) were used to study the effect of different doses of inorganic fertilizer on water quality and fish production. Each pond was stocked with 150 fish of Nile tilapia; Oreochromis niloticus (25-30 g/fish). The ponds received inorganic fertilizer (20:20:5 NPK) with doses of 0, 20, 40, 60 and 100 kg/acre/month. The obtained results revealed that fertilization had no significant effect on water temperature, dissolved oxygen, pH value, free ammonia water conductivity, nitrate concentration, total hardness, and total alkalinity. Only Secchi disk reading, orthophosphate concentration and total nitrogen were significantly affected by the same treatments. Chlorophyll 'a' content over all the rearing period was increased upon increasing the applied doses and the highest was obtained at the 100 kg/acre/month dose. The production of Nile tilapia is optimum at the 60-kg dose. Data of carcass proximate analyses on fish showed that there were no significant differences in dry matter, while crude protein, total lipids and ash contents were significantly affected by different doses.