Effects of inorganic fertilizer application and supplementary feeding on water physico-chemical parameters, growth performance and yield of Nile Tilapia (Oreochromis niloticus) cultured in earthen ponds

International Journal of Fisheries and Aquatic Research, Volume 5; Issue 3; 2020; Page No. 29-37This study was carried out for 180 days to assess the growth performance, water physico-chemical parameters, yield and profitability of Nile tilapia (Oreochromis niloticus) culture in earthen ponds. The fish were reared in nine earthen ponds with average size of 177 m 2 and subjected to three treatments i.e. pond fertilization alone (T 1 ), concentrate feeding alone (T 2 ) and a combination of pond fertilization plus concentrate feeding (T 3 ). Sex- reversed Nile tilapia fingerlings were stocked at a density of 3 fish/m 2 . For T 1 and T 3 , urea and Diammonium phosphate (DAP) fertilizers were applied in pond water weekly at a rate of 3 g/m 2 and 2 g/m 2 , respectively. For T 2 and T 3 the fish were fed a diet containing 25.1% crude protein (CP) at a rate of 5% and 2.5% of body weight, respectively. Pond water physico-chemical parameters were measured weekly. A total of 30 fish from each pond were harvested biweekly and individually measured for body weight and length. Dissolved oxygen (DO), pH, Secchi disk reading, conductivity, salinity, phosphorous, nitrate and alkalinity differed (p ≤ 0.05) but temperature did not differ (p > 0.05) among treatments. In all treatments the water quality parameters were within the acceptable range for tilapia culture. Within a 24 hours period, DO, pH and temperature were highest at 1500 hours and lowest at 0600 hours. The fish reared under T 3 showed higher (p < 0.05) body weight gain (194.1 ± 4.5 g), growth rate (GR) (1.5 ± 0.1 g/day), estimated yield (13 065 ± 458 kg/ha/year) and gross margin (12 364.41 ± 1 376.75 USD/ha) than those under the other treatments. The FCR was higher (4.1 ± 0.3) for the fish subjected to T 2 and lower (2.0 ± 0.1) for the fish reared under T 3 . The highest condition factor (K) (2.54 ± 0.0) was observed for the fish reared in ponds under T 1 whereas fish under T 2 had the lowest value (2.05 ± 0.0). It is concluded that, the combination of pond fertilization plus concentrate feeding (T 3 ) is the best strategy for rearing Oreochromis niloticus, since it reduces feed utilization and results into higher growth performance and profit