Effects of stocking density on growth performance, digestive enzyme activity, biochemical composition, and economic efficiency of a new strain of <i>Oreochromis niloticus</i> reared in cage culture system at Sindh Pakistan

The latest strain of <i>Oreochromis niloticus</i> is an altered ecological adaptation for sustainable aquaculture and is necessary to sustain stocking density and reduce physiological stress of the new strain. The present study aimed to determine the optimum stocking density, biological performance, and economic efficiency of the Nile tilapia. The 14,000 healthy seeds and uniform weight (40 ± 2.4 g) sex-reversed <i>Oreochromis niloticus</i> were stocked in four cages, which are cage (1) 20 fish/m³, cage (2) 30 fish/m³, cage (3) 40 fish/m³, and cage (4) 50 fish/m³. The fish were fed 30% dietary protein and feeding frequency three times per day and the feeding rate adjusted according to the fish body weight. Results showed a significantly higher growth, weight gain, and specific growth rate in Nile tilapia stocking density on cage (1), 20 fish/m³ and cage (2), 30 fish/m³ compared to cage (3), 40 fish/m³ and cage (4), 50 fish/m³ (<i>p</i> < .05). The survival and growth rate showed an inverse relationship with stocking density. The feed conversion ratio (FCR) is the lowest in cage (1) and cage (2), which is significantly different from those of other cages (<i>p</i> < .05). The profit index (%) was significantly higher at low density. There was no significant variation in the HSI, VSI and CF. The digestive enzymes such as lipase and amylase were secreted highly in the cages (3) and (4) but high protease was secreted in cage (1). The lipid, ash, and protein of the whole fish were reduced to a lower density, but the moisture levels in the fish bodies raised significantly (<i>p</i> < .05) with increasing stocking density. The phenomenal regression indicates that 25-35 fish/m³ are optimum stocking density for Nile tilapia in the cage culture system. The current study has made significant step toward optimizing the stocking density of a new strain and developing cage culture in Pakistan.