Effect of stocking density on growth performance, serum biochemical parameters, and muscle texture properties of genetically improved farm tilapia, Oreochromis niloticus

The objective of this study was to assess the effects of stocking density on growth performance, serum biochemical parameters, and muscle texture properties of genetically improved farmed tilapia (Oreochromis niloticus, GIFT). Juvenile GIFT with an average initial weight of 12.54 +/- 0.45g (mean +/- SD) were randomly stocked in 16 tanks (80L) in a recirculation aquaculture system at four densities of 10 (D1), 20 (D2), 30 (D3), and 40 (D4) fish per tank for 56days, with quadruplicate for each density. There were no significant differences in water temperature among the four treatments (P>0.05). D4 had the significantly lowest dissolved oxygen content (5.52 vs 5.69-6.09mgL(-1)) (P>0.05) and pH (6.63 vs 6.87-7.20) (P<0.05). NO2-N and NH4-N concentrations significantly increased with increasing stocking density (P<0.05). Weight gain (WG) and specific growth rates (SGR) decreased with increasing stocking density. The lowest WG (617.20 vs 660.45-747.06%), SGR (3.52 vs 3.62-3.81% day(-1)), and highest feed conversion ratio (1.68 vs 1.53-1.58) were observed in D4. Fish at D4 had significantly lower condition factor (3.11 vs 3.29-3.37%) and survival rate (91.25 vs 97.50%) than those from D1 and D2 (P<0.05). With increasing stocking density, serum total cholesterol, triglyceride, and total protein concentrations decreased (P<0.05) and aspartate aminotransferase and alanine aminotransferase activities increased (P<0.05). D4 fish had higher moisture content (78.80 vs 76.97%) and lower crude protein content (18.14 vs 19.39%) in muscle than D1 fish (P<0.05). Compared to D1 and D2, D3 and D4 had lower muscle hardness (1271.54-1294.07 vs 1465.12-1485.65g), springiness (0.62-0.65 vs 0.70-0.72), gumminess (857.33-885.32 vs 1058.82-1079.28g), and chewiness (533.04-577.09 vs 757.53-775.69g) (P<0.05). High stocking density resulted in growth inhibition, declines in flesh quality, and disturbance to several serum biochemical parameters.