Comparative study of growth performance of three strains of Nile tilapia, Oreochromis niloticus, L. at two stocking densities

This study was conducted to investigate the effect of stocking density (125 or 200 fish m−3) on the growth performance of three strains of the Nile tilapia, Oreochromis niloticus: the non-improved strain (NS), the genetically improved farmed tilapia (GIFT) and the Freshwater Aquaculture Center selected tilapia known as the FaST selected line (SL). Each strain and density combination was triplicated in 0.42 m3 fibreglass tanks within a re-circulating water system. Water temperature was maintained at 29.0±1.0°C. Large Nile tilapia having a mean body weight of 100–110 g were stocked in each tank and hand-fed four times daily with commercial tilapia pellets (35% protein) for 104 days. Results showed that at the two stocking densities, the GIFT and SL strains showed a significantly higher (P<0.05) mean weight (MWT), daily growth rate (DGR), specific growth rate (SGR), feed conversion ratio (FCR) and gross yield (GY) than the NS. In all three strains, growth performance was negatively affected by stocking density. The lower density (125 fish m−3) treatments had significantly higher MWT, DGR and SGR than the higher density one (200 fish m−3). However, higher FCR and GY were observed at the higher density. Survival rates were high in all treatments and were not affected by strain or density. In general, the SL strain had better growth parameters than the GIFT strain. The findings of this study demonstrated the superior growth performance of the improved strains at both densities compared with the NS. The higher density (200 fish m−3) could be more profitable for the tilapia farms in Kuwait than the lower density of (125 fish m−3) in terms of reduced land cost and facilities, demand on the limited low-salinity underground water and manpower.