GROWTH PERFORMANCE AND METABOLIC RATES OF GENETICALLY IMPROVED AND CONVENTIONAL STRAINS OF NILE TILAPIA, Oreochromis niloticus L. REARED INDIVIDUALLY AND FED AD LIBITUM

The introduction of the GIFT (Genetically Improved Farmed Tilapia) strain of Nile tilapia (Oreochromis niloticus) was aimed at improving the genetic quality of farmed tilapia in order to give better growth, higher survival rates and delayed sexual maturation. To investigate whether the GIFT strains are metabolically superior to other Nile tilapia strains, a 17 week experiment was conducted with three types of Nile tilapia namely, sex reversed GIFT male (GIFT-SR), GIFT mixed sex (GIFT-NSR) and mixed sex conventional Nile tilapia (CNT-NSR). Fish were kept individually at 27°C in respiration chambers of a computer controlled respirometer system. The fish were fed ad libitum with a diet containing 41 % crude protein, 9 % lipid and 20 kJ g–1 gross energy. The standard metabolic rates (SMR) were 49.0, 47.6 and 54.5 mg O2 kg-0.8 h-1 and the average or routine metabolic rates (RMR) were 148.4, 147.2 and 153.6 mg O2 kg-0.8 h-1 for GIFT-SR, GIFT-NSR and CNT-NSR, respectively. The SMR and RMR values did not differ significantly between the different strains. The scope for spontaneous activity, a theoretical indicator of the growth potential of fish, also showed no significant difference between the three groups (220, 234 and 224 mg O2 kg-0.8 h-1 for GIFT-SR, GIFT-NSR and CNT-NSR, respectively). The growth performance of the three groups at the end of the experiment was similar. There were no differences in body composition except for lipid content, which was higher in both GIFT groups. Other parameters such as feed conversion efficiency (FCE), protein productive value (PPV) and apparent lipid conversion (ALC) also showed no statistically significant differences. The results indicate that there are no significant differences in metabolic rates, or any parameters related to growth between GIFT and conventional Nile tilapia under our standardized laboratory conditions