Growth and nutritional trials on transgenic Nile tilapia containing an exogenous fish growth hormone gene

In a long-term growth trial, transgenic tilapia Oreochromis niloticus L. showed a 2·5-fold increase in growth compared with non-transgenic siblings. At 7 months, mean mass of transgenic tilapia was 653 g compared with 260 g for non-transgenic siblings. A significant increase (P<0·01) in head : total length ratio, viscera-somatic index and hepato-somatic index was observed in transgenic fish. Female gonado-somatic index (IG) was found to be lower in transgenics than non-transgenic siblings in both mixed and separate culture conditions. Transgenic male IG values were found to be higher in mixed culture and lower in separate culture than that of their non-transgenic siblings. Food conversion efficiency was more than 20% greater in the transgenic fish. In a second shorter-term growth performance trial, the transgenic fish grew to about four times the size of their non-transgenic siblings. A digestibility trial suggested that transgenic tilapia were more efficient utilizers of protein, dry matter and energy. Apparent digestibility of protein and apparent energy digestibility were higher in the transgenic fish