The fish growth hormone gene has been cloned and characterized from a number of fishes, including many salmon species (Du et al. 1992, Devlin et al. 1994). Researchers from the University of Southampton in the United Kingdom (Rahman et al. 1998) developed transgenic tilapia fish (Oreochromis niloticus) transformed with growth hormone genes of several salmonids.
Rahman et al. used different types of constructs in their experiment, but the one that gave the best results was the construct with a Chinook salmon GH gene under the control of the ocean pout antifreeze promoter. The method used for the insertion of the transgene construct was the cytoplasmic microinjection of fertilized fish egg.
The researchers reported the successful genomic integration of the construct in the founder (G0) tilapia and subsequent transfer of the transgene to the G1 and G2 generations. Transgenic tilapia expressing the transgene showed a growth rate three times greater than the wild-type tilapia and had a 33% higher food conversion ratio, which would reduce farmers’ production cost. This transgenic tilapia also showed infertility at mature age, which is a desirable trait for commercial transgenic fish (Rahman et al. 1998).