GENE-TRANSFER IN TILAPIA (OREOCHROMIS-NILOTICUS)

The microinjection of the human growth hormone gene into the germinal disc and the development of 90-day live transgenic tilapia are reported. Three different spawns, treated 10 min, 21-24 h or 40-43 h after spawning, were used. For microinjection a linear 4.0 kb EcoRI-DNA fragment containing the mouse metallothionein-I promoter (mMT-I) fused to a structural gene coding for the human growth hormone (hGH) was used. The injection pipette was inserted through the micropyle and several nanoliters of DNA solution (103 copies/pl) were injected. Hatching frequencies of injected eggs were very similar to those of control eggs. Out of 67 fish which had developed to an age of 90 days, four were found to be transgenic and had integrated 1-5 copies/cell of the human growth hormone gene construct. The number of fish containing foreign DNA was highest (3 out of 18) in the group injected 21-24 h after spawning. We have observed that the integration rate is lower than in mammals.