The researchers then compared the viability of normal medaka with another group to which they had added a human growth-hormone gene. The final step was to plug these and other results into a computer to model to see what would happen when 60 transgenic fish were introduced into a population of 60,000 wild medaka. The results were disturbing. It took only 40 generations for the GM fish, which mated more successfully but produced offspring that did not survive as well, to drive the population to extinction. The Purdue researchers stressed that their results should be treated with caution.
Shock treatment Creating sterile salmon is relatively simple.
If salmon eggs are subjected to a heat or pressure shock shortly after fertilization, they retain an extra set of chromosomes, ending up with three sets, rather than the normal two. The resulting 'triploid' fish do not develop normal sexual characteristics, and the females are sterile. It is also possible to raise female salmon as fertile males by treating them with male sex hormones. Fletcher argues that skilled aquaculturists can apply this method unerringly, but other scientists are less confident. But other scientists point out that these results have not been published in the peer-reviewed literature.