Biologists in the UK and US have genetically engineering salmon to grow quicker and larger by introducing the human growth hormone gene hGH. As of 2000, no-one had started to produce them commercially.

Two researchers from Purdue University in Indiana (US), William Muir and Richard Howard, decided to test the long-term effects of such engineering. Genetically-modifying Japanese Medaka fish (a fish widely used in research), they also managed to create faster and greater growth, and higher levels of eggs in the females. The weakness of the GM fish, however, was that only two thirds survived to reproductive age.

Aware of several studies showing that larger fish, including salmon, attract up to four times as many mates as their smaller rivals, William and Richard turned to computer modelling to predict what might happen to the salmon population. The prediction was that, because the GM fish would pass on their short-life genes to 80% of the population, it would be extinct within 40 generations. Muir comments, “You have the very strange situation where the least fit individual in the population is getting all the matings - this is the reverse of Darwin’s model”.

Ed.- Recent news reports suggest that commercial production of a sterile ‘super salmon’ is imminent in the UK.