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'Trojan gene' could wipe out fish
 GM salmon are currently confined to labs |
Just one genetically-modified (GM) fish could wipe out local populations of the species if released into the wild, biologists have warned.
 The least fit individual in the population is getting all the matings - this is the reverse of Darwin's model  |
| Professor William Muir |
William Muir and Richard Howard of Purdue University, Indiana, US, have dubbed their proposal the "Trojan gene" hypothesis, which is reported in New Scientist magazine.
"This resembles the Trojan horse," said Professor Muir. "It gets into the population looking like something good and it ends up destroying the population."
Human growth hormone
The researchers studied fish carrying the human growth hormone gene hGH, which increases growth rate and final size. Biologists in the US and Britain are experimenting with salmon engineered in a similar way, although no-one has yet begun commercial production.
Muir and Howard included hGH in embryos of a fish called the Japanese medaka (Oryzias latipes), a common aquarium fish that is widely used in research. They found that modified individuals became sexually mature faster than normal fish and produced more eggs.
 The model predicts a wipe-out |
Professor Muir predicts that fish made bigger by genetic engineering would enjoy the same reproductive advantages. So the hGH gene would quickly spread through a fish population.
But Muir and Howard also found that only two-thirds of engineered medaka survived to reproductive age, compared with wild medakas. So the spread of the growth hormone gene could make populations dwindle and eventually become extinct.
It would make it very difficult for anyone at the moment to approve the release of GM fish carrying growth hormone |
| Professor John Beringer |
"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," said Professor Muir. "Sexual selection drives the gene into the population and the reduced viability drives the population to extinction."
Professor David Penman, a fish geneticist at the University of Stirling, said there is evidence that some GM fish modified with growth hormone have reduced sperm production and mating success.
"If large males tend to mate with large females, this would often result in matings between GM fish," he added. This would decrease rather than increase the spread of the gene.
GM warning
But Professor John Beringer of Bristol University, a former chairman of the committee that advises the UK Government on GM organisms, says the research is a warning.
"It would make it very difficult for anyone at the moment to approve the release of GM fish carrying growth hormone," he said. "I would have to give a great deal of consideration about whether that's an intelligent route to go down."
Professor Muir says that the model may prove an invaluable tool in assessing the dangers of GM organisms. He now hopes to test its predictions in tightly controlled fish farm ponds.
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Internet links: | |
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| Purdue University Animal Sciences |
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| Stirling University Aquaculture |
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| New Scientist |
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