Since their first production, genetically modified organisms have been a polarizing issue, especially when it comes to using genetically modified organisms for food. Some people consider genetically modified organisms a sensible solution to food production shortages, while others condemn them as anything from inherently immoral to an environmental disaster. Genetically modified Atlantic salmon, carrying a gene that enhances growth, may be the first animal to be approved as a human food source, and as such, heated debate surrounds this fish. Amidst the raging debate, a group of scientists decided to study the potential effects of genetically modified salmon on wild fish populations, should fish escape from farms.

In the wild, Atlantic salmon will sometimes reproduce with the more common brown trout, creating hybrid offspring. In this study, Krista Oke, Peter Westley, Derek Moreau and Ian Fleming from Memorial University in St John's, Newfoundland, Canada, decided to investigate whether genetically modified Atlantic salmon would also reproduce with brown trout, and whether the modified genes would appear in hybrid offspring. Taking this a step further, the researchers wanted to know whether salmon–trout hybrids carrying the modified gene would have the accelerated growth rates typical of their genetically modified Atlantic salmon parent. Finally, how would the hybrids carrying the modified gene interact with wild-type Atlantic salmon, and hybrids without the modified gene?

Using genetically modified Atlantic salmon as both mothers and fathers in crosses with brown trout, the authors established that the salmon and trout would reproduce, and that the modified gene appeared in about half of the hybrid offspring. They also found evidence that there is an advantage to carrying this modified gene. When the brown trout was the mother of the hybrid, the offspring carrying the modified gene had higher survival rates than their siblings without the modified gene. Regardless of whether the genetically modified Atlantic salmon was the mother or father, hybrids carrying the modified gene also grew more quickly than hybrids without the modified gene, or wild-type fish of either species when raised in a typical fish farm setting.

However, things got really interesting when the researchers raised these fish in artificial streams more similar to their natural environment. The fish in these streams had to compete for food and jockey for space just as they would in the wild. Within these streams, the patterns of growth shifted dramatically. Unlike in the fish farm setting, the wild-type fish consistently grew at faster rates than the fish carrying the modified gene. Even more exciting was the discovery that in mixed-species streams, hybrids carrying the modified gene suppressed the growth of both genetically modified and wild-type Atlantic salmon. This growth suppression appeared to be a response specifically to hybrids carrying the modified gene, rather than to hybrids without the modified gene. How hybrids carrying a modified gene suppressed the growth of Atlantic salmon remains unclear, but it may be that these hybrids are more aggressive.

While this research offers no definitive answers in the debate on genetically modified organisms, it is clear that an escaped genetically modified Atlantic salmon could reproduce with a wild brown trout, and produce viable hybrid offspring carrying the modified gene. Even more importantly, this research revealed unexpected consequences of introducing genetically modified fish on natural populations, as hybrids carrying the modified gene suppressed the growth of wild Atlantic salmon. In summary, the findings emphasize that good scientific research is indispensable when assessing the viability of using genetically modified animals.

K. B.
P. A. H.
D. T. R.
I. A.
Hybridization between genetically modified Atlantic salmon and wild brown trout reveals novel ecological interactions
Proc. R. Soc. Lond. B