Something fishy. An unmodified male medaka (background) sneaks in and joins a mating between a GM male (foreground) and a female (middle).

Modified Medaka Mate More

Fish genetically modified (GM) to grow faster and larger have great appeal for fish farmers. GM salmon, catfish, and other varieties are already under development, but it's largely unknown what would happen if such fish escaped into the wild. Now research suggests that GM fish could push natural populations of their counterparts to extinction in a matter of years.

The possibility of GM organisms escaping and invading wild populations is no small worry. It topped the list of concerns in a 2002 National Research Council report on animal biotechnology. Around the world there have been many incidents of large numbers of farm-reared fish escaping from their pens and cages into surrounding waters. To date none of these events have involved GM fish, which haven't yet come to market. To study the risk of ecological harm, biologist Richard Howard and colleagues at Purdue University in West Lafayette, Indiana, studied the behavior of male medaka--a freshwater fish commonly used in lab experiments--modified with a growth-hormone gene from salmon.

The GM medaka turned out to be 83% heftier than their unmodified kin, and when they competed one-on-one with unmodified males to mate with females in laboratory tanks, the big fellas were the unequivocal champions. Despite the normal males' "sneak" tactics to disrupt GM couplings with females or to join in, the modified males outscored them three to one.

That could be bad news. GM-sired offspring proved less hardy than those sired by the unmodified males. Because of their success at mating, the modified fish would quickly spread their genes through the wild population, Howard says. Just 60 GM fish would drive a native population of 60,000 to extinction within 50 generations--about 12 years for the medaka, according to a mathematical model the researchers developed. Multiple invasions could shorten the time to extinction, Howard says. The findings are reported online 17 February in the Proceedings of the National Academy of Sciences.

It's certainly possible that GM animals could out-compete their wild kin, says zoologist John Vandenbergh, of North Carolina State University in Raleigh. However, he notes that various kinds of confinement, including sterilization, can lower the odds that an inserted gene will run wild. Whether such safety measures would be required for commercial GM fish remains to be seen. They're now only voluntary for research on GM fish under U.S. Food and Drug Administration guidelines.

Related sites
More about the 2002 NRC report, Animal Biotechnology: Science-Based Concerns
FDA Web site on GM fish

Posted in Environment