Robert H. Devlin/Fisheries and Oceans Canada

Two 1-year-old coho salmon--one transgenic (top), one not--both raised in a hatchery.

Super Salmon Face Their Kryptonite

In the struggle between nature and nurture, score a point for nurture. A new study shows that salmon genetically modified to grow 25 times larger than their wild relatives end up far punier when reared in a natural-looking environment. But even if the modified fish won't grow so huge in the wild, researchers say it's too early to know whether it's safe to let them out of the lab.

Scientists have engineered salmon, tilapia, and other fish to grow faster and bigger, but no transgenic fish is approved for commercial farming in the United States. Concerns linger over the risks such fish pose in the wild. Conservationists worry, for example, that escaped transgenic fish could threaten wild stocks by increasing competition for food (Science, 13 September 2002).

To gauge the validity of these worries, researchers at the Center for Aquaculture and Environmental Research in Vancouver, Canada, took a look at the transgenic coho salmon. The fish make extra growth hormone, and when raised in a hatchery they bulk up to 25 times the size of normal coho. But what if they grew up in an environment more like their natural home? The researchers designed a 5-meter-by-1-meter "stream" in their lab, complete with rocks, logs, and small rainbow trout for the salmon to devour. Coho grown in this simulated environment grew to just twice the size of their wild cousins and gorged on less prey than did their hatchery-grown counterparts, the team reports online this week in the Proceedings of the National Academy of Sciences.

Despite these seemingly reassuring findings, the researchers warn against concluding that genetically modified fish pose no threat to natural populations. "Certainly the ecosystem we created does not fully represent the wild," says Robert Devlin, a molecular biologist at the noncommercial center.

William Muir, a geneticist at Purdue University in West Lafayette, Indiana, who has developed computer models to predict how transgenic fish might fare in the wild, agrees that simulated environments are no substitute for the great outdoors. Still, he calls the study "extremely important" and notes that it provides the strongest evidence yet that "transgenic fish are less risky than we thought."

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