• 22:00 26 February 2007
• NewScientist.com news service
• Bob Holmes

Some genetically modified fish appear to undergo a personality change when they leave laboratory conditions for a more natural environment, according to new research.

Transgenic fish that behave ferociously in a bare tank, appear meek under more natural conditions, meaning it will not be easy for biologists to predict the ecological consequences of escaped GM animals.

Salmon genetically engineered to overproduce growth hormone can put on up to 25 times the weight of wild salmon and could provide "aqua-culturists" with a faster way to raise fish to market size.

However, lab tests suggested that transgenic fish are more aggressive predators than wild salmon, raising concerns that they could harm native fish if they escape into the wild.

Stream tanks

Fredrik Sundström and colleagues at Canada's Center for Aquaculture and Environmental Research, Fisheries and Oceans, in Vancouver, tested whether the GM fish would have the same superiority in more natural conditions.

When they raised the fish in stream tanks complete with gravel, large rocks, logs and natural food items, they found that the GM fish still grew a little faster and ate a little more than unmodified fish, but their advantage was much smaller than when the fish lived in a simple metal tank and ate food in pellet form.

That does not mean escaped GM fish would not cause ecological damage, says Sundström, only that biologists will need to work harder to answer the question. “You can’t use fish reared in the lab to predict what will happen in nature,” he says.

Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0608767104)