GloFish tetras reproduce at half the rate of regular black tetras, and the fry survive at 97 percent the rate of their natural peers, Hallerman said. Furthermore, fluorescence takes energy and is a burden that makes the fish less fit, so it will be bred out, he said — eventually the trait "is going to disappear.''
But some scientists disagree. "There is no way of predicting any species's fitness in the absence of environmental settings, because species do not behave as predicted by models,'' Paulo Petry, a freshwater fish specialist in Latin America for the Nature Conservancy, said.
"I would opt for the precautionary principle and not allow the commercialization of these things in regions where there is even a remote chance of establishing a viable population," he said.
GM fish are not allowed in Canada and much of Europe, and GloFish cannot be sold in California. The FDA determined in 2003 that GloFish did not need to go through a full approval process, saying there was no evidence that the altered fish posed an increased risk to the environment and there was an absence of a clear risk to public health.
(Florida, which hosts a large ornamental fish industry, including the two fish farms that raise GloFish, requires approval before genetically modified fish can be raised there.)
"We think the feds should step in whether or not [GloFish] pose a threat. It shows the big holes in our regulatory system, in how we deal with genetically engineered animals,'' said Eric Hoffman, food and technology campaigner at Friends of the Earth.
"If people look down into water and look at glowing fish, they might be pretty, but it's a sign of genetic contamination and a type of pollution we don't want,'' Hoffman said.
Appel is a science writer based in Boston.