Yorktown's chief executive, Alan Blake, said the company chose the black tetra to modify because it is nonaggressive and shows no tendency to be invasive.
"The black tetra has been sold for over 60 years and there has never been an ecological concern with it,'' Blake said.
There have been reports of natural black tetras in Florida's waters. But Blake said there is no evidence that groups of them live there permanently; probably, he said, they are eaten by predators.
Blake pointed to research by Jeffrey Hill, who was part of the task force that reviewed Yorktown's successful application to raise the GloFish tetra in Florida. In a 2011 study, Hill found that largemouth bass and mosquito fish in Florida ate twice as many red GloFish as regular zebra fish when they were all put in tanks together.
"Florida is a predator-rich environment. [The GloFish] is considerably more vulnerable'' than its non-modified counterparts, said Hill, a nonnative fish specialist at the University of Florida's Tropical Aquaculture Laboratory.
That' s not reassuring to environmentalists such as Chernoff.
"So their plan for not having these things take over the wild is predation by other species? Great," he said.
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Breeding between escaped GloFish and native fish could weaken the progeny and negatively affect the native fish species in future generations, said Brian Zimmerman, aquarium curator at the Zoological Society of London.
The fluorescence in the GloFish may give them an unfair advantage or a disadvantage as they forage for food or in their roles as prey and predator, Zimmerman said. The point is, nobody knows for sure. "GM fish have only been around for a few years, and I don't think we know enough to say they are safe," he said.
If GloFish tetras breed with wild black tetras, the fluorescent gene would be passed on for only a limited number of generations, said Eric Hallerman, a scientific adviser to Yorktown and chair of the Department of Fish and Wildlife Conservation at Virginia Tech in Blacksburg.