SINGAPORE--Fears that escapee zebrafish, genetically engineered to glow in fluorescent color, would interbreed with their drab brethren in the wild, may be unfounded. A study presented at the Biology in Asia conference here last week suggests that the mutant fish don't shine with sex appeal.
The zebrafish Danio rerio, native to streams in southern Asia, is normally silvery-grey with dark stripes. But in the 1990s, scientists in Taiwan and Singapore genetically modified strains with genes from jellyfish and anemones, giving the fish a green or red "glow" under UV or even visible light. Originally developed to aid in the detection of water pollutants (with a switch gene added, the fish would glow whenever the target pollutant was in the water), these and similar fish have been popular in the aquarium trade in the U.S. since late last year, with the red variety marketed under the name GloFishTM. But environmentalists have expressed concern that the modified fish will escape and interbreed with wild zebrafish, particularly in their native tropical Asia.
Wee-Khee Seah, Zhiyuan Gong, and Daiqin Li of the National University of Singapore made aquariums where a normal or green fluorescent zebrafish female would be confronted with the choice between a normal and a glowing green male behind glass. They found that both types of female spent more than 80% of their time with their noses glued to the glass of the unaltered males' compartments, with the green males jealously courting in vain.Suspecting that the green-glowing fish might have subdued courtship behavior, they then showed the females videos of courting males after digitally doctoring the images of some of the wild males' courtships to make them look fluorescent green. Sure enough, the females always preferred wild males' courtships, whether cloaked in green or not. Finally, when forced to mate with green males, females would show their dissatisfaction by laying only half as many eggs as when paired with a wild male, the researchers found. Seah thinks the genetically-engineered fishes' lethargic courtship behavior may be the result of having too much energy drained by the glowing jellyfish protein in their muscles.Fish ethologist Adam Shohet of the University of Sussex in Brighton, U.K., agrees that the insertion of a foreign fluorescent protein may upset the fishes' finely-balanced energy budget. He's convinced that the new results show that there is "little threat posed by the popular proliferation of these fish."