Too Tired to Be Sexy

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.