The Texas-based Yorktown Technologies has licensed to sell as pets the zebra fish, originally developed to detect environmental toxins.

"These fish were bred to help fight environmental pollution," company spokesman Alan Blake said on Friday.

"They were bred to fluoresce in the presence of toxins," he said.

Scientists have for decades used a gene called green fluorescent protein, taken from jellyfish, to help in research.

GloFish

The fish, sold under the trademarked name GloFish, carry similar gene taken from a sea coral that makes it glow all the time.

Blake said there is no evidence the fish will pose any threat to the environment.

Normal zebra fish are commonly used in aquariums and cannot survive in non-tropical waters.

"They are very bright under any type of light," Blake said.

"Under ultraviolet light in a dark room they will appear to be glowing in the dark," he explained.

The fish, developed at the National University of Singapore, will sell for about $5 apiece at pet stores from January.