Tsai and his fluorescent fish.

CREDITS: H. J.TSAI

Until an aquarium company chanced upon them, the fluorescent fish that microbiologist H. J. Tsai had bioengineered in his lab were just an interesting sidelight. But 2 years after the company struck a partnership with the National Taiwan University (NTU) microbiologist to market his creations to hobbyists, developing ornamental fish has become an important part of his research.

Tsai, 53, routinely inserts a jellyfish gene into the zebrafish genome to track the development and behavior of specific cell types. In 2000, he was testing a gene-delivery promoter that would make the organs of the engineered fish visible without a microscope and found that it made the entire body fluorescent. Tsai dropped a slide of the bright green fish into his presentations, where it caught the eye of a manager from Taikong Corp., a Taipei aquarium company.

In return for helping Taikong commercialize the transgenic fish, Tsai gets money for his research, including efforts to create new ornamental fish. So far Tsai has developed zebrafish with different patterns of green and red fluorescence by combining genes from jellyfish and marine coral. His next goal is a glowing dragon fish, which many Asians consider to be a good omen.

Tsai says his work shouldn't adversely affect the environment: "Since these fish are for aquariums only, they don't present the usual concerns associated with genetically modified organisms." But to be safe, he says more than 90% of Taikong's Night Pearls, its transgenic zebrafish now on sale in Taiwan, have been sterilized. Eric Hallerman, a fisheries scientist at Virginia Polytechnic Institute and State University in Blacksburg, says that figure may not be safe enough for certain tropical ecosystems with large zebrafish populations.

Tsai hopes his creations will spark interest in biotechnology among Taiwanese schoolchildren, who are thronging an exhibit at NTU featuring the glowing fish. As a demonstration of genetic engineering, Tsai says, the fish has "an advantage over a genetically modified pig, which looks no different from a normal one." And it glows in the dark.