More two-headed transgenic fluorescent zebrafish have been created by Taiwanese scientists, who are trying to determine the association between the occurrence of conjoined creatures and genes, according to the Academia Sinica.

A two-headed zebrafish was inadvertently created early last month by scientists at the Academia Sinica's Institute of Biological Chemistry who are studying muscular dystrophy. They used zebrafish as a model organism for the study of functional genomics.

They put a certain gene into 200 zebrafish embryos at the one-cell stage through a microinjection procedure. Basically, scientists said, the injected gene causes the death of muscle cells and affects the early development of embryos.

Unexpectedly, one of the 200 embryos developed 24 hours later into a fish with two-heads and two hearts.

A review of academic papers found no documentation of such a creature ever existing before. The journal Science, in its issue released on Feb. 20, reported on the fish.

The rare fish inspired the scientists to start studying the mechanisms causing conjoined creatures. Between the end of last month and early this month, they injected different genes into 750 embryos at the one-cell stage.

As of yesterday, eight more conjoined fish have been created

"These conjoined fish are all different. Some share tails and some share other parts," said Huang Chang-jen (¶À»Í¬Ã), an associate research fellow at the institute.

Huang initially injected deoxyribonucleic acid (DNA) of certain genes into the fish embryos. In his follow-up research, ribonucleic acid (RNA) of certain genes will be used.

"We hope to offer an alternative angle, the genetics, to approach the occurrence of conjoined creatures, including humans," Huang said.

Conjoined twins occur when one egg splits to become two identical eggs. What factors trigger the mechanism exactly, however, remain uncertain, Huang said.

According to Huang, there are three to four conjoined births per 100,000 in Taiwan, a much higher rate than in other countries. In some countries, Huang said, there is only one conjoined birth in more than 200,000.