Researchers are pondering how an exclusively-female fish species has survived without genetically self-destructing itself into extinction, the BBC reports.

The Amazon Molly, found in Mexico and Texas, reproduces by cloning, and while it does "interact" with chaps from other species to "trigger its reproduction process", doesn't utilise any of their DNA in producing offspring.

While this might be considered proof of the old saw that "a woman needs a man like a fish needs a bicycle", scientists from the University of Edinburgh applied "complex mathematical models" to demonstrate that the Amazon Molly should in fact have become extinct within the last 70,000 years as a result of the adverse genetic changes resulting from asexual reproduction.

Quite how it has survived remains a mystery, although one theory suggests occasional liaisons with males in which DNA is taken on board to "refresh" the species' genetic make-up.

Dr Laurence Loewe, of the uni's School of Biological Sciences, said: "What we have shown now is that this fish really has something special going on and that some special tricks exist to help this fish survive. Maybe there is still occasional sex with strangers that keeps the species alive. Future research may give us some answers."

The team's findings are published in the journal BMC Evolutionary Biology. ®

Related stories

• All-female species goes 100 million years without a shag (22 March 2007)