London, Apr 23 : It doesn't have sex and should be extinct by now, but the tiny fish, Amazon Molly - that has survived for 70,000 years - is still swimming against the evolutionary tide, say researchers.
Scientists have shown that the Amazon Molly is defying some laws of evolution by avoiding extinction.
Researchers believe that the fish may be employing special genetic survival "tricks", and they are now trying to understand more about how the species has managed to stay alive.
Amazon Molly fish, all of which are female, interact sexually with males of other species to trigger their reproduction process.
The males' sperm sparks the development of an embryo, but none of the male DNA is actually passed on to the offspring. Only the mother's genes are inherited.
Typically, when creatures reproduce asexually, harmful changes creep into their genes over many generations.
The species will eventually have problems reproducing and can often fall victim to extinction.
University of Edinburgh researchers have been studying complex mathematical models on a highly powerful computing system to look at the case of the Amazon Molly.
Researchers calculated the time to extinction for the fish, based on modelling genetic changes over many thousands of generations.
They are now able to say conclusively, for the first time, that the fish ought to have become extinct within the last 70,000 years, based on the current simple models.
Scientists believe the fish, which are still thriving in rivers in south-east Texas and in north-east Mexico, are using special genetic survival "tricks" to help them stay alive.
One theory is that the fish may occasionally be taking some of the DNA from the males that trigger reproduction, in order to refresh their gene pool.
"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 to survive. Maybe there is still occasional sex with strangers that keeps the species alive. Future research may give us some answers," The Scotsman quoted Dr Laurence Loewe, of the university's School of Biological Sciences, as saying.
The study is published in the journal BMC Evolutionary Biology.