Scientists from the University of Edinburgh think the Amazon Molly may be employing special genetic survival "tricks" to avoid becoming extinct.
The species, found in Texas and Mexico, interacts with males of other species to trigger its reproduction process.
The offspring are clones of their mother and do not inherit any of the male's DNA. 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.
Scientists at Edinburgh University 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, the fish ought to have become extinct within the past 70,000 years, based on the current simple models. Scientists believe the fish, which are still thriving in rivers in south-east Texas and 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.
Dr Laurence Loewe, of the university'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."
He added that their findings could also help them understand more about how other creatures operate.
"I think one of the interesting things is that we are learning more about how other species might use these tricks as well," he said.
"It might have a more general importance."
The Edinburgh-led study was carried out in collaboration with Dr Dunja Lamatsch at the University of Wuerzburg, now at the Austrian Academy of Sciences.
The research is published in the journal BMC Evolutionary Biology. - bbc