BACKGROUND: The Amazon molly (Poecilia formosa) is a small unisexual fish that 
has been suspected of being threatened by extinction from the stochastic 
accumulation of slightly deleterious mutations that is caused by Muller's 
ratchet in non-recombining populations. However, no detailed quantification of 
the extent of this threat is available.
RESULTS: Here we quantify genomic decay in this fish by using a simple model of 
Muller's ratchet with the most realistic parameter combinations available 
employing the evolution@home global computing system. We also describe simple 
extensions of the standard model of Muller's ratchet that allow us to deal with 
selfing diploids, triploids and mitotic recombination. We show that Muller's 
ratchet creates a threat of extinction for the Amazon molly for many 
biologically realistic parameter combinations. In most cases, extinction is 
expected to occur within a time frame that is less than previous estimates of 
the age of the species, leading to a genomic decay paradox.
CONCLUSION: How then does the Amazon molly survive? Several biological processes 
could individually or in combination solve this genomic decay paradox, including 
paternal leakage of undamaged DNA from sexual sister species, compensatory 
mutations and many others. More research is needed to quantify the contribution 
of these potential solutions towards the survival of the Amazon molly and other 
(ancient) asexual species.