With an extremely limited distribution, and an accordingly small population, the Barren’s topminnow is particularly vulnerable to extinction from both natural and artificial causes (3). In 1998, a drought at the pool where this species was discovered required the removal of the entire local population. The fish were housed in an artificial facility and re-released after heavy rains replenished the water (5). Along with natural incidents, habitat degradation and development are also significantly affecting this species (3) (5). Perhaps the most severe threat to this species, however, is the introduced non-native western mosquitofish Gambusia affinis (6) (7). Artificially introduced to control mosquitoes by preying on the aquatic larvae, this species has becomes widespread, and has invaded the range of the Barren’s topminnow (7). The invasive species preys on the larval and juvenile stages of Barren’s topminnow, resulting in catastrophic local population declines (6) (8).