Alternative conservation outcomes from aquatic fauna translocations: Losing and saving the Running River rainbowfish

The translocation of species outside their natural range is a threat to aquatic biodiversity globally, especially freshwater fishes, as most are not only susceptible to predation and competition but readily hybridize with congeners. Running River rainbowfish (RRR, Melanotaenia sp.) is a narrow-ranged, small-bodied freshwater fish that recently became threatened and was subsequently listed as Critically Endangered, owing to introgressive hybridization and competition following the translocation of a congeneric species, the eastern rainbowfish (Melanotaenia splendida). To conserve RRR, wild fish were taken into captivity, genetically confirmed as pure representatives, and successfully bred. As the threat of introgression with translocated eastern rainbowfish could not be mitigated, a plan was devised to translocate captive raised RRR into unoccupied habitats within their native catchment, upstream of natural barriers. The translocation plan involved careful site selection and habitat assessment, predator training (exposure to predators prior to release), soft release (with a gradual transition from captivity to nature), and post-release monitoring, and this approach was ultimately successful. Two populations of RRR were established in two previously unoccupied streams above waterfalls with a combined stream length of 18 km. Post-release monitoring was affected by floods and low sample sizes, but suggested that predation and time of release are important factors to consider in similar conservation recovery programmes for small-bodied, short-lived fishes.