Conservation breeding and reintroduction of pygmy perches in the lower Murray-Darling Basin, Australia: two similar species, two contrasting outcomes.

The Southern pygmy perch (SPP) (Nannoperca australis) and the Yarra pygmy perch (YPP) (N. obscura) are freshwater fishes of the family Percichthyidae found in southeastern Australia, including in the Murray-Darling Basin (MDB). These small (up to 85 mm) fishes live in small groups on the vegetated margins of slow flowing habitat, such as streams and wetlands. Extended droughts and human-induced environmental degradation have caused unprecedented decline of aquatic biodiversity in the MDB. This is epitomized in the current conservation status of pygmy perches in the Basin. The SPP lineage has experienced large-scale extinctions from most of the middle MDB, and survives now only in very small population fragments mainly in tributaries of the upper Murray River and in pockets of the lowermost reaches of the basin. The MDB YPP lineage, originally restricted to the lower reaches of the basin, has not been detected in the wild since 2015 and in 2019 it was considered extinct. The SPP is listed as critically endangered in South Australia, threatened in Victoria and endangered in New South Wales. The YPP is listed as Endangered by the IUCN and Vulnerable nationally in Australia.