Nannatherina balstoni, commonly known as Balston’s Pygmy Perch, is a small freshwater fish that can grow between 60mm and 90mm.
This species is brownish dorsally and silver underneath, usually with a prominent brown mid-lateral stripe and a series of vertical brown bars on its sides bearing cross-hatched markings.
Sadly, it is listed as Vulnerable under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and under the Western Australian Wildlife Conservation Act 1950.
Studies have found that the Balston’s Pygmy Perch demonstrates fascinating examples of adaptation such as leaping from the water to catch terrestrial invertebrate prey.
Inundated vegetation is thought to be important habitat for the larvae of the Balston’s Pygmy Perch.
Balston’s Pygmy Perch reaches sexual maturity at one year of age and generally die after spawning in their first year. However, individuals have been recorded, in the wild, living to three years of age. The short lifespan of this species makes it vulnerable if juvenile recruitment is low.
With a past distribution range from Moore River down to Goodga River east of Albany and Collie River north-east of Bunbury, the Balston’s Pygmy Perch has been lost from the northern half of its range, including the Moore River.
It is currently regarded as the rarest of all the endemic freshwater fish of Australia’s south-west and a recent survey reports its occurrence is approximately 69 per cent of its historical distribution.
Populations have become severely fragmented or lost from many of the rivers within their current distribution and the trend towards population decline is predicted to continue in the future.
Threats to the Balston’s Pygmy Perch include increased salinity, surface flow and groundwater reductions due to climate change and water extraction, riparian degradation, invasive aquatic species, damming, eutrophication and dewatering of habitat.
Further studies are necessary to quantify the impacts of these threats and of instream barriers. A recovery plan is also critical for the management of the species, with on-ground surveys required in order to confirm ongoing population viabilities.
Information Source: Government of Australia, Department of Environment and Department of Parks and Wildlife Western Australia