New fish species discovered in Murray-Darling Basin

The Yarra Pygmy Perch, Edelia osbcura.
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Honours student Michael Hammer studies a gell to identify fish species.
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Monday, 2 April 2001

With the many problems besetting the River Murray, tales of species decline and extinction are expected. Discovering a new species is not.

"We were doing some survey work at Lake Alexandrina," said Michael Hammer, an honours student in Adelaide University's Department of Environmental Biology. "A volunteer was helping me out and found what we thought was a local pygmy perch. Later we ran genetic tests to see if it was different from other local populations of pygmy perch, and it turned out to be a totally different species," he said.

Mr Hammer is currently studying the southern pygmy perch (Nannoperca australis), a locally endangered species now found only in selected spots in the Mount Lofty Ranges. The new species turned out to be a Yarra Pygmy Perch (Edelia obscura), apparently far from home.

"As its name suggests, it was originally found in the Yarra, but it's distributed from Melbourne up to Bool Lagoon in South Australia, so it's a fair way from the Murray," said Mr Hammer.

"No-one's ever identified it in the Murray-Darling Basin before," he said. " It's definitely a new species for the area, so we're trying to work out if it's a genetically distinct population in the species, or a new species altogether."

That involves preparing tissue samples from different fish and, in a technique known as allozyme electrophoresis, letting them move through a series of gels. Different fractions separate as visible bands. Those of genetically similar specimens form the same pattern, while genetically dissimilar animals produce patterns that are conspicuously different.

"As far as we know, the other populations of the Yarra Pygmy Perch are all distinct genetically," said Mr Hammer, "But we're looking at that during the next couple of months. That will help us decide whether this is a truly isolated population, or could perhaps have been released into the region historically. That seems unlikely but, in any case, it is a refugee population of an threatened species," he said.

The Yarra Pygmy Perch is nationally potentially threatened, which means it is still common in certain regions but overall has suffered a large decrease in its range. The discovery of this population has significant implications for the management of the region.

"We need to map its range as a first step." said Mr Hammer. "We need to find out what its habitat requirements are in order to secure that habitat, and also look at forming refuge populations in case of catastrophe or extinction in the wild," he said.

Before the introduction of the barrages near Goolwa, Lake Alexandrina alternated between being a freshwater and an estuarine lake. The barrages now prevent the introduction of seawater to the lake system, a development that has had implications for many aquatic species.

"Traditionally, when the lake was saline, the pygmy perch would have retreated into the fresh water streams or swamps," said Mr Hammer. " Now the lake is permanently fresh water, the fish seems to have colonised small sections among its reeds, snags and aquatic plants, but we don't really know yet," he said. "We've just found a few fish at one spot in the lake, so we really need to study it further to find out how endangered it is, and what to do to protect it."

Pygmy perch reach a maximum size of 8 cm (the juvenile was 2 cm) and threats to them are many. "Introduced Gambusia, misguidedly known as mosquito fish, eat the eggs of many native fish and are a threat to the juveniles of this species," said Mr Hammer. "And being aggressive, they nip at the fins of the adults and compete for their food. These pygmy perch eat small invertebrates, but are themselves eaten by introduced redfin and trout," he said.

The volunteer who discovered the fish, and the survey work which may help to save it, reflect the involvement of a wide range of conservation bodies in this research.

"This has been a collaborative venture between Adelaide University, the Museum, Native Fish Australia (SA) and other community groups," said Mr Hammer. "The project is being funded through the Commonwealth's Murray-Darling 2001 FishRehab Program, a program of the Natural Heritage Trust, and the Mount Lofty Ranges Catchment Program," he said.

Mr Hammer will return to the Lake to try to discover more specimens, and perhaps more populations, of this addition to South Australian wildlife. "There are really only 10 or 11 local native fish species capable of completing their lifecycle in fresh water, with about 26 species in the whole Murray-Darling Basin," said Mr Hammer," so the finding represents a significant boost to local biodiversity."

"It gives you hope that some of the fish that we've lost might still be around. There are 3 or 4 fish that are believed to be extinct, but they could still be around; you never know."

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