Recently, Dr Kerezsy played a key role in a project that found and protected a new group of small, endangered fish. Although his work is conducted independently of the MDBA, we are sharing his story to bring attention to native fish recovery in the Basin.
Olive perchlet are some of the rarest fish in the Murray–Darling Basin.
In November and December 2023, a cooperative effort between state and federal governments, independent researchers, academics and landholders, helped save a population of olive perchlet from becoming extinct.
Until mid-2023, it was believed that just one population of the endangered perchlet was known in the southern Basin: within a weir pool close to Lake Brewster in the mid-Lachlan region of New South Wales.
Growing to around 5 or 6 cm, the olive perchlet are sometimes called ‘glassfish’ due to their translucent appearance. Before the 1970s, they were easily found in large numbers in a wide range of habitats including wetlands, lagoons, channels and drains. Their decline is mainly due to the introduction of feral fish species – especially carp – which compete with the perchlets for food, eat them, and degrade their wetland habitats. River regulation can also impact the lifecycles of the glassfish.
The chance discovery of a new population was made in April 2023, during a fish monitoring trip with the University of Canberra, as part of a funded project under the Commonwealth Environmental Water Holder’s science program, Flow Monitoring, Evaluation and Research (Flow-MER). The perchlet were found using fyke net sampling, which are non-harmful, permit-approved mesh net traps. The nets are usually set late in the afternoon and checked early the next morning, with any species caught identified and recorded before being released.
On a cold autumn morning in 2023, a decent number of olive perchlet were found during sampling of 2 isolated lakes in Booligal, New South Wales. Later, genetic testing showed the fish had unique DNA when compared to the known population near Lake Brewster. It turns out that the fish had been hiding in plain sight for decades – or longer.
Exciting as this find was, there was a problem. One of the lakes is ‘ephemeral’. This means it is usually dry, but it fills up during wetter periods, often with shallow water. There was concern the lake would be completely dry by mid-2024.
A plan was hatched to find the endangered fish a new home. Government agencies, fish experts, and community members teamed up to help. In June 2023, the NSW Department of Climate Change, Energy, the Environment and Water (then called the NSW Department of Planning and Environment) did surveys to find suitable places to move the fish. Only one ticked all the boxes: a dam close to the Lachlan River, that had a screened inlet to limit carp.
The MDBA's Native Fish Recovery Strategy made some Emergency Response Funds available to catch and move the fish. These funds help encourage community involvement in State-supported rescue efforts. NSW Fisheries also provided a permit to allow researchers to move a population of a threatened or endangered species.
Throughout November and December 2023, using 24 nets, a boat, and a ute, almost 300 olive perchlet were rescued from the drying wetland. They were taken across approximately 50 kilometres of dirt roads, to their new home in a landowner's dam.
Ongoing monitoring will continue over the next few years to see if the experiment works. If so, the ‘Booligal glassfish’ – or at least their young – may be part of breeding programs that help save the olive perchlet across an even wider area.
5 fish facts about the olive perchlet
Olive perchlet are mostly found in wetland habitats. They like slow moving or still water that is shallow.
Being carnivorous, these fish prey on tiny aquatic species, such as water insects, beetles and larvae – usually hunting at night.
Perchlet help keep insect numbers at low levels. This can help ensure waterways stay healthy, and the environment liveable.
They are not closely related to commonly known larger perch species. They’re called ‘perchlet’ because they share a similar shape, but are much smaller.
You can help monitor the Basin – and you might even find rare species, like the olive perchlet. See what community efforts you can get be a part of on the MDBA Get Involved page.