After a seven year conservation effort NSW Department of Primary Industry staff predict this will be the year the endangered Macquarie perch begin to breed naturally.
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Close to 20,000 Macquarie perch fingerlings taken from a pioneering captive breeding program in Narrandera have been released into the Retreat River deep in rural NSW bushland 50 kilometres south-east of Bathurst.
The species, once dominant in the central tablelands, was nearing local extinction when the program began.
The restocking project aimed to create a new population in the Retreat River and create an upstream safe-haven from the impacts of redfin perch, an introduced predator, that recently invaded the source population in the Abercrombie River.
Reaching a stage where the threatened fish began to repopulate naturally was a significant conservation milestone, said NSW Department of Primary Industries fisheries manager Luke Pearce.
"If breeding is shown to have been successful it will be a big step forward ... the first time this has ever been achieved for this species," he said.
"Whilst this is an important step forward there is still a long way to go before the species would be in sufficient numbers and distribution for it to no longer be considered threatened or vulnerable."
Mr Pearce said it took two years for male and three for female fish introduced into the area to reach sexual maturity. Timelines would suggest breeding could have begun earlier however so far dry conditions have not been conducive to spawning.
The ACT government has focused on conservation efforts in place, supporting naturally spawning and expanding habitat by creating fish ways for Macquarie perch in the Cotter River, upstream of the ACT in the Murrumbidgee River and areas of the Molonglo River.
"The ACT has the largest and densest population left in the Murrumbidgee catchment area with the Cotter being one of the most abundant populations," ACT aquatic ecologist Matthew Beitzel said.
Mr Beitzel said carp and redfin were common threats but the threatened species was protected from recreational fishing and its population level was under close surveillance by authorities.
Co-operative focus across jurisdictions helped to protect more populations and ensure there was genetic diversity within the species across river systems.
"It is one of the largest upland species left. And an important ecological species. It requires clean water and good habitat to breed, so when they are thriving it is a good indicator of a healthy habitat."
Central Acclimatisation Society Oberon branch treasurer Peter Byrom and other local anglers have been on board with reviving the native fish population from the start and have dedicated countless volunteer hours to assist with monitoring and restocking.
"A lot of fisherman are interested in conservation," he said. "We like catching them but realistically we are interested in fish. Any of our species that disappear has an impact on the fish we try and catch. We want to keep a balance in the river system."
Mr Byrom has been involved in every survey and release operation with DPI over the past six years.
He has fished the area since he was a young boy and hoped in decades to come the conservation project meant there would be stable and plentiful Macquarie perch to fish again.
"A lot of our streams that we used to fish for trout in we find these days are too hot in the summer and they die out," he said.
"Macquarie perch won't. They are not as affected by the temperature. Hopefully these Macquarie perch could give us another viable fishing fish in a section of rivers that don't fish particularly well anymore."
