Australia's smallest and rarest freshwater fish has been on the brink of extinction for decades.
The red-finned blue-eye is an Australian native species found only in the Great Artesian Basin springs on Edgbaston Reserve in remote western Queensland and nowhere else in the world.
At 3 centimetres long when fully grown — the size of a matchstick — the tiny fish did not stand much of a chance against the aggressive, invasive gambusia, or mosquito fish.
But a never-before-trialled conservation and breeding program has given the red-finned blue-eye a fighting chance at survival.
For the first time, captive-bred populations of the fish have been released into wild springs.
The scientific community is now hopeful the future is looking better for one of the nation's rarest species.
'The species was on a knife edge'
When the red-finned blue-eye was first discovered in 1990, it was living in about a dozen springs on Edgbaston Reserve.
The Queensland president of the Australia New Guinea Fishes Association, Graeme Finsen, said the population quickly dwindled.
"Slowly but surely as the scientific community visited them and started analysing them, instead of being in 12 springs they were in 10," Mr Finsen said.
Pippa Kern is a freshwater ecologist for Bush Heritage, which owns Edgbaston Reserve, and has been in charge of the captive breeding program for the past three years.
She said the main reason for the population decline was gambusia.
"When they get into populations with red-finned blue-eye in them, they're really aggressive," Dr Kern said.
"They do fin-nipping, they might predate on the eggs and the juveniles and, eventually — actually pretty rapidly — just push those populations to extinction."
Mr Finsen said gambusia posed a far greater threat as an invasive species than cane toads.
"Gambusia is probably the single-most individual species that is successfully outcompeting everything else in Australia," he said.
When Bush Heritage bought Edgbaston Reserve in 2008, the outlook for the red-finned blue-eye was grim.
"The species was on a knife edge," Dr Kern said.
"There [were] only two populations left and one of those populations had already been invaded by [gambusia] and subsequently went extinct in the following years.
"So, we kind of ended up with one remaining wild population.
Captive-bred fish released into wild for first time
Thirteen years ago, Bush Heritage began what would become a two-pronged approach to try to save the red-finned blue-eye.
Firstly, it moved fish from the single remaining wild population to other springs safe from gambusia and took measures to control gambusia numbers on the property, like installing small mesh fences to stop the invasive species moving between springs during floods.
More recently, the conservation group has run a never-before-trialled program to breed red-finned blue-eye in captivity, by creating artificial springs that replicate the fish's natural habitat.
Now, for the first time, those fish have been released into wild springs on the property.
"[We] hope that they'll establish into the spring and then in the coming years they'll start to breed and populate this spring and we might have a big, healthy population of red-finned blue-eye."
As a self-described "fish geek", Mr Finsen said he was excited to return to Edgbaston soon and see the flourishing populations with his own eyes.
"Coming back later in one, two, three years' time and seeing there's now 200 fish in there, 300 fish in there, 500 fish in there — it just makes me so happy. I'm getting goosebumps."
Budjiti man Stephen Brown, who has been working as an Indigenous field officer with Bush Heritage and assisted with the project, agreed.
"[I'm looking forward to] coming out here and looking in this little pond and seeing these little fellas swimming around with a heap of their mates," Mr Brown said.
What could have been lost?
The red-finned blue-eye is not the only species endemic to Edgbaston's artesian springs.
More than two dozen species of flora and fauna, including 11 types of snails and at least a dozen plants, are found nowhere else in the world.
While scientists have not studied the red-finned blue-eye long enough to be certain what flow-on effects its extinction could have had, its role as the top predator in such a rare ecosystem means they are not willing to find out.
"Because what happens if the red-finned blue-eye eat the seeds of the [endangered plant] eriocaulon, and by doing that it allows the seeds of [that plant] to germinate?" Mr Finsen said.
"If we lose the red-finned blue-eye, do we lose the eriocaulon? And if we lose that plant, is that plant food for 11 different species of snail?
"It's not just this one little thing, it's a whole interconnected community of unique little springs that we risk losing."
The fish's population numbers have been boosted from a couple of hundred to about 3,000.
While that is a drop in the ocean compared to the collective threat facing Australia's native plants and wildlife, Mr Brown says the success of the red-finned blue-eye captive breeding program should not be understated.
"When you remove one species, you're taking out more.
"So, if we can keep that one going, we can probably keep more species going that are on the endangered list."
