Beneath the freshwater creeks of the world's largest sand island, an elusive and ancient creature darts along the gritty riverbed.
The Australian brook lamprey is a surprise discovery in Queensland's waterways with researchers previously believing the unique fish species only lived in cool climates.
Griffith University ecologist Luke Carpenter-Bundhoo has returned to K'gari (Fraser Island), the world-heritage-listed island where he stumbled upon the species in 2022.
"At first glance I thought, 'Oh, tiny eel'," Dr Carpenter-Bundhoo said.
"[Then I realised] that's not an eel, that's a lamprey. What's that doing here?"
The species was first identified in the 1960s in two rivers on the New South Wales far south coast but is now believed to be extinct from that area.
After finding it 1,500 kilometres away in Queensland, Dr Carpenter-Bundhoo teamed up with scientist David Moffatt to investigate other potential sites in the state.
The pair's research — which confirmed Mordacia praecox populations also on the Sunshine Coast and near Rockhampton — was published in the journal Endangered Species Research in April.
"They were such an unusual find in this part of the world that we had a lot of trouble convincing the experts that they were actually [a] resident … and not just occurrences from individuals swimming up from down south," principal scientist at Queensland's Department of Environment, Science and Innovation, David Moffatt, said.
Not a 'vampire fish'
A distinguishing feature of the lamprey is that it does not have a jawbone, but grows hundreds of teeth.
Mr Moffatt said the 14-centimetre fish spent about six years buried in the sand, filter fed as larvae, before it developed fins, eyes and teeth.
"They have this sucking disc and around the outside of it is a myriad of little, tiny teeth, which are used to form a seal and to suck onto an animal in the parasitic version," Mr Moffatt said.
"The non-parasitic version [Australian brook] has exactly the same teeth, but it never feeds."
It is a far cry from other lamprey species, such as the sea lamprey in the Atlantic Ocean, which can grow to 1.2 metres and kills up to 18 kilograms of fish each year.
"Lampreys, across the world, are generally parasitic," Dr Carpenter-Bundhoo said.
"They're also known as vampire fish.
"These [Australian brook] lampreys forego that parasitic feeding phrase — they're the vegan Dracula of lampreys."
'Importance to human medicine'
Dr Carpenter-Bundhoo said the discovery of the "world's first truly tropical lamprey" was a positive sign for the species' future.
"Above 28 degrees Celsius, there's something within the lamprey's body that starts breaking down — that was thought to be the case," he said.
"If global temperatures increase, species that are resistant to those higher temperatures might be a bit more resistant to climate change."
Dr Carpenter-Bundhoo said the species was also valuable for developmental research.
"Because they're so ancient, they have a really well-known neural network," he said.
"If you can figure something out in a lamprey brain … it will really help figuring out something in a more sophisticated organism's brain, such as a human."
Mr Moffat added that the species had "quite a bit of importance to human medicine" including giving an insight into treatment options for babies with jaundice.
He explained that in an adult Australian brook lamprey, the digestive system and liver break down — a process known as biliary atresia.
"By understanding what happens in the lampreys, what turns on this process of biliary atresia in their genes … perhaps we can work out a remedy for infants who haven't had their liver processes switched on yet," Mr Moffatt said.
"Australian researchers will get the opportunity to look at these animals, [and] even though they're protected, there still is the potential to take small numbers of individuals for research."
In the meantime, Dr Carpenter-Bundhoo said he was still coming to terms with the magnitude of the find.
"As a modern ecologist, you work under the loose assumption that everything's already been discovered," he said.
"It sort of harks back to a bygone era when people were discovering things everywhere.
"It's very rare to get to do that today, so I feel very privileged, very lucky to be able to have done that."
The study was part-funded by the National Environmental Science Program's Resilient Landscapes Hub which hopes to deliver more research in this field in the future.
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