By Hilary Whiteman, CNN
Brisbane, Australia (CNN) — Along a nine-mile stretch of river between two waterfalls in the Australian rainforest lives a tiny fish that’s been there for millions of years, hiding between rocks along the riverbank by day and emerging at night to feed.
This is the only place in the world you’ll find the planet’s sole tropical cod –– a remnant of times past that is believed to have split from its closest southern relatives about 25-30 million years ago.
For all that time, the tiny cod swam undetected and undescribed by modern science until 1993 when two researchers –– Mark Kennard and Brad Pusey –– stumbled upon the fish in the Bloomfield River, along the northern reaches of the Daintree Rainforest, which is recognized by UNESCO as the world’s oldest rainforest and is brimming with rich and unique biodiversity.
“It’s a beautiful little fish,” said Kennard, now deputy director of the Australian Rivers Institute at Griffith University, who still works with Pusey, a senior research fellow at the same university, more than 30 years on.
Back then, Kennard and Pusey named the fish the Bloomfield River Cod, with the scientific name Guyu wujalwujalensis, after the Aboriginal name for fish and the Wujal Wujal community, the land’s traditional owners. It’s also known as the tropical nightfish.
But this ancient species that grows to just 10 centimeters is now under threat from introduced predators and violent storms produced by man-made global warming.
Cyclone Jasper, one of Australia’s most destructive tropical cyclones, tore through the cod’s habitat between two waterfalls on the Bloomfield two years ago –– felling trees, flooding the river and washing more introduced predators into its sanctuary.
This October, Kennard and Pusey returned to the river to survey the damage and count the cod in the hope of having it formally listed as endangered under Australia’s biodiversity laws, which would offer it more protection.
“If we lost this, we’d lose a representative of a really complex and long period of evolution,” said Pusey. “It would be a tragedy… certainly a personal tragedy.”
Getting to the Bloomfield River takes at least four hours along an inland road from Cairns, where tourists board boats to visit the Great Barrier Reef.
The longer, wilder and more scenic route winds around the coast, on unsealed roads through “croc country” where Australia’s giant saltwater crocodiles dominate the briny waterways and smaller freshwater crocs occupy rivers and streams.
At this time of year, summer dials up the heat and humidity, steam rises from roads after sudden downpours, and the smell of sweat mixed with sunscreen and insect repellent lingers in the air.
Kennard and Pusey were on a research trip to survey Queensland’s Wet Tropics when they found the fish in the 1990s.
They initially had no idea what it was. But on a return trip a few years later they found enough information to confirm it was a new species.
“When you find new species here, they’re almost always so minor a difference, and most of the time it’s not until people do the genetics, and they go, ‘oh, that is a new species.’ But this was clearly new, and it is quite exciting to find that,” Pusey said.
The stretch of river that’s home to the Bloomfield Cod is inaccessible to most visitors – but not remote enough to guarantee the cod’s safety.
Their biggest predatory threat is the Tully Grunter, a larger native Australian fish up to 35 centimeters long, that scientists believe was introduced to the river by recreational fishers wanting a decent catch.