How Red-finned Blue-eyes evolved

The Red-finned Blue-eye fish is remarkable for being found in just one small group of artesian springs on Edgbaston Reserve in central Queensland. But how did it get there? Grab a cuppa, because it’s a looong convoluted story that began on the ancient Gondwanan supercontinent.

First up, it helps to know how our hero is related to other species of fish.

The Red-finned Blue-eye (Scaturiginichthys vermeilipinnis) is just one species of 16 within the Blue-eye fish family – the Pseudomugilidae. They occur only in Australia and New Guinea.

Of the six Australian species, the Red-finned Blue-eye is the only one found in the arid interior of the continent. The others are in waterways that flow east toward the Pacific Ocean or toward the north.

Two other families of fish are relatively closely related to the blue-eyes. These are the Australasian Rainbowfishes (Melanotaeniidae), including over 100 species, and the Madagascan Rainbowfishes (Bedotiidae), including at least 26 species.

Like the Blue-eyes they are all restricted to fresh or brackish waters. The Australasian Rainbowfish species are found in Australian, New Guinea and Sulawesi. The Madagascan Rainbowfish are of course restricted to Madagascar.

Madagascar is a long way from Queensland, but it used to be closer. Until about 120 million years ago, during the Cretaceous period, Africa, India and Australia were all attached to Antarctica, as part of the Gondwanan supercontinent. Madagascar was then attached to the western side of India.

Early in the Cretaceous period central Australia was flooded by the Eromunga sea. Sediments laid down on the floor of that ancient expanse capped the Great Artesian basin, ultimately being responsible for the existence of springs around its periphery, including the springs at Edgbaston.

90-70 millions of years ago Gondwana began to break apart. India headed north, detaching from Madagascar as it continued its journey toward a rendezvous with Asia. Australia completed its separation 35 million years ago and made a bee-line toward south-east Asia, with New Guinea forming as a crumple zone on the advancing continental margin. Through most of this Australia had a temperate climate and was cloaked by lush forests criss-crossed by rivers and swamps.

So, it seems that the ancestor of the Pseudomugilidae, Melanotaeniidae and Bedotiidae must have been a freshwater fish schooling in the waterways of the great southern land. As the continents separated, its decendents went along for the ride. And over the course of millions of years they evolved, giving rise to the aforementioned families and their many species, including the Red-finned Blue-eye.

As Australia travelled north it became progressively more arid. By about 15 million years ago the lush forests of the interior were all but gone. One-by-one the inland crocodiles, platypus, freshwater dolphins and flamingos were lost. Even a few tens of thousands of years ago, there were still vast freshwater lakes in the centre, including a much larger and deeper Lake Eyre. They were fed by streams and rivers that were less ephemeral than they are today.

It‘s likely that there were many more species of fish, and possibly other blue-eyes, in the inland waters and that many extinctions occurred over the millennia.

These eventually left us with the few that managed to adapt to survive in artesian springs, ephemeral waterways, rock pools and billabongs. Perhaps we’ll find fossils of the others, or it may be that they are lost forever, buried below dry river channels and shifting desert sands.

Pelican Creek on Edgbaston flows into Aramac Creek, the Thompson River, Cooper Creek and ultimately to Lake Eyre. We know that the Red-finned Blue-eye requires the still, clear, shallow water and abundant vegetation characteristic of spring environments to thrive and breed. This specialisation is why it isn’t present lower in the river system.

Perhaps when inland lakes and waterways were far more extensive, permanent and fresh it was more widespread – maybe even living around the swampy margins of Lake Eyre itself. Or it could be that it has long been adapted to the specific chemistry of this particular set of springs and has therefore been confined to Edgbaston for thousands or even millions of years.

What we do know, is that together we can save this one tiny species of fish. It has survived and thrived for millennia and deserves to continue for many more – until eventually, Australia slides into the tropics, the rains return and the vast inland waterways are once again flowing and verdant.

More reading

Shaping a Nation: A Geology of Australia
Published by the Commonwealth of Australia (Geoscience Australia) and ANU Press.

Phylogeny and biogeography of the Malagasy and Australasian rainbowfishes (Teleostei: Melanotaenioidei): Gondwanan vicariance and evolution in freshwater
Sparks J.S. & Smith W.L.
Molecular Phylogenetics and Evolution 33 (2004) 719–734

Phylogeny and biogeography of rainbowfishes (Melanotaeniidae) from Australia and New Guinea
Unmack P.J. et al.
Molecular Phylogenetics and Evolution 67 (2013) 15–27

Phylogenetic relationships and historical biogeography of melanotaeniid fishes in Australia and New Guinea
McGuigan A.D. et al.
Marine and Freshwater Research, 2000, 51, 713–23

Water resource assessment for the Central Eromanga region
A report to the Australian Government from the CSIRO Great Artesian Basin Water Resource Assessment