Red-finned Blue-eye

Australia’s smallest freshwater fish is perilously close to extinction.

At only 3cm long, Red-finned Blue-eye fish are easily overlooked; little wonder the species was only described by scientists in 1991.¹

The Red-finned Blue-eye is listed as critically endangered by the International Union for Conservation of Nature (IUCN), and was included in their report of the planet’s 100 most endangered species. It’s also listed as endangered under Australian (EPBC) and Queensland legislation.

Great Artesian Basin springs are a unique environment and provide habitat for many species only found in artesian springs.

These ‘spring endemics’ include plants, molluscs, macro-invertebrates and a total of eight fish species.

For this reason, the springs themselves are listed as a nationally endangered ecological community.

Despite the huge area of the Great Artesian Basin, the springs at Edgbaston are not large. The biggest spring has a wetland of about one hectare, but most of the springs are much smaller, sometimes only a few square metres. The total area of all springs currently supporting Red-finned Blue-eye is less than 0.5 hectares.

The Red-finned Blue-eye has very specific habitat requirements. It lives in the sparsely-vegetated wetlands associated with the springs themselves; they’re shallow (less than 80mm deep and often only 5mm deep), clay-bottomed, interspersed with sedge tussocks and covered in globular algae.

Amazingly, the water temperature of the wetlands can fluctuate between 3°C and 38.5°C throughout the year, and shallow areas can vary by 27°C during a 24-hour period!

Importantly, water temperature in areas close to the spring vent (where the water emerges from the Great Artesian Basin) remains a relatively constant 24°C – a temperature preferred by the Red-finned Blue-eye.

Adult Red-finned Blue-eye prefer deeper water for feeding and egg laying, but the tiny blue and yellow babies can usually be found in shallow areas only 5 to 10 mm deep.²

Threats to Red-finned Blue-eye

The introduced and highly invasive fish Eastern Gambusia (Gambusia holbrooki) – also known as the Mosquitofish – is the biggest threat to the Red-finned Blue-eye’s survival.⁵

Eastern Gambusia compete with the Red-finned Blue-eye for food and habitat, display aggressive behaviour such as fin-nipping, and probably eat the eggs and newborn Red-finned Blue-eye (and other native fish). Gambusia are implicated in the extinction of Red-finned Blue-eye from seven springs since 1991.

Added to this, Red-finned Blue-eye have most likely also been affected by habitat degradation caused by cattle and feral pigs that trample plants, increase turbidity, and degrade water quality to an intolerable level for Red-finned Blue-eye.

The effect of thousands of bores also threatens the entire Great Artesian Basin spring community, including the Red-finned Blue eye.

Since 1878, bores have been drilled into the Great Artesian Basin to provide permanent water for stock. While beneficial for the pastoral industry, bores have reduced water levels, spring flows and aquifer pressure.