Australia’s smallest freshwater fish is perilously close to extinction. The only wild population of this diminutive fish is found in a few small artesian springs on our Edgbaston Reserve in central Queensland.
At only 3cm long, they're 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 is included in their report of the planet’s 100 most endangered species. It's also listed as endangered under Australian (EPBC) and Queensland legislation.
Where do Red-finned Blue-eye fish live?
The Red-finned Blue-eye has an extremely restricted distribution and is only found in the group of natural springs at Edgbaston Reserve in central western Queensland.
These springs are part of a large inland drainage basin that runs to Lake Eyre. Water for the springs comes from the Great Artesian Basin that underlies much of central Australia and also feeds other groups of springs – collectively called Great Artesian Basin springs.
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
Red-finned Blue-eye behaviour
Little is known about what they eat, though it’s thought that they’re omnivorous (eating both plant and animal matter), depending on the availability of food. They'll pick at food amongst the algae globules, or eat tiny insects landing on the water surface.2
Once mature (after 4 months) the males develop the characteristic red fins and start displaying to females or defending an area from other males.
Females remain a silvery yellow-olive colour and are able to breed almost continuously. They lay one to three eggs per day for a 4 to 6-week period.3 The opaque eggs are quite large and stick to vegetation or to the substrate. The young hatch after a week or two, grow rapidly, and live to about 18 months.4
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 species). Gambusia is 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. A number of springs have also been excavated to increase water storage, directly destroying the fish’s habitat.
What's Bush Heritage doing?
Since we bought Edgbaston and began restoring the former cattle station in 2008, we’ve been busy protecting these critically endangered fish.
We've maintained boundary fences, removed the livestock and put programs in place to control feral pigs; We also removed introduced plants like Para Grass (Urochloa mutica), Prickly Acacia (Vachellia nilotica) and Parkinsonia (Parkinsonia aculeata) from springs and managed woody weeds throughout the reserve.
Monitoring of both native and introduced fish populations has been ongoing each quarter with annual audits of all springs. We've also trialled various ways of getting rid of Eastern Gambusia and installed barrier fencing to prevent them migrating to new springs.
We've relocated Red-finned Blue-eye to new springs, expanding their range and established insurance populations – both onsite in artificial springs and at a secure offsite location.
Most importantly we seem to have figured out how to breed them in captivity. Previous attempts by others to breed the fish in traditional aquariums had failed: the fish survived, but didn't breed. The solution has been to create artificial springs that replicate their naturally occurring homes.
This has been done by sinking bores that release water into tanks buried in the ground, creating artificial spring wetlands. These captive-bred fish will be translocated into a natural spring to create new wild populations.
250-500 Captive-bred Red-finned Blue-eye fish on Edgbaston Reserve continue to breed, with the population having approximately doubled since the program’s inception in 2018
with 180 fish.
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1. Ivantsoff et al.
2. Wager 1995b
3. Tappin 1995
4. Fairfax et al. 2007