Taxonomy & naming
Scaturiginichthys vermeilipinnis was described in 1991 by Walter Ivantsoff, Peter Unmack, Bushra Saeed and Lance Crowley. It is the sole member of the monotypic genus Scaturiginichthys, placed in the family Pseudomugilidae — the blue-eyes — within the order Atheriniformes. Eschmeyer's Catalog of Fishes records the valid name as Scaturiginichthys vermeilipinnis Ivantsoff, Unmack, Saeed & Crowley, 1991; because the species has remained in the genus in which it was originally described, no parenthetical authority is used.
The generic name derives from the Latin scaturigo (genitive scaturiginis), meaning a spring or flowing water, joined to the Greek ichthys, fish — an apt name for a fish restricted to spring-fed pools. The specific epithet vermeilipinnis combines vermilion with the Latin pinna, fin, in reference to the bright red fins of mature males. The English common name, redfin blue-eye (also written red-finned blue-eye), reflects both that feature and the family to which it belongs. The blue-eyes are a small radiation of Australian and New Guinean fishes related to the rainbowfishes proper; the red-finned blue-eye is their southernmost and most isolated Australian representative.
Morphology
This is a tiny fish. Reported maximum length is about 1 in standard length, and it is frequently cited as the smallest freshwater fish in Australia, with adults often described at around 1 in in total length. The body is slender and the eye is relatively large, in keeping with the blue-eye group.
The species is sexually dimorphic, and the difference is the first thing you notice. Mature males develop the vivid red or vermilion fins for which the fish is named, intensifying the colour while displaying to females and defending territory. Females and immature fish are far plainer, a silvery yellow-olive without the red fin pigment. Tiny juveniles are described as blue-and-yellow and occupy the very shallowest water. Beyond the male's fin colour, there is little to single out anatomically — a small, lightly built pseudomugilid whose biology, not its body, is what makes it worth a second look.
Habitat
The red-finned blue-eye is an extreme habitat specialist. Its only wild population lives in a cluster of natural Great Artesian Basin springs at Edgbaston, in central-western Queensland, in country that drains internally toward the Lake Eyre basin. The total area of springs that support it is tiny — reported at less than half a hectare. The fish inhabits sparsely vegetated, clay-bottomed shallow wetlands among sedge tussocks and globular algae, in water that is often only a few centimetres deep and in places as little as five millimetres.
These spring pools sit in open, very dry country and are fully exposed to sun. The thermal swings are punishing for so small a fish: water temperature is reported to fluctuate annually from roughly 37 °F in winter to about 101 °F in summer, and shallow areas can vary by as much as 81 °F within a single day. Near the spring vents, however, the water stays relatively constant at around 75 °F, which appears to be the species' preferred temperature; adults tend to use the slightly deeper, more stable water for feeding and egg-laying, while the smallest juveniles occupy the warmest, shallowest margins. The dependence on artesian spring flow is total — the habitat exists only because groundwater reaches the surface here.
Feeding
The natural diet of the red-finned blue-eye is poorly documented, a consequence of its rarity and the difficulty of observing fish in millimetre-deep water. It is thought to be omnivorous, taking both plant and animal matter. FishBase places it at a trophic level of roughly 3.1, consistent with a small, mixed-feeding fish rather than a dedicated predator or grazer.
Observations from its spring habitat suggest it picks small food items from among the globular algae that carpet parts of the pools and takes tiny insects from the water surface. Given the shallow, sun-warmed, algae-rich nature of the springs, microinvertebrates, insect larvae, and the biofilm and algae of the pool floor are all plausible components of its diet. Specific quantitative dietary data are sparse, and the species' feeding ecology is better understood in broad terms than in detail.
Mating
Mating in the red-finned blue-eye centres on the male's red fins and territorial display. Fish reach maturity quickly — at roughly four months of age — after which mature males develop the characteristic vermilion fins and use them in display toward females and in defending small territories against rival males. The brighter, more dominant a male, the more conspicuously he signals.
Females, by contrast, remain silvery yellow-olive throughout and do not develop the red coloration. Rather than spawning in discrete seasonal bouts, females are reported to breed almost continuously over an extended period, depositing eggs steadily over several weeks. This near-continuous, trickle-spawning strategy spreads reproductive effort across time, which may help buffer a tiny population against the extreme day-to-day swings of its spring habitat.
Breeding
Breeding is well documented relative to the species' diet, largely because the fish has been bred in captivity as part of its conservation. Females breed almost continuously over a four-to-six-week period, laying only one to three large, opaque, adhesive eggs per day. The eggs stick to vegetation and substrate within the shallow pools.
Development is rapid in keeping with the short life cycle. Eggs hatch after roughly one to two weeks, and the young grow quickly, reaching maturity at about four months. Total lifespan is short — reported at around eighteen months — so the population turns over fast and depends on steady recruitment. Early maturity, continuous low-volume egg-laying, fast growth, a short life — it is the pattern of a small fish tuned to an unstable, easily lost habitat. It is also what has made captive propagation feasible: under controlled conditions the species reproduces readily enough to support population-recovery efforts.
In the aquarium
The red-finned blue-eye is not an ordinary aquarium fish and should not be thought of as one. It is Critically Endangered, legally protected, and the focus of dedicated conservation breeding rather than the general ornamental trade; the small captive holdings exist to safeguard the species, not to supply hobbyists. Anyone encountering it in a managed setting is essentially looking at a conservation animal.
Where it is maintained, the husbandry mirrors its wild requirements: very shallow, sun-exposed, algae-rich spring-like wetlands, with a preferred temperature near 75 °F even though the fish endures a far wider range in the wild. Bush Heritage Australia has bred it successfully in artificial spring wetlands, with a captive population reported in the low hundreds of fish, roughly doubled from a starting group of about 180 in 2018. The key lessons from that work — shallow water, stable spring temperatures near the vent value, a continuous breeding rhythm, and absolute exclusion of predatory or competing fish — are husbandry facts in service of conservation rather than a recipe for a home tank.
Conservation
Scaturiginichthys vermeilipinnis is assessed as Critically Endangered on the IUCN Red List, under criteria B1ab(iii,v)+2ab(iii,v). The listing reflects an extraordinarily small range — a single location, a cluster of artesian springs covering less than half a hectare at Edgbaston in Queensland — and ongoing decline in habitat quality and population. The species has also been included in IUCN's report on the world's most endangered species and is listed as Endangered under Australia's EPBC Act and under Queensland legislation.
The gravest threat is the introduced eastern gambusia (Gambusia holbrooki), the invasive mosquitofish, which competes with the blue-eye, nips its fins, and preys on its eggs and fry; gambusia have been implicated in the loss of the red-finned blue-eye from several springs since its 1991 description. Trampling and turbidity from cattle and feral pigs, and drawdown of the Great Artesian Basin from bores that reduce spring flow, compound the danger — any one of which could extinguish a population confined to a few millimetres of water.
The species survives because of intensive intervention. Bush Heritage Australia has owned the Edgbaston Reserve since 2008, removing livestock, controlling feral pigs and weeds, managing gambusia through control and barrier fencing, translocating fish to new and artificial springs, and breeding the fish in captivity. Captive numbers have grown from about 180 fish in 2018 to roughly 250–500, and in 2024 Edgbaston was granted Special Wildlife Reserve status. The red-finned blue-eye remains one of Australia's most threatened freshwater fishes, and its persistence is a direct product of sustained, hands-on conservation.