Taxonomy & naming
Pseudomugil mellis was formally described by Gerald R. Allen and Walter Ivantsoff in 1982, in the Revue Française d'Aquariologie (9(3): 83–86). Before that description the fish had long been treated as a southern, small-bodied colour form of the Pacific blue-eye, Pseudomugil signifer, to which it remains closely related. Allen and Ivantsoff separated it on the basis of its much smaller adult size and its distinct coloration: where male P. signifer reach roughly 3.5 in and females 2.5 in, P. mellis males top out near 1.5 in. Eschmeyer's Catalog of Fishes records the valid name as Pseudomugil mellis Allen & Ivantsoff, 1982, in the family Pseudomugilidae (the blue-eyes), order Atheriniformes.
The genus name Pseudomugil combines the Greek pseudes, 'false', with the Latin mugil, 'grey mullet', a reference to a superficial resemblance to mullet rather than any real relationship. The specific epithet mellis derives from the Latin for 'honey', describing the warm amber body colour of the males that also gives the fish its universal common name, the honey blue-eye. As with the other blue-eyes, the 'blue-eye' of the common name refers to the iridescent blue ring around the eye that is characteristic of the family.
Morphology
This is a small, elongate fish with a moderately compressed body. It rarely tops 1.5 in and is most often seen at 1 in; the literature gives a maximum standard length of roughly 1.5 in. That small size is one of the clearest characters separating it from its larger relative, the Pacific blue-eye. The body is slender and streamlined, built for life among reeds and submerged vegetation in still and slow-flowing water.
Mature males are honey- to amber-coloured, the warm tone set off by the iridescent blue eye-ring shared across the blue-eyes. The first two rays of both the dorsal and anal fins are distinctively coloured and somewhat elongated, which males put to use in display. As in most Pseudomugilidae, the dorsal fin is divided into two parts. Females and juveniles are plainer and less intensely coloured than a display-conditioned male — a modest dimorphism, typical of the genus. Beyond that, fine morphometric detail for the species is data sparse in accessible sources.
Habitat
Pseudomugil mellis is endemic to the coastal lowlands of southeastern Queensland, Australia. Its range runs from around Mellum Creek near Beerwah north to the Tin Can Bay area, including populations on Fraser Island (K'gari), with disjunct records at the northern Dismal Swamp and Valentine Creek south of Shoalwater Bay. Historically the species may have extended further — possibly north toward Woodgate in central Queensland and south to the Myall Lakes of northern New South Wales — but the modern, confirmed distribution is far more restricted and severely fragmented across roughly 18 known locations.
The fish is a specialist of the 'wallum' country: sandy coastal heathlands whose waters are soft, clear or tea-coloured from dissolved tannins, and distinctly acidic. Field measurements report pH as low as 4.4–5.8. It lives in slow-flowing creeks, coastal dune lakes, and wetlands over sandy or muddy bottoms with little or no current, sheltering along grassy banks among reeds, sedges, and water lilies in dense emergent and submerged vegetation. Wallum systems swing widely with the seasons — from around 57 °F in winter to well above 86 °F in summer — and the honey blue-eye is built for that fluctuating, low-mineral, blackwater world rather than for stable conditions.
Feeding
The honey blue-eye is a micropredator and opportunistic omnivore, occupying a trophic level around 3.2. In its tannin-stained creeks and dune lakes it takes small aquatic and terrestrial invertebrates — insect larvae, tiny crustaceans, and items drifting at or near the surface — together with some plant and algal material. Its small mouth and surface-and-midwater feeding style suit a diet of zooplankton and small insects.
In the aquarium the species accepts a range of small foods. Live and frozen items such as Daphnia, microworm, baby brine shrimp, and finely chopped bloodworm bring males into best colour and breeding condition, and small dry foods are taken once the fish are settled. The mouth is tiny, so the food has to be too; small, frequent meals suit this active little fish better than the occasional large one.
Mating
Males hold and defend small display areas, courting females within them using their coloration and their elongated, distinctively marked first dorsal and anal fin rays. They keep these territories year-round, but defence sharpens from around September, marking the onset of the breeding season. Display is fiercest when rival males are present — competition is what pushes them to their brightest honey tones.
Spawning takes place within a male's territory among submerged vegetation. As in related blue-eyes, the fish are continuous, drawn-out spawners during the season rather than producing a single large clutch: a female deposits only a few eggs at a time — typically one to four — laying a total on the order of 42 to 125 eggs over roughly a week. The eggs are demersal and adhesive, anchored to plants and roots by fine adhesive tendrils. Recorded spawning temperatures fall around 80–82 °F, with the main spawning months spanning roughly September and October and mostly tapering off by January or February.
Breeding
Pseudomugil mellis spawns over fine-leaved plants, roots, or spawning mops, to which its demersal eggs adhere by tendrils. The spherical, water-hardened eggs measure about 0.5 in in diameter. Incubation is strongly temperature-dependent: eggs hatch in roughly 12–14 days at 75 °F, shortening to about 4.6–7.9 days at 77–81 °F. Reproductive output scales with female size, with reported broods of roughly 11–41 young at a time and total fecundity in the range of about 42–145 eggs.
Maturation differs markedly between wild and captive fish. In the wild, sexual maturity is reached at around 10–12 months, but aquarium fish under good conditions can mature far faster — first spawning has been recorded at about 1 in and roughly 95 days of age. That fast captive maturity, plus a willingness to spawn continuously on mops or fine plants, makes it a tractable breeder for experienced hobbyists. Like other blue-eyes, adults eat eggs and fry given the chance, so breeders usually move the spawning medium or eggs to a separate rearing container. The fry are tiny and need correspondingly tiny first foods — infusoria or rotifers — before progressing to microworm and newly hatched brine shrimp.
In the aquarium
A small, peaceful schooling fish, the honey blue-eye suits a planted nano or species tank. Keep it in a group: males display against one another and hold their warmest colour only when there are rivals to display to. It does best in the conditions it came from — soft, acidic, tannin-stained water — so a blackwater setup with botanicals, fine-leaved plants, and gentle filtration is the right starting point, and dense marginal planting gives males the territories and cover that spawning depends on. It tolerates the temperature swings of its native habitat, but ordinary tropical temperatures in the mid-20s °C are fine. FishBase cites a captive pH tolerance of roughly 6.0–8.0, even though wild waters run considerably more acidic.
Tiny, slow, and small-mouthed, it belongs with similarly small, gentle tankmates — other blue-eyes, small rainbowfishes, peaceful nano species — and away from anything boisterous or large enough to beat it to food. Once the water is right, it asks for little. It does turn up in the trade, but given its threatened wild status, take captive-bred stock over wild-collected; over-collection by hobbyists is one of the documented pressures on wild populations.
Conservation
Pseudomugil mellis is assessed as Endangered (EN) on the IUCN Red List under criteria B2ab(i,ii,iii,iv), in an assessment dated 6 February 2019 (Brooks, S. & Arthington, A.; e.T18543A123378987). The listing reflects a very small area of occupancy — about 40 mi² — across a range that is severely fragmented into roughly 18 locations and subpopulations, with a continuing decline documented in extent of occurrence, area of occupancy, habitat quality, and the number of subpopulations. The overall population trend is decreasing.
The principal threats are habitat-driven: residential and urban development, forestry plantations, and agriculture all degrade or destroy the soft-water wallum wetlands the species depends on. Compounding this is the spread of the invasive eastern mosquitofish (Gambusia holbrooki), which preys on and competes with native fishes, and over-collection of the honey blue-eye for the aquarium hobby. The species receives legal protection in Australia: it is listed under Queensland's Nature Conservation Act 1992 and as Vulnerable under the Commonwealth EPBC Act.
For a fish confined to a narrow coastal band of specialised, easily disturbed habitat, that combination is serious — there is little outlying population to buffer local losses. Its readiness to breed in captivity offers some relief, letting the hobby supply itself without further pressure on wild stock. But the priority stays the same: protecting the wallum creeks, dune lakes, and wetlands of southeastern Queensland the species cannot do without.