Taxonomy & naming
Pseudomugil paskai was described by Gerald R. Allen and Walter Ivantsoff in 1986. It belongs to the family Pseudomugilidae — the blue-eyes — small atheriniform fishes allied to the rainbowfishes proper (Melanotaeniidae) and grouped with them in the broader rainbowfish radiation of Australia and New Guinea. Eschmeyer's Catalog of Fishes records the valid name as Pseudomugil paskai Allen & Ivantsoff, 1986; the species was described in Pseudomugil and remains there, so no parenthetical authority is used.
The genus Pseudomugil contains on the order of sixteen species, all endemic to Australia and New Guinea — small, colourful fishes that rarely exceed about 2 in, with bright blue irises, two closely set dorsal fins, and, in the males, elongated fin filaments used in courtship. P. paskai is one of the New Guinea members. It closely resembles the red-neon blue-eye Pseudomugil luminatus, and the two have long been confused in the hobby; paskai is the less vivid of the pair, lacking the saturated red of luminatus.
The genus name Pseudomugil combines the Greek pseudes, 'false', with the Latin mugil, 'grey mullet', a reference to the superficial resemblance of these fishes to small mullets. The specific epithet honours John Paska, a fisheries technician with the Papua New Guinea Ministry of Fisheries who co-collected the type material and assisted Allen's New Guinea fieldwork — making the name a patronym recognising local collaboration in the species' discovery.
Morphology
Paska's blue-eye reaches only about 1 in. FishBase gives a maximum of 1 in standard length, while the Australian risk-assessment literature citing Saeed, Ivantsoff and Allen (1989) and Tappin (2011) describes adults at roughly 1 in. The body is fusiform and, as in all blue-eyes, carries the bright blue iris that gives the group its name. Two dorsal fins sit very close together, the first noticeably smaller than the second; meristic counts run to 3–5 dorsal spines, 6–7 dorsal soft rays, a single anal spine, and 9–11 anal soft rays.
The species is strongly sexually dimorphic. Mature males are semi-translucent, bluish on the lower flanks and yellowish above the mid-lateral line, with narrow dark outlines to the scales and a pink flush over the opercular region. The first dorsal and the pelvic rays are elongated into display filaments. The fins are translucent with white-to-yellow margins and a scattering of oval black spots; the caudal lobes are tipped in white, yellow, or reddish, and the pelvic fins are yellowish. Females are far plainer, lacking both the fin spots and the male colours.
The small size, paired close-set dorsals, spotted pale-edged fins and elongate male filaments are all classic blue-eye traits, and they account for the fish's appeal to keepers of nano species — even though its colours stay more restrained than those of the showiest members of the genus.
Habitat
Pseudomugil paskai is known only from a few small creeks along the Kiunga–Tabubil road in the upper Fly River system of Papua New Guinea, roughly 516–528 mi upstream from the sea. Earlier reports from the Timika area of Papua Province, Indonesia have been shown by the IUCN assessment to rest on misidentifications of Pseudomugil luminatus, so the species' confirmed range is the upper Fly system alone (photographs from the Aru Islands may represent a similar fish, but this is uncertain). FishBase places the species at roughly 5–6°S latitude.
The habitat is lowland rainforest waters at modest elevation, on the order of 328–492 ft. The species occupies permanent rivers, streams and creeks, together with swampy lagoons, lakes, and small side channels of larger rivers, always associated with abundant aquatic vegetation. The flow is typically slow, and the water is often turbid or stained tea-coloured by tannins. Field measurements reported via Tappin (2011) give warm water around 77–79 °F and a slightly acidic pH near 6.0–6.5, while FishBase's broader climate envelope spans about 72–79 °F with pH 6.5–7.5 and hardness up to roughly 15 dH.
What stands out is how little of this habitat the fish now seems to hold. Its area of occupancy and extent of occurrence are both best-estimated at around 2 mi² — a tiny footprint. Common in the 1980s, it is now rare, and recent targeted searches in parts of its former range came up empty. It was, however, 'rediscovered after roughly 40 years' during recent Ok Tedi Mining fish-survey work, a reminder that detection in these turbid forest creeks is itself difficult.
Feeding
Paska's blue-eye is an omnivore, recorded by FishBase as an omnivorous egg-layer with a trophic level around 3.2. In its vegetated rainforest creeks it would take small invertebrates — tiny crustaceans, insect larvae, and other zooplankton drifting among the aquatic plants — along with some plant and algal material, feeding in the upper and middle water column as blue-eyes characteristically do.
In captivity the species is best treated as a micro-predator. Its small mouth restricts it to correspondingly small foods: fine, high-quality dry foods, and especially small live and frozen items such as newly hatched brine shrimp, microworm, Daphnia, Cyclops, and other small invertebrate prey. A varied diet weighted toward live and frozen foods brings males into their best colour and conditions adults for spawning.
Dietary studies specific to P. paskai are sparse, and much of what is kept and fed in the hobby has historically been confused with the more common red-neon blue-eye. So the feeding picture here leans on FishBase's omnivore classification and general blue-eye husbandry rather than species-specific observation — read it as the reliable pattern for the genus.
Mating
Like other blue-eyes, Pseudomugil paskai is a small egg-laying fish in which courtship is driven by the males' fins and colour rather than by size or aggression. Males of the genus are noted for elongated fin filaments used in courtship displays, and in paskai it is precisely the elongate first-dorsal and pelvic rays, the spotted and pale-edged fins, and the pink opercular flush that the male spreads and presents to females and rival males.
Display works best with several males present to posture against one another; the rivalry keeps them in peak colour and stimulates spawning. Receptive females, which lack the male's fin spots and bright colours, move into fine vegetation with a displaying male to spawn. The fish is a peaceful community species, and its 'aggression' amounts to harmless fin-flaring between courting males.
Published accounts of courtship in P. paskai specifically are thin — the data are sparse and much hobby reporting has been mixed up with that of P. luminatus — so the description here follows the well-documented blue-eye pattern of filament-display courtship among vegetation, which the species' morphology and FishBase's notes both support.
Breeding
Pseudomugil paskai is an egg-laying species — FishBase records it explicitly as an omnivorous egg-layer — and, like blue-eyes generally, it is a continuous plant-spawner rather than a clutch-laying nest builder. Conditioned pairs deposit small adhesive eggs among fine-leaved aquatic plants or, in the aquarium, spawning mops, releasing a few eggs at a time over an extended period rather than a single large batch.
The adults offer no parental care and will eat eggs and fry given the chance, so breeders following blue-eye practice typically remove the spawning medium to a separate rearing container or spawn the fish over a substrate the eggs can fall through. Warmth in the mid-to-upper 20s Celsius suits incubation. The fry are very small on hatching and need correspondingly tiny first foods — infusoria, rotifers, or commercial liquid fry food — before they can take newly hatched brine shrimp.
As with feeding and courtship, species-specific breeding data for P. paskai are thin, and no dedicated hobby account turned up that is cleanly separated from the more commonly bred P. luminatus. The outline given here is the standard blue-eye breeding pattern applied to a fish whose own published record is sparse; precise figures for egg counts and incubation time in paskai itself are not reliably documented.
In the aquarium
Paska's blue-eye is a nano fish through and through, suited to a small, mature, densely planted tank kept for the pleasure of tiny, peaceful species. Its size and gentle temperament mean it must never share a tank with anything large or boisterous enough to bully it or beat it to food. Keep it in a group — these are shoaling display fish, and the males colour up best with rivals to spar against; a male-skewed group in a well-planted tank draws out the most courtship.
It does best in warm, soft to moderately hard water with plenty of vegetation, echoing its tannin-stained creek origins. FishBase's general aquarium suggestion of around 82 °F, pH near 7.5 and about 10 dH gives a workable target, though the wild figures of 77–79 °F and a slightly acidic pH around 6.0–6.5 sit closer to the natural envelope. Stable, clean, gently filtered water matters more than hitting exact numbers. Fine-leaved plants and subdued, tea-coloured water show the fish off and give it somewhere to spawn.
One practical caution: much of what is sold and discussed under blue-eye names has long been confused with the red-neon blue-eye P. luminatus, so anyone after genuine P. paskai should expect identification uncertainty in the trade. The species is scarce in the wild and Critically Endangered, which makes captive-maintained lines worth more than usual and argues for sourcing tank-bred fish where they can be found.
Conservation
Pseudomugil paskai is assessed by the IUCN Red List as Critically Endangered under criteria B1ab(iii)+2ab(iii), with the assessment dated 4 June 2020 (IUCN species ID 18547). The listing rests on an extraordinarily small and declining range: both the area of occupancy and the extent of occurrence are best-estimated at around 2 mi², and the population trend is decreasing. The species is harmless to humans and is not evaluated under CITES or the CMS.
The trajectory is stark. Common around its southern New Guinea creeks in the 1980s, the fish is now rare, and recent searches across parts of its former range have come up empty. The threats are the familiar ones for a narrowly endemic lowland fish hemmed in by development: pressure from surrounding human settlements, mining in the upper Fly River region, and pollution of its small creeks. A range this confined leaves no buffer — there is no large outlying population to absorb local losses.
There is a thread of better news. The species was 'rediscovered after roughly 40 years' during recent Ok Tedi Mining fish-survey work, which both confirms it persists and shows how hard it is to detect in turbid forest creeks; some of the apparent decline may be survey difficulty rather than genuine loss. Even so, the Critically Endangered listing is a serious one, and keeping accurately identified captive populations — distinct from the commonly traded P. luminatus — is a real hedge against the loss of a fish with so little wild ground left to stand on.