Taxonomy & naming
Pseudomugil ivantsoffi was described by Gerald R. Allen and Samuel Renyaan in 1999. The genus Pseudomugil belongs to the family Pseudomugilidae, the blue-eyes, within the order Atheriniformes (silversides) — a lineage distinct from the true rainbowfishes of the family Melanotaeniidae, though the two groups are close relatives and share the New Guinea–Australia distribution. Eschmeyer's Catalog of Fishes records the valid name as Pseudomugil ivantsoffi Allen & Renyaan, 1999; because the species was described in Pseudomugil, where it remains, no parenthetical authority is used.
The genus name Pseudomugil joins the Greek pseudes, 'false', to the Latin mugil, 'grey mullet' — a nod to the superficial resemblance these fish bear to mullets. The specific epithet ivantsoffi honours Dr Walter (Jack) Ivantsoff, an Australian ichthyologist who worked at length on the silversides and their allies. The hobby name follows straight from the epithet: Ivantsoff's blue-eye.
Data on this species is sparse, and some online hobby material conflates it with other West Papuan blue-eyes or repeats unsourced and internally contradictory locality claims; the authoritative records (FishBase, Catalog of Fishes, IUCN) consistently place it in Indonesian New Guinea and should be preferred over secondary accounts.
Morphology
This is a tiny fish, reaching a maximum recorded length of about 1 in standard length. Like the rest of the genus it is a slender, laterally compressed blue-eye, with the family's two separated dorsal fins and the bright iris that gives the group its name.
Published morphometric and colour descriptions for this species are limited, and the site won't reproduce colour or finnage detail that can't be traced to a reliable source. Pseudomugil blue-eyes generally have paired dorsal and anal fins that males extend and flare in display, and many show modest sexual dimorphism in fin development and colour intensity. How far that holds for P. ivantsoffi specifically isn't well documented in the literature available here, so firm claims are withheld.
Habitat
Pseudomugil ivantsoffi is a freshwater, benthopelagic species of tropical lowland waters in Indonesian New Guinea (West Papua). FishBase reports its distribution as Indonesia — that is, the western, Indonesian half of the island of New Guinea, not Papua New Guinea — and the IUCN assessment treats it as a restricted-range, narrowly distributed species.
The IUCN listing falls under criterion B1, reflecting a small extent of occurrence together with a continuing decline in habitat quality. Beyond that, precise water-body and microhabitat data is sparse in the sources available here, so the site avoids asserting specific stream, lake, temperature, or chemistry values for the wild habitat that cannot be traced to a measurement. As with many West Papuan blue-eyes, the small range is the central fact of its biology, and the reason its conservation status is precarious.
Feeding
Pseudomugil ivantsoffi is a micro-predator. FishBase places it at a trophic level of about 3.2, consistent with a diet of small invertebrates rather than plant material. Like other blue-eyes it feeds in the upper and middle water column, taking small aquatic invertebrates, insects and insect larvae, and zooplankton.
In the aquarium, blue-eyes like this want very small foods to match their tiny mouths — micro-pellets and finely crushed flake, with plenty of small live and frozen fare such as Daphnia, Cyclops, microworm, and baby brine shrimp. A varied diet leaning on live or frozen food keeps them in condition and ready to spawn. Dietary detail for P. ivantsoffi specifically is thin, so these are general blue-eye husbandry points rather than species-specific observations.
Mating
Detailed published accounts of courtship and spawning behaviour specific to Pseudomugil ivantsoffi are sparse, and the site does not fabricate species-specific behaviour. In general, Pseudomugil blue-eyes are non-guarding, plant-spawning egg-scatterers in which males court females with fin displays among fine vegetation, and males are most colourful and most active in display in the presence of rivals and in the early part of the day.
Hobby reports describe Ivantsoff's blue-eye as a peaceful, social fish best kept and conditioned in small groups — consistent with the group-displaying behaviour seen across the genus. Beyond that, firm species-specific mating detail is withheld pending reliable sources.
Breeding
As with the rest of the genus, Pseudomugil ivantsoffi is understood to be an egg-scattering plant spawner that offers no parental care, depositing small adhesive eggs among fine-leaved plants or spawning mops over an extended period rather than in a single clutch. Hobby accounts of this species describe eggs laid among plants, with fry raised separately on small live foods — a pattern typical of blue-eye breeding generally.
Blue-eyes this small produce tiny fry that need very small first foods — infusoria, rotifers, or commercial liquid fry food — before they graduate to newly hatched brine shrimp. Precise figures for egg counts, incubation period, and growth rate specific to P. ivantsoffi are not well documented in the sources available here, so the site states no exact numbers. The genus-standard approach of moving eggs or mops to a separate rearing container applies.
In the aquarium
Ivantsoff's blue-eye is a peaceful, sociable nano fish suited to a small, well-planted, mature aquarium kept as a group rather than in ones or twos. Its tiny size and gentle temperament make it a poor match for larger or boisterous tankmates, which may out-compete it at feeding or simply intimidate it; it is best kept either in a species tank or alongside other small, peaceful fishes and invertebrates.
Hobby sources cite aquarium conditions of roughly 72–82 °F (72–82 °F) and a pH of about 6.5–7.5, with a reported captive lifespan of three to five years. These are hobby generalities, not measurements from the wild, and are presented as such. Like most blue-eyes, it does best in stable, clean, well-oxygenated water with gentle flow and dense planting broken by open swimming space; a group with several males together brings out the most activity and colour.
Conservation
Pseudomugil ivantsoffi is assessed as Endangered (EN) on the IUCN Red List, under criterion B1ab(iii); the assessment was dated 6 December 2019. The listing reflects a restricted range — a small extent of occurrence — combined with a continuing decline in the quality of the species' habitat. CITES and CMS list the species as Not Evaluated.
A fish confined to a small area has little resilience to localised habitat pressure, with no large outlying population to buffer declines. FishBase rates it as having low vulnerability to fishing and as harmless to humans, so the concern centres on habitat quality and range size rather than direct harvest. As with other threatened blue-eyes, captive breeding within the hobby helps keep the species in aquaria and eases collecting pressure on wild stock; aquarists are best served by sourcing tank-bred fish. Some online accounts circulate specific wild-population figures, but these are unsourced and not repeated here.