Taxonomy & naming
Haplochromis iris was described in 1981 by the Dutch ichthyologists Rob J. C. Hoogerhoud and Frans Witte, in a revision of the 'Haplochromis empodisma group' published in the Netherlands Journal of Zoology (vol. 31). The holotype (RMNH 28346) and a series of paratypes were collected in the northern part of the Mwanza Gulf, Lake Victoria, at a depth of 23–36 ft, and are held at the Naturalis museum in Leiden (RMNH) with additional paratypes at the Natural History Museum, London (BMNH). The species was named together with its close relative Haplochromis hiatus in the same paper; the two are so similar in external appearance and in standard taxonomic characters that they were treated as a textbook example of how subtle the species limits are within the Lake Victoria flock. Eschmeyer's Catalog of Fishes and the CLOFFA checklist (van Oijen et al. 1991) both list it as a valid species. As with hundreds of Victoria endemics, iris has long sat in the catch-all genus Haplochromis. Greenwood's later partitioning of the flock and modern molecular work have moved many rock- and sand-dwelling lineages into segregate genera such as Paralabidochromis, Mbipia, Lithochromis and Pundamilia, but the mud-dwelling 'empodisma'/insectivore assemblage to which iris belongs has not been formally reassigned, so the name Haplochromis iris remains in current use.
Morphology
Haplochromis iris is a small, moderately deep-bodied haplochromine; the type series spans roughly 3–5 in standard length, and FishBase records a maximum of about 4.5 in SL. In overall shape it is an unremarkable 'generalized' haplochromine — a compressed oval body, a moderately sloped head, and the bicuspid and tricuspid jaw teeth typical of the group — which is precisely why it and its sister Haplochromis hiatus could only be separated by careful study. The two were distinguished by Hoogerhoud and Witte on a combination of fine morphometric and meristic characters and on pigmentation rather than on any single obvious feature. The species name iris (the Greek goddess of the rainbow) points to live coloration: like most Victoria haplochromines, breeding males would have carried an iridescent, multi-hued nuptial dress, while females and non-breeding fish are a plainer silvery-grey to brassy. As is the rule across the flock, the species is sexually dimorphic and dichromatic: males develop the bright structural colours used in courtship and typically grow somewhat larger, whereas females are drab. Detailed live-colour notes are sparse because the fish was studied largely from trawl and gill-net material rather than from aquarium stock.
Habitat
Haplochromis iris is endemic to Lake Victoria and was documented in detail only from the Mwanza Gulf, in the lake's Tanzanian south. It is a fish of the sub-littoral zone over bottoms of soft organic mud; FishBase gives a depth range of 10–89 ft, and the type material came from 23–36 ft. This is not a rock-dwelling 'mbipi' cichlid but a soft-bottom species of the open inshore floor, where it shared the mud habitat with its sister Haplochromis hiatus and other small insectivores. Lake Victoria is warm and only weakly mineralized: surface waters typically run about 73–81 °F, with pH on the alkaline side of neutral, roughly 7.2–9.0, and low to moderate hardness. Historically the sub-littoral mud zone that iris occupied was reasonably well oxygenated and clear enough to permit the colour-based behaviour these fish depend on; from the 1980s onward, eutrophication and rising turbidity progressively degraded exactly this band of the lake, contributing to the loss of the deeper inshore haplochromine community.
Feeding
Haplochromis iris is an insectivore. In Witte and van Oijen's classification of the Lake Victoria haplochromine trophic groups, iris and Haplochromis hiatus make up the 'empodisma' subgroup of bottom-dwelling insectivores, and before the Nile perch upsurge they were among the most important predators of chironomid (midge) and Chaoborus (phantom-midge) larvae over the sub-littoral mud of the Mwanza Gulf. The two sister species were not ecological duplicates: Hoogerhoud, Witte and Barel (1983) showed they partition resources, with iris classed as a partly molluscivorous insectivore — that is, an insect-larva feeder that also takes some snails, processed with the strengthened pharyngeal jaws characteristic of mollusc-eating haplochromines. This partitioning of the same mud habitat between two near-identical species is a small illustration of how the Victoria flock packed so many forms into one lake. Functionally, iris was a key link converting benthic invertebrate production into fish biomass in the inshore mud community.
Mating
No courtship has been described specifically for Haplochromis iris, but its breeding biology can be read from the well-studied Lake Victoria haplochromines, which share a highly conserved mating system. These are polygynous, lekking maternal mouthbrooders: ripe males take up small temporary territories and court passing females with quivering displays that show off their iridescent nuptial colours, and females choose among displaying males largely on the basis of that male coloration. Male–male competition and colour are central to how the flock's hundreds of species keep themselves reproductively distinct. This colour-based, visual mate choice is also the system's great vulnerability — and the reason the rising turbidity in Lake Victoria has been so damaging. Where the water clouds, females can no longer reliably discriminate male colour, mate choice breaks down, and closely related species hybridize. For a species like iris, with a near-twin sister (Haplochromis hiatus) on the same bottom, loss of water clarity threatens not just survival but the very colour signals that kept the two apart.
Breeding
Like essentially all Lake Victoria haplochromines, Haplochromis iris is a maternal mouthbrooder: the female takes the fertilized eggs into her mouth and broods the developing embryos and larvae there, releasing free-swimming fry after a period of weeks with no further parental investment from the male. Direct fecundity data for iris are lacking, but congeneric Victoria insectivores are small-clutch brooders — a Mwanza Gulf rock-frequenting insectivore studied by Goldschmidt produced large eggs (mean major egg axis about 0.5 in) in correspondingly small clutches, on the order of a few dozen eggs, which is typical of the trade-off these mouthbrooders make between egg number and the large, well-provisioned young that mouthbrooding favours. Spawning in the group ranges from seasonal to more or less continuous through the year. Beyond this genus-typical picture, the specific reproductive details of iris — clutch size, brooding duration, spawning season — were never documented before the population collapsed.
In the aquarium
Haplochromis iris is effectively absent from the aquarium hobby. It is a small, drab-bodied, scientifically described mud-dwelling insectivore that was never a trade fish, and it had largely disappeared from Lake Victoria by the time the 'Victorian' haplochromines became popular with specialist keepers. Whatever stocks of Lake Victoria cichlids circulate among hobbyists and conservation breeders belong to other, more colourful and more available species; there is no evidence that iris is held in captivity anywhere, and given its Critically Endangered (Possibly Extinct) status it may no longer exist to be kept. Any general guidance, therefore, is by analogy to its better-known relatives rather than to the fish itself. Lake Victoria haplochromines are warm-water fish that do best around 75–81 °F in hard, alkaline water (pH roughly 7.5–8.5), are vigorous and often aggressive, and are typically maintained in single-species groups of one male to several females in a tank with open swimming room and clear, well-filtered water — the last point being especially relevant, since these fish depend on water clarity to display and choose mates normally. None of this should be read as a husbandry recommendation for iris specifically: the honest position is that this species is a museum and conservation subject, not an aquarium one.
Conservation
The IUCN Red List assesses Haplochromis iris as Critically Endangered (Possibly Extinct) — criterion C2a(ii) — assessed on 31 March 2010 by Witte, de Zeeuw and Brooks, with a decreasing population trend. The principal threat identified is predation by the introduced Nile perch (Lates niloticus), described as a potentially reversible pressure, compounded by the threat of hybridization driven by decreased water transparency, with incidental capture in fisheries a further factor. The species is one of the many casualties of Lake Victoria's ecological transformation: from the 1980s the explosive increase of the Nile perch, combined with intensifying eutrophication and turbidity, eliminated haplochromines from much of the sub-littoral and deep-water zones — exactly the mud habitat that iris occupied. Sub-littoral insectivores of the 'empodisma' group were among the casualties, and Eschmeyer's Catalog of Fishes flatly lists the species as extinct, while the IUCN leaves open the 'Possibly Extinct' qualifier. Rock-dwelling Victoria haplochromines as a whole weathered the perch invasion better than open- and mud-bottom species, because rocky refuges offered cover and the perch hunted less effectively there; iris, as a soft-bottom fish of the open inshore floor, had no such refuge. Whether any population survives is unknown, which is precisely what the 'Possibly Extinct' tag is meant to convey.