Taxonomy & naming
Haplochromis percoides was described by the Belgian-British ichthyologist George Albert Boulenger in 1906, in the Annals and Magazine of Natural History, from specimens collected at Entebbe on the Ugandan shore of Lake Victoria (Victoria Nyanza). Boulenger placed it, as he did almost every Victorian haplochromine of his era, in the catch-all genus Haplochromis; his original series is held at the Natural History Museum, London, where Peter Humphry Greenwood selected the lectotype (BMNH 1906.5.30.313) in his 1962 revision of the lake's larger species. Greenwood's monographs of the 1950s through 1980s broke Boulenger's unwieldy Haplochromis into many smaller, ecologically coherent genera, and percoides was assigned to Prognathochromis — a genus of slender, large-mouthed open-water and inshore piscivores. That generic name is still widely used (the Catalog of Fishes and IUCN both cite Prognathochromis percoides as a synonym), but because the boundaries of these Greenwoodian genera remain contentious and many are not demonstrably monophyletic, most modern checklists — FishBase and Eschmeyer's Catalog of Fishes among them — return the species to a broadly defined Haplochromis. We keep the Haplochromis heading here while noting that Prognathochromis is the genus under which much of the older literature files it. The species epithet, "percoides," is the descriptive heart of the name: Boulenger thought the fish perch-like.
Morphology
Haplochromis percoides is a small cichlid, reaching about 3.5 in in standard length — perch-like in build rather than deep-bodied, with a straight cranial profile and a pronounced premaxillary appendage (the bony hump at the front of the upper jaw typical of the lake's predatory haplochromines). The dentition betrays its diet: the outer tooth rows in both jaws are enlarged and made up mainly of slender unicuspid (single-pointed) teeth, with a few weakly bicuspid teeth toward the rear of the lower jaw, backed by one to three inner rows of small tricuspid teeth, all curved slightly inward to grip prey. Greenwood reported five or six dark vertical bars running down the flanks from the back. Like nearly all of Lake Victoria's haplochromines, the species would have been sexually dichromatic in life — breeding males flushed in bright nuptial colour while females and non-breeding fish stayed a drab silvery-brown — but because percoides was described from preserved material and has not been studied alive, its live male colours were never recorded and are simply unknown. The sexes can be assumed to have differed in colour and in the egg-spots on the male anal fin, as in its congeners, but no detailed account of its dimorphism exists.
Habitat
The species is endemic to Lake Victoria, the vast, shallow equatorial lake shared by Uganda, Kenya, and Tanzania. Within the lake it was an inshore, shallow-water fish: records place it in shallow water over exposed or partly exposed sandy beaches, generally close to shore and within the uppermost few metres of the water column. Greenwood characterised it as a northern species, documented near Entebbe in Uganda and at Majita Beach on the Tanzanian (Mara) coast, and FishBase notes it was nowhere common but seemed to be widely if thinly distributed around the lakeshore. Lake Victoria itself is a warm, well-mixed tropical lake, historically clear over its sandy littoral, with surface waters typically around 75–82 °F and circumneutral to alkaline chemistry (pH roughly 7.2-9.0); these are the conditions under which percoides lived. As a sand-beach specialist it occupied a habitat that was among the first to be altered by the lake's late-twentieth-century ecological collapse.
Feeding
Haplochromis percoides was a piscivore — a fish-eater — and sits high on the food web, with FishBase estimating a trophic level above four. Greenwood's examination of gut contents found the remains of small cichlids, leading him to conclude that the species preyed on schools of young fish and fry over the open sandy shallows where it lived. Its morphology fits that role precisely: the enlarged, inward-curved unicuspid teeth and the projecting premaxillary appendage are the tools of a fish that seizes and holds slippery prey. In the pre-perch Lake Victoria, percoides was one of a large guild of inshore haplochromine predators that cropped the lake's enormous standing crop of juvenile cichlids — a guild that has been almost entirely erased from the modern lake.
Mating
No direct observations of courtship or social behaviour in Haplochromis percoides were ever published; the species vanished before its breeding biology could be studied in the wild or in captivity. What can be said comes from the broader pattern of the Lake Victoria haplochromine flock, to which it belongs. These cichlids are maternal mouthbrooders in which males establish and defend small courting territories and display their nuptial colours to attract females. The bright, species-specific male coloration is itself the principal mechanism of mate recognition: females choose mates largely by colour, which keeps the many closely related, ecologically overlapping species reproductively isolated. In percoides this courtship would have played out over the sandy shallows it inhabited, though the specifics — the male's colours, his display, the territory he held — were never recorded.
Breeding
Like all members of the Lake Victoria haplochromine radiation, Haplochromis percoides was a maternal mouthbrooder: after spawning, the female took the fertilised eggs into her mouth and brooded them there, sheltering the developing young until they were released as free-swimming fry, and taking them back into her mouth when threatened. The male contributes only gametes and plays no part in guarding eggs or fry. No clutch count was ever published for percoides specifically; in the small inshore haplochromines of Lake Victoria, broods are typically modest — on the order of a few dozen eggs, often roughly 20-60 — reflecting the trade-off between fecundity and the safety of oral brooding. The combination of small clutch size, drab brooding females, and reliance on clear water for the colour-based mate choice that keeps species distinct left these fish acutely vulnerable to the changes that overtook the lake.
In the aquarium
Haplochromis percoides is not an aquarium fish. It is not kept in the hobby, is not bred in captivity, and almost certainly no living specimens exist anywhere — the species is known only from museum material and has not been collected in decades. It should not be confused with the colourful Lake Victoria haplochromines that do circulate among specialist keepers (the various "Victorian cichlids" such as Pundamilia nyererei or Haplochromis sp. "all-red"), which are different species. There is consequently no husbandry to report. The general husbandry of surviving Victorian haplochromines — hard, alkaline water around pH 7.5-8.5 and 75–81 °F, a sand substrate, robust filtration, and the understanding that the males are highly aggressive and the fish are prolific maternal mouthbrooders — would presumably have applied, but for percoides this is conjecture, not experience. The honest statement is that this fish belongs to conservation history, not to the aquarium.
Conservation
The IUCN Red List assesses Haplochromis percoides as Critically Endangered (Possibly Extinct) under criterion C2a(ii), assessed on 31 March 2010 by Witte, de Zeeuw and Brooks, with a decreasing population trend; an earlier 1996 assessment had listed it as Extinct before the status was revised to reflect uncertainty. It has not been reliably recorded since around the time of Greenwood's work and the subsequent transformation of the lake. The principal driver was the Nile perch (Lates niloticus), a large introduced predator that erupted across Lake Victoria between the late 1970s and 1980s and, together with intensifying eutrophication, drove an estimated several hundred endemic haplochromine species to extinction or near-extinction in one of the most severe vertebrate mass extinctions of modern times. The IUCN flags predation by Nile perch as the main threat — a potentially reversible one — and adds that decreasing water transparency from eutrophication threatens the species indirectly, because the turbid water collapses the colour-based mate recognition on which these cichlids depend, promoting hybridisation and the loss of distinct species. Harrison & Stiassny (1999), in their review of the lake's lost fishes, cautioned that parts of Lake Victoria remain inadequately surveyed and that haplochromines have reappeared after years of apparent absence, so percoides cannot be declared definitively extinct — but no rediscovery has been reported, and its prospects are bleak.