Taxonomy & naming
Haplochromis argenteus was described by the British ichthyologist Charles Tate Regan in 1922, in his account of the cichlid fishes of Lake Victoria in the Proceedings of the Zoological Society of London, where it was figured (his fig. 12). The original combination is the one still in use, Haplochromis argenteus. Regan based the species on material from Bunjako, in the Ugandan part of Lake Victoria; the Catalog of Fishes records a lectotype in the Natural History Museum, London (BMNH 1906.5.30.266) with one paralectotype (BMNH 1906.5.30.267), the lectotype having been selected by Peter Humphry Greenwood in his 1967 revision of the lake's Haplochromis. Greenwood spent decades dismantling the unwieldy genus Haplochromis into a series of smaller, ecologically coherent genera, and argenteus — a comparatively large, large-mouthed predator — falls within the group he treated as the piscivorous haplochromines; it is sometimes placed in the genus Harpagochromis on that basis. Many ichthyologists, the Catalog of Fishes and FishBase among them, continue to keep these Lake Victoria predators within a broadly defined Haplochromis, and that is the heading used here. The specific epithet is unambiguous: argenteus is Latin for 'silvery', and ETYFish glosses it as 'silvery (but with a darker back), referring to its coloration'.
Morphology
FishBase gives a maximum size of 8 in standard length, which makes argenteus a large haplochromine by the standards of the Victoria flock, where most species top out between roughly 8 and 4.5 in. The build is that of a typical lacustrine predator: an elongate, laterally compressed body and a sizable, somewhat oblique mouth suited to seizing active prey. Its name records its most obvious feature — an overall silvery sheen, darker along the back, that would have served as effective open-water camouflage. As in essentially all haplochromines, breeding males would have been the more colourful sex, carrying the nuptial pattern and the yellow or orange egg-spots (ocelli) on the anal fin that figure in courtship, while females and non-breeding fish stayed plainer and more cryptically silver; the early literature on the species does not document the male colours in detail, so the specifics are not reliably known. Beyond the silvery ground colour and predatory proportions, no distinctive ornament is on record for the species.
Habitat
Haplochromis argenteus is endemic to Lake Victoria, the great shallow equatorial lake shared by Tanzania, Uganda and Kenya, and it is known from no other water body. FishBase places it between about 1°N and 3°S and records it from the surface down to roughly 39 ft, so it was a fish of the lake's shallow sub-littoral rather than its deeper offshore basins. Collectors found adults over sheltered mud bottoms, with some specimens also taken from more exposed, hard-substrate sites, while juveniles were netted along exposed beaches — a pattern of inshore nursery habitat shifting to quieter soft-bottom areas as the fish matured. Lake Victoria itself is warm, generally alkaline freshwater: surface temperatures sit around 73–81 °F and pH typically runs from about 7.2 to 9.0, the chemical envelope shared by the whole haplochromine flock. The species was not associated with rocky reefs or with the deepest water; its habitat was the productive, near-shore margin of the lake.
Feeding
The gut contents of examined specimens place Haplochromis argenteus among the predatory, rather than the algae- or detritus-eating, members of the flock. Stomachs held insect remains — both terrestrial insects taken at or near the surface and the aquatic larvae of mayflies (Ephemeroptera) — together with the remains of fish, identified as Rastrineobola (Engraulicypris) argenteus, the small silver cyprinid that schools in open water and is itself a staple of the lake's food web. FishBase estimates a trophic level of about 3.6, consistent with an insectivore-piscivore that hunted moving prey rather than grazing the bottom. This combination of aerial and emergent insects with small shoaling fish marks argenteus as a generalist predator of the sub-littoral, exploiting the seasonal abundance of lake-fly swarms and the ever-present sardine-like Rastrineobola.
Mating
No courtship or social behaviour has been documented for Haplochromis argenteus specifically. As a Lake Victoria haplochromine it would have followed the reproductive pattern that is near-universal in the flock: a polygynous, lek-like system in which males establish and defend small display territories and court passing females, while females range more widely and choose among displaying males. The anal-fin egg-spots that males of these cichlids carry are central to that courtship, exploited during the spawning sequence described below. Pair bonds are not formed; the male's role ends at fertilisation. Because the species likely vanished before any field study of its behaviour, this account is necessarily drawn from the well-studied biology of its close Victoria relatives rather than from direct observation.
Breeding
Haplochromis argenteus is recorded as a mouthbrooder, and like the rest of the Lake Victoria haplochromine flock it was a maternal (female-only) mouthbrooder. In this mode the female lays a relatively small clutch of large, yolky eggs, takes them immediately into her mouth, and is fertilised by the male via the egg-spot mechanism — she snaps at the ocelli on his anal fin and so draws his milt into her buccal cavity to fertilise the eggs she is already carrying. She then incubates the developing eggs and larvae in her mouth for roughly two to three weeks, taking no food, before releasing free-swimming fry; for a short period afterwards the young may retreat back into her mouth when threatened. Clutch size is not on record for argenteus, but Lake Victoria haplochromines of this body size typically carry on the order of a few dozen to around a hundred eggs — small broods offset by the protection of oral incubation. No spawning of this species has been documented in the wild or in captivity, so the figures here are the genus-typical pattern rather than measured values.
In the aquarium
Haplochromis argenteus is not an aquarium fish. It was a wild-only Lake Victoria endemic that was probably never kept or bred in captivity, and given its Critically Endangered (Possibly Extinct) status it is effectively unavailable to hobbyists; there is no husbandry record to report. This sets it apart from a handful of Lake Victoria haplochromines — fish such as Pundamilia nyererei and a few Astatotilapia and Haplochromis 'types' — that were brought into the aquarium trade and conservation programmes before or during the lake's collapse and are now maintained in captivity partly as a hedge against extinction in the wild. Had argenteus entered the hobby it would have demanded the conditions those relatives need: hard, alkaline water around pH 7.5–8.5 and 75–81 °F, a long tank with open swimming room, and — as a 8 in predator that ate insects and small fish — a diet of meaty and live foods and tankmates too large to be swallowed. None of that is more than inference: the practical reality is that this is a species known only from museum specimens and the historical fishery record, not from anyone's tank.
Conservation
The IUCN Red List assesses Haplochromis argenteus as Critically Endangered (Possibly Extinct), under criterion C2a(ii), with a decreasing population trend; the assessment was carried out on 31 March 2010 by Witte, de Zeeuw and Brooks and published that year. The Catalog of Fishes goes further and flags the species' distribution simply as 'extinct'. Its decline is part of the best-known mass extinction of vertebrates in modern times: from the late 1970s the introduced Nile perch (Lates niloticus) erupted across Lake Victoria, and over the following decade some 200 or more endemic haplochromine species disappeared from the sub-littoral and offshore zones, the same shallow waters argenteus inhabited. Predation by Nile perch acted alongside severe eutrophication — nutrient loading from a growing human population caused algal blooms and deep-water deoxygenation — and the two pressures together gutted the flock. Many smaller, rock- and shore-associated haplochromines have since shown partial recovery as Nile-perch numbers were fished down, but the larger predatory species that competed most directly with Lates, the group to which argenteus belongs, have fared worst and several appear genuinely lost. For this species there is no confirmed recent record, and 'Possibly Extinct' is an honest reading of the evidence.