Taxonomy & naming
Haplochromis venator was described by the British ichthyologist Peter Humphry Greenwood in 1965, in his monograph 'The Cichlid Fishes of Lake Nabugabo, Uganda' (Bulletin of the British Museum (Natural History) Zoology, volume 12, number 9, pages 313-357). The species was figured in that work (Fig. 9) and is anchored by a holotype in the Natural History Museum, London (BMNH 1933.2.23.240), together with a series of paratypes (BMNH 1933.2.23.234-239 and 1964.7.1.80-85) collected in Lake Nabugabo. The Catalog of Fishes lists the name as valid as Haplochromis venator Greenwood 1965, in the family Cichlidae, subfamily Pseudocrenilabrinae, and flags the species as extinct. In the second part of his sweeping revision of the haplochromine cichlids of lakes Victoria, Nabugabo, Edward, George and Kivu, Greenwood (1980) distributed the old catch-all genus Haplochromis among some twenty genera, and assigned the slender piscivores - venator among them - to his genus Prognathochromis. That arrangement has never been universally adopted: many workers retain the conservative 'Haplochromis' for the whole Lake Victoria flock because the molecular relationships within this very young, rapidly radiated assemblage remain unresolved. We keep the species under the Haplochromis heading here, while noting that Prognathochromis venator (Greenwood, 1980) is the same fish. The Nabugabo flock to which it belongs is young in geological terms: the lake was cut off from Lake Victoria by a sand bar perhaps only four thousand years ago, and its handful of endemic haplochromines evolved in that short window.
Morphology
Haplochromis venator is a slender, elongate cichlid built for pursuit. FishBase records a maximum size of 7 in standard length, making it one of the larger members of the Nabugabo flock; figures of this kind come from Greenwood's type material rather than from any modern population, so they should be read as the size of preserved museum specimens. The genus Prognathochromis, into which Greenwood placed it, is diagnosed as a group of slender-bodied, comparatively large-mouthed haplochromines - the body shape and jaws of an open-water fish-eater. As in the great majority of Lake Victoria haplochromines, the species would have shown the family's typical sexual dichromatism, with breeding males more strongly and brightly coloured than the cryptically patterned females and juveniles; Greenwood's original description is the authority for the precise meristics and live coloration, which are not reproduced in the readily available secondary literature. No photograph of a living Haplochromis venator is held by FishBase, and with the wild population apparently gone, the published description and type specimens are effectively the only record of how the fish looked.
Habitat
The species is endemic to Lake Nabugabo, a shallow freshwater lake of roughly 24 square kilometres lying just west of Lake Victoria in southern Uganda, within the Lake Victoria Basin freshwater ecoregion. Nabugabo was once part of Victoria itself before a sand spit sealed it off, and its fish fauna is essentially a small subset of the Victoria flock that has been evolving in isolation since. Unlike most of its inshore relatives, Haplochromis venator was a fish of the open water: Greenwood noted it was more abundant in offshore, open areas than elsewhere in the lake and that it was possibly pelagic over the mud bottoms in the middle of the lake. FishBase classes it as a freshwater, benthopelagic species and gives a single depth datum of about 10 ft, consistent with a shallow lake; Nabugabo as a whole is only a few metres deep. Like all the Lake Victoria-basin waters it inhabited warm, near-equatorial, circum-neutral to alkaline water, broadly in the range of pH 7.2 to 9.0 and 23 to 27 degrees Celsius that characterises the basin's surface waters.
Feeding
Haplochromis venator was a piscivore - its species epithet, the Latin for 'hunter', was chosen by Greenwood precisely because he described it as 'predominantly a piscivorous predator'. FishBase records that it is predominantly piscivorous, though insects, especially adult mayflies (Ephemeroptera), are also taken, and assigns it a trophic level of about 3.9, near the top end for the lake's cichlids. Its slender body and large mouth are the equipment of a fish that chased and engulfed smaller fishes - in Nabugabo, that prey base would have been the lake's many smaller haplochromine cichlids and other small fishes. In the food web of the open lake it occupied the macro-predator role, one of only a couple of abundant piscivores recorded for the Nabugabo system. That ecological position - a native fish-eater of the open water - is exactly the niche the introduced Nile perch came to dominate, and it is no coincidence that the lake's indigenous piscivores were among the hardest hit.
Mating
No courtship or social behaviour has been documented specifically for Haplochromis venator; the species was described from preserved material and was effectively gone from the open lake before its biology could be studied in the wild. Its mating system can only be inferred from the Lake Victoria haplochromines as a whole, which are famously uniform in this respect. They are polygynous maternal mouthbrooders in which the sexes separate at spawning time: a breeding male takes on bright nuptial colour and defends a small territory or display site, courting passing females with lateral displays and quivering, while the drab female visits only to spawn. Mate choice in this flock is strongly visual and colour-based, which is one reason the radiation produced so many closely related species distinguished chiefly by male coloration. Pair bonds are momentary - the male's role ends at fertilisation - and there is no biparental care.
Breeding
FishBase lists Haplochromis venator simply as a mouthbrooder, and like the rest of the Lake Victoria-Nabugabo flock it would have been a maternal mouthbrooder: the female takes the fertilised eggs into her mouth, where they are incubated and where the fry shelter for some time after hatching, with no parental contribution from the male. No clutch size, egg count or fry-development data have been published for this particular species. By the genus-typical standard of these haplochromines, broods are small - usually on the order of a few dozen eggs (roughly 20 to 80), a low fecundity that is offset by the protection mouthbrooding gives each egg and larva. This reproductive strategy, with the brooding female carrying her young into sheltered marginal and wetland habitats, is part of why some Nabugabo haplochromines were able to persist in vegetated refugia even as open-water populations collapsed - though there is no evidence that Haplochromis venator itself was among the survivors.
In the aquarium
Haplochromis venator is not an aquarium fish. It is a Lake Nabugabo endemic, never part of the ornamental trade, known almost entirely from museum specimens, and regarded as very likely extinct - so there is no husbandry tradition to report and no realistic prospect of keeping it. The note here is therefore about the wider group rather than the species. Lake Victoria-basin haplochromines that ARE kept (largely through conservation-oriented hobbyist and public-aquarium breeding programmes) are maintained much like their Lake Malawi relatives: hard, alkaline water around pH 7.5 to 8.5 and 24 to 27 degrees Celsius, a well-filtered tank with open swimming room, and the males-to-females ratio of a polygynous mouthbrooder (one male to several females) to spread aggression. Piscivorous members of the flock need length rather than mere volume, grow large by haplochromine standards, and will eat any tankmate small enough to swallow. For Haplochromis venator specifically, the responsible statement is the honest one: the place to conserve it would have been its lake, and that opportunity appears to have been lost.
Conservation
The IUCN Red List assesses Haplochromis venator as Endangered (criteria A1ace, B1+2cd), in an assessment by L. Kaufman dated 1 August 1996 and still current on the live Red List, which records the species from Uganda in inland wetland habitat. The Catalog of Fishes goes further and lists the species outright as extinct. The cause is the textbook tragedy of the Lake Victoria region: the introduction of the predatory Nile perch (Lates niloticus) to Lake Nabugabo in 1960 and 1963, compounded by the stocking of Nile tilapia, eutrophication and rising fishing pressure. Roughly half of Nabugabo's indigenous fish species disappeared from the open waters after the Nile perch became established, and as an open-water piscivore - occupying exactly the niche the perch seized - Haplochromis venator was among the most exposed. Studies of Nabugabo by Chapman, Ogutu-Ohwayo and colleagues have shown that some native haplochromines survived in marginal wetland refugia and have resurged since Nile perch numbers were fished down; whether venator persists anywhere in such a refuge, or has been lost entirely, is not established in the published record, and the safest reading is that it is at best critically imperilled and quite possibly already extinct. Its story stands as one small entry in the broader collapse of the Lake Victoria haplochromine flock, the largest documented vertebrate extinction event of modern times.