Taxonomy & naming
Haplochromis nyanzae was described by the British ichthyologist Peter Humphry Greenwood in 1962, in the fourth instalment of his monographic revision of the Lake Victoria Haplochromis published in the Bulletin of the British Museum (Natural History), Zoology (volume 9, number 4, page 159, figure 6). That instalment dealt with the lake's large predatory haplochromines — the piscivores of the so-called 'serranus group' and their relatives — and nyanzae was erected as a new species among them. The holotype (BMNH 1962.3.2.495) and the paratype series were collected at and around Jinja, Uganda, at the northern outflow of the lake, with additional type material drawn from beaches in what were then Uganda, Kenya and Tanganyika (now Tanzania); the Catalog of Fishes accordingly fixes the type locality as Jinja, Lake Victoria. The genus Haplochromis as Greenwood used it has since been recognised as a vast, polyphyletic catch-all, and many Victorian species have been reassigned to segregate genera (Greenwood himself later split out Harpagochromis, Prognathochromis, Lipochromis and others for the predatory forms). Modern checklists nonetheless retain Haplochromis nyanzae in Haplochromis, and that is the heading used here; the binomial Haplochromis nyanzae Greenwood 1962 remains the valid, currently accepted name (FishBase; Catalog of Fishes; van Oijen et al. 1991, CLOFFA).
Morphology
Haplochromis nyanzae is a moderately large haplochromine, reaching about 6.5 in in standard length, placing it among the bigger members of the Victorian flock rather than the small rock- and sand-dwellers. Like the other large predatory haplochromines Greenwood treated alongside it, it has the build of a fish-eater: an elongate, fairly robust body, a large mouth and jaws, and unicuspid (or weakly bicuspid) teeth suited to seizing prey rather than the tricuspid scraping dentition of the algae-grazers. As is the rule across haplochromines, the lateral line is interrupted, divided into an upper and a lower portion. Detailed live colours were never recorded for this fish, which is known only from preserved museum material; like most haplochromines it would have shown the strong sexual dichromatism typical of the group, with breeding males assuming bright nuptial colours (and the genus-characteristic orange or yellow 'egg-spots' on the anal fin) while females and non-breeding fish remained a plainer silvery-brown. No reliable published account distinguishes the sexes of this particular species beyond that genus-typical pattern, so the specifics of its dimorphism are best treated as undocumented.
Habitat
The species is endemic to Lake Victoria, the great shallow lake shared by Uganda, Kenya and Tanzania and the cradle of the most spectacular cichlid species flock on Earth. Within the lake Haplochromis nyanzae was a fish of comparatively shallow, firm-bottomed inshore zones: FishBase, drawing on the CLOFFA treatment, records it from relatively sheltered or exposed areas over hard bottoms of sand or shingle, at depths down to about 20 ft. This is shallower, harder ground than the soft-mud and offshore habitats favoured by some of its congeners. Lake Victoria is a warm, well-oxygenated tropical lake; surface waters there typically run roughly 73–81 °F and the water is moderately alkaline, with pH on the order of 7.2 to 9.0 and conductivity reflecting a moderately mineralised, hard-water chemistry. No in-situ chemistry was published for this species specifically, so those figures describe the lake it lived in rather than measurements taken at its collecting sites.
Feeding
Haplochromis nyanzae was a piscivore — a fish-eater. The single most direct evidence is the gut contents of the type and reference specimens Greenwood examined: their stomachs contained the remains of fish identifiable as other Haplochromis. That places nyanzae squarely in the piscivore guild of the Lake Victoria haplochromine community, the trophic group that Witte and van Oijen, in their classification of the flock into fifteen (sub)trophic groups, termed the piscivores sensu stricto — predators that hunt and swallow whole smaller fishes, in this case largely the lake's own abundant smaller haplochromines. FishBase's model-based trophic-level estimate of about 4.2 is consistent with a top-level predatory diet. In a lake whose fish biomass was overwhelmingly made up of haplochromine cichlids, such intra-flock predators were a major link in the food web, and it was precisely this predatory guild that proved most vulnerable when a far larger non-native predator arrived.
Mating
No courtship or social behaviour was ever described for Haplochromis nyanzae itself; what can be said is inferred from the well-studied biology of the Lake Victoria haplochromine radiation to which it belongs. These fishes are maternal mouthbrooders with no pair bond. Ripe males establish and defend small temporary territories or courting stations, intensify into bright nuptial colour, and display to females — quivering, lateral presentation and 'leading' movements toward a spawning site — using the anal-fin egg-spots as a signal during the spawning act. Females visit, spawn, and depart to brood alone; males play no part in parental care and may court and spawn with several females in succession. Mate choice on the basis of male colour is thought to be one of the engines of the flock's explosive speciation. Whether nyanzae courted over its hard sand-and-shingle bottoms in the same way is plausible but unrecorded.
Breeding
Haplochromis nyanzae is, like essentially all Lake Victoria haplochromines, a maternal (female-only) mouthbrooder; FishBase records it simply as a mouthbrooder. After spawning, the female takes the fertilised eggs into her mouth and incubates them there through hatching and the early free-swimming stage, releasing the fry only when they are well developed and able to feed, and briefly re-admitting them to her mouth when danger threatens. No clutch size, egg size or brooding duration was published for this species. Among Victorian haplochromines of comparable body size, clutches are typically modest — on the order of a few tens of relatively large yolky eggs (frequently cited ranges run from roughly 20 to 80 eggs, scaling with female size) — a low-fecundity, high-investment strategy that is the haplochromine norm; those figures are offered here as genus-typical context, not as measurements of nyanzae. Parental care is entirely maternal and ends once the brood is released and independent.
In the aquarium
Haplochromis nyanzae is not an aquarium fish in any practical sense. It is known only from museum specimens collected in and before the early 1960s, it has no presence in the ornamental trade, and it may well be extinct in the wild. There is no body of hobbyist husbandry experience for it to draw on. The general picture for the Lake Victoria predatory haplochromines that are occasionally kept by specialists is informative by analogy: they are active, fast-growing maternal mouthbrooders that need a long tank with open swimming room and a sand or fine-gravel floor, hard alkaline water in the pH 7.5–8.5 range at roughly 75–81 °F, and — because the males are aggressive and the fish are piscivorous — careful stocking, typically one male with several females and no tankmates small enough to be eaten. None of that is a recommendation to seek out Haplochromis nyanzae, which is unavailable; it simply describes the kind of care its surviving relatives require. The honest statement for this page is that the species is effectively unkept and, in all likelihood, unkeepable.
Conservation
The IUCN Red List assesses Haplochromis nyanzae as Data Deficient (assessed 31 March 2010 by F. Witte and M. P. de Zeeuw), meaning that too little recent information exists to judge its status with confidence — the species has simply not been reliably recorded in modern surveys. Eschmeyer's Catalog of Fishes goes further and lists its status outright as extinct. The two assessments are not really in conflict: both reflect the catastrophe that overtook the Lake Victoria cichlid flock in the late twentieth century. Following the establishment of the introduced Nile perch (Lates niloticus), whose population exploded through the 1980s, an estimated 200 or more endemic haplochromine species vanished from the lake — one of the largest mass extinctions of vertebrates attributed to a single cause in modern times. The decline fell hardest on exactly the groups to which nyanzae belonged: the larger species and the piscivores, eaten by the perch and squeezed by concurrent eutrophication and the loss of water clarity. Some haplochromine groups — the zooplanktivores and detritivores in particular — showed a partial recovery as Nile perch catches fell in the 1990s, but many large predators did not reappear. Whether Haplochromis nyanzae survives in some refuge or is truly gone is unknown, which is precisely why it sits in the Data Deficient column — a fish described from a lake that, within a generation of its naming, was transformed beyond recognition.