Taxonomy & naming
Haplochromis sulphureus was described by the British ichthyologist Peter Humphry Greenwood and the Dutch morphologist Cornelis D. N. Barel in 1978, in the eighth part of Greenwood's long-running revision of the Lake Victoria Haplochromis species (Bulletin of the British Museum (Natural History), Zoology, volume 33). The holotype (BMNH 1977.1.10.106), together with a long series of paratypes, is held at the Natural History Museum in London; the type was taken in the Ugandan waters of northern Lake Victoria near 0°45'S, 32°38'E. The Catalog of Fishes still lists the species as valid in the catch-all genus Haplochromis. That placement is, however, an artifact of how little the Lake Victoria flock has been resolved. Greenwood himself, in his 1980 attempt to break the unwieldy genus into smaller, diagnosable units, split off many Victoria species into new genera, and the slender, large-eyed zooplankton- and insect-feeders of sulphureus's ecological type are the kind of fish later workers have discussed under names such as Yssichromis. No such recombination has been formally fixed for sulphureus, so the original binomial stands, and — following the convention used throughout this atlas for the Victoria, Edward and Kivu haplochromines — it is kept under the Haplochromis heading. The species belongs to the haplochromine tribe Haplochromini within the African cichlid subfamily Pseudocrenilabrinae.
Morphology
This is a small cichlid: the type series tops out at about 4.5 in in standard length, and most specimens are smaller. In life the fish is, as its name promises, sulphur-yellow — Greenwood and Barel chose the epithet for the sulphur-yellow adult coloration shown by both sexes, an unusual trait in a family where bright colour is normally a male advertisement and females stay drab. The body is the moderately deep, laterally compressed haplochromine form, with the large eye and somewhat oblique mouth typical of the flock's small invertebrate-feeders. Beyond the colour and a handful of meristic and osteological characters used in the original description to separate it from its many close relatives, little has been published on its external appearance, and no photograph of a living specimen appears to survive — FishBase carries only the generic cichlid placeholder. Sexual dimorphism in haplochromines is normally strong, with males developing nuptial colour and egg-spots on the anal fin; in this species the striking point is instead that the yellow ground colour is shared by both sexes, while finer differences in male nuptial pattern were not detailed at description.
Habitat
Haplochromis sulphureus is endemic to Lake Victoria, the vast, shallow equatorial lake shared by Tanzania, Uganda and Kenya, and was recorded across both the northern (Ugandan) and southern (Tanzanian, Mwanza Gulf) parts of the lake. It was a fish of open water over soft bottoms: FishBase, drawing on the original survey data, describes it as occurring in exposed areas with a soft mud bottom, and the close congeners described in the same revision were taken over mud in open but relatively sheltered water. Depth records are mixed and worth stating honestly — the holotype was collected from comparatively deep water, around 57 metres, while FishBase lists a benthopelagic depth range of about 16 to 20 metres for the bulk of the material; together these indicate a sub-littoral to offshore fish rather than a shoreline or rocky one. As a Lake Victoria endemic it lived in warm, well-buffered tropical hardwater: the lake's surface waters run roughly 75–81 °F and distinctly alkaline, with pH commonly around 8 to 9, very different from the soft, acidic blackwaters of the South American cichlids. These same open mud habitats were among the worst hit by the lake's late-twentieth-century deoxygenation and clouding.
Feeding
The species was an invertebrate feeder of the soft-bottom and open-water zone. The few specimens whose stomachs were examined contained the remains of dipteran (midge and related fly) pupae together with fragments of unidentifiable crustaceans — a diet of small benthic and drifting invertebrates that places it among the insectivore/zooplanktivore guild of the Victoria flock rather than among the snail-crushers, algae-scrapers, or fish-eaters. FishBase estimates a trophic level near 3.4, consistent with a small secondary consumer. Within Lake Victoria's haplochromine community these small invertebrate-feeders were enormously abundant and formed a critical link in the food web, converting insect larvae, zooplankton and bottom detritus into prey for larger predators; their collective biomass is exactly what the introduced Nile perch went on to exploit and then exhaust.
Mating
No courtship or pair-formation behaviour has been described for Haplochromis sulphureus specifically — it was named and characterized from preserved museum material, not observed in the wild or in aquaria. What can be said is drawn from the biology of the Lake Victoria haplochromines as a whole, which are overwhelmingly polygynous maternal mouthbrooders. In such fish, males establish small temporary territories or lek-like display areas and court passing females with quivering displays of nuptial colour, often using egg-spots on the anal fin as a spawning lure; females, having been courted and having spawned, take the eggs into the mouth and provide all subsequent care. The shared sulphur-yellow coloration of both sexes in this species is an intriguing departure from the usual sexually dimorphic colour signalling of the flock, but its behavioural significance was never studied before the population collapsed.
Breeding
Like the rest of the Lake Victoria haplochromine flock, Haplochromis sulphureus is a maternal (female) mouthbrooder: FishBase records mouthbrooding by females, and this reproductive mode is essentially universal across these cichlids. The female takes the fertilized eggs into her mouth and incubates them there through hatching and the early free-swimming stage, releasing the fry only when they can fend for themselves and taking them back in at any sign of danger. No clutch count, egg size, incubation period or fry-development data have been published for this particular species; the gap reflects how little it was studied before it vanished. As a guide, small Lake Victoria haplochromines of comparable size typically carry modest broods on the order of a few dozen relatively large, yolk-rich eggs — a low-fecundity, high-investment strategy that trades egg number for the safety of oral incubation. That strategy, ironically, offered no protection against a predator that simply ate the brooding adults.
In the aquarium
Haplochromis sulphureus is not an aquarium fish in any practical sense. It was never established in the hobby, it has no trade or common name, and — being assessed as Critically Endangered (Possibly Extinct) with no confirmed records in decades — it is almost certainly not available to aquarists at all. It is conceivable that it survives unrecognized in the broodstock of a haplochromine conservation programme, since several presumed-extinct Victoria species have turned up in captive 'survival' populations or been rediscovered in the lake, but there is no evidence that this particular species is among them. Anyone keeping Lake Victoria haplochromines should treat the husbandry needs as a guide to what this fish would have required: hard, alkaline water (pH roughly 7.5 to 8.5) at 75–81 °F, a long tank with open sand or fine substrate and broken sightlines, and a population structured to spread the relentless male aggression typical of the flock — one male to several females, or a crowded group, rather than isolated pairs. None of that, however, describes a fish you can actually buy; the honest position is that Haplochromis sulphureus belongs to the museum and the conservation record, not the home aquarium.
Conservation
The IUCN Red List assesses Haplochromis sulphureus 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; the assessment lists its range within Tanzanian waters of Lake Victoria. It is not listed by CITES. The species is one of hundreds of Lake Victoria haplochromine endemics caught in what is often called the most dramatic vertebrate mass extinction of modern times. From the 1950s onward the predatory Nile perch (Lates niloticus) was introduced and, by the 1980s, exploded across the lake, while at the same time rapid human population growth drove eutrophication, deoxygenation of deeper water, and clouding that collapsed the clear-water visibility on which the cichlids' colour-based mate choice depended. Open soft-bottom feeders like this one were among the most exposed, and surveys around Mwanza recorded the disappearance of much of this fauna by the mid-1980s; Haplochromis sulphureus has not been reliably recorded since. Some haplochromine trophic groups have partially recovered in the sub-littoral as Nile perch stocks were fished down, and a handful of 'lost' species have been rediscovered, so possible-extinction is not the same as confirmed extinction — but for this little-studied yellow cichlid the most likely status is that it is already gone.