Taxonomy & naming
Haplochromis paraplagiostoma was described in 1969 by the British ichthyologist Peter Humphry Greenwood and his colleague J. M. Gee, in the Bulletin of the British Museum (Natural History) Zoology (volume 18, number 1, page 60, figure 35), as part of a revision of the Lake Victoria Haplochromis species flock. The holotype (BMNH 1968.8.30.127) and seven paratypes (BMNH 1968.8.30.128–134) are held in the Natural History Museum, London, and were taken west of Bulago Island in Lake Victoria (Victoria Nyanza), Uganda, at a depth of 70 feet (about 69 ft). The Catalogue of Fishes and van Oijen et al. (1991, in the CLOFFA checklist) both treat the name as valid in its original combination, Haplochromis paraplagiostoma Greenwood & Gee, 1969. The epithet is a deliberate signal of relationship: para- ('beside') prefixed to plagiostoma marks the fish as a near-relative or look-alike of the older Haplochromis plagiostoma Regan, 1922. The Lake Victoria flock has long strained the limits of a single genus, and many of its members are today distributed among segregate genera (Greenwood himself proposed several); this species is therefore frequently discussed under a modern lineage label, but it has never been formally recombined, so Haplochromis remains its valid genus.
Morphology
This is a small cichlid: the type series gives a maximum of 4 in standard length (snout to tail base), placing it among the more modestly sized members of the flock. Detailed morphometric and colour notes survive only in Greenwood & Gee's original account and are not widely reproduced; like most generalized Victoria haplochromines it would have been a laterally compressed, deep-bodied fish with the family's typical row of lateral blotches or bars and, in nuptial males, the iridescent blues and the red or yellow flush that drive the flock's explosive visual diversity. The name paraplagiostoma points to a resemblance to Haplochromis plagiostoma, a species characterized by a somewhat oblique, upward-slanted mouth. Beyond these points, fine diagnostic detail (tooth form, the exact pattern, live male colour) rests with the primary description and museum material rather than with any modern field photograph — no live image of the species is in general circulation, and FishBase carries none.
Habitat
Haplochromis paraplagiostoma is endemic to Lake Victoria, the largest of the African Great Lakes and the second-largest freshwater lake in the world by surface area, shared by Uganda, Kenya and Tanzania. The only documented record is the type material, taken west of Bulago Island in Ugandan waters over a mud bottom at roughly 69 ft; FishBase accordingly gives a depth range to about 69 ft and notes the species is 'known from only one locality.' That places it in the lake's sub-littoral zone — in the Witte school's scheme, Lake Victoria is divided into littoral (0–20 ft), sub-littoral (20–66 ft) and deep-water (>66 ft) regions, and this fish sits at the lower edge of the sub-littoral over soft sediment. Lake Victoria is a warm, well-buffered tropical lake: surface waters typically run about 73–81 °F and pH is circumneutral to alkaline, broadly in the 7.2–9.0 range across the basin, with the open lake tending toward the higher (more alkaline) end. No in-situ chemistry specific to the type locality was published with the description.
Feeding
The diet of Haplochromis paraplagiostoma has not been established. In Witte & van Oijen's standard classification of the Lake Victoria flock into fifteen trophic groups, this species is listed among the taxa of 'unknown' trophic group — its feeding ecology was never determined from stomach contents, a direct consequence of its being known from so little material. Its name invites comparison with Haplochromis plagiostoma, which falls within the lake's insectivore guild, and the oblique-mouthed body plan that comparison implies is consistent with picking small invertebrates from the substrate or water column rather than crushing snails or taking fish. FishBase's model-based estimate places it at a trophic level near 3.4, the value typical of a small invertebrate feeder. All of this is inference: the honest position is that no observed diet exists for the species, and any guild assignment is provisional pending fresh material.
Mating
No courtship or social behaviour has been described for Haplochromis paraplagiostoma specifically. It belongs to the Lake Victoria haplochromine radiation, in which mating behaviour is well studied at the group level: these are polygynous, lek-style breeders in which males establish and defend small territories, develop intense nuptial colour, and display to females with quivering and fin-flaring; egg-dummy spots on the anal fin feature in the spawning sequence of many members. Females are not territorial in the same way and move among displaying males. Whether this small mud-bottom species formed leks, displayed over open sediment, or paired more discreetly is unrecorded — the behavioural picture is drawn entirely from its better-studied relatives.
Breeding
Like the entire Lake Victoria haplochromine flock, Haplochromis paraplagiostoma is a maternal mouthbrooder: the female takes the fertilized eggs into her mouth and broods the clutch and the early free-swimming fry there, with no paternal care. The species' own clutch size and fry development were never recorded, but small Victoria haplochromines of this body size are typically modest-fecundity brooders, carrying on the order of a few dozen comparatively large eggs (roughly 20–80) — a labelled, genus-typical figure rather than a measurement for this fish. Brooding females hold the young until the yolk is absorbed and may continue to shelter free-swimming fry in the mouth when threatened. No spawning of this species has been observed in the wild or in captivity.
In the aquarium
Haplochromis paraplagiostoma is, for practical purposes, not an aquarium fish. It is known from a single old museum collection, has not been knowingly kept in the hobby, and may well be extinct in the wild, so there is no husbandry record to report and none of the location-variant trade that surrounds the popular 'Victorian Hap' cichlids applies to it. The fish reaching aquarists under the 'Lake Victoria Haplochromis' banner are a small set of hardier, more colourful survivors (and a few species maintained through conservation breeding programmes), not obscure mud-bottom forms like this one. The only honest general note is the one that applies to the whole flock: were such a fish available, it would call for hard, alkaline water (pH on the order of 7.5–8.5) at about 75–81 °F, an open sandy or fine substrate, and the spacious, structured tank that lets a male hold territory without lethal harassment of females and rivals. For this species in particular, none of that is more than hypothetical.
Conservation
The IUCN Red List assesses Haplochromis paraplagiostoma as Data Deficient (assessed 31 March 2010 by F. Witte and M. P. de Zeeuw): too little is known of its range, abundance and current status to assign a threat category, precisely because it is documented from a single old collection. The Catalogue of Fishes flatly lists its distribution as 'Lake Victoria; extinct,' and it is widely presumed lost, but the formal Red List position remains Data Deficient rather than Extinct. The context is the catastrophic decline of the Lake Victoria haplochromine flock: from the 1980s the introduced Nile perch (Lates niloticus), compounded by eutrophication, falling water clarity, and intense fishing, drove a collapse in which an estimated several hundred endemic haplochromine species declined sharply and many disappeared, one of the largest mass losses of vertebrate species in recorded history. A small, rarely collected, soft-bottom sub-littoral specialist of exactly this kind is among the most vulnerable to that pressure, which is why so few have been seen since.