Taxonomy & naming
Haplochromis rufocaudalis was described in 1998 by Ole Seehausen and Niels Bouton, in the landmark monograph 'Mbipi, the rock-dwelling cichlids of Lake Victoria: description of three new genera and fifteen new species' (Seehausen, Lippitsch, Bouton & Zwennes, Ichthyological Exploration of Freshwaters 9(2):129-228). It was erected not in Haplochromis but in the genus Neochromis, and the Catalog of Fishes treats Neochromis rufocaudalis Seehausen & Bouton, 1998 as the valid name to this day. The atlas keeps the 'Haplochromis' heading because the Lake Victoria flock is so densely interrelated that the great majority of its members were originally lumped under the catch-all genus Haplochromis, and the literature, the hobby and the older databases still file most 'furu' that way; the split into Neochromis, Pundamilia, Mbipia and other small genera (proposed in this same 1998 paper) reflects ecological and morphological clusters within that radiation rather than deep divergence. The holotype (RMNH 33221) and a large paratype series are held at the Naturalis collection in Leiden, with additional paratypes at TAFIRI in Tanzania. The type locality is the eastern shore of the Mwanza Gulf entrance, on the Bwiru Peninsula, Lake Victoria, Tanzania, taken at about one metre depth. Among Neochromis, rufocaudalis belongs to the algae-scraping guild and is closely allied to — and at some sites fully syntopic with — N. omnicaeruleus, from which it is most readily told apart by male nuptial colour.
Morphology
This is a small, robust cichlid: FishBase gives a maximum of about 4 in standard length, with sexual maturity reached at roughly 2.5 in. The body is fusiform and deep-headed in the manner of the rock-grazing haplochromines, built around a broad, ventrally set mouth packed with the closely spaced, often bicuspid teeth used to rasp algae from stone. Meristics from the original description run to 15-17 dorsal spines, 8-10 dorsal soft rays, 3 anal spines and 9-10 anal soft rays, with 28-30 vertebrae. As in nearly all haplochromines the species is strongly sexually dichromatic. Females, juveniles and non-territorial males are a cryptic brownish to grey, frequently barred — the drab livery that lets a foraging shoal blend into the algae-covered rock. Breeding males, by contrast, turn a bright metallic blue over the body and develop the feature that names the fish: a strongly reddened caudal (tail) fin, from the Latin rufus 'red' and cauda 'tail'. Seehausen and Schluter characterised rufocaudalis males simply as 'blue with red tail', distinguishing them at a glance from the syntopic, blue-tailed N. omnicaeruleus. As in several Lake Victoria rock cichlids, some populations also carry an orange-blotched (OB) colour morph, expressed mainly in females.
Habitat
Haplochromis rufocaudalis is endemic to Lake Victoria, the great shallow East African lake shared by Tanzania, Uganda and Kenya. It is a 'mbipi' fish — one of the haplochromines specialised on the lake's rocky shores and isolated rocky islets, which function as habitat 'islands' separated by stretches of sand and open water. FishBase records it from the shallow waters of most rocky areas, and the original material and subsequent ecological work centre on the Mwanza Gulf and nearby islands such as Makobe in the lake's southern (Tanzanian) sector. It is a shallow-water specialist: the type series was collected at about one metre, brooding females are reported among rock boulders in very shallow water, and the documented occurrences cluster within the uppermost few metres of the rocky littoral rather than in deep water. Lake Victoria's surface waters are warm and alkaline — broadly pH on the order of 7.2-9.0 and temperatures around 23-27 C — and these mineral-rich, hard, well-lit conditions are what the species is adapted to. The exact depth band has not been published as a precise range, but all the field evidence places it in roughly the 0–10 ft shallow rock zone.
Feeding
Haplochromis rufocaudalis is an epilithic-algae grazer — it feeds predominantly on the algal felt that coats the submerged rocks, scraping the 'aufwuchs' from stone surfaces with its broad, tooth-studded jaws. FishBase places its trophic level at about 2.0, the floor of the scale and exactly what is expected of a near-strict herbivore/detritivore working the rock film; incidental small invertebrates living within the algal mat are taken along with the plant matter. Foraging is social: females, subadults and non-territorial males move over the rocks in shoals of size-matched individuals, a grouping that both improves grazing access against territory-holders and dilutes predation risk in the open shallows. The species shares this algae-scraping niche with its close relative N. omnicaeruleus and with other mbipi grazers, and the partitioning of so many similar species onto the same rocks is part of what makes the Lake Victoria rock-cichlid community a textbook case of explosive adaptive radiation.
Mating
Reproduction is organised around male-held breeding territories on the rock. Mature males stake out and defend spawning sites against rival conspecific males and against males of other Neochromis species, and it is here that the blue body and red tail do their work: the nuptial colour is a signal in male-male competition for territory as much as a cue to females. Seehausen and Schluter (2004), mapping a 256 m2 spawning site at Makobe Island by scuba, found that territory holders are spaced by colour — a red-tailed rufocaudalis male is less likely to sit next to another red-tailed male than chance would predict, and more likely to abut a differently coloured (blue-tailed omnicaeruleus) neighbour. They argued that this male-male competition, by giving rare colour morphs a breeding-site advantage, is itself a force driving the diversification of nuptial colour and ultimately speciation in the Victoria flock. Females and non-territorial fish remain in their wandering shoals, visiting the territories of displaying males to spawn.
Breeding
Like virtually all Lake Victoria haplochromines, Haplochromis rufocaudalis is a maternal mouthbrooder with no paternal care. A male courts a ripe female over his territory; she lays a small clutch of eggs and takes them immediately into her mouth, where the classic haplochromine egg-spot mechanism aids fertilisation. The female then carries and broods the developing eggs and larvae orally for the incubation period, releasing free-swimming fry once they are developed and continuing to offer them mouth shelter when threatened in the early days. A species-specific clutch count has not been published, but mbipi haplochromines of this size are small-clutch brooders, typically laying on the order of a few dozen eggs (roughly 10-40) — the trade-off of mouthbrooding, where fecundity is sacrificed for the survival of well-guarded young. Brooding females are found among rock boulders in very shallow water, where the warm, oxygen-rich shallows suit the incubating clutch. Beyond oral incubation the female gives no nest care, and the male contributes only the genes and the defended spawning patch.
In the aquarium
Haplochromis rufocaudalis is one of the relatively few Lake Victoria rock cichlids that reaches the hobby, where it is sometimes traded under the misleading label 'Nigricans'; even so it is uncommon and is mostly a fish for keepers who specifically seek out Victorian haplochromines rather than a general-stock aquarium cichlid. Its needs follow directly from the wild biology. House it as a harem — the standard advice is one male to at least three or four females, because a single male will relentlessly harass a lone female during breeding and can injure or kill her. Give it a hard, alkaline tank (pH roughly 7.5-8.5, moderately high hardness) at about 24-27 C, mirroring the lake's mineral-rich shallows; aquarium guidance for Victorian cichlids generally is to keep pH stable between about 7.2 and 8.6 and to change conditions only gradually. The layout should be a rock aquascape with caves and crevices over a fine substrate, both to provide the algae-grazing surfaces and territorial boundaries the fish expects and to give subdominant fish and harassed females places to retreat. A tank of around 47 in / four feet or more suits a colony better than anything cramped, since the action is all about defended territories. Diet should be vegetable-forward — a quality spirulina or algae-based flake or pellet, since this is a near-strict herbivore, with only sparing animal protein; a fatty, meat-heavy diet is a poor match for a fish built to rasp algae. The major husbandry caution, beyond water chemistry, is conspecific aggression and hybridisation: closely related Victorian haplochromines interbreed readily in tanks, so a species-maintenance keeper should not mix rufocaudalis with congeners such as N. omnicaeruleus if pure offspring are the goal.
Conservation
The IUCN Red List assesses Haplochromis rufocaudalis as Least Concern, assessed on 1 April 2010 (published 2016) by Witte, de Zeeuw and Brooks, with a population trend recorded as stable; it carries no CITES or CMS listing. As a shallow rock-shore specialist confined to hard rocky substrate, it was less exposed than the lake's open-water and soft-bottom haplochromines to the catastrophe that overtook Lake Victoria in the late twentieth century, when the introduced Nile perch (Lates niloticus), combined with eutrophication, falling water clarity and overfishing, drove a large fraction of the endemic cichlid flock to extinction or collapse. The rocky 'mbipi' habitat offered both physical refuge from the perch and the structurally complex, well-lit conditions algae-grazers need, and species like rufocaudalis persisted where pelagic relatives did not; secure populations are reported throughout the Mwanza Gulf. That relative security is not unconditional, however — the lake remains under pressure from nutrient loading, shoreline change and the long shadow of the Nile perch, and because clear water is essential to the visual mate-choice that keeps these closely related species distinct, declining water clarity poses a subtler long-term threat of hybridisation and species collapse across the whole rock-cichlid community.