Taxonomy & naming
Haplochromis gigas was described in 1998 by Ole Seehausen and Erwin Lippitsch in the landmark monograph 'Mbipi, the rock-dwelling cichlids of Lake Victoria' (Seehausen, Lippitsch, Bouton & Zwennes, Ichthyological Exploration of Freshwaters 9(2):129–228), the paper that erected three new genera and fifteen new species among the lake's rock cichlids. In that work the species was placed in the genus Neochromis, the assemblage of robust epilithic algae-scrapers, and Eschmeyer's Catalog of Fishes, the Cichlid Room Companion and most subsequent literature carry it as Neochromis gigas (Seehausen & Lippitsch, 1998). Like the rest of the Lake Victoria 'species flock', however, its generic placement is provisional: the explosive radiation that produced these fish is so recent and so reticulate that genus boundaries within the flock are notoriously unstable, and many databases — FishBase among them — retain the catch-all genus Haplochromis as a conservative heading. We follow that convention here while noting that Neochromis is the genus of the original description. Before formal naming the fish circulated among researchers under provisional 'working' labels of the kind Seehausen used throughout his 1996 field guide 'Lake Victoria Rock Cichlids'. The species belongs to the Haplochromini, the great mouthbrooding tribe whose Lake Victoria branch is thought to have radiated into several hundred species within roughly the last fifteen thousand years.
Morphology
Haplochromis gigas is a stout, fusiform haplochromine reaching about 5.5 in in standard length, with sexual maturity reported at around 4 in — making it the largest of the Neochromis-type algae-scrapers and the source of the epithet 'gigas', 'giant', which refers to its size relative to its small congeners rather than to any standing among Lake Victoria cichlids at large. The fin formula given in the original description is sixteen dorsal spines with nine to ten soft rays, three anal spines with nine to ten soft rays, and twenty-nine to thirty-one vertebrae. The mouth and jaws are those of a dedicated grazer: closely set, often bicuspid teeth packed into broad bands, the specialised scraping dentition that lets the fish rasp algae from rock. As in most haplochromines the sexes differ markedly in colour. Territorial males carry the bright nuptial livery typical of the rock cichlids, while females, subadults and non-territorial males are far more subdued and cryptic — the basis for the strong sexual dichromatism listed below. Detailed in-life colour notes for this particular species are thin in the public literature, and we decline to invent them; the diagnostic characters that separate it from its neighbours are primarily its larger size and the meristic and dental features of the formal description.
Habitat
The species is endemic to Lake Victoria and, within that vast lake, is known with certainty only from the Speke Gulf, the south-eastern arm on the Tanzanian side; reports elsewhere are unconfirmed. It is a rock-dweller — one of the 'mbipi', the Swahili-derived collective name Seehausen adopted for Lake Victoria's rock cichlids — and is found over and among rocky substrates rather than on open sand or mud. FishBase notes that it is more abundant on gently sloping rocky shores than on steep ones, a preference shared by several Neochromis-group scrapers because the broader, sun-lit horizontal rock surfaces of a gentle slope carry the richest growth of the epilithic 'algal lawn' or aufwuchs on which they feed. Its bathymetric range runs from the shallows down to about 13 ft, with the highest densities of related algae-scrapers concentrated in the brightly lit 3–7 ft band where algal productivity peaks. Lake Victoria is warm, hard, alkaline water: surface temperatures generally sit in the mid-20s Celsius and pH runs high, typically from about 7.2 up toward 9.0, conditions reflected in the parameters below.
Feeding
Haplochromis gigas is a herbivorous epilithic algae-scraper. FishBase records its diet simply as feeding on plants, and assigns it a trophic level of 2.0 — the value expected of a near-pure primary consumer. The genus Neochromis to which it belongs is defined ecologically by exactly this niche: the fish rasp the film of diatoms and filamentous algae growing on rock surfaces, using their broad bands of closely set teeth to scrape the aufwuchs free. Females, non-territorial males and subadults are frequently seen foraging together in loose groups over the rocks, while breeding males remain tied to their territories. This trophic role is worth emphasising because the species' name invites a misreading: 'gigas' has led to its being described in passing as a large piscivore, but the actual dietary and trophic evidence places it firmly among the algae-grazers of the rocky littoral, not the fish-eaters. In the lake's food web it functions as a grazer converting epilithic primary production into fish biomass, the same guild that includes the better-known 'blue scraper' and 'black nigricans' Neochromis forms of the same shores.
Mating
Like the other Lake Victoria rock cichlids, Haplochromis gigas has a polygynous, lek-like mating system built around male-held territories. Males establish and defend territories on the rock — in related Neochromis scrapers these are patches of horizontal or gently sloping bottom often exceeding a square metre — and advertise to passing females in their bright nuptial colours, chasing off rival males and other grazers that intrude. Females are not territorial in the same way; they range over the rocks, frequently in foraging groups with subadults and non-breeding males, and visit males' territories to spawn. As in the haplochromine tribe generally, courtship and fertilisation are tied to the male's anal-fin egg-spots and the female's immediate uptake of the eggs into her mouth (described under Breeding). Species-specific courtship detail has not been published for Haplochromis gigas itself; the account here is the well-documented pattern of the Neochromis rock-scraper group to which it belongs, and which the FishBase notes on territorial males and group-foraging females directly corroborate for this species.
Breeding
Haplochromis gigas is a maternal mouthbrooder, the reproductive mode shared by the entire Lake Victoria haplochromine flock. After spawning on the male's territory the female takes the fertilised eggs into her mouth and incubates them there, and she alone carries and broods the developing young — FishBase records 'mouth brooder with usually maternal parental care' and notes that the male's role ends with defending the spawning territory. The female then withdraws from the rocky breeding grounds to shallow water to release and guard her fry: FishBase reports that the brooding female guards her young in water often no more than half a metre deep, where she establishes a small temporary territory of her own. Specific clutch counts for Haplochromis gigas have not been published; among Lake Victoria rock-dwelling haplochromines of this size, broods are typically modest — on the order of a few dozen eggs — reflecting the trade-off mouthbrooders make between fecundity and the safety of oral incubation. Larvae complete yolk absorption inside the mother's mouth and are released as free-swimming fry that can shelter back in her buccal cavity when threatened, the standard haplochromine pattern.
In the aquarium
Haplochromis gigas is essentially an ichthyologist's and conservationist's fish rather than a hobby staple, and it is rarely if ever kept. It does not appear in the general aquarium trade; the Cichlid Room Companion treats it as a scientific species record, and unlike a handful of charismatic Lake Victoria haplochromines (the 'nyererei' and 'flameback' types) it has not entered hobbyist or public-aquarium breeding programmes in any documented way. No species-specific husbandry has been published, so anything written here is extrapolated honestly from its biology and from the keeping of related Lake Victoria rock-scrapers, not from direct experience with Haplochromis gigas. Were it ever maintained, it would need what those relatives need: a long, rockwork-dominated tank — realistically 47 in or more for a male and several females — aquascaped with stacked stone to provide algae-grazing surfaces and the broken sight-lines that defuse male aggression. The water should match the lake: hard, alkaline (pH well above 7.5) and warm, around 24–27 Celsius. These are aggressive, polygynous mouthbrooders, so the standard rule applies — keep one male with a group of females and avoid crowding two adult males, and never house Lake Victoria haplochromines where they could hybridise with congeners, a real risk in this readily-interbreeding flock. Diet should be predominantly vegetable: spirulina-based foods and algae rather than a protein-heavy regime, in keeping with its grazing gut. None of this should be read as encouragement to seek the species out; its conservation status makes responsible, record-kept maintenance the only justification for keeping it at all.
Conservation
The IUCN Red List assesses Haplochromis gigas as Vulnerable under criterion D2 (assessed 1 April 2010 by Witte, de Zeeuw & Brooks), the D2 listing reflecting a very restricted known range — effectively the Speke Gulf — that leaves the species exposed to stochastic threats over a short time frame. The assessment lists its threats as hybridisation driven by decreased water transparency, capture as bait for the long-line fishery, and agricultural and forestry effluents; the population trend is recorded as unknown. These pressures are the local face of the wider catastrophe that overtook Lake Victoria's cichlids in the late twentieth century. The introduced Nile perch (Lates niloticus) erupted across the lake from the 1980s and, together with eutrophication and the loss of water clarity from catchment deforestation and nutrient runoff, drove an estimated several hundred haplochromine species to extinction or near-extinction. Reduced transparency is doubly damaging to visually mating rock cichlids like this one: it does not only let perch ambush them, it collapses the colour signals that keep species reproductively distinct, so that formerly separate forms interbreed and merge — the hybridisation hazard the Red List flags here. That Haplochromis gigas persists at all places it among the survivors of that collapse, but as a narrow-range Speke Gulf endemic its long-term security depends on the recovery of the lake's clarity and the management of perch and pollution.