Taxonomy & naming
Jay Stauffer and Kenneth McKaye first described this fish in 1985 as Cyrtocara macrocleithrum, in the journal Copeia, working from material trawled out of the deep south end of Lake Malawi. Three years later, in their 1988 Copeia paper "Description of a genus and three deep water species of fishes (Teleostei: Cichlidae) from Lake Malawi," the same two authors erected the genus Alticorpus to hold a cluster of deep-living haplochromines and moved macrocleithrum into it. Because the species was named before the genus, its authorship carries parentheses — Alticorpus macrocleithrum (Stauffer & McKaye, 1985) — and that is how Eschmeyer's Catalog of Fishes lists it, valid in the family Cichlidae, subfamily Pseudocrenilabrinae. The holotype (USNM 268475) was taken at Cape Maclear at a depth of 246 ft.
The genus name is literal: Alticorpus blends the Latin altus (deep, high) with corpus (body), for the comparatively deep-bodied build shared across the group. Its type species is Alticorpus mentale Stauffer & McKaye, 1988, named for its prominent chin. The epithet macrocleithrum points straight at this fish's most distinctive feature — a 'large cleithrum,' the paired shoulder-girdle bone that here is hypertrophied to the point of deforming the body outline. Alticorpus is a small genus of roughly six valid species — Alticorpus mentale, Alticorpus macrocleithrum, Alticorpus peterdaviesi, Alticorpus profundicola, Alticorpus geoffreyi and their kin — all endemic to Lake Malawi and all tied to deep, offshore, sediment-bottomed water rather than the rocky shallows of the mbuna or the weed beds of the better-known 'haps.'
Molecular work has complicated the tidy Mbuna/non-Mbuna split that once seemed to track habitat. A 1994 mitochondrial DNA phylogeny of the Malawi haplochromine flock (Moran, Kornfield and Reinthal) placed Alticorpus — together with Aulonocara and Lethrinops — firmly nested within the Mbuna clade, the rock-dwelling radiation it looks nothing like ecologically. It is a reminder that 'Mbuna' and 'non-Mbuna' describe habitat and appearance more than ancestry: some soft-bottom and deep-water specialists, Alticorpus among them, trace their lineage back into the rocky-shore radiation rather than sitting outside it.
Morphology
This is a modest-sized cichlid with two outsized specializations. FishBase records a maximum of about 5 in standard length from the CLOFFA checklist, while the IUCN assessment and offshore-fishery work cite up to 7 in total length; the honest figure is a fish in the 5–7 in range, depending on whether you measure to the tail fork or the tail tip. The body is fusiform and laterally compressed, and the fin counts are unremarkable for a Malawi haplochromine (roughly 15–16 dorsal spines, 9–11 dorsal soft rays, 3 anal spines).
What sets it apart lies in the skeleton. The cleithrum — the curved bone that anchors the pectoral girdle to the back of the skull — is enormously enlarged, its lower tips drawn out into a point that protrudes as a clear bony prominence on the chest. Stauffer and McKaye noted that this bulge already shows in juveniles as small as 2 in, so it is a lifelong diagnostic trait rather than something that appears only in big adults. The second specialization is in the head: the cranial sensory pores and lateral-line canals are greatly enlarged, opening as conspicuous cavities across the snout, cheek and lower jaw. This is the hallmark of the whole genus, and the reason Alticorpus turns up so often in studies of cichlid sensory evolution. No sexual dimorphism is well documented — unsurprising for a fish that breeds in the dark, where the flamboyant breeding colors of shallow-water cichlids would be wasted.
Habitat
Alticorpus macrocleithrum is endemic to Lake Malawi and a genuine deep-water animal. FishBase gives a depth range of 98–492 ft, usually 197–492 ft; the IUCN assessment, drawing on demersal trawl surveys in the south of the lake, reports it from 115–453 ft and notes it is common between 90 and 420 ft. For perspective, the shallow reef community that draws aquarists and divers occupies roughly the top 98 ft. This fish lives below all of it, in water that is cold, dim to fully dark, and — below the lake's permanent oxycline — close to the limit of where fish can survive at all.
Its floor is soft sediment. The species is most strongly associated with bottoms of diatomaceous ooze — a fine, pale sludge of silica diatom skeletons that rains down and accumulates in the deep basins — though it is also taken over sand and mud. This is a benthic, sediment-sifting niche, not a rock or plant one. Like the rest of the Malawi fauna it lives in hard, alkaline water (the lake sits around pH 7.7–8.6), but the surface chemistry aquarists fuss over is only part of the story for a fish whose real environment is defined by depth, cold and the perpetual gloom of the deep lake.
Feeding
This is a benthic invertebrate feeder, and its anatomy reads as a sediment-processing toolkit. The IUCN assessment lists its diet as insect larvae, insects, diatoms and small fish — the menu of a fish that drives its snout into the soft ooze and works through it for buried prey. FishBase places it at a trophic level of about 3.5, consistent with an animal that takes mostly invertebrates with the occasional small fish rather than a dedicated piscivore; it lacks the heavy jaws of the specialist fish-eaters.
Two of its peculiarities make functional sense here. The hypertrophied cleithrum gives the pectoral girdle a large, distinctive anchor, and the working interpretation is that it provides leverage and strong pectoral musculature to back the fish out after it has driven its head down into the sediment — a useful trick if you make your living nose-first in soft mud. The cavernous head pores are exactly what you would build into an animal hunting in the dark: an expanded mechanosensory lateral-line system that picks up the faint water movements of invertebrates hidden in or on the bottom, where eyes are close to useless. In the deep lake, this fish hunts more by feel than by sight.
Mating
Almost nothing has been seen directly of courtship in Alticorpus macrocleithrum, for the obvious reason that no diver reaches its world; the fish is known mainly from trawl catches and preserved specimens. What can be said comes from fishery biology and from the strong family resemblance to the rest of the Malawi haplochromine flock. Like essentially all of them, it is a non-pair-forming mouthbrooder in which the sexes come together only to spawn, and the absence of obvious breeding dress fits a fish that pairs in water too dark for visual display to matter much.
The trawl study by Duponchelle and colleagues in the South West Arm of the lake found a clear breeding signal. The species appears to spawn seasonally, with the breeding season falling roughly between March and September, and spawning may take place at depths around 328 ft. So instead of the bower-building, color-flashing ritual of a shallow sand-dweller, the picture here is of a deep-water fish that ripens on a seasonal schedule and spawns in cold darkness on the lake floor.
Breeding
Alticorpus macrocleithrum is treated as a maternal mouthbrooder, in line with its relatives and with the limited reproductive data from the deep south of the lake. After spawning, the female is presumed to carry the developing eggs and larvae in her mouth, releasing free-swimming fry once they are large enough to fend for themselves — the standard Malawi haplochromine strategy, simply played out far deeper than usual.
The one hard number comes from the South West Arm trawl work of Duponchelle et al.: fecundity ranged from 96 to 304 eggs in females weighing between 26 and 76 grams. That is a moderate clutch of relatively large eggs, exactly what you expect of a mouthbrooder that invests in a few well-provisioned young rather than scattering many tiny ones. Beyond these figures the early life history is essentially undescribed; like most of the deep-water Malawi fauna, this fish has had its eggs counted in a fisheries lab but has never been watched breeding.
In the aquarium
For practical purposes, this is not an aquarium fish. Alticorpus macrocleithrum is a deep-water specialist caught by commercial demersal trawls, not by ornamental collectors working the reefs, and it does not appear in the hobby trade in any meaningful way. The few sources that mention it in an aquarium context — including FishBase's blanket 'aquarium: commercial' tag, applied broadly to Malawi cichlids — overstate how available or keepable it is. A fish adapted to life at 295–427 ft faces real problems on the way up: the pressure change of a trawl haul is hard on a deep-bodied cichlid, and even a healthy specimen would need the cold, dark, sediment-floored conditions that a typical brightly lit Malawi display tank cannot provide.
The useful way to think about it is as the deep-water counterpart to the haps and peacocks that hobbyists do keep. To understand the full Lake Malawi cichlid radiation, Alticorpus is the part of the story that happens off the bottom of the chart — the lineage that colonized the cold, lightless, soft-bottomed deep and rebuilt its sensory system to live there. It belongs in a serious keeper's mental map of the lake, even though it will almost certainly never belong in their tank.
Conservation
The IUCN Red List assesses Alticorpus macrocleithrum as Least Concern (assessed 22 June 2018, by Konings, Kazembe & Makocho; reviewed by Snoeks). The reasoning is that the species is endemic to Lake Malawi but widespread through its deep waters, so localised pressures are unlikely to dent the population as a whole; its population trend is listed as unknown, simply because the deep lake is so hard to survey. The assessment is candid that essentially no population data exist, and it names monitoring the trend as the priority action.
The one threat it does flag is specific and worth taking seriously: over-exploitation by the demersal (bottom) trawl fishery. Unlike the shallow reef cichlids, mostly caught incidentally by subsistence hook-and-line fishers, this is a deep-bottom fish that sits squarely in the path of the trawls working the south of the lake for food fish — and demersal trawling bears down hardest on exactly the slow-to-survey, slow-recovering deep communities that are least understood. That pressure sits inside a broader strain on the whole Lake Malawi/Niassa/Nyasa system, where fishing, catchment sedimentation and a warming, more strongly stratified water column are all documented. For a fish this specialized — tied to a narrow band of cold, deep, ooze-floored habitat and reproducing slowly in the dark — the honest reading is that it is secure on paper today but genuinely under-monitored, and that the deep trawl fishery is the pressure to watch.