Taxonomy & naming
Ethelwynn Trewavas described this fish in 1935 as Haplochromis orthognathus, in her landmark synopsis of the cichlid fishes of Lake Nyasa — the older name for Lake Malawi — published in the Annals and Magazine of Natural History (Series 10, volume 16, pp. 85 and 99). The type series came from the South West Arm of the lake, in what Trewavas recorded as 'rather deep water'; the Natural History Museum in London holds the lectotype (BMNH 1935.6.14.1336) and three paralectotypes (BMNH 1935.6.14.1337–1339). For half a century it sat, like most of Malawi's haplochromines, inside the catch-all genus Haplochromis, and older aquarium and museum literature still lists it that way.
Eccles and Trewavas erected the genus Caprichromis for it in their 1989 monograph, Malawian Cichlid Fishes: The Classification of Some Haplochromine Genera, designating Haplochromis orthognathus as the type species. Eschmeyer's Catalog of Fishes lists the name as valid: Caprichromis orthognathus (Trewavas, 1935), family Cichlidae, subfamily Pseudocrenilabrinae. The genus name pairs the Latin capra ('she-goat') with chromis, an old word for a perch-like fish — a nod to the steep, butting set of the snout — while the epithet orthognathus, from the Greek orthos ('straight') and gnathos ('jaw'), points to the same near-vertical mouth. Caprichromis is a small genus of just two species; its only congener is Caprichromis liemi, which differs in having thinner gums, more visible teeth and a slightly less steeply angled jaw.
Morphology
Caprichromis orthognathus is a modestly sized, elongate haplochromine. FishBase records a maximum of about 7.5 in total length, citing the CLOFFA checklist, so this is a medium-small Malawi 'hap' rather than one of the lake's giants. The body is fairly slender and laterally compressed, in keeping with a fish that spends much of its time hovering in open mid-water rather than wedged among rocks.
The defining feature is the head. The mouth is set at a steep, almost vertical upward angle, and the gums are notably thick with the teeth largely hidden — a blunt, reinforced snout rather than a delicate grasping one. That construction separates it from its congener Caprichromis liemi, in which the jaws are less steeply pitched and the teeth more exposed. The steep jaw is not decoration: it is the business end of the fish's feeding behavior, a battering ram aimed upward at the chin of a brooding female. As with most Malawi haplochromines, dominant males in breeding condition flush with color and carry egg-spot ocelli on the anal fin, while females and subordinate males stay comparatively plain — useful when sexing a group, since the genus is uncommon and easily confused with other slim, open-water haps.
Habitat
Caprichromis orthognathus is endemic to the Lake Malawi basin. The IUCN assessment lists it from Lake Malawi itself and from Lake Malombe, the shallow satellite lake downstream on the upper Shire River, with a range spanning the Malawi, Mozambique and Tanzania shores. The type series came from the South West Arm of the lake, the same productive southern basin — anchored by Monkey Bay and the Nankumba Peninsula — that yielded so many of the species Trewavas described in 1935.
FishBase classes the fish as benthopelagic and reports that it is most commonly recorded off sandy beaches at depths of around 49 ft, though it occurs in both shallow and deep water and is usually seen in mid-water, sometimes ranging over rocks. That open-water, sand-associated habit fits its predatory lifestyle: a paedophage that hunts brooding females needs room to maneuver and approach from below, not the tight cover of a rock reef. Like the rest of the Malawi fauna it lives in hard, alkaline water — pH roughly 7.7–8.8 and temperatures of about 75–82 °F — the famously stable, mineral-rich biotope chemistry that any captive setup must reproduce.
Feeding
This is where Caprichromis orthognathus earns its reputation. It is a paedophage — a specialist that feeds on the eggs and larvae of other cichlids — and it has one of the most aggressive ways of getting at them. FishBase places it at a high trophic level of about 4.0 and reports that, although feeding on the larvae has not been directly observed in the act, the species is understood to ram the head of a mouth-brooding female from below. The blow forces the startled mother to gape, spilling some of the developing young she is carrying, which the attacker then snaps up. The steep, reinforced upward-angled jaw and the thick, padded gums are the anatomy of that head-butt.
Paedophagy has evolved repeatedly in Lake Malawi's enormous cichlid flock, and the lake hosts several unrelated lineages that exploit the same rich, defenseless resource — a mouthful of larvae represents a concentrated, pre-packaged meal. What sets the Caprichromis strategy apart is its mechanical directness: rather than sneaking eggs during a spawning sequence, or engulfing a whole brooding female's head as some larger predators do, it physically jolts the clutch loose. The recently described Protomelas krampus (Dierickx & Snoeks, 2020) is another Malawi paedophage, and behavioral parallels have been drawn between these ram-feeding egg- and larva-robbers — a reminder that in a lake this crowded, even the act of guarding young in the mouth has spawned its own guild of specialized thieves.
Mating
Like essentially all of Lake Malawi's haplochromine cichlids, Caprichromis orthognathus is a polygynous, non-pair-forming species: there is no lasting bond between male and female, and the male's role ends at fertilization. In breeding condition a dominant male intensifies in color and courts ripe females with the quivering, circling displays typical of the lake's haps, leading a receptive female through the spawning sequence over open or sandy substrate rather than on a built bower of the kind mbuna favor.
Because the genus is uncommon in the wild and rare in the hobby, the fine detail of its courtship is poorly documented compared with showpiece haps like the eyebiter or the peacocks. What can be said with confidence is that it follows the standard Malawi maternal-mouthbrooding template, in which the anal-fin egg spots of the male play their role in the egg-dummy ritual at spawning — the same mechanism the fish itself exploits, with grim irony, when it later raids the broods of its neighbors.
Breeding
Caprichromis orthognathus is a maternal (female-only) mouthbrooder, the reproductive mode shared across the Malawi haplochromine radiation. The female lays a small clutch, takes the eggs into her mouth almost at once, and draws in the male's milt by nipping at the egg-spot ocelli on his anal fin, fertilizing the eggs she is already carrying. She then broods the developing embryos and larvae in her buccal cavity for roughly three weeks, not feeding while she carries them, before releasing free-swimming fry.
That very strategy is what makes brooding females across the lake vulnerable to paedophages like this one — a mouth full of larvae is a defenseless, calorie-dense target. There is little published aquarium breeding data for the species, owing to its scarcity in the trade, but its reproductive biology is expected to mirror that of other slim, open-water Malawi haps: a modest clutch, a multi-week brooding period, and fry large enough at release to take small live and prepared foods immediately. A brooding female should be given quiet, low-traffic space, since the same head-ramming pressure she would face in the wild can be mimicked by boisterous tankmates in a crowded aquarium.
In the aquarium
Caprichromis orthognathus is a genuine specialist's fish, only occasionally available, and it is not a beginner's Malawi hap. It is a predator of other fishes' young, which shapes everything about how it should be housed: a single male with several females, in a roomy tank with a sand substrate, open swimming water in the mid-column, and some structure around the edges — the open, sand-associated mid-water it occupies in the lake, not a wall-to-wall rock pile. Because adults reach around 8 in and the fish ranges through mid-water, a long four- to six-foot tank is the sensible floor, with hard, alkaline Malawi water (pH comfortably above 7.5) at roughly 75–82 °F (75–82 °F) and the strong filtration the genus's clean native zone implies.
Feeding a captive Caprichromis is straightforward where it would otherwise be macabre: deprived of brooding females to raid, it readily takes quality cichlid pellets and meaty frozen foods, and there is no need to supply living broods. The real planning is in tankmate choice. Mixing it with actively mouthbrooding females of other species invites exactly the larva-robbing behavior it is built for, so a display intended for breeding other haps is a poor fit. Pair it instead with similarly sized, robust Malawi haps that are not in constant brooding cycles, avoid the delicate and the much smaller, and accept that any small fish in mid-water is, to this animal, potential food. Kept well, it is a fascinating, understated fish whose interest lies less in color than in watching a living illustration of one of Lake Malawi's most pointed evolutionary specializations.
Conservation
The IUCN Red List assesses Caprichromis orthognathus as Least Concern (assessed 22 June 2018, published 2019, by Konings, Kazembe & Makocho). The reasoning is the familiar one for a widespread Malawi hap: the species ranges across the lake and into Lake Malombe, spans the Malawi, Mozambique and Tanzania shores, and faces no specific, species-level threat severe enough to warrant a higher category. Its population trend is not flagged as declining, and it is not a targeted commercial or aquarium fish in any volume.
That secure listing, as always, describes the fish and not the lake. The Lake Malawi/Niassa/Nyasa basin is under real and growing strain — over-fishing and the collapse of the chambo tilapia fishery, heavy sediment and nutrient loading from deforested catchments, and measurable warming of the shallow upper layer that strengthens stratification and trims productivity. For a mid-water predator whose whole living depends on the abundance and brooding activity of other cichlids, those pressures matter at one remove: a less productive, more disturbed lake with fewer breeding haplochromines is a poorer hunting ground for a paedophage. The honest summary is the usual divided one for Malawi's endemics — the species itself is judged secure today, but it is bound tightly to the health of a crowded, productive lake that is being squeezed, and a specialist this finely tuned has little room to adapt if that community thins.