Taxonomy & naming
Otopharynx ovatus was originally described as Haplochromis ovatus by Ethelwynn Trewavas in 1935, in her work on the cichlid fishes of Lake Nyasa (now Lake Malaŵi); the parentheses in the current binomial record its later transfer from the catch-all Haplochromis to Otopharynx. Eschmeyer's Catalog of Fishes lists it as valid as Otopharynx ovatus (Trewavas, 1935), in the family Cichlidae, subfamily Pseudocrenilabrinae. The genus Otopharynx Regan, 1920 is diagnosed by a melanic colour pattern of three discrete dark blotches — a suprapectoral spot, a supra-anal spot and a spot on the caudal peduncle — and ovatus is one of the species whose pattern Oliver (2018) cited as essentially identical to that of Otopharynx lithobates and Otopharynx brooksi. The specific epithet ovatus is Latin for 'egg-shaped' or 'ovate', describing the body outline. The type locality is the southern end of Lake Malaŵi, and the species is recorded from the southern part of the lake.
Morphology
Otopharynx ovatus is among the larger species of its genus, reaching about 8 in total length according to FishBase. As its name suggests, it has an ovate, deep-bodied and laterally compressed outline, with the generalised haplochromine head and a mouth suited to taking soft prey. The defining external markings are the genus's three dark melanic blotches — suprapectoral, supra-anal and on the caudal peduncle — borne over a ground colour that, in nuptial males, takes on the metallic blue and yellow tones characteristic of the Malaŵi flock. As is typical of these haps, dominant males in breeding condition are markedly more colourful than females and subordinate males, and the live male pattern is the most reliable field character; preserved specimens are separated from close relatives by fine counts and proportions.
Habitat
The species is endemic to Lake Malaŵi and is recorded from the southern part of this large, deep rift lake. FishBase describes it as a freshwater, demersal cichlid that is normally seen in midwater over rocks or sand — that is, hanging above the substrate in the intermediate zone rather than resting on it, a position that suits a fish on the lookout for spawning activity below. FishBase's husbandry-oriented figures give the species' tolerances as roughly pH 7.0–8.5, hardness around 12–20 dH and temperatures of about 75–79 °F, the warm, clear, strongly alkaline conditions of Lake Malaŵi's inshore waters under which the whole species flock evolved.
Feeding
Otopharynx ovatus is a paedophage — an eater of the eggs and young of other cichlids. FishBase states plainly that it 'feeds on the eggs of other cichlids', and its habit of cruising in midwater over rock and sand fits that strategy: such a fish patrols above the substrate watching for mouthbrooding females and spawning pairs, then darts in to snatch eggs or larvae. Egg- and larvae-robbing is a recurring specialisation in the Lake Malaŵi flock, where the sheer density of mouthbrooding cichlids makes their broods an abundant, if well-guarded, food source. This places ovatus among the more specialised feeders of its genus, in contrast to the small-fish-hunting Otopharynx brooksi or the generalist benthic foragers. Konings makes the point explicitly: of all the described Otopharynx, ovatus is the single exception that does not feed from the bottom — every other species in the genus is a benthic forager, while ovatus alone has taken up this midwater, egg-stealing habit.
Mating
Spawning behaviour has not been described in detail for ovatus, but it shares the reproductive biology of the Lake Malaŵi haplochromines: maternal mouthbrooding with polygynous, lek-style courtship. A mature male in nuptial colour holds a territory or display site and courts females with lateral displays and quivering; a receptive female lays a small clutch and immediately takes the eggs into her mouth, the male's anal-fin eggspots mediating fertilisation as she snaps at them. There is a certain irony in an egg-eating species relying, like its prey, on oral incubation to protect its own offspring. Males provide only display and genes, with no role in brood care — the standard arrangement across the flock, inferred here for ovatus.
Breeding
Breeding has not been documented in detail for Otopharynx ovatus specifically, but as a Lake Malaŵi haplochromine it is a maternal mouthbrooder. The female incubates the fertilised eggs in her buccal cavity for roughly three weeks, fasting throughout, then releases free-swimming fry that she continues to shelter in her mouth when threatened. Clutch sizes in haps of this size are typically modest — a few dozen eggs — trading fecundity for the strong survival advantage of oral incubation, which is itself the very defence that paedophages such as ovatus try to defeat in other species. Specific clutch size, incubation period and fry behaviour for ovatus remain unrecorded; the account here is inferred from the genus and the wider flock.
In the aquarium
Otopharynx ovatus turns up in the aquarium trade — FishBase notes it is of commercial interest both as a food fish and as an ornamental — but it is not a hobby mainstay and there is limited published keeping experience specific to it.
A fish of about 8 in needs a large tank with a sand substrate and rockwork recreating its natural rock-and-sand zone, and crucially plenty of open midwater swimming space, since this is a fish that naturally hovers above the bottom. Lake Malaŵi conditions apply: hard, alkaline water (pH about 7.5–8.5), stable temperatures in the mid-20s Celsius and strong filtration with consistently clean water. Its natural diet of eggs and larvae translates in captivity to a carnivorous menu of quality pellets and meaty frozen foods; as a known paedophage it will readily eat the eggs and fry of tankmates, so it is a poor choice for a community breeding tank. It is best kept with robust, similarly sized cichlids that are neither small enough to be harassed nor likely to have their broods raided. In short, a handsome but specialised and fairly large hap for the experienced Malaŵi keeper.
Conservation
Otopharynx ovatus was assessed by the IUCN Red List as Least Concern in 2018. That status reflects a reasonably wide occurrence across the southern part of a very large lake and no specific identified threat, rather than detailed population data. The broader Lake Malaŵi picture warrants caution: the lake supports the most species-rich freshwater fish fauna on Earth, almost entirely endemic, and the 2018 Red List assessment of its fishes found a significant share at elevated risk from intense fishing pressure, inshore habitat degradation and sedimentation. As a fairly widespread, mobile midwater predator, ovatus is not currently of conservation concern, but its long-term prospects — like those of the whole flock — depend on the continued health of Lake Malaŵi's inshore ecosystem.