Taxonomy & naming
Serranochromis cacuchi was described in 2021 by Jay R. Stauffer Jr., Roger Bills and Paul H. Skelton in the journal Zootaxa, in a paper that simultaneously named four new Angolan largemouths — Serranochromis swartzi, Serranochromis cuanza, Serranochromis alvum and Serranochromis cacuchi — from the Cuanza and Okavango drainages and set out a preliminary identification key for the whole genus. The holotype, an adult male of 7 in standard length (SAIAB 186684), was netted with four paratypes (SAIAB 186674, 5–7.5 in) from the Cacuchi River at the road bridge roughly 9 mi southwest of Chitembo Village, on the main road north from Menongue, by R. Bills, P. H. Skelton and F. de Almeida on 11 May 2012. The Cacuchi is a tributary of the Cuchi, part of the Cubango (Okavango) River system in southeastern Angola. The specific name is a noun in apposition referring to that river, where the species is most likely a narrow endemic. No earlier names apply, so the species has no synonymy, and the Catalog of Fishes lists it as valid as Serranochromis cacuchi Stauffer, Bills & Skelton 2021. The genus Serranochromis was erected by C. Tate Regan in 1920 and last revised in full by Ethelwynn Trewavas in 1964; it belongs to the African cichlid subfamily Pseudocrenilabrinae and to the serranochromine lineage of riverine haplochromines that radiated across the Zambezi, Okavango, Cunene and upper Congo systems. The describers place Serranochromis cacuchi in the genus on a suite of shared characters — four or five scale rows between the orbit and the ascending arm of the preoperculum, widely spaced unicuspid (canine-like) jaw teeth, widely separated gill rakers, and egg-spot ocelli on the anal fin. They diagnose it against its congeners chiefly by the ocelli being spread throughout the anal fin of breeding males (versus restricted to the rear membranes in Serranochromis robustus and Serranochromis jallae), its exposed rather than lip-buried teeth, an emarginate caudal fin, a short jaw (47.8–52.3 % of head length), a shallow 25-degree gape, and a relatively wide interorbit (20.0–21.7 % HL). Its discovery is part of a broader wave of ichthyological exploration of the Angolan highlands, the source region of the Okavango, where drainage isolation appears to have splintered the serranochromines into many narrowly distributed species.
Morphology
This is a slender, fusiform, laterally compressed cichlid, deepest at the start of the dorsal fin, with an elongate, pointed head a little over a third of the standard length and a predorsal profile rising at about 30 degrees to a shallow kink at the interorbit. The known specimens span 5–7.5 in SL, so the recorded maximum is about 7.5 in SL (FishBase, from the paratype series) — and as a member of a genus whose larger species exceed 15.5 in, the species may well grow bigger than the modest type series suggests. The mouth is the genus hallmark: terminal, large and protrusible, the lower jaw 47.8–52.3 % of head length, armed with exposed, narrowly spaced caniniform teeth in two rows on the upper jaw and two or three on the lower, set at a shallow 25-degree gape. The eyes are large and high-set, the snout long (35.2–39.6 % HL, two to three times the orbit diameter), and the caudal fin is broad, short (around half the head length) and emarginate. Fin counts run to XIV–XV dorsal spines and 12–13 soft rays, three anal spines and nine anal soft rays, with 32–33 lateral-line scales and four to five rows of scales on the cheek. Coloration is where the fish stands out. The preserved holotype is shades of brown and grey, but in life the head carries a dark interorbital and a dark bar from the orbit to the rear maxilla, a white gular region, green-blue highlights and small orange-red spots on the cheek and gill cover, and a dark opercular spot. The flanks are yellow to light green below, whitish on the belly and dark olive-grey across the back, crossed by a single thin lateral band and eight or nine short bars, with dark orange-red spots in the centre of each scale forming eight to ten longitudinal rows and blue-green highlights between them. The soft dorsal and its lappets are tipped bright red with a pale blue submarginal band; the anal fin is yellow-cast with rows of two to five red ocelli (egg spots) along the membranes. As in other mouthbrooding haplochromines, this bright dress is the nuptial coloration of breeding males; females and non-nuptial fish are far plainer.
Habitat
Serranochromis cacuchi is, on present evidence, a point endemic, known only from its type locality on the Cacuchi River — a tributary of the Cuchi, in the Cubango (Okavango) headwaters of interior southeastern Angola. That places it in the rain-fed Angolan highland catchment whose flood pulse sustains the great inland Okavango Delta far downstream in Botswana. Unusually for a largemouth, the describers found it in genuinely rheophilic conditions: the Cacuchi at the collection site is a fast-flowing, rocky-substrate river with several channels, only one of which was flowing at the time of sampling. The type specimens were taken in the margins of the main rocky channel, from deep boulder crevices, using electric fishing and large hand D-nets, at water depths of roughly 2–3 ft. No in-situ water chemistry was published with the description, but the Okavango headwaters of the Angolan highlands are clear, soft, weakly mineralised Kalahari-sand and rock rivers; by the general standards of the region, suitable water would be warm and run roughly pH 6.5–8.0 at about 68–82 °F. Whether the species is genuinely confined to this single rocky reach or simply under-sampled across the poorly surveyed Angolan Okavango headwaters cannot yet be said — much of the basin has never been collected, and the sister species described alongside it are likewise each known from one locality.
Feeding
No gut contents have been examined for Serranochromis cacuchi specifically, so its diet is inferred from its anatomy and from the well-documented ecology of the genus. Serranochromis are the "largemouths" of south-central Africa precisely because they are ambush piscivores: the big protrusible mouth and exposed, widely spaced canine teeth are the equipment of a fish that seizes and holds slippery prey. Across the genus the larger species feed predominantly on smaller fishes, supplemented by aquatic insects, snails and crustaceans, with the diet broadening in the younger and smaller-bodied forms. FishBase places Serranochromis cacuchi at an estimated trophic level of about 3.8, squarely in the predator range, a figure derived from its size and the trophic ecology of its closest relatives. In the rocky, fast channel where it was found, Serranochromis cacuchi would function as a mid-sized predator hunting from the cover of the boulder crevices it was netted in — exactly the structured habitat that other Serranochromis use to ambush small fishes and invertebrates. Until specimens are dissected, however, the precise composition of its wild diet remains an informed extrapolation rather than an observation.
Mating
The reproductive behavior of Serranochromis cacuchi has not been observed; what follows is drawn from the consistent pattern across Serranochromis and the serranochromine haplochromines. These are maternal mouthbrooders, and the genus is characterised by seasonal breeding tied to the flood cycle, with spawning generally beginning around the end of the low-water period as rivers and floodplains start to fill. Males develop the bright nuptial coloration — here the orange-red scale spotting, blue-green highlights, red-tipped dorsal and anal-fin ocelli — and take a territory, courting and displaying to females rather than forming a lasting pair bond. The egg-spot ocelli that spangle the male's anal fin are the classic haplochromine courtship device: as the female mouths at the spots she is induced to take up the male's milt, fertilising the clutch she already carries. The spread of these ocelli throughout the anal fin of breeding males, rather than only across the rear membranes as in some relatives, is one of the species' diagnostic traits and presumably figures in this courtship signalling. After spawning the male's involvement ends; parental investment falls entirely to the female.
Breeding
Direct breeding observations of Serranochromis cacuchi are lacking, but its mode is not in doubt: like all Serranochromis it is a maternal mouthbrooder. The female takes the fertilised eggs into her mouth and incubates them there through hatching and the early larval stage, the brood sheltered in the buccal cavity from the egg- and fry-predators of the channel; after release the fry may continue to shelter in her mouth when threatened, a hallmark of advanced haplochromine care. Clutch size has not been measured for this species; in the genus, fecundity is genus-typical and modest by cichlid standards — on the order of tens to a few hundred relatively large eggs, scaling with female size, a trade-off inherent to mouthbrooders, which sacrifice egg number for the heavy parental protection of oral incubation. Spawning is expected to be seasonal, triggered by the rising-water phase of the Okavango flood pulse, consistent with the breeding phenology recorded for other largemouths. Beyond this genus-level template, the specifics of egg number, incubation period and fry development in Serranochromis cacuchi remain undocumented — a direct consequence of the species being known from a single collecting event.
In the aquarium
Serranochromis cacuchi has, to all appearances, never been kept in the aquarium. It is a very recently described fish, known from a single remote rocky reach in interior Angola, and there is no record of it entering the ornamental trade — it should be regarded as a wild scientific subject, not a hobby species. Any husbandry guidance can therefore only be extrapolated from its larger, occasionally kept congeners, which are demanding fish. Serranochromis are robust, fast-growing predators: at the size documented for Serranochromis cacuchi (and very possibly larger), a single specimen would need a long, broad tank measured in hundreds of litres, with open swimming room and a substrate echoing its natural channel — here a coarse, rocky bed with boulder structure rather than the sand of its sister species — plus the strong, oxygenating flow of the fast river it inhabits. Water should be kept warm and clean — roughly 72–82 °F, pH near neutral (about 6.5–7.5), soft to moderately hard — with powerful filtration and generous water changes to cope with the heavy waste load of a piscivore. It would have to be fed as the predator it is, on meaty foods, and could not be trusted with any tankmate small enough to be swallowed; like other largemouths it would likely be intolerant of conspecifics outside of breeding. None of this has been tested for Serranochromis cacuchi itself, and given its conservation profile — a point endemic of an under-surveyed basin — the honest position is that this is a fish to study and protect in the wild rather than to seek out for a tank.
Conservation
Serranochromis cacuchi has not been evaluated by the IUCN Red List; its status remains Not Evaluated (NE), and it carries no CITES or CMS listing. That blank is itself telling: the species is known from a single locality and only five specimens, collected on one day in 2012, so the basic data needed for a formal assessment — range, population size, trend — simply do not exist. A fish documented from one point on one river is, on the face of it, the kind of narrow-range endemic that warrants concern, though it may equally prove to be more widespread once the poorly explored Angolan Okavango headwaters are properly surveyed. The type locality lies on the Cacuchi at the Chitembo road bridge, in the source catchment of the Okavango Delta — a system whose long-term integrity depends on the Angolan highland rivers remaining unaltered. The broad pressures on that catchment, including potential hydropower and agricultural development of the headwater rivers and catchment degradation, are the backdrop against which the species' future should be read, even though none has been documented as a specific threat to Serranochromis cacuchi. For now its conservation status is best summarised as genuinely unknown, pending the field survey and assessment the species has yet to receive.