Taxonomy & naming
Serranochromis altus was described by Kirk O. Winemiller and Leslie C. Kelso-Winemiller in 1991, in the journal Copeia, on material the pair collected during a year of fieldwork on the Barotse floodplain of Zambia's Western Province. The holotype is an adult male, 12 in standard length, taken on hook and line along the west bank of the Zambezi River west of Mongu on 9 September 1989, and lodged in the U.S. National Museum of Natural History (USNM 308402); paratypes are spread across the Smithsonian, the Texas Natural History Collection, and the Natural History Museum in London. The genus Serranochromis was erected by Charles Tate Regan in 1920 and revised by Ethelwynn Trewavas in 1964; following Bell-Cross's (1975) and Greenwood's (1979) work it is split into two subgenera — the large-mouthed, piscivorous subgenus Serranochromis (the true "largemouths"), to which altus belongs, and the smaller-mouthed, invertebrate-eating Sargochromis. The describers' central point was that altus had been overlooked for a century because it so closely resembles its sympatric sister species Serranochromis angusticeps. Earlier authors — Jubb among them — had treated the unspeckled, plain-faced fish as simply the male or immature form of speckle-faced angusticeps. Winemiller and Kelso-Winemiller showed otherwise: examining hundreds of fresh specimens, they found altus consistently lacked the red-brown facial spotting and eye-stripe pattern that every angusticeps carries, and they backed the split with multivariate morphometrics (complete separation on principal-component axes), distinct fixed allozyme differences at two enzyme loci, and major ecological divergence. The two are regarded as sympatric sister species whose separation likely traces to the dynamic geological history of the upper Zambezi region.
Morphology
This is a deep-bodied, laterally compressed, big-jawed cichlid — the common name captures the steep, concave forehead and high-shouldered "hump" at the front of the body, where depth is greatest near the dorsal-fin origin. FishBase gives a maximum of 22 in total length and a published weight of 3.9 kg, making altus one of the largest Serranochromis; in the original study the biggest female measured 14.5 in and the biggest male 16 in standard length. The mouth is large and the jaws highly protrusible, angling sharply upward when closed, with broad tooth pads of short, unicuspid teeth deeply embedded in the gums — the toolkit of a fish-eater. The diagnostic features all turn on what altus does not have: no small red, rust, or brown spots and no "wormy" markings on the head, jaws, chest or belly; no eye-stripes across the snout, cheek, opercle or forehead; no dark blotch on the scales at the pectoral-fin base; and a lateral body stripe that is weak in juveniles under about 4.5 in and gone entirely in adults. The opercle bears a distinctive broad, shallow notch (sometimes two) giving its rear edge a concave profile. Compared with angusticeps at the same size, altus has a shorter snout, larger eyes, broader head, wider interorbital and tooth pads, and longer pectoral fins. Coloration is subtle: head and chest turn dark olive-green in ripe and breeding adults (much darker in males), the caudal and soft dorsal fins are pink to red, and the medial fins carry small red, purple and indigo spots on a silvery-indigo and pink ground, edged with a thin orange-yellow band. Sexual dimorphism is moderate — males grow larger, mature later, and develop longer dorsal and anal rays; their pelvic fins turn black when ripe, and the anal fin bears 30–40 pale ovate "egg-dummy" ocelli that are most strongly ringed in prespawning males.
Habitat
Serranochromis altus is a fish of the upper Zambezi River system above Victoria Falls and the adjoining Okavango basin. FishBase records it from the upper Zambezi in Zambia and the Okavango drainage of Botswana and Namibia, with reports also from the Zambezi and Okavango in Angola; the IUCN range adds Zimbabwe, and the genus's centre of diversity is precisely this upper-Zambezi/Okavango/Cuando-Chobe region. It is a warm-water, soft-water fish. During Winemiller's 1989 fieldwork the Zambezi main channel ran 70–82 °F with pH 6.3–6.9, while floodplain waters spanned 64 °F (in a deep canal in August) to 82 °F (a November surface reading) and pH from 5.5 in floodplain pools to 7.0 in tributaries; the water was always near oxygen saturation and clear, though often tea-stained brown with dissolved organics draining off the ancient, acidic Kalahari sands of the catchment. What separates altus ecologically from its weed-dwelling sister is where it lives within this landscape. As the annual flood recedes and the plain drains down to the low-water period (roughly September to December), the largest adults — altus among them, alongside the river-dwellers Serranochromis robustus and Sargochromis giardi — retreat into the deep main channel of the Zambezi. There altus was caught mostly in overnight gillnet sets set above deep shoreline stretches, taken from mid-depths or near the surface beneath or beside dense floating vegetation rather than down on the bottom. Juveniles, by contrast, were found in the quieter lagoon and canal margins. FishBase classes the species as demersal, but the field data place foraging adults higher in the water column of the open channel.
Feeding
Serranochromis altus is a specialist piscivore — FishBase places it at trophic level 4.2, near the top for the genus. Examination of 114 wild stomachs showed it feeding almost exclusively on fish, and on a particular kind of fish: nocturnal elephant-fishes (Mormyridae) of the genera Mormyrus, Hippopotamyrus and Marcusenius, plus a schilbeid catfish (Schilbe). This is a notably narrow diet — the narrowest measured among the upper-Zambezi largemouths — and it neatly partitions the river channel among the big predators: Serranochromis robustus crushes armoured Synodontis catfishes, Sargochromis giardi takes molluscs, and altus claims the soft-bodied mormyrids. Because mormyrids are themselves nocturnal, altus appears to forage at twilight and after dark; the only two specimens taken on hook and line were caught just before dusk, and gillnet patterns point to a crepuscular-to-nocturnal hunter. A telling 77% of stomachs were empty — consistent with a large, sit-and-wait predator that eats infrequently but well. Fish under about 6 in have not yet specialized and take a broader mix of small prey before settling onto the adult mormyrid diet. In its community altus functions as a nocturnal counterpart to the day-active piscivores of the channel, exploiting a prey resource — the elephant-fishes — that few other predators target.
Mating
Like all Serranochromis, Serranochromis altus is a maternal mouthbrooder, and its reproduction is tightly geared to the flood cycle of the Barotse plain. Through the low-water months the fish are concentrated into the shrinking permanent channels, and this crowding is thought to make it easier for ripe adults to find one another for courtship. The males are the larger sex and mature later — roughly 11–13 in standard length, against 10–12 in for females — and a ripe male darkens to deep olive-green about the head, blackens his pelvic fins, and flares the bold ringed "egg-dummy" ocelli on his anal fin, which in this species show their strongest contrast in the prespawning phase. Detailed courtship has not been described in the wild, but the timing is well documented: gonads ripen through October and November, and the original studies repeatedly netted ripe males and females of altus together in single gillnet sets and castnet throws, indicating that pairs come together in the open channel as spawning approaches. The decisive observation came on 10 November 1989, when a 14.5 in female carrying developing embryos in her mouth was taken alongside a 16 in male with spent testes in the same net — a snapshot of a mouthbrooding female and the male that had just fertilized her clutch.
Breeding
Serranochromis altus spawns at the very start of the rains, just before the river rises and floods the plain — timing that lets brooding females carry their young out onto the newly inundated grassland, where predator densities are low and the fry have room to grow. In the 1989 study, altus was among the species that had begun spawning by November, with about a quarter of adults ripe in October and most of the rest preparing as the field season closed in mid-December. As a maternal mouthbrooder, the female alone incubates: she takes the fertilized eggs into her buccal cavity and broods them there through hatching and early development, releasing free-swimming fry onto the flood. Fecundity is high for a mouthbrooder — seven ripe females averaged 920 mature oocytes (range roughly 560–1280), each egg large at about 0.5 in diameter, with egg number rising with female size. Whether females spawn more than once during the four-to-five-month flood is unknown; faint extra rings on the scales hint at the possibility but could not be confirmed. Maximum oocyte size and the single-female brood are typical of the genus, in which all members are believed to be mouthbrooders (Trewavas 1964; Jubb 1967). Age data from scale annuli suggest altus, like the other large channel species, does not reach maturity until about three years old — a slow-maturing, long-lived strategy that fits its size and position near the top of the river food web. The species has not, as far as the published record shows, been bred in captivity.
In the aquarium
Serranochromis altus is essentially never seen in the ornamental trade, and for sound reasons: this is a metre-class-adjacent predator that reaches well over half a metre and nearly four kilograms, eats fish for a living, and hails from a region whose fishes rarely enter the hobby. There is no established body of aquarium experience for the species, and nothing in the literature describes keeping or spawning it. Any honest husbandry account is therefore an extrapolation from the closely related largemouths (Serranochromis robustus, the "nembwe," is the one occasionally kept by specialist keepers of African riverine predators) and from the documented wild biology. On that basis a single adult would need a very large tank — on the order of several hundred litres at an absolute minimum, realistically a 2-metre-plus, 1,000-litre-class system — with strong filtration, brisk but not torrential flow, and open swimming room over a sand bottom, reflecting its life in the deep main channel rather than the weed beds. Water should be warm and soft to neutral, matching the wild envelope: roughly 72–82 °F, pH about 6.5–7.5, low hardness, with the tannin-stained, clear blackwater character of the Zambezi. It is a committed piscivore that would treat any tankmate small enough to swallow as food and would itself be intolerant of crowding; only similarly large, robust riverine fishes could share its space, and conspecifics would likely be problematic outside the brief breeding window. In short: a magnificent fish, but a public-aquarium or specialist-only proposition rather than a realistic home-aquarium subject, and one best appreciated in its native rivers.
Conservation
The IUCN Red List assesses Serranochromis altus as Least Concern, in an assessment by B. E. Marshall and D. Tweddle published in 2007 (assessed 1 March 2007); the population trend is listed as unknown. The species is recorded from Angola, Botswana, Namibia, Zambia and Zimbabwe. The favourable rating reflects its association with the upper Zambezi and Okavango systems, which are among the least-disturbed large river basins in Africa — lightly impacted by the dams, pollution and habitat loss that threaten freshwater fishes elsewhere on the continent. It carries no CITES listing. As one of the "breams," altus is taken in the commercial and subsistence gillnet and trap fisheries of the Barotse floodplain, where its genus forms an important part of the catch; in the 1989 survey, though, only the more heavily targeted Sargochromis giardi showed clear signs of local over-exploitation, and the strongly seasonal dynamics of the floodplain — fish dispersing across the inundated plain each wet season to repopulate fished-out channels — appear to buffer the populations. The longer-term concerns for this fish are the same ones that hang over the whole upper-Zambezi/Okavango system: proposed water-resource and hydropower development, and the climate-driven changes to the flood pulse on which its spawning depends. None is documented as a present threat to the species, but the flood-cycle dependence of its reproduction makes it sensitive to anything that would alter the timing or extent of the annual inundation.