Taxonomy & naming
Lethrinops altus was described by the British ichthyologist Ethelwynn Trewavas in 1931, in 'A revision of the cichlid fishes of the genus Lethrinops' (Annals and Magazine of Natural History, series 10, volume 7, page 146, with a figure of the head profile). The species was originally written as Lethrinops alta — the Latin adjective agreeing in feminine gender with the then-feminine treatment of the genus — and is now standardised as altus. Catalog of Fishes lists it as valid as Lethrinops altus Trewavas 1931, with the unique holotype catalogued as BMNH 1930.1.31.102 in the Natural History Museum, London; the type locality is given only as Lake Nyasa (Lake Malawi), without a narrower reef or coordinate. The genus Lethrinops was erected by Charles Tate Regan in 1922 for sediment-sifting Malawi cichlids defined by a distinctive 'Lethrinops-type' lower-jaw dental arcade, in which the outer tooth row curves smoothly inward to end just behind the inner rows. Trewavas's 1931 revision expanded the genus to 23 species; Eccles and Trewavas (1989) later split off Tramitichromis and Taeniolethrinops, leaving Lethrinops without a unique defining character of its own. Workers since Ngatunga and Snoeks (2004) have informally divided Lethrinops into 'shallow-water' and 'deep-water' groups, and altus is one of a handful of intermediate species — together with christyi, longimanus, longipinnis and micrentodon — that mix traits of both and are often taken at depths of roughly 66–197 ft. It carries no settled English common name, so none is asserted here.
Morphology
Lethrinops altus is a moderately deep-bodied, laterally compressed cichlid of the sand-sifting build. FishBase lists a maximum size of about 6 in total length, a useful upper bound for a fish that is otherwise modest in size. The epithet altus ('tall, deep') reflects its comparatively deep body relative to many of its congeners, and Trewavas figured the head in her original account precisely because the head profile is diagnostic. In Turner's 2022 comparison of Lake Malawi Lethrinops, altus is separated from its nearest relatives by its hooked maxillae, which give it a markedly curved lower profile to the head — a feature that sets it apart from the small, pointed jaws and concave snout of Lethrinops christyi and the longer snout of Lethrinops longipinnis. It has a comparatively low lower-gillraker count, reported as about 10 to 11, which is one of the meristic characters used to distinguish it from the higher-raker deep-water species. As in most Malawi haplochromines, females and non-breeding fish are countershaded and silvery, while sexual dimorphism is expressed mainly in the nuptial coloration and prolonged finnage of mature, breeding males; detailed live-colour notes for this particular species are sparse in the literature.
Habitat
The species is endemic to Lake Malawi (Lake Nyasa / Lago Niassa), the great rift-valley lake shared by Malawi, Mozambique and Tanzania. FishBase characterises it as a freshwater, demersal fish with a depth range of roughly 66–262 ft, placing it among the deeper-living members of the genus — deeper than the true shallow-water Lethrinops of the beaches, but it is one of the intermediate-depth species that Turner (2022) notes can occur from about 66–197 ft. Like the rest of the genus it is a fish of soft sandy and muddy bottoms and intermediate zones rather than the rocky mbuna shore, where its sediment-sifting feeding mode can operate. Lake Malawi's open water is warm, hard and alkaline: surface temperatures run roughly 75–82 °F seasonally and pH is generally between about 7.7 and 8.6, with high mineral content — the chemical envelope this species inhabits, though at its preferred depths the water is cooler and more stable than the surface.
Feeding
Lethrinops altus is a benthic, sand-sifting invertivore. FishBase records the genus-typical behaviour directly for this species: it is 'frequently found over sand and feeds on invertebrates which are taken from the sand.' The mechanism is the winnowing that defines the genus — the fish drops its mouth to the substrate, takes in a mouthful of sand or mud, tumbles it briefly, and ejects the cleaned sediment through the mouth and gill openings while retaining buried insect larvae, small crustaceans and other invertebrates. FishBase places it at an estimated trophic level of about 3.5, consistent with a small-invertebrate predator. This sediment-processing role is shared across the Lethrinops flock and underpins the diverse benthic fish community that exploits Lake Malawi's sandy and intermediate-depth zones.
Mating
Like essentially all of Lake Malawi's haplochromine cichlids, Lethrinops altus is a polygynous maternal mouthbrooder, and its courtship is expected to follow the lek-style pattern of the sand-dwelling Lethrinops. In that pattern a breeding male establishes and defends a spawning site on the open bottom, often working the sediment into a low mound or shallow depression, and displays his nuptial colours to passing females, leading a receptive female onto the site to spawn. Detailed observations of courtship specific to Lethrinops altus have not been published, so the behaviour described here is inferred from the well-documented biology of the genus and the lake's mouthbrooding flock rather than recorded directly for this species.
Breeding
Reproduction follows the maternal-mouthbrooding pattern universal to Lake Malawi's haplochromines. After spawning on the male's site, the female takes the fertilised eggs into her mouth, where they are incubated and the larvae sheltered until the fry are free-swimming and able to feed and avoid predators; the male provides no parental care beyond defending the spawning territory during courtship. Specific clutch counts for Lethrinops altus are not documented in the literature, but sand-dwelling Lethrinops are comparatively modest brooders, typically carrying on the order of a few dozen eggs and fry — the trade-off for the protection that buccal incubation confers. As with most Malawi mouthbrooders, warming water and good condition are the likely seasonal trigger for spawning. These statements are inferred from the genus rather than recorded for this particular species, which has no published breeding account.
In the aquarium
Lethrinops altus is not a fish of the general aquarium trade. FishBase tags it as having a commercial aquarium use, reflecting that Malawi Lethrinops are occasionally exported by specialist African-cichlid importers, but it is unlikely to appear in an ordinary fish shop and there is little species-specific keeping or breeding experience on record. The husbandry notes here are therefore extrapolated from what is known of sand-sifting Lethrinops generally, and should be read as genus-level guidance rather than data specific to altus.
The central requirement for any sand-sifting Lethrinops is a deep bed of fine sand — silica or smooth play sand, at least 3–4 in deep across the whole footprint of the tank — because the fish feeds by driving its jaws into soft sediment and straining invertebrates across its gill rakers. Coarse gravel or a bare bottom prevents this natural behaviour and causes chronic stress. Because altus is a comparatively deep-living species, a large tank with open swimming space over the sand and only sparing rockwork suits it best. Water chemistry should match the lake: temperature 75–82 °F, pH 7.7–8.6, hard and alkaline, achieved with crushed coral or equivalent buffering, with strong filtration and good oxygenation. Weekly partial water changes of around 25–30% are standard for Malawi tanks and help guard against Malawi bloat, the serious digestive illness that afflicts these cichlids when kept in poor water or fed an over-rich, fatty diet. A varied diet of quality cichlid pellet or flake plus sinking frozen foods such as bloodworm, Mysis and Daphnia that the fish can sift from the sand is appropriate; high-fat meaty foods should be avoided. Peaceful, similarly sized sand- and open-water Malawi cichlids make the best tankmates, and boisterous mbuna are best avoided. Breeding, where attempted, would be expected to follow the standard maternal-mouthbrooder routine described above.
Conservation
The IUCN Red List assesses Lethrinops altus as Least Concern (assessed 20 June 2018; published as part of the Lake Malawi cichlid assessments, e.T61032A155048946), on the basis that it is considered reasonably widespread within the lake with no major lake-wide threats currently identified. That status should be read against the broader pressures bearing on Lake Malawi as a whole: a heavily fished and food-insecure shoreline, sedimentation and nutrient loading from catchment deforestation and agriculture, and warming-driven changes in lake mixing and productivity that are documented in the lake's fisheries and limnology literature. As a deeper-living, sediment-sifting endemic, altus is somewhat buffered from the beach-seine pressure that bears most directly on the shallow-water sand species, but it shares in the long-term, basin-scale uncertainties facing the lake's benthic fish community. None of these is recorded as an imminent danger to this particular cichlid.