Taxonomy & naming
Lethrinops atrilabris was described by George F. Turner in 2022, in the Journal of Fish Biology (volume 101, pages 1405–1410), under the title 'A new species of deep-water Lethrinops (Cichlidae) from Lake Malawi'; an open preprint of the description was posted on bioRxiv earlier the same year. The holotype is a male of 3 in standard length, catalogued as BMNH 2022.4.20.1 in the Natural History Museum, London, with six male paratypes (BMNH 2022.4.20.2–7, 2.5–3 in SL); all were taken from a 1992 research trawl northeast of Monkey Bay, in the south-east arm of Lake Malawi, at a reported depth of 276–308 ft, aboard the Malawi Government trawler Ethelwynn Trewavas — itself named for the ichthyologist who revised the genus. The fish had been informally known as Lethrinops 'black chin' since at least Turner's 1996 'Offshore Cichlids of Lake Malawi'. The genus Lethrinops was raised by Regan in 1922 and is defined by a 'Lethrinops-type' lower-jaw dental arcade; Eccles and Trewavas (1989) split off Tramitichromis and Taeniolethrinops, leaving Lethrinops without a unique synapomorphy. Turner places atrilabris unambiguously in the genus's informal 'deep-water' group — fishes that mostly occur below about 164 ft, are relatively deep-bodied and laterally compressed, and whose males show strong vertical flank barring — a group that whole-genome work (Malinsky et al. 2018) suggests is allied to Aulonocara and Alticorpus and will eventually require its own generic name. The name 'black chin' is the only common name in use, and that is noted here as an informal field tag rather than an established English name.
Morphology
Lethrinops atrilabris is a small, laterally compressed cichlid: the seven known specimens span 2.5–3 in standard length, and Turner argues the maximum adult size is probably under 3 in SL, since the types came from an unselective trawl alongside many larger fish of other species. The body is deep and strongly compressed (maximum depth about 2.6–2.7 times the maximum head width), with a short, rounded snout (27–30% of head length), a small mouth set low on the head, and conspicuously large eyes (about 38–41% of head length). The lower gillraker count is 13–14, and the lower pharyngeal bone is small and lightly built, with small slender teeth showing no molarisation. Only mature males have been identified, all in breeding dress: strong dark-brown vertical bars on a silvery-white background — six under the dorsal fin, two on the caudal peduncle and one or two on the nape — with the upper head dark brown and, most distinctively, black lips, lower jaw, throat and chest. The pelvic and anal fins are black, the dorsal a dark golden-brown edged with a broad black margin and white submarginal band. The colours of females and immatures are unknown, but by analogy with related deep-water species are expected to be countershaded — sandy above, silvery on the flanks, probably with faint bars. Prolonged pelvic, dorsal and anal fin tips appear to be sexually dimorphic, exaggerated in males.
Habitat
The species is known from deep, offshore water in the south-east arm of Lake Malawi, the rift-valley lake shared by Malawi, Mozambique and Tanzania. The type series came from a trawl at 276–308 ft depth northeast of Monkey Bay, and Turner classes atrilabris firmly among the genus's deep-water species, which 'mostly occur at depths of 164 ft or more.' This is a soft-bottom, offshore demersal habitat far below the lit, rocky mbuna zone — the dim, cool, stable deep water that supports a distinctive community of barred, deep-bodied cichlids in the genera Lethrinops, Alticorpus, Aulonocara and deep-water Placidochromis. Because such species can only be sampled by trawling rather than by diving, their habitats and behaviour are far less well documented than those of the shallow lake. Lake Malawi's water is hard and alkaline throughout, with surface pH generally around 7.7–8.6; at the depths atrilabris occupies the water is considerably cooler and more constant than the warm surface layer, and oxygen becomes limiting below the thermocline, which constrains how deep the fish community can extend.
Feeding
No direct dietary study has been published for Lethrinops atrilabris, but its anatomy points firmly to the sediment-sifting, invertebrate-feeding habit that defines the genus. The 'Lethrinops-type' dental arcade, the small lightly built lower pharyngeal bone with small slender (non-molariform) teeth, and the simple well-spaced gill rakers are all consistent with a fish that winnows soft bottom sediment — taking a mouthful of mud or sand, tumbling it, and ejecting the cleaned substrate through the mouth and gills while retaining small buried invertebrates. Over the soft offshore bottoms it inhabits, the available prey would be the benthic invertebrate fauna of the deep lake. The deep-water Lethrinops as a group are part of the offshore benthic fish community that exploits these soft sediments, and atrilabris is best read as a small member of that guild; its precise diet remains undocumented.
Mating
Direct observations of courtship in Lethrinops atrilabris are impossible at present, since the species is known only from trawled specimens and has not been observed alive in its deep habitat. All seven known fish are males in full breeding dress and were probably taken together on a breeding ground, which is itself suggestive: in haplochromine cichlids, males aggregating in nuptial colour typically indicates lek-style courtship, with males displaying to females from defended sites. The strongly contrasting black-and-silver male dress — bold barring and a black chin, throat and chest — is the kind of high-contrast signal used in male display among the barred deep-water cichlids. By the consistent biology of Lake Malawi haplochromines, atrilabris is expected to be a polygynous maternal mouthbrooder with lek-style courtship, but this is inferred from the flock rather than observed for the species.
Breeding
There is no published breeding account for Lethrinops atrilabris, and none is likely soon given that the fish lives in deep offshore water and is known only from preserved trawl specimens. By the maternal-mouthbrooding pattern universal to Lake Malawi's haplochromines, the female would take the fertilised eggs into her mouth after spawning, incubating them and sheltering the larvae until the fry are free-swimming; the male would contribute no care beyond defending a courtship site. The apparent collection of multiple breeding-coloured males together is consistent with that reproductive mode. Clutch size, brooding duration and fry development are all unrecorded for the species and would, by analogy with small sand-dwelling Lethrinops, be expected to be modest — on the order of a few dozen young — but this is genus-level inference, not data.
In the aquarium
Lethrinops atrilabris is not in the aquarium hobby and is, in practical terms, unkeepable from the wild: it is a small deep-water fish known only from a 1992 research trawl, recovered already dead from the net, and has no history in the trade. The description itself notes that deep-water trawl species like this are rarely available and that the catch is normally sold for human consumption. There is therefore no body of husbandry experience, no trade in the species, and no breeding record.
Any remarks on keeping are purely hypothetical and extrapolated from related fish. Were specimens ever to become available, a deep-water, soft-bottom, large-eyed cichlid of this kind would imply a dim, cool, well-oxygenated tank with a deep fine-sand bed for its sediment-sifting feeding, hard alkaline Malawi water (pH roughly 7.7–8.6), subdued lighting to suit its large eyes, and peaceful tankmates — emphatically not the bright, crowded, boisterous mbuna setup. For now, atrilabris is best understood as a fish of scientific rather than aquarium interest: a recently named member of the lake's poorly known deep-water fauna, documented from a handful of museum specimens.
Conservation
Lethrinops atrilabris has not been evaluated by the IUCN and carries no Red List status. This is a direct consequence of its taxonomic history: it was described only in 2022, well after the 2018 Lake Malawi cichlid assessments, and Turner's paper explicitly notes that undescribed species are 'ineligible to receive IUCN redlisting, or incorporation into standard reference systems such as FishBase, GBIF etc.' — one of the motivations for formally naming it. Its conservation prospects are hard to judge from seven specimens taken at a single locality on one trawl in 1992, but two points are worth making honestly. First, as a deep-water offshore species it is exposed to the lake's expanding commercial trawl fishery, which operates in exactly the demersal zone where it was caught. Second, the deep, oxygenated offshore water that this and other deep-water cichlids depend on is sensitive to lake-wide warming and changes in mixing, which can compress the habitable deep zone. Neither is documented as a specific threat to this species, which simply remains too little known to assess; its status is recorded here honestly as Not Evaluated.