Taxonomy & naming
Placidochromis acutirostris was described in 2004 by the Belgian ichthyologist Mark Hanssens, in his chapter 'The deep-water Placidochromis species' (pages 104-197) in The Cichlid Diversity of Lake Malawi/Nyasa/Niassa: Identification, Distribution and Taxonomy, edited by Jos Snoeks and published by Cichlid Press. That monograph revised and greatly expanded the deep-water members of the genus, naming many species — including acutirostris — in a single work. The genus Placidochromis was established by Digby Lewis in 1982 for Malawi haplochromines of generally placid, unspecialised form; it belongs to the tribe Haplochromini within the subfamily Pseudocrenilabrinae, part of the lake's enormous radiation of non-mbuna 'hap' cichlids. Hanssens grouped the deep-water Placidochromis informally by shape, with acutirostris falling among the more elongate, sharp-snouted members. Catalog of Fishes lists it as valid — Placidochromis acutirostris Hanssens, 2004 — and its FishBase SpecCode is 62392. The epithet acutirostris is Latin, from acutus, 'sharp' or 'pointed,' and rostrum, 'snout,' describing the species' attenuated, pointed snout.
Morphology
Placidochromis acutirostris is a small cichlid, reaching about 4.5 in standard length (FishBase). It is among the more elongate of the deep-water Placidochromis, with a notably pointed, drawn-out snout that gives the species its name. As with the rest of the group, its formal diagnosis is built on proportional measurements — head length, snout length, jaw and cheek dimensions as percentages of standard or head length — and on meristic counts of fin spines, rays and gill-rakers, rather than on striking live coloration, which is subdued in these deep-dwelling fish and largely lost in preservation. The type and reference material was collected by deep trawling, and the species is documented chiefly from preserved adults (the Cichlid Room Companion figures a preserved adult from Matema). Notes on live colour, breeding dress and sexual dimorphism are correspondingly sparse; in build it is a slender, sharp-faced open-water and sand hap.
Habitat
The species is endemic to Lake Malawi and, on current records, known only from Wissman Bay in the far north of the lake, in Tanzanian waters near Matema. FishBase gives a depth range of about 30 to 61 metres, placing it firmly in the deep-water community that Hanssens revised — fish that live and breed below the well-lit, oxygen-rich shallows in the lake's cooler, dimmer middle depths. Lake Malawi is permanently stratified and its deepest water is anoxic, so deep-water cichlids occupy a limited band over soft sediment between the productive surface layers and the lifeless depths. Within that band, acutirostris appears to be a northern, soft-bottom specialist. As with several of its relatives, its known range is probably constrained as much by the difficulty of sampling deep water as by genuine rarity, so the single-bay record should be read with that caveat.
Feeding
No dedicated dietary study has been published for Placidochromis acutirostris. Placidochromis are generally invertebrate-feeders and generalist micropredators, and the deep-water members are presumed to forage over soft sediment for benthic invertebrates and other small prey in the dim light. The slender body and pointed snout of acutirostris are consistent with picking or probing for small invertebrates rather than crushing hard prey, but this is morphological inference, not a documented feeding mode. FishBase places the deep-water Placidochromis at trophic levels around 3.2-3.3, the expected value for a small benthic invertivore. For this species in particular, diet is extrapolated from the genus and its habitat rather than recorded from stomach contents.
Mating
Courtship and spawning behaviour are undescribed for Placidochromis acutirostris. Lake Malawi haplochromines, Placidochromis included, are maternal mouthbrooders, and the species is confidently expected to follow that template: males court receptive females with displays, the female takes the fertilised eggs into her mouth, and there is no lasting pair bond. Whether the deep-water Placidochromis defend display territories on the sediment or simply spawn over open bottom is not known, and in the perpetually low light at 98–197 ft the elaborate visual signalling typical of shallow Malawi cichlids is presumably muted. What can be stated is only the general pattern the flock makes near-certain — a brief, polygynous, female-mouthbrooding system — rather than anything observed for acutirostris itself.
Breeding
There is no published account of spawning, clutch size or larval development specific to Placidochromis acutirostris. By the consistent biology of Malawi haplochromines, it is a maternal mouthbrooder: the female incubates a modest clutch of large, yolky eggs in her buccal cavity for around three weeks, then releases free-swimming fry and continues to take them back into her mouth for shelter for a short time. Comparable small haps carry clutches ranging from a few tens to roughly a hundred eggs. None of these figures has been measured for acutirostris, which has not been bred in aquaria or studied for reproduction in the wild; the account here is inferred from the genus and the wider mouthbrooding flock rather than recorded for the species.
In the aquarium
Placidochromis acutirostris is not part of the aquarium hobby. It is a deep-water, far-northern endemic known from trawled specimens rather than from live collection, and it has no hobby name, husbandry literature or breeding record. Any keeping notes are necessarily generic to the genus.
The Placidochromis that aquarists do keep are mostly shallow-water species — Placidochromis electra, Placidochromis phenochilus and a handful of others — managed as relatively peaceful, sand-associated Malawi haps in spacious tanks with a deep sand bed, hard alkaline water (pH roughly 7.8-8.6, moderately hard) and temperatures in the mid-20s Celsius, alongside other non-aggressive haps. A genuinely deep-water fish like acutirostris, adapted to cool, dim, comparatively low-oxygen depths, would be a far more demanding and unrealistic subject, and is not in the trade. In short, this is a species of scientific rather than aquarium interest.
Conservation
Placidochromis acutirostris was assessed by the IUCN in 2018 and listed as Data Deficient: too little is known of its range, abundance and ecology to evaluate its extinction risk. That is a recurring verdict for the deep-water, narrowly recorded cichlids of Lake Malawi, where the difficulty of surveying deep, stratified water leaves many species effectively undersampled. If its restriction to Wissman Bay reflects a genuinely narrow range, the species would be vulnerable to localised disturbance; but the record may simply mirror where deep trawls have been dropped. At the lake scale, Lake Malawi faces intensifying fishing pressure, catchment-derived sedimentation and a gradually expanding deoxygenated deep layer, and deep trawling can disturb exactly the benthic communities these fish depend on. For acutirostris the appropriate stance is the IUCN's — a poorly known endemic whose status awaits the kind of dedicated deep-water survey the whole group needs.