Taxonomy & naming
Placidochromis koningsi was described in 2004 by the Belgian ichthyologist Mark Hanssens, in his chapter 'The deep-water Placidochromis species' in Jos Snoeks's volume The Cichlid Diversity of Lake Malawi/Nyasa/Niassa: Identification, Distribution and Taxonomy (Cichlid Press). That study formally named several deep-living haplochromines that had previously gone unrecognised among the lake's diffuse 'hap' fauna. The genus Placidochromis was established by Eccles and Trewavas in 1989 for a set of generally calm-mannered Malawi haplochromines; its name combines Latin placidus, 'placid', with the cichlid name-element chromis. The specific epithet honours Dr Ad Konings, the Dutch-born ichthyologist, aquarist, photographer and publisher whose books and Cichlid Press imprint have done more than almost any other single source to document the cichlid faunas of Lakes Malawi and Tanganyika. Catalog of Fishes lists the species as valid: Placidochromis koningsi Hanssens, 2004.
Morphology
This is a small, fusiform cichlid reaching about 2.5 in standard length, with a moderately deep body (depth around 39 percent of standard length). Fin counts are 14–15 dorsal spines and 10–11 dorsal soft rays, with 3 anal spines and 9–10 anal soft rays. Several oral and pharyngeal features set it apart within the deep-water group: the outer oral-jaw teeth are unicuspid (single-pointed), there are no inner rows of oral teeth, and — most distinctively — the lower pharyngeal dentition is enlarged and molariform, that is, broadened into crushing molar-like teeth. Hanssens also cited a relatively long snout (about 33–35 percent of head length), a deep cheek, a broad orbit and a stout premaxillary pedicel among the diagnostic proportions. The molariform pharyngeal mill is the morphological signature of a fish that processes hard items, and it distinguishes koningsi from relatives that retain slender, conical throat teeth. Life coloration and any sexual differences in pattern are not documented for this trawl-known species.
Habitat
Placidochromis koningsi is endemic to Lake Malawi and is known only from the area off Nkhotakota, on the central-western shore of the lake — a single recorded locality. It is a deep-water fish, with FishBase giving a narrow depth range of about 390–404 ft, deep within the lake's cool, dimly lit benthic zone. At such depths the water is strongly stratified and the bottom is generally soft sediment, far below the rock and sand habitats of the better-known littoral cichlids. The very tight depth band and single locality on record almost certainly reflect the limited deep-net sampling behind the species' discovery rather than a true picture of its range, but on present evidence it qualifies as a narrow-range, deep-water endemic.
Feeding
No direct dietary study exists for Placidochromis koningsi, but its dentition is unusually informative. The combination of unicuspid outer oral teeth with an enlarged, molariform lower pharyngeal bone is the classic toolkit of a durophagous cichlid — one that grasps prey with the jaws and crushes it with the pharyngeal mill in the throat. In Lake Malawi this pattern is typically associated with mollusc-feeding, suggesting that koningsi may take snails or other hard-shelled invertebrates from the deep bottom, in contrast to the soft-prey, plankton-and-larvae feeding of most deep-water Placidochromis. FishBase places it at an estimated trophic level of about 3.2. In the absence of stomach contents this durophagous habit is an inference from morphology rather than an observed fact, but it is a well-supported one.
Mating
Mating behaviour has not been observed in Placidochromis koningsi. As a Lake Malawi haplochromine it is expected to be a maternal mouthbrooder, in keeping with the near-universal reproductive mode of the lake's cichlid flock. In that system males court females — generally over a chosen display site on the substrate — and females select among suitors before taking the fertilised eggs into the mouth. For a deep-water, evidently scarce species the natural courtship arena would lie on the open benthic plains, well beyond ordinary observation. The details of male breeding colour, display form and spawning season are entirely unrecorded for this species, and the account here is generalised from the broader Malawi radiation.
Breeding
There is no published account of egg number, brood development or fry-rearing for Placidochromis koningsi. By the consistent biology of the Lake Malawi haplochromines, it is a female mouthbrooder: the female incubates eggs and larvae in her buccal cavity for several weeks before releasing free-swimming fry, which may dart back to her mouth when threatened. Small haps of this size generally produce modest clutches of a few dozen eggs, trading low fecundity for the high offspring survival that mouthbrooding provides. Given that the species is known only from deep-net captures, none of these particulars have been observed, and what is stated is the standard flock pattern rather than a species-specific record.
In the aquarium
Placidochromis koningsi has no presence in the aquarium hobby. It is a rare, single-locality, deep-water endemic known only from scientific sampling, with no trade history, common name or body of keeping experience attached to it. The notes here are extrapolated purely from the genus and from general Lake Malawi husbandry and should be treated as such. In principle a small Malawi hap like this would need the lake's characteristic hard, alkaline water (high pH, moderate-to-high hardness), clean and well-oxygenated conditions, a soft sandy substrate and calm tankmates of similar temperament. If its inferred snail-crushing diet were real, a keeper might offer hard-shelled foods such as small snails alongside frozen and live invertebrates. In reality, however, koningsi is a taxonomic and faunistic entity rather than a fish anyone is likely to encounter alive.
Conservation
Placidochromis koningsi is listed by the IUCN Red List as Data Deficient, with the assessment dated 19 June 2018 — a category that reflects exactly its situation: a species known from a single locality and a handful of deep-net specimens, with no information on population size, trend or precise range. It has no CITES listing. A Data Deficient rating is not a clean bill of health; a genuinely narrow-range, deep-water endemic could be vulnerable to the very pressures that bear on the wider lake — intensive and expanding fisheries, including demersal trawling over the deep bottom, together with catchment erosion, sedimentation and the warming and deoxygenation of deep water under climate change, all of which the Lake Malawi conservation literature flags as ecosystem-level threats. For koningsi specifically, the priority is simply better information: targeted deep-water survey to establish whether its apparent restriction to Nkhotakota is real or an artefact of sampling, and protection of the lake's deep benthic environment in the meantime.