Taxonomy & naming
Placidochromis sp. "Hennydaviesae IV" has no describing author and no entry in Eschmeyer's Catalog of Fishes. Its trade name references Placidochromis hennydaviesae (Burgess & Axelrod, 1973), a small haplochromine described from a single specimen dredged off Monkey Bay at roughly 259 ft depth and known almost entirely from that deep, sediment-floored habitat. The Roman numeral "IV" is a collector's convention distinguishing this South East Arm population from other informally tracked hennydaviesae-type forms, including sp. "Hennydaviesae V," recorded at the same general locality. Because the nominal species is defined from a single deep-water specimen and remains poorly characterised, the relationship between these numbered trade forms and true P. hennydaviesae — whether local colour variants of the same species, related but distinct lineages, or something collectors have simply grouped under a convenient name — has not been settled by any published study.
Morphology
No formal description of this population's colour, fin shape or measurements exists, and none is invented here. Described P. hennydaviesae itself is a modestly sized cichlid, reaching about 4 in total length, with the generalised laterally compressed body typical of the genus and no pronounced head or jaw modifications; its outer oral-jaw teeth are tricuspid, consistent with a fish that picks small invertebrates rather than grazing algae or crushing shells. If this South East Arm population shares that build, as its trade name suggests, similar proportions would be expected, though nothing beyond that genus-typical inference is asserted here. Life colouration of the nominal species is poorly documented even in the original description, so no colour pattern is claimed for this form.
Habitat
The South East Arm is a large bay in the southeastern corner of Lake Malawi, predominantly sand- and mud-floored and generally shallower than the deep offshore plains from which the nominal P. hennydaviesae was originally dredged at around 259 ft. This is a meaningful discrepancy worth flagging honestly: the depth at which this South East Arm trade form is actually collected is not documented in the sources available here, and it is plausible that fish sold under the hennydaviesae name from this bay come from shallower water than the extreme deep-benthic habitat of the nominal species' single known specimen. Whether this reflects a genuinely shallower-living population, a different species entirely, or simply incomplete depth records is not resolved.
Feeding
Feeding observations summarised for described P. hennydaviesae indicate it takes planktonic invertebrates from just above the bottom as well as insect larvae probed from the sediment, a dual strategy consistent with its tricuspid teeth and soft-floored deep habitat. Placidochromis sp. "Hennydaviesae IV" is presumed to feed in a broadly similar invertivorous manner if it shares that ecology, though no dedicated feeding study exists for this South East Arm population.
Mating
No courtship account has been published for described P. hennydaviesae or for this trade form. As a presumed Lake Malawi haplochromine, males would be expected to establish a display site — a cleared patch of sand or sediment — and court passing females with lateral displays, in keeping with the broad pattern of the non-mbuna "hap" radiation. The specifics of timing, male coloration, and display intensity are undocumented for the nominal species and are not asserted here for this form.
Breeding
Reproduction is expected to be by maternal mouthbrooding, the near-universal mode across Lake Malawi's cichlid flock: the female alone incubates the fertilised eggs and subsequent fry in her mouth for several weeks, feeding little or not at all, before releasing free-swimming young with no further parental role for the male. No clutch size or brooding duration has been published for described P. hennydaviesae, and none exists for this South East Arm form; small Malawi haps of this general size class typically produce modest clutches of a few dozen eggs.
In the aquarium
This form is not an established aquarium fish, and no husbandry account specific to it exists. Were it kept, care would need to account for the genuine uncertainty over its natural depth and habitat noted above; a conservative approach would follow general Malawi cichlid practice — alkaline, well-buffered water matching the lake (pH roughly 7.7–8.6, temperature 75–82 °F), a soft sand substrate, and gentle rock or open structure. As a presumed non-mbuna sand-dweller it would likely be a relatively calm tankmate by Malawi standards, best kept with other peaceful open-water or sand-associated haps. A varied diet of small frozen invertebrates alongside a quality cichlid pellet would suit its presumed plankton-and-larvae feeding.
Conservation
Placidochromis sp. "Hennydaviesae IV" has not been evaluated by the IUCN and, as an undescribed form, carries no Red List status. Its close relative P. hennydaviesae was assessed as Least Concern in 2018, reflecting the deep, wide-ranging benthic habitat typical of the nominal species; whether the same applies to this South East Arm form depends on ecology and range that remain undocumented. The South East Arm faces general lake-wide pressures — fishing activity, catchment sedimentation, and the effects of a warming climate on stratification and deep-water oxygen — that affect Malawi's cichlid fauna broadly.