Taxonomy & naming
Otopharynx sp. "Argyrosoma Deep" has no describing author, no publication date, and no entry under a validated name in Eschmeyer's Catalog of Fishes. The trade name follows the standard convention for an undescribed form allied to a known species: the genus, a reference to the described relative Otopharynx argyrosoma (Regan, 1922) — Greek for "silver body," for its bright, scaly flanks — and a qualifier, "Deep," recording that this population was taken from notably greater depth than the roughly 33 ft at which O. argyrosoma is usually reported schooling over open sand. Whether the South East Arm population represents a genuinely distinct depth-adapted form of argyrosoma, or simply deeper-living individuals of the same widespread species, has not been settled by any published study. It should be treated as an unresolved, undescribed entity, and no authority or date should be attached to it.
Morphology
No morphometric study has been published for this specific population. Its trade name points to a silvery body colour matching Otopharynx argyrosoma, the described relative it is named after, which carries the laterally spotted melanic pattern typical of the genus — discrete dark blotches rather than bold vertical bars — against bright, reflective flanks. Otopharynx argyrosoma reaches about 6 in total length, and that figure is used here only as a genus/species-typical reference rather than a measurement of this population. Sexual dichromatism is expected on general Malawi cichlid grounds, with breeding males more strongly marked than the plainer, silvery females, though the specific pattern for this deep-water form has not been documented.
Habitat
Otopharynx sp. "Argyrosoma Deep" is recorded from the South East Arm of Lake Malawi, one of the lake's three principal arms and a broad expanse of open sandy bottom in the southern basin that has long been fished commercially, including by trawl, for chambo and other demersal cichlids. The "Deep" trade name signals that this population was collected well below the depths at which O. argyrosoma is typically observed schooling, in the cooler, dimmer water of the lower water column over open sand rather than the sunlit shallows. The precise depth range has not been documented in the published literature, and the water itself follows the general Lake Malawi profile — warm, alkaline and well-buffered, though deep zones run cooler than the well-lit shallows above them.
Feeding
Otopharynx argyrosoma, the described relative this form is named after, feeds on small invertebrates and plankton taken both from the sand and from the water column. A deep-water population, however, forages in far dimmer light than shallow schools of the same species, which may favour benthic sediment feeding over picking plankton from open water, since visual plankton foraging becomes progressively harder as light fades with depth. No dedicated feeding study has been published for this population, and this account should be read as a reasonable expectation drawn from the described relative's known diet rather than a documented finding.
Mating
No courtship or spawning behaviour has been documented for this deep-water form. By analogy with Otopharynx argyrosoma and the wider assemblage of Lake Malawi's sand-dwelling haplochromines, mating is expected to follow the familiar polygynous, lek-like pattern: males in nuptial colour establishing a display site on the sand and courting passing females, with no lasting pair bond. Whether males of this population hold territories in the open, low-light depths where they were collected, or move into shallower water to breed, is unknown.
Breeding
As with all Lake Malawi haplochromines, reproduction is presumed to be by maternal mouthbrooding: the female would take the fertilised eggs into her mouth after spawning and incubate them for several weeks without normal feeding, releasing free-swimming fry once they are ready for independent life, with no further role for the male. Clutch size, incubation period and fry behaviour have not been documented for this form; the reproductive picture given here is inferred from the consistent biology of the genus rather than measured directly.
In the aquarium
Otopharynx sp. "Argyrosoma Deep" is rarely, if ever, seen in general retail, reflecting the difficulty of collecting a deep-water fish compared with shallow rocky-shore mbuna. Where it is kept, a tank should provide a fine sand substrate with a large open footprint, since this is a sand-associated fish that needs room to forage, along with subdued lighting reflecting its deep-water origin. Water chemistry should match the Lake Malawi standard — alkaline and well-buffered, pH roughly 7.7 to 8.6, temperature in the mid-20s Celsius — and, given the likely stresses of collection from depth, a stable, well-filtered setup is advisable. Diet should follow the general sand-hap template: a quality cichlid pellet supplemented with small frozen or live invertebrates such as brine shrimp and bloodworm.
Conservation
Otopharynx sp. "Argyrosoma Deep" has not been evaluated by the IUCN and, as an undescribed form, has no Red List status of any kind. The South East Arm has been subject to sustained commercial and artisanal fishing pressure for decades, particularly targeting the chambo (Oreochromis) fishery, and deep-water demersal cichlid populations across the lake's southern basins are generally less thoroughly surveyed than shallow rocky-shore species. No population-specific data exist to assess whether this particular form is affected by that pressure. In the absence of a formal assessment, the honest statement is that it is unevaluated, with its status inferred only from general conditions in the South East Arm rather than direct study.