Taxonomy & naming
Melanochromis sp. "Robustus Mbenji" carries no describing author, no type specimen, and no listing in Eschmeyer's Catalog of Fishes. The trade name invokes Melanochromis robustus, described by Donald S. Johnson in 1985, a stout, large-bodied mbuna whose breeding males combine light horizontal stripes with dark vertical bars, a pattern unique within the genus. True M. robustus is confirmed only from Chinyankwazi Island and Mumbo Island, within Lake Malawi National Park; the Mbenji Island population resembles it closely enough to be traded under the robustus name with a locality qualifier, but is treated by field workers as a distinct, intermediate-habitat form rather than a third population of the same species, since M. robustus itself is a pure rock-habitat specialist and Mbenji Island fish occupy different, intermediate ground. This account follows that distinction and does not treat the two as one taxon.
Morphology
Melanochromis sp. "Robustus Mbenji" is expected to share the stout, deep-bodied build associated with the robustus type within the genus, larger and heavier than most other Melanochromis. Breeding males of true M. robustus are dark blue to near-black with a light-blue mid-lateral stripe, a fainter stripe above it, and dark vertical bars superimposed on the front of the body, along with small orange-yellow ocelli on the anal fin; whether the Mbenji Island population matches this pattern precisely has not been documented in a published account, and this description should be read as an expectation based on the trade association rather than a confirmed record for Mbenji Island fish specifically.
Habitat
This form is documented from Mbenji Island in southern Lake Malawi. Unlike true Melanochromis robustus, which is confined to very shallow, pure-rock habitat at its two known islands, the Mbenji Island population is associated with intermediate habitat — the transition zone between rock and sand — a distinction that is part of why it is treated as a separate form rather than simply another M. robustus locality. Water at the site follows the lake's standard chemistry: warm, hard and alkaline, roughly 24-28 degC and pH 7.7-8.6.
Feeding
No feeding study specific to this population has been published. True Melanochromis robustus feeds unusually loosely for a rock cichlid, taking drifting particles from the water column rather than systematically grazing aufwuchs, alongside plankton, algae and occasional terrestrial insects; whether the Mbenji Island form shares this generalist habit, consistent with its intermediate rock-sand habitat, has not been documented, and this account does not assume it without evidence.
Mating
Mating behaviour has not been documented for this population specifically. Melanochromis generally are territorial, polygynous mbuna with no pair bond; males hold and defend caves or crevices in the rock, displaying to attract ripe females that visit briefly to spawn. Subdominant males in the genus are known to mimic female colouration to avoid the attention of dominant males, a pattern documented across Melanochromis broadly.
Breeding
As in all Lake Malawi haplochromines, reproduction is by maternal mouthbrooding: the female takes the fertilised eggs into her mouth after spawning and broods them alone before releasing free-swimming fry, with no further parental care from either parent. Clutch size and brooding duration have not been documented for this population; in the described M. robustus, broods are on the order of a few dozen eggs.
In the aquarium
This form is only irregularly available and is not established under a settled name in the general aquarium trade; no dedicated husbandry record exists for it. Were it kept, care would follow the standard Melanochromis template, which is demanding for the genus's larger members: hard, alkaline water in the mid-20s Celsius, strong filtration and aeration, and a spacious tank with a rockscape offering abundant caves to manage the genus's well-documented aggression. Because it is traded under the same name as the true M. robustus, which is rare and range-restricted, care should be taken not to conflate the two or to mix stock if maintaining either as a distinct, documented line matters.
Conservation
Melanochromis sp. "Robustus Mbenji" has not been evaluated by the IUCN Red List, and as an undescribed form it is not currently eligible for formal assessment. Its documented range is a single island, and no dedicated survey of collecting pressure or habitat condition there has been published. The true Melanochromis robustus that it is traded alongside is assessed as Near Threatened owing to its extremely restricted two-island range, but that status applies to the genuine M. robustus and should not be extended to the Mbenji Island population without its own assessment.