Taxonomy & naming
Maylandia sp. "Black Dorsal Mbenji" has no describing author and no entry in Eschmeyer's Catalog of Fishes; it is a hobby and locality-database trade name, not a validated scientific one. Maylandia was split out of the broader Pseudotropheus complex and honours the German aquarist Hans J. Mayland; it holds most of the classic Lake Malawi "zebra" mbuna, a colour pattern that recurs with substantial local variation at rocky localities across the lake. Mbenji Island, an offshore island in central-west Lake Malawi, is one of the best-known such localities, documented repeatedly in Ad Konings' field guides as home to unusually large and richly coloured zebra-type Maylandia populations. "Black Dorsal" identifies the diagnostic feature used to separate this particular Mbenji form from the island's other zebra-complex populations, which vary in dorsal fin, body-bar and background colour from one micro-locality to the next around the island.
Morphology
"Black Dorsal Mbenji" is expected to follow the classic Maylandia zebra-complex build: a moderately deep, laterally compressed body, blunt head, and specialised grazing dentition, carrying the vertically barred pattern typical of the complex. As the name indicates, the dorsal fin is reported as black or blackish, a feature used to tell this form apart from other Mbenji zebra populations with differently coloured dorsals. Genus-typical size for zebra-type Maylandia runs to roughly 3.5–5 in total length, but Mbenji Island populations are specifically noted in the hobby literature for growing unusually large, with some reports of individuals reaching toward the upper end of that range and beyond; no validated maximum has been published for this exact form.
Habitat
Mbenji Island sits offshore in central-west Lake Malawi and is composed largely of steep, boulder-strewn rock shoreline dropping into deeper water, prime zebra-complex mbuna habitat. "Black Dorsal Mbenji" was recorded there; specific depth data are not available, but genus-typical Maylandia at comparable rocky localities occupy roughly 7–49 ft, with larger individuals sometimes ranging somewhat deeper. Mbuna in general show strong site fidelity, rarely moving more than a few dozen metres from a home rock pile over a lifetime — a pattern of limited dispersal identified by early Lake Malawi researchers such as Ribbink and colleagues as a key driver of the group's extraordinary local diversification, since populations on separated rock outcrops become genetically isolated from one another even at short distances.
Feeding
As in other Maylandia, this form is presumed to be an aufwuchs grazer, scraping algal film and associated diatoms and small invertebrates from rock surfaces. No feeding study specific to this form has been published, but there is no reason from genus placement to expect a different diet. Mbuna dentition is adapted for this grazing lifestyle: numerous small, closely packed teeth arranged in rows are shed and replaced continuously through life, and different mbuna genera and species partition the same rock surface by targeting algae at different depths within the aufwuchs mat, a trophic specialisation documented across the group since Fryer and Iles' influential 1972 ecomorphological study.
Mating
Maylandia breeding follows the standard mbuna pattern: males hold and defend a cave or rock crevice territory, displaying to visiting females before spawning. No courtship observations specific to this form have been published, though Mbenji's zebra-type populations are generally described in the hobby literature as robust and assertive breeders, consistent with their reputation for large size. As in essentially all Malawi mbuna, courting males are expected to display the egg-spot markings on the anal fin that mimic eggs, prompting the female to mouth at them during spawning and draw in sperm to fertilise the clutch she is already collecting.
Breeding
Reproduction is maternal mouthbrooding, as in all Maylandia: after spawning at the male's territory, the female carries the fertilised eggs alone in her mouth for roughly three weeks before releasing free-swimming fry. Clutch size has not been documented for this specific form; larger-bodied zebra-complex Maylandia, a category Mbenji populations often fall into, tend toward the higher end of the genus's typical range of a few dozen eggs. Incubation at typical Lake Malawi temperatures runs close to three weeks, during which the brooding female feeds little if at all and often withdraws to a sheltered rock crevice; fry are released well developed and immediately able to shelter among the rocks.
In the aquarium
Mbenji Island forms are relatively well known to Malawi cichlid specialists because of the island's reputation for size and colour, but "Black Dorsal Mbenji" specifically should still be treated as a limited, locality-specific import. Standard mbuna care applies: a heavily rock-aquascaped tank with generous swimming space to match the larger adult size expected of Mbenji populations, hard alkaline water matching Lake Malawi chemistry, and a vegetable-forward diet suited to its grazing habit. A tank of at least 47 in with dense, stable rockwork built to the substrate rather than resting on it, to prevent collapse, best replicates its natural territory structure, and a vegetable-based flake or pellet diet with limited protein helps avoid the digestive problems mbuna are prone to on richer foods.
Conservation
As an undescribed form, "Black Dorsal Mbenji" has not been assessed by the IUCN and carries no conservation status. Mbenji Island is a well-known and long-collected locality for the aquarium trade; sustained collecting pressure on an isolated island population is a general concern for such localities, but no population data specific to this form are available. More broadly, this is a structural gap common to many Malawi mbuna: an undescribed, single-locality form cannot receive an IUCN assessment without a formal description, even though a population confined to one rock reef can be as vulnerable to local over-collection or habitat disturbance as many formally listed species.