Taxonomy & naming
Mylochromis sp. "Guentheri Mbenjii" has no scientific description, no describing author or year, and does not appear in Eschmeyer's Catalog of Fishes or on FishBase. The trade name is built the way most undescribed Malawi cichlid names are: a resemblance tag to a described species, here Mylochromis guentheri (Regan, 1922), plus a locality qualifier, "Mbenjii," referring to Mbenji Island. Mylochromis guentheri itself is a widespread, well-documented sand-dweller named for the ichthyologist Albert Günther. This form is presented in the hobby as similar in build and habits to M. guentheri but collected from areas away from that species' best-documented sites, and it has never been assigned to the described species with confidence. Until a taxonomic revision examines specimens directly, it should be treated as an open question rather than a settled identification, and no authority or publication date should be attached to it.
Morphology
As a form allied to Mylochromis guentheri, this fish is expected to share that species' build: an elongate, moderately compressed sand-dwelling haplochromine body with the low, gently sloping head profile typical of Mylochromis species that forage over open sediment rather than ambush prey. Mylochromis guentheri reaches roughly 8 in TL, and a similar maximum is a reasonable estimate here pending direct measurement. No colour description specific to the Maleri Island population has been published. Genus-typical dimorphism is expected — non-breeding fish and females carrying a silvery body with a dark oblique lateral stripe, breeding males intensifying that pattern with stronger contrast — but the details have not been documented for this particular form, and none are invented here.
Habitat
The only locality recorded for this form in this dataset is Maleri Island, one of a small group of islands in the central-western part of Lake Malawi that sit on a mix of rock, intermediate sand-and-rubble, and open sand habitat. Mylochromis species in general, and M. guentheri specifically, are sand-associated foragers rather than rock specialists, typically working the sediment adjacent to rocky structure rather than the reef itself. Water in this part of the lake follows the typical Malawi profile: warm, hard, and strongly alkaline, with the sandy foraging zone generally lying in the upper tens of metres of the water column rather than the deep basin.
Feeding
This form is presumed to feed as Mylochromis guentheri and its relatives do: foraging over sand and taking small invertebrates and organic material from the sediment surface. Mylochromis as a genus spans a range of feeding modes from generalist sand-sifting to more specialised molluscivory and piscivory in certain species; without a confirmed identity for this Maleri Island form, the safest statement is the genus-typical one — a benthic invertivore working loose sand and the fine layer of detritus and micro-invertebrates on top of it, rather than a committed hunter of fish or snails.
Mating
No dedicated study of courtship exists for this form. Lake Malawi haplochromines in general, and Mylochromis species specifically, are polygynous with no pair bond: males hold loosely defended territories on or near sand, display to passing females with fin-spreading and lateral posturing, and females move between territories to select a mate. Aggression levels vary across the genus from relatively mild sand-dwellers to more combative species; without species-level certainty here, a cautious, genus-typical level of male territoriality during breeding condition should be assumed.
Breeding
Mylochromis sp. "Guentheri Mbenjii" is presumed to be a maternal mouthbrooder, the universal reproductive strategy of the Lake Malawi haplochromine flock. Spawning would take place on a cleared patch of sand or a shallow depression, with the female taking fertilised eggs into her mouth immediately after laying and carrying them through several weeks of development before releasing free-swimming fry. No male or biparental care is expected beyond fertilisation. Clutch size has not been documented for this form; for a mid-sized Mylochromis, a range of a few dozen eggs per spawning is a reasonable estimate by analogy with better-studied congeners rather than a measured figure.
In the aquarium
This form is uncommon in the hobby and does not have an established husbandry record distinct from other Mylochromis sand-dwellers. A keeper who obtains it should follow the general template for a mid-sized Malawi sand hap: a tank of at least 47–59 in in length, a soft sand substrate of several centimetres to support natural foraging, and water matched to the lake's chemistry — roughly 75–82 °F, pH 7.7 to 8.6, and moderately hard to hard. It is expected to be reasonably peaceable by Malawi standards, suitable for a community of similarly sized haps and peacocks rather than the rock-holding mbuna, though this has not been directly tested for the form specifically.
Conservation
No IUCN Red List assessment exists for Mylochromis sp. "Guentheri Mbenjii", and none can until it receives a formal taxonomic description. Its described relative, Mylochromis guentheri, is a widespread species across much of the lake and has not raised particular conservation concern. Whether this specific Maleri Island population faces different pressures — from the general threats affecting the lake's inshore fisheries, including small-scale netting and habitat disturbance near settled islands — is not documented. The honest position is that this form is unassessed and its status unknown.