Taxonomy & naming
Protomelas sp. "Mbenji Thick-lip" is an informal, undescribed taxon: no describing author, no publication date, and no entry in Eschmeyer's Catalog of Fishes. The trade name follows the standard pattern for such forms — a locality ("Mbenji," for Mbenji Island) paired with the field character that distinguishes it ("Thick-lip"). Mbenji Island is also home to a described, locality-documented population of Protomelas spilonotus, and this form should not be confused with that fish; the two are recorded as separate populations at the same reef, distinguished chiefly by the lip character. Protomelas as a genus is notoriously difficult to key on external features alone — species boundaries typically rest on pharyngeal-bone shape and dentition rather than colour — and several distinctive field populations, this one included, still circulate under provisional "Protomelas sp." tags pending any formal taxonomic review.
Morphology
This form follows the standard Protomelas body plan: a fusiform, laterally compressed haplochromine shape, a continuous dorsal fin, and the genus-typical one or two horizontal stripes along a silvery flank in most colour phases. What sets it apart in the field is dental and soft-tissue rather than meristic: noticeably hypertrophied, fleshy lips, a trait independently evolved in several unrelated Malawi cichlids — Placidochromis milomo and Cheilochromis euchilus among the best documented — usually associated with feeding from tight rock crevices. Detailed colour has not been published for this specific population; Protomelas males are typically far more vividly coloured than females across the genus, and this form is presumed, without direct documentation, to follow that pattern.
Habitat
Protomelas sp. "Mbenji Thick-lip" is recorded from Mbenji Island, an isolated offshore reef roughly midway down the Malawian shore of the lake, in open water well clear of the mainland coast. Most Protomelas are shallow, well-lit-zone fish, generally in the upper 33 ft or so, and the rock-sand transition typical of the genus is the most likely habitat here as well, though no dedicated depth record exists for this particular form. The surrounding water is warm, hard and strongly alkaline, consistent with Lake Malawi generally.
Feeding
A feeding study specific to this population has not been published. In the handful of other Malawi cichlids where hypertrophied lips have been documented in detail, the enlarged, fleshy tissue is understood to cushion the mouth while the fish probes tight rock crevices for hidden invertebrates, letting it work surfaces that a thinner-lipped fish would avoid. Whether this Mbenji form's lip enlargement serves the same crevice-feeding role is a reasonable inference by analogy rather than a documented fact for this specific population. Protomelas more broadly is a genus of shallow-water grazers and gleaners, and absent direct evidence this form is presumed to take a mixed diet of aufwuchs and small invertebrates worked from rock surfaces.
Mating
No courtship account specific to this form has been published. By analogy with the wider genus, a colour-charged, territorial male is expected to hold and defend a site on or near the reef, displaying to passing females with no lasting pair bond — the standard lek-like or loosely polygynous pattern documented across Protomelas. Males of the genus are broadly reported as persistently territorial and aggressive toward similarly coloured rivals, which would apply to this form as well if it follows the genus norm, though that has not been separately confirmed.
Breeding
Protomelas sp. "Mbenji Thick-lip" is presumed to be a maternal mouthbrooder, in keeping with essentially the entire Lake Malawi haplochromine flock. The female is expected to take fertilised eggs into her mouth following courtship and to brood them alone through to free-swimming fry, with no paternal care. No clutch data have been published for this form specifically; documented Protomelas clutches generally scale with adult size and typically run from several dozen to over a hundred eggs, though where in that range this population sits is not known.
In the aquarium
This form has essentially no documented presence in the general aquarium hobby; it is known chiefly through field and collection-locality records rather than trade volume. Where it does appear, standard Protomelas husbandry is the reasonable starting point: a spacious tank with open swimming room and some rockwork, hard alkaline water, and a diet weighted toward vegetable matter and aufwuchs-style foods rather than heavy protein, since Malawi haps are prone to bloat on rich diets. As with any undescribed "sp." fish sharing a locality with a described relative — here, the Mbenji population of P. spilonotus — keepers should avoid mixing the two and should be cautious about provisional trade labels on purchased stock, since hybridisation between similar Protomelas is a recurring problem in the hobby.
Conservation
Protomelas sp. "Mbenji Thick-lip" has no IUCN Red List assessment, since it has never been formally described and no valid scientific name exists for it to be evaluated under. As an island-reef population, it shares the general exposure of Mbenji Island's cichlid community to lake-wide pressures — intensifying artisanal fishing, sediment loading from a deforesting catchment, and gradual warming of the lake's shallow layer — without any dedicated survey of its own numbers or trend. Offshore island reefs like Mbenji are harder to fish intensively than mainland shoreline, which may offer this population some incidental protection relative to inshore mbuna and haps, but that is speculation rather than a documented finding. Its co-occurrence with a described, separately recorded P. spilonotus population at the same reef at least establishes that Mbenji Island is being watched by field surveys, even though this particular thick-lipped form has not itself been the subject of dedicated study.