Taxonomy & naming
Pseudotropheus sp. "Aggressive Grey" is an informal, undescribed taxon with no describing author, no publication date, and no entry in Eschmeyer's Catalog of Fishes. The placeholder name follows the standard convention for undescribed mbuna: the genus Pseudotropheus, the abbreviation "sp." marking it as an unnamed species, and a descriptive tag — here, "Aggressive Grey" — drawn directly from the fish's most obvious traits in the field and in captivity, rather than from a locality or a resemblance to a described relative. Within Pseudotropheus sensu stricto (the genus as it stands after the splitting-off of Maylandia, Metriaclima, Tropheops, Chindongo, and Cynotilapia from the older, broader "Pseudotropheus" concept), this form has not been assigned a close relative in the published literature available to us. It should be treated strictly as a Likoma-area, informally recognised form pending any future taxonomic review.
Morphology
This form carries the standard mbuna body plan shared across Pseudotropheus: a moderately elongate, laterally compressed body, a blunt-to-moderately pointed snout, and the robust jaws and specialised dentition — an outer row of movable bicuspid or unicuspid teeth backed by inner rows of tricuspid teeth — that the genus uses to scrape algae and associated microfauna from rock surfaces. As its trade name indicates, its most notable feature is coloration rather than form: both sexes are predominantly grey, without the strongly saturated blues, yellows, or oranges seen in many showier mbuna, though the precise extent of sexual dichromatism in colour intensity or pattern has not been documented in detail for this specific population. Size has not been separately documented for this form; it is presumed to fall within the genus-typical range for Pseudotropheus, roughly 3–4.5 in.
Habitat
Pseudotropheus sp. "Aggressive Grey" is documented from the rocky habitat around Likoma Island and the nearby islands of Maingano and Masimbwe in central Lake Malawi — an area of the lake well known for dense rock piles and a correspondingly dense, diverse mbuna community. Like other Pseudotropheus, it is expected to occupy the intermediate-to-shallow rocky zone typical of the genus, holding territory among boulders and crevices rather than venturing onto open sand. Conditions here match the lake generally: warm, hard, and strongly alkaline water year-round.
Feeding
As with other members of the genus, Pseudotropheus sp. "Aggressive Grey" is expected to be a specialised algae grazer, using its genus-typical dentition to rasp the mat of filamentous algae and associated diatoms and small invertebrates — collectively known as Aufwuchs — from the surface of rocks. A feeding study specific to this form has not been published, but this diet is essentially universal across rock-dwelling Pseudotropheus and closely related mbuna genera. The Aufwuchs mat itself is not a single food type but a mixed community of filamentous green algae, diatoms, cyanobacteria, and the small invertebrates that live within it, and different mbuna species partition this resource by grazing angle, bite force, and preferred rock texture rather than competing head-on for an identical diet. Dense mbuna populations can crop the algal turf on a favoured rock down to a fine stubble, and territorial males often defend a feeding patch as fiercely as a spawning site, since a well-grazed rock represents a defensible, renewable food source rather than a one-off meal.
Mating
Breeding in this genus is polygynous, with no pair bond: territorial males hold and defend rock or crevice sites and display to passing females, who visit males rather than forming lasting associations. The temperament that gives this form its trade name is relevant here — Pseudotropheus mbuna are already among the more combative Lake Malawi cichlids, and this population is specifically noted for aggression beyond what is typical even within that context, which shapes how it needs to be managed both in its natural rock community and in captivity. Courtship follows the conventional haplochromine sequence: a territorial male performs a quivering lateral display in front of a visiting female, leading her toward his spawning site if she is receptive. The male's anal fin typically carries egg-spot markings — round, egg-like blotches — that the female is drawn to peck at after depositing her own eggs, a mechanism that draws sperm into her mouth and fertilises the clutch she is already holding. A dominant male may court and spawn with several females in the course of a single day, and females themselves show no lasting preference for one male over another beyond his current colour and territory quality.
Breeding
Pseudotropheus sp. "Aggressive Grey" is a maternal mouthbrooder, as are all Pseudotropheus. Following courtship at a male's territory, the female takes the fertilised eggs into her mouth and carries them through incubation, foregoing normal feeding for much of that period before releasing free-swimming fry with no further male involvement. Clutch size has not been documented for this specific form but is expected to fall within the modest range typical of similarly sized Pseudotropheus, on the order of a few dozen eggs. At Lake Malawi's stable warm temperatures the female typically broods for roughly three to four weeks, during which she retreats into rock crevices for shelter and largely stops feeding, drawing on body reserves to see the clutch through development. Fry are released as fully formed, free-swimming miniatures able to feed independently from the moment of release, and they immediately seek cover among rocks to avoid predation, including from adult cichlids of their own species. There is no further parental care once the fry are released, and a healthy female can produce several broods per year under stable conditions.
In the aquarium
"Aggressive Grey" is a niche form in the hobby, generally sought by keepers who specifically want a Likoma-area Pseudotropheus rather than one of the more colourful mainstream mbuna.
Because of the elevated aggression its name references, this fish needs a rockwork-dense tank with abundant broken sightlines and more territories than the tank's male population, so that subordinate fish always have somewhere to retreat and hide. A tank of at least 47 in is a reasonable minimum, and it should be stocked densely with other robust mbuna rather than kept sparsely, since crowding actually diffuses aggression in this group by preventing any single fish from monopolising the whole tank. Water should replicate Lake Malawi conditions: warm, hard, and alkaline, with stable pH clearly above neutral.
Diet should be predominantly vegetable and algae-based — a quality spirulina-based flake or pellet as a staple, with occasional blanched vegetables — since a high-protein diet is poorly tolerated by algae-grazing mbuna and predisposes them to bloat. Given its temperament, tankmates should be chosen from similarly robust, similarly sized mbuna rather than gentler or slower species that would be outcompeted or bullied.
Conservation
Pseudotropheus sp. "Aggressive Grey" has no IUCN Red List assessment, because it has never been formally described and has no valid scientific name available to be assessed. This reflects its taxonomic status, not a claim about its population health. As a rock-restricted mbuna from a well-known and actively collected part of the lake, it faces the general pressures common to Lake Malawi's ornamental cichlids, but no dedicated population data exists to characterise its actual conservation status. Because Lake Malawi's mbuna are typically confined to narrow, rock-specific home ranges and rarely cross expanses of open sand, a locality-restricted form like this is inherently more exposed to over-collection or localised habitat disturbance than a wide-ranging species would be, even though the lake as a whole supports enormous numbers of related mbuna.