Taxonomy & naming
Pseudotropheus sp. "Aggressive Yellow Fin" is an informal, undescribed taxon: no describing author, no publication date, and no entry in Eschmeyer's Catalog of Fishes. The tag follows the standard convention for undescribed mbuna field forms: the genus, "sp." marking it as unnamed, and a descriptive pair of traits — temperament and colour — drawn from direct field and hobby observation rather than locality or resemblance to a described species. "Aggressive" is used across several such Pseudotropheus field forms recorded at different reefs in the lake, of which "Aggressive Yellow Fin" at Chizumulu Island is one; a separately recorded "Aggressive Grey" form from the Likoma Island cluster is another. The shared tag does not imply the two are the same population — they are recorded at different reefs with different colour characters — only that field workers use the same temperament-based label across more than one distinct group.
Morphology
This form carries the standard mbuna body plan shared across Pseudotropheus: a moderately elongate, laterally compressed body, 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. Its trade name identifies yellow-toned fins as the defining colour character, setting it apart from the drab grey body colour reported for the separately recorded "Aggressive Grey" form; how the rest of the body is patterned, and how strongly males and females differ, has not been documented in detail for this Chizumulu population. Size has not been separately measured for this form and is presumed to fall within the genus-typical range for Pseudotropheus, roughly 3–5 in.
Habitat
Pseudotropheus sp. "Aggressive Yellow Fin" is documented from the rocky habitat around Chizumulu Island, a smaller island lying between Likoma Island and the Mozambican mainland in central Lake Malawi, an area known for dense boulder piles and a correspondingly rich mbuna community. Like other Pseudotropheus, it is expected to hold territory among rocks and crevices in the shallow-to-intermediate rocky zone rather than venturing onto open sand. Water conditions match the lake generally: warm, alkaline and well-buffered year-round.
Feeding
As with other members of the genus, this form is expected to be a specialised algae grazer, using its genus-typical dentition to rasp the aufwuchs mat — a mixed community of filamentous algae, diatoms, cyanobacteria and small invertebrates — from rock surfaces. No feeding study specific to this Chizumulu population has been published, but the diet is essentially universal across rock-dwelling Pseudotropheus and closely related mbuna genera. Territorial males often defend a well-grazed feeding patch as fiercely as a spawning site, and the combative temperament that gives this form its trade name would be expected to extend to resource defence at the rock face as much as to spawning territory.
Mating
Breeding in this genus is polygynous with no lasting pair bond: territorial males hold rock or crevice sites and display to passing females, who visit rather than pair permanently. The temperament flagged in this form's trade name is directly relevant to its social behaviour — Pseudotropheus mbuna are already among the more combative Lake Malawi cichlids, and "Aggressive"-tagged forms are specifically noted as standing out even within that baseline, which shapes how the species needs to be managed both on the reef and in captivity. Courtship follows the standard haplochromine sequence, with the male's anal-fin egg-spots drawing the female to peck and thereby fertilise the clutch she is already holding in her mouth.
Breeding
Pseudotropheus sp. "Aggressive Yellow Fin" 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, largely foregoing normal feeding, 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, with brooding lasting roughly three to four weeks at Lake Malawi's stable warm temperatures.
In the aquarium
"Aggressive Yellow Fin" is a niche form sought by keepers specifically wanting a Chizumulu-area Pseudotropheus rather than one of the more mainstream mbuna. Because of the elevated aggression referenced in its name, this fish needs a rockwork-dense tank with abundant broken sightlines and more territories than the tank's male population, so subordinate fish always have somewhere to retreat. A tank of at least 47 in stocked densely with other robust mbuna is a reasonable approach, since crowding tends to diffuse aggression in this group rather than concentrate it on one victim. Diet should be predominantly vegetable and algae-based, since a high-protein diet is poorly tolerated by algae-grazing mbuna and predisposes them to bloat.
Conservation
Pseudotropheus sp. "Aggressive Yellow Fin" has no IUCN Red List assessment, because it has never been formally described and has no valid scientific name available to be assessed. As a rock-restricted mbuna tied to a specific island in a part of the lake that is actively collected for the ornamental trade, it faces the general pressures common to Lake Malawi's mbuna community, but no dedicated population data exists to characterise its actual status. Locality-restricted mbuna forms like this one are inherently more exposed to over-collection or localised habitat disturbance than wide-ranging species, since mbuna rarely cross expanses of open sand between rocky reefs.