Taxonomy & naming
Petrotilapia sp. "Yellow Chin" has no formal scientific name, describing author, or Catalog of Fishes entry. It is placed in the genus Petrotilapia — literally "rock tilapia," from Greek petra, rock — on the strength of the genus's diagnostic dentition: exceptionally dense, multi-cusped teeth arranged in many rows, among the most specialised algae-scraping mouths of any Lake Malawi mbuna. Petrotilapia is a genus in which even described species are notoriously difficult to separate, because individual populations frequently contain multiple distinct male colour morphs coexisting at the same site rather than a single uniform pattern — a major reason the genus has produced so many informal, locality-based trade names alongside its formally described species. "Yellow Chin" refers to a yellow marking reported on the lower jaw and should not be assumed identical to any similarly named form recorded from elsewhere in the lake.
Morphology
Petrotilapia is built more robustly than most other mbuna genera — a thick-set, "chubby" body with a blunt head housing exceptionally dense rows of long, multi-cusped teeth, among the most specialised algae-scraping dentition in the Lake Malawi cichlid fauna. This form's trade name indicates a yellow marking on the chin or lower jaw, but because Petrotilapia populations are documented as frequently containing several distinct male colour morphs at a single locality, a single simple colour description would likely understate the real variation present in this form; no detailed independently published description beyond the "yellow chin" trait is available for this account.
Habitat
This form is recorded from a set of localities in the south-central part of Lake Malawi, spanning both the Malawian shore — including Maleri Island, Mbenji Island, and Nakantenga Island — and the Mozambican shore at Metangula and Lumessi. Like other Petrotilapia it occupies rocky habitat in the wave-exposed shallow-to-intermediate zone, where its specialised dentition lets it exploit algal turf that other mbuna graze less efficiently. Water conditions follow the lake's standard chemistry: warm, hard, and alkaline, with temperature in the mid-20s Celsius and pH on the alkaline side of neutral.
Feeding
Petrotilapia sp. "Yellow Chin" is among the most specialised algae grazers in the Lake Malawi cichlid fauna, using its exceptionally dense rows of multi-cusped teeth to scrape aufwuchs from the wave-battered rock surfaces the genus favours. This specialisation lets Petrotilapia exploit high-energy surf-zone rock that is less accessible to less specialised grazers. The aufwuchs itself is not a single food but a whole microhabitat -- filamentous and diatomaceous algae bound up with detritus and the small invertebrates that live within it -- so a grazing mbuna takes in a mixed, protein-and-fibre diet in a single bite rather than pure plant matter. Because algal turf grows fastest where sunlight and wave action are both strong, feeding activity and territorial defence of good grazing patches are concentrated in the same shallow, wave-exposed rock that territorial males also use for breeding, tying the two behaviours to the same stretch of habitat.
Mating
No dedicated behavioural study of this specific form exists, but Petrotilapia as a genus follows the standard mbuna pattern of male territoriality: dominant males hold and defend small rock territories and display breeding colouration to attract passing females, with no pair bond and no male involvement beyond courtship and fertilisation. The genus's tendency toward multiple coexisting male colour morphs at a single site adds a layer of complexity to mate choice that is not fully understood even for well-studied Petrotilapia species.
Breeding
Reproduction follows the standard Lake Malawi haplochromine pattern of maternal mouthbrooding: the female collects fertilised eggs into her mouth immediately after spawning and broods them for roughly three to four weeks before releasing free-swimming fry, with no further parental care. Clutch size has not been documented for this form; by analogy with similarly sized Petrotilapia, a clutch of a few dozen eggs is a reasonable expectation. After release, free-swimming fry of Lake Malawi cichlids typically seek out shallow, structurally complex refuge -- crevices among rocks or, for sand-associated species, cover near the shoreline -- where they are less exposed to predators than in open water, sometimes continuing to shelter near the mother for a short period even though she provides no further direct care once they are released.
In the aquarium
Petrotilapia sp. "Yellow Chin" is kept less commonly than the smaller mbuna genera, in part because its larger, more robust build and strongly territorial behaviour call for a bigger tank than a typical Tropheops or Pseudotropheus setup. A rock-dominated tank of at least 59 in with a fine sand base and well-broken sightlines suits a harem group of one male to several females.
Water should replicate Lake Malawi conditions: temperature in the mid-20s Celsius, pH roughly 7.7 to 8.6, and moderately hard to hard water, held stable. Diet should lean strongly vegetable, given the genus's extreme specialisation for algae grazing; a spirulina-based flake or pellet should form the staple, with protein-rich foods kept to a minimum to reduce the risk of bloat.
Conservation
Petrotilapia sp. "Yellow Chin" has not been evaluated by the IUCN and, as an undescribed form, has no Red List assessment of any kind. Its recorded range spans several Malawian and Mozambican island and mainland localities in the south-central lake, but like other rock-restricted mbuna it likely occurs only at specific reefs within that range rather than continuously, leaving individual sites vulnerable to concentrated over-collection. No formal conservation status should be attached to it pending taxonomic description.