Taxonomy & naming
Pseudotropheus sp. "Acei" is undescribed. It has no holotype, no describing author, no publication year and no entry of its own in Eschmeyer’s Catalog of Fishes; despite its popularity in the aquarium trade — arguably greater than that of many formally named mbuna — it remains, strictly, an informal trade name. Pseudotropheus in its modern, restricted sense (following the splitting-off of Maylandia, Tropheops and other genera from the old broadly defined "Pseudotropheus") retains a smaller set of species, and "Acei" is placed here on general resemblance and long-standing trade convention rather than a published phylogenetic analysis. The origin of the specific label "Acei" itself is not documented in the accessible literature; it functions purely as a proper trade name rather than a descriptive term, and different populations along the western shore — sometimes distinguished in the hobby as "Acei" versus the more golden "Msobo" form from further north — may not all represent the same lineage.
Morphology
What sets "Acei" apart from most mbuna at a glance is its body shape: distinctly more slender and elongated than the typical barrel-bodied rock-scraper, an adaptation that suits its habit of feeding in open water rather than pressed against rock. Adults reach roughly 4–5 in, males somewhat larger than females. Colour varies by collection locality — populations along this stretch of the western shore tend toward a pale blue-grey body with a yellow or cream dorsal fin and, often, yellow tinting to the caudal fin, the pattern behind the "yellow-tail" trade name — while males generally show more saturated blue than females. Females and juveniles are typically paler and less contrastingly finned. As an undescribed form, no published measurements or meristic counts exist; the above reflects consistent hobby and field observation rather than a formal diagnosis.
Habitat
This form has been recorded from Dwangwa, Chimwalani Reef, Luwala Reef, Msuli Point and Senga Bay, a span of the central-western Malawian shore. Unlike most mbuna, which stay close to rock, "Acei" is often found over mixed rock-and-sand habitat and in open water near rocky shorelines, including around submerged wood and plant debris where it forages — a broader habitat use consistent with its midwater feeding style. Water at these sites follows the lake’s typical profile: warm, hard and alkaline, roughly 75–82 °F and pH 7.7–8.6, generally in shallow to moderate depths of a few to around 49 ft.
Feeding
Pseudotropheus sp. "Acei" is unusual among mbuna in feeding substantially in the water column rather than scraping algae directly from rock. It picks loose algae, diatoms and fine organic material from the surface of submerged wood, plants and debris, and also takes food items suspended in open water, a strategy closer to plankton-picking than to the classic rock-grazing mode of most Pseudotropheus, Tropheops and Petrotilapia. This feeding style is reflected in its comparatively relaxed social behaviour: because it is not defending a fixed grazing patch on rock in the way most mbuna do, it is markedly less aggressive and more comfortable in loose aggregations than the majority of its rock-bound relatives.
Mating
Like other mbuna, "Acei" is polygynous with no pair bond, but its social temperament away from spawning is notably more relaxed than most Pseudotropheus. Males establish a breeding territory, typically near rock or structure, and display to attract females, though they are markedly less relentlessly aggressive toward tankmates and conspecifics outside active spawning than deep-bodied rock-scraping mbuna tend to be — a trait widely noted by hobbyists and consistent with its habit of feeding and schooling in loose groups rather than defending a continuous grazing territory. Courtship follows the standard haplochromine pattern of display and quivering leading to spawning at the male’s site.
Breeding
Pseudotropheus sp. "Acei" is a maternal mouthbrooder, as are all Malawi mbuna. After spawning, the female takes the fertilised eggs into her mouth, fertilisation completed via the egg-spot mechanism on the male’s anal fin, and carries the clutch through incubation for roughly three to four weeks, feeding little during this period. She then releases free-swimming fry that receive no further parental care. Clutch size runs from roughly 20 to 40 eggs depending on female size, broadly typical for a mbuna of this size class, and "Acei" is considered one of the easier and more prolific mbuna to breed in captivity.
In the aquarium
Pseudotropheus sp. "Acei" is among the more forgiving mbuna for a mixed-species Malawi tank, precisely because its midwater feeding habit and looser social structure make it less relentlessly territorial than typical rock-scrapers. A tank of at least 47 in with rockwork for shelter and open swimming space suits it well, and it does best kept in a group rather than a single pair, since its natural inclination is loose aggregation rather than strict territoriality.
Water should replicate Lake Malawi: temperature 75–82 °F, pH 7.7–8.6, and hard, alkaline chemistry maintained consistently. Diet should lean vegetable — a spirulina-based flake or pellet as the staple — supplemented with occasional small live or frozen invertebrates; because it naturally picks food from the water column, sinking foods are less essential for it than for strict bottom feeders. Its comparatively calm temperament makes it a popular choice for stocking a community mbuna tank alongside other moderately assertive species, though it remains a true mbuna and should not be housed with peaceful non-Malawi fish.
Conservation
No IUCN Red List assessment exists for Pseudotropheus sp. "Acei", and none can while it remains formally undescribed — an unusual situation given how widely and commercially the fish is kept, but the trade popularity of an undescribed form has no bearing on its taxonomic or conservation status. No status, category or year should be attached to it. Because it is heavily collected for the aquarium trade along an accessible stretch of the western shore, ornamental collection pressure is a more relevant consideration for this form than for many less-traded mbuna, though no data quantify the scale of that pressure on wild populations. The accurate statement remains that it is unevaluated.