Cichlid Atlas — the world's cichlid waters, in depth

Taxonomy & naming

The species was described by the English ecologist Geoffrey Fryer in 1956, during his doctoral fieldwork on what was then called Lake Nyasa, from rocky shores at Nkhata Bay; the holotype resides in the Natural History Museum, London (BMNH). Fryer separated it from its close relative Labeotropheus fuelleborni and named it for Ethelwynn Trewavas (1900–1993), the British Museum ichthyologist whose earlier synopsis of Lake Malawi's cichlids had advanced the field. The feminine ending "-ae" marks that the honoree was a woman.

The genus Labeotropheus (Ahl, 1927) sits in the cichlid subfamily Pseudocrenilabrinae and belongs to the mbuna, the rock-dwelling species flock of Lake Malawi. The name blends Latin labeo, "one with large lips," with a Greek root, a nod to the conspicuous mouth and feeding apparatus. For decades the genus was treated as holding only two or three species, but Pauers and Phiri's 2023 revision in Ichthyology & Herpetology described six new species, restricting the older names to better-defined populations; under that work L. trewavasae remains valid alongside congeners such as L. fuelleborni, L. chlorosiglos and L. artatorostris. Eschmeyer's Catalog of Fishes lists it as valid. In the trade it is usually sold under its scientific name or by color-form labels such as "red top."

Appearance

This is a small cichlid. FishBase gives a maximum of about 11.7 cm (4.6 in) total length, and Seriously Fish cites roughly 4.5 in (11.25 cm) standard length; in practice most aquarium fish mature smaller. The defining feature is the genus hallmark: a fleshy, rounded snout that overhangs a ventrally placed mouth, with the nose and chin often visibly callused from constant scraping against rock. Compared with its stockier sister species L. fuelleborni, L. trewavasae is noticeably more slender, which is the quickest way to tell the two apart in a tank.

Color is where the species earns its reputation. It is extraordinarily polymorphic, with more than forty recorded color forms across the lake, and the dorsal fin is especially variable from place to place. The common male morph is a barred blue fish, frequently with an orange to red dorsal that is characteristic of southern populations such as Thumbi Island West. Females are most often orange-blotch (OB) — a mottled orange-and-black pattern whose frequency reaches nearly 95% at some localities — with rarer plain-orange (O) females also occurring. The blue-blotch male, the celebrated "marmalade cat," is genuinely rare; collectors in the early 1970s reported finding only about one per year at the southern tip of Thumbi West. Males carry well-defined egg-spots on the anal fin; in females these are faint or absent.

Range & habitat

Labeotropheus trewavasae is a Lake Malawi endemic with a near lake-wide distribution, recorded along the shores and around the islands of Malawi, Mozambique and Tanzania; the IUCN notes it is absent from Mbenji Island. It is a fish of the rocky littoral, favoring large rocks, caves and crevices, and it tolerates both sediment-free reefs and the more turbid, sediment-laden stretches.

Reports of its depth range vary, which is worth stating plainly. Ribbink and colleagues' 1983 survey found it fairly evenly distributed from the surface to about 20 m (65 ft), with records to 34 m (112 ft); FishBase lists a shallower ceiling of about 15 m (49 ft), while the IUCN assessment cites occurrence down to roughly 40 m (130 ft). The fish generally ranges deeper than L. fuelleborni, which concentrates in the top 5 m. In situ the water is hard and alkaline — around pH 8 — and the upper rocky zone it favors is often turbulent and oxygen-rich, conditions its body plan and feeding posture are built for.

Ecology & diet

This is a trophic specialist, an algae scraper that grazes the aufwuchs — the carpet of filamentous algae and the small invertebrates living within it — that coats rocks in the littoral. The mechanics are elegant. With its mouth pointed down and body held parallel to the rock, the fish closes its jaws on firmly attached filaments; the fleshy snout then acts as a fulcrum, so it can shear the algae off by leverage rather than the energy-wasting body jerks other grazers rely on. Three or more rows of tricuspid teeth in the outer jaws crop the loosened algae. Because the body is slender, it can work into narrow caves and the undersides of rocks that bulkier herbivores cannot reach, and it is known to leave visible scrape marks on the stone.

Its diet is not purely vegetarian. Ribbink et al. recorded it feeding on loose aufwuchs and several categories of attached filamentous algae, but also on benthic crustaceans and plankton in varying proportions, and FishBase notes it takes small crustaceans and worms. FishBase places it around trophic level 3.3. Functionally it occupies the abundant grazer guild that converts rock-surface primary production into fish biomass — a central role in the energy budget of Malawi's rocky reefs.

Behavior & breeding

Like all mbuna, L. trewavasae is a maternal mouthbrooder. Territorial males are present year-round and spawn inside a cave within a defended territory. Interestingly, Ribbink and colleagues characterized it as only weakly territorial relative to its congener: males hold large, loosely defended patches among big rocks, often centered on caves, and frequently leave them to feed elsewhere, while females, juveniles and non-territorial males drift singly or in small groups. Hobbyist experience adds a useful nuance — keepers consistently report that the species directs most of its aggression at its own kind rather than at other species, so in a mixed mbuna tank it can be comparatively well-behaved while still bullying conspecifics.

Spawning follows the classic mbuna script. The male displays in intense color over a cleaned site, the female lays a few eggs at a time and takes them into her mouth, and the male's anal-fin egg-spots help ensure fertilization as she mouths near his vent in the characteristic "T" position. Reported clutch sizes run roughly 10 to 40 eggs, with captive accounts of around 19 to 25 fry common. The female broods for about three to four weeks without feeding. A charming detail noted by breeders: fry can often be sexed on release, with males emerging dark grey and females yellowish.

In the aquarium

This is a rewarding but not a beginner fish, and the honest framing matters. It is hardy and readily bred, but males are persistently aggressive toward conspecifics and the species is best kept as a single male with several females. Specialists recommend at least a 200-liter (about 55-gallon) tank, and many experienced keepers want a four-foot (120 cm) footprint as a practical minimum so subordinate fish have room to escape. Aquascape with stacked rock forming caves and crevices over a sandy bottom; live plants are pointless, as they will be grazed.

Water should mirror the lake: hard and alkaline, roughly pH 7.6–8.8 (around 8 is ideal), 10–25 dH, and warm, about 75–82°F (24–28°C). Diet should lean heavily vegetable — spirulina-based flakes, blanched greens — supplemented modestly with frozen or live daphnia, brine shrimp and the like; a protein-heavy diet invites the bloat that plagues mbuna. Keep it with other robust mbuna rather than gentler peacocks or utaka, which it will stress, and slight overstocking with plenty of rockwork helps spread aggression. Two cautions keepers raise often: do not mix it with congeners such as L. fuelleborni or different L. trewavasae color forms, since they hybridize readily, and be patient with brooding females, which may spit or eat a clutch if harassed or moved too soon.

Conservation

The IUCN Red List assesses Labeotropheus trewavasae as Least Concern (assessed 22 June 2018; errata version 2019; assessors Konings and Kazembe), with a stable population trend. It is widespread across the lake — estimated extent of occurrence around 29,600 km² and area of occupancy about 1,220 km² — common at deeper rocky habitats, and it occurs within Lake Malawi National Park, which affords some protection. The assessment flags two specific, ongoing pressures: sedimentation, and extraction by the ornamental fish trade, the latter noted as continuing without an apparent decline in the population. In short, the species itself is not currently threatened.

That verdict, however, sits inside a lake under real strain, and a rocky-shore grazer is exposed to exactly the pressures the basin faces. The 2023 status review of the Lake Malawi/Niassa/Nyasa basin by Chavula and colleagues (Journal of Great Lakes Research 49(6):102241) documents heavy over-fishing and the collapse of the chambo (Oreochromis) fishery, rising sediment and nutrient loading from deforested catchments, and roughly +0.7°C of shallow-water warming that strengthens stratification and suppresses the deep mixing that fuels productivity, alongside invasive-species risk. For L. trewavasae the most direct link is sedimentation: silt smothers the rock-surface aufwuchs it grazes and degrades the clear, oxygen-rich reefs it favors, while warming and reduced mixing reshape the productivity base of the littoral. None of this has yet moved the species off Least Concern, and it would be an overstatement to call it imperiled — but its security depends on the health of a shallow rocky habitat that the basin's trajectory is steadily eroding.

Labeotropheus trewavasae

About this species