Taxonomy & naming
Protomelas pleurotaenia was described in 1901 by the Belgian-British ichthyologist George Albert Boulenger, in the Annals and Magazine of Natural History, as Tilapia pleurotaenia, from material taken in Lake Malawi (then Lake Nyasa). It passed for a time through the genus Haplochromis — Trewavas listed it as Haplochromis pleurotaenia in 1946 — before Eccles and Trewavas placed it in their newly defined genus Protomelas in 1989, on the basis of the continuous dark midlateral stripe that characterises the group. Catalog of Fishes records it as valid as Protomelas pleurotaenia (Boulenger 1901), the parentheses marking its removal from the original genus; the lectotype (BMNH 1906.9.6.139) was designated by Eccles and Trewavas. The specific epithet pleurotaenia combines Greek pleura, 'side' or 'flank,' with tainia, 'band' or 'stripe' — 'side-stripe' — a direct reference to the dark lateral band that runs along the fish's flank, the very feature that later justified its placement in Protomelas.
Morphology
Protomelas pleurotaenia is one of the smaller members of its genus, attaining about 4.5 in standard length (around 5.5 in total length). Its meristics are 16–18 dorsal spines with 11–12 soft rays, 3 anal spines with 7–9 soft rays, and 33 vertebrae, and the caudal fin is emarginate (gently notched). The body is fusiform and laterally compressed, and the genus-defining continuous dark midlateral stripe — the 'side-stripe' of the name — runs along the flank. A key diagnostic feature is the small mouth, less than a third of the head length, which separates pleurotaenia from larger-mouthed congeners such as Protomelas kirkii, Protomelas labridens, Protomelas similis, Protomelas marginatus and Protomelas spilonotus. Like Protomelas kirkii and Protomelas labridens it carries some enlarged pharyngeal teeth, the partial crushing dentition that lets it deal with harder-bodied prey. It closely resembles the rare Protomelas macrodon in body form and colour, differing in its smaller eye, shorter premaxillary pedicel and narrower head and body.
Habitat
Protomelas pleurotaenia is endemic to Lake Malawi and has been recorded chiefly from the Monkey Bay area in the south and Nkhata Bay on the western shore. It lives in vegetated areas in the transition zone between rock and sand, at shallow depths — FishBase gives a depth range of roughly 0 to 10 metres. This intermediate rock-and-sand habitat, with patches of vegetation and open sandy floor, is exactly suited to its feeding style: it needs sandy substrate to sift through and the cover and structure of nearby rocks and plants. As a shallow-water inshore species it occupies the well-lit, productive margins of the lake rather than its deep open water.
Feeding
Protomelas pleurotaenia is a sand-sifting invertivore with a distinctive technique: it locates small invertebrates in the sand and exposes them by blowing into the upper layer of sediment, disturbing the surface so that buried prey is revealed and can be picked out. This is a refined version of the substrate-foraging strategy seen in many sand-dwelling Malawi cichlids, where a jet of water or a mouthful of sand is used to winnow edible animals from the grains. Its small mouth suits the delicate picking of small prey, while the enlarged pharyngeal teeth it shares with Protomelas kirkii and Protomelas labridens allow it to crush harder-shelled items once taken. FishBase places its trophic level at about 3.5, the value expected of a small-invertebrate carnivore.
Mating
Courtship in Protomelas pleurotaenia has not been described in detail, but it conforms to the polygynous, maternal-mouthbrooding system that prevails throughout the Lake Malawi haplochromine flock. Males in breeding coloration take up and defend a display site or small territory and court females with lateral displays and quivering runs; a receptive female spawns a small clutch and takes the eggs straight into her mouth, with no enduring pair bond. As a sand-associated species, males would be expected to display over or near the open substrate. The specifics of nuptial colour and display behaviour for pleurotaenia are inferred from its relatives rather than documented in the literature.
One behavioural detail is on record: unlike many Malawi sand-dwellers, mouthbrooding females of this species stay close to the bottom individually rather than forming schools. Konings used exactly this point to question a widely cited literature record — McKaye & Kocher (1983, Animal Behaviour 31) reported the egg-and-larva thief Maravichromis (Caprichromis) liemi stealing broods specifically from P. pleurotaenia, but Konings argued the authors likely misidentified the victim as Nyassachromis microcephalus, whose mouthbrooding females do form schools and are a much better ecological match for that predator's hunting style.
Breeding
Protomelas pleurotaenia is a maternal mouthbrooder, as is standard for its genus and the wider Lake Malawi assemblage. The female incubates a clutch of large, yolk-rich eggs in her buccal cavity for about three weeks, then releases free-swimming fry and continues to take them back into her mouth for protection when threatened for a short period after release. Precise clutch sizes, incubation periods and fry counts specific to pleurotaenia have not been widely published, but the mode is well established by analogy with its many close relatives. Spawning would take place in or near the shallow rock-and-sand habitat the species occupies.
In the aquarium
Protomelas pleurotaenia is recorded by FishBase as being of both commercial and aquarium interest, and as a comparatively small, attractively striped Protomelas it is a plausible aquarium subject, though it is far less of a hobby staple than the well-known 'spilo'/taeniolatus-group Protomelas. Where kept, it suits the standard Lake Malawi setup: a roomy aquarium with a generous open area of sand — important for a fish that naturally sifts the substrate — alongside rockwork and some structure, hard alkaline water (high pH and hardness) at warm rift-lake temperatures, and strong filtration.
Giving it a real sand bed to work is the one husbandry detail that matters most, since substrate-sifting is central to its natural behaviour; fine sand also avoids damage to mouth and gills. A varied diet of small frozen and live invertebrates and a quality cichlid staple suits its small-prey, sand-foraging biology. As a smaller, relatively peaceful hap, it is best matched with similarly sized, non-aggressive Malawi tankmates rather than large, boisterous cichlids.
Conservation
The IUCN Red List assessed Protomelas pleurotaenia in 2018 and listed it as Least Concern. Although its documented records cluster around the Monkey Bay and Nkhata Bay areas, it is not regarded as a threatened species, and the Least Concern listing reflects the absence of evidence for significant decline. As with every Lake Malawi endemic, its longer-term security depends on the health of the lake as a whole, which faces growing pressure from intensive fishing, sedimentation from catchment deforestation, falling water levels and a warming climate. A shallow, sand-associated inshore species like pleurotaenia is particularly exposed to the degradation of inshore habitats through siltation and shoreline disturbance — the very sandy, vegetated margins it depends on. For now it is not of conservation concern in its own right, but it shares the broad vulnerabilities of the lake's inshore cichlid community.