Taxonomy & naming
Protomelas spilopterus was described by Ethelwynn Trewavas in 1935, in the Annals and Magazine of Natural History, as Haplochromis spilopterus, from material collected between the Shire Bar and Nkhudzi at the southern end of Lake Malawi (then Lake Nyasa). Eccles and Trewavas transferred it to their newly erected genus Protomelas in 1989, on the basis of the continuous dark midlateral stripe shared by the group; the lectotype (BMNH 1935.6.14.644) was designated in that work. Its generic placement has not been entirely settled: Konings (2016) treated it as Hemitaeniochromis spilopterus, and the 2020 description of the paedophage Protomelas krampus used spilopterus as a key comparison, since the two share a paedophagous habit but differ in numerous proportions and in dentition. Catalog of Fishes, the nomenclatural authority, lists the current status as valid as Protomelas spilopterus (Trewavas 1935). The specific epithet spilopterus combines Greek spilos, 'spot,' with pteron, 'wing' or 'fin' — 'spotted-fin' — referring to spotting on the fins.
Morphology
Protomelas spilopterus is the largest Protomelas treated here, reaching about 9.5 in total length, with the fusiform, laterally compressed body typical of the genus and the genus-defining continuous dark midlateral stripe along the flank. The epithet records spotting on the fins as a colour feature. Its functional anatomy is the most telling thing about it: the structure of the mouth and pharyngeal dentition led earlier workers to infer that it is a paedophage, a fish adapted to feeding on the broods of other cichlids. The 2020 study describing Protomelas krampus contrasted the two in detail and recorded spilopterus as having a gentler gape inclination (40–60 degrees versus krampus's 70–80), a deeper body and head, a longer premaxillary pedicel, fewer vertebrae (29), inner teeth that are mixed unicuspid and tricuspid or wholly unicuspid, and outer lower-jaw teeth angled forward — characters that distinguish it from its more recently described, single-tooth-rowed relative. As with most Malawi haps, breeding males are expected to be more colourful than females.
Habitat
Protomelas spilopterus is endemic to Lake Malawi and, unlike some of its more localised relatives, occurs throughout the lake. FishBase describes it as uncommon, and gives a temperature range of roughly 75–79 °F consistent with the warm surface and inshore waters of the lake. As a suspected paedophage, it is tied to areas where other cichlids breed, so it would be expected wherever the lake's dense mouthbrooding communities concentrate. Detailed depth and microhabitat data have not been published, but its lake-wide distribution and its dependence on the broods of host species place it within the broad inshore and intermediate zones where Malawi's haplochromine and mbuna fishes are abundant.
Feeding
Protomelas spilopterus is regarded as a paedophage — a specialist predator on the eggs and larvae of other cichlids — an inference drawn from the structure of its mouth and pharyngeal dentition rather than from a large body of feeding observations. In Lake Malawi, paedophagy has evolved repeatedly, and several species make their living by extracting broods from mouthbrooding females, whether by ramming them to dislodge the clutch or by other means. The contrast with the more recently described Protomelas krampus is instructive: both are paedophagous Protomelas, but spilopterus has a less extreme upturned gape and a different dentition, suggesting a related but distinct approach to the same unusual food source. FishBase places its trophic level at about 3.3, the value expected of a carnivore feeding on small, high-protein animal prey.
Mating
No detailed courtship account exists for Protomelas spilopterus, but as a Lake Malawi haplochromine it is a polygynous, maternal mouthbrooder. Males in breeding colour establish and defend a display site and court females with lateral displays and quivering runs; a receptive female spawns a small clutch and immediately takes the eggs into her mouth, with no lasting pair bond. FishBase notes mouthbrooding by females for this species. The finer points of male nuptial colour and display behaviour are inferred from the broader flock rather than recorded specifically for spilopterus.
Breeding
Protomelas spilopterus is a maternal mouthbrooder — FishBase explicitly records mouthbrooding by females. The female incubates a clutch of large, yolk-rich eggs in her buccal cavity for roughly three weeks, then releases free-swimming fry and continues to gather them back into her mouth for protection when threatened for a short period afterward. As with the other paedophagous cichlids of the lake, there is a certain irony in a brood-robber being itself a mouthbrooder, exposed to the same predation it practises. Precise clutch sizes, incubation times and fry counts specific to spilopterus have not been widely published, and the details rest on analogy with the well-studied breeding biology of the Malawi flock.
In the aquarium
Protomelas spilopterus is listed by FishBase as being of both commercial and aquarium interest, but it is an uncommon fish and not a mainstream hobby species, and its suspected paedophagy makes it an awkward proposition for a breeding community tank. Where kept, it would follow the standard large-Malawi-hap regime: a spacious aquarium with sand, rockwork and open swimming space, hard alkaline water (high pH and hardness) at warm rift-lake temperatures around the mid-20s Celsius, and robust filtration.
The practical catch is the same as for other paedophages: housing spilopterus alongside actively breeding mouthbrooders simply gives it the opportunity to predate their broods, so it is poorly suited to a tank intended for raising other cichlids' fry. At around 9.5 in it is also a substantial fish needing real space and similarly robust tankmates. In short, it is a species of more interest for its biology than for general aquarium keeping, with little established husbandry track record to draw on.
Conservation
Protomelas spilopterus has not been given a current IUCN Red List status in the data reproduced by FishBase, so it is best treated here as Not Evaluated pending confirmation of any assessment. It is described as uncommon but occurs throughout Lake Malawi, which argues against it being a narrow-range endemic; as a suspected paedophage, however, it would naturally be scarcer than the host species it exploits. Its conservation outlook is therefore best read at the scale of the lake, whose remarkable cichlid flock faces intensifying fishing pressure, sedimentation from catchment deforestation, declining water levels and the cascading effects of a warming climate on the lake's productivity. A naturally uncommon specialist embedded in that community shares those broad risks, and basic survey and assessment work would be needed before its status could be judged with confidence.