Taxonomy & naming
Pollimyrus nigripinnis was described by the Belgian-born zoologist George Albert Boulenger in 1899, originally as Marcusenius nigripinnis, in the Annales du Musée du Congo. The type locality is Kutu, on Lake Leopold II in the Upper Congo — a lake known today as Lac Mai-Ndombe, in the Democratic Republic of the Congo. Syntypes are held at the Natural History Museum in London and the Royal Museum for Central Africa in Tervuren. The species belongs to the family Mormyridae within the order Osteoglossiformes, the bonytongues, and is currently placed in the subgenus Pollimyrus of the genus Pollimyrus.
A 2024 morphometric synthesis of the genus by Dierickx and colleagues, published in the Journal of Fish Biology, compared the type series of P. nigripinnis against the similarly Boulenger-described Pollimyrus pulverulentus and found slight to no consistent differences between them. The authors proposed nigripinnis as a junior synonym of pulverulentus. That revision is not treated as settled here — this account is kept separate pending wider taxonomic consensus, and anyone researching Congo basin Pollimyrus should be aware the two names may refer to the same fish.
Morphology
Pollimyrus nigripinnis is a small mormyrid, reaching about 4.5 in in total length — one of the smaller of the so-called dwarf stonebashers in its genus. Detailed morphometric description beyond the original 1899 account and the 2024 comparative study is limited; like other small Pollimyrus species it has a laterally compressed body, a blunt head, and a single dorsal fin set back over the anal fin, a build shared across the genus rather than a feature unique to this species.
As in all mormyrids, an electric organ near the base of the tail produces a weak pulse discharge, read through electroreceptors that cover the head and the dorsal and ventral body — though notably not the flanks or the caudal peduncle itself, where the organ sits. No species-specific electric organ discharge waveform has been published for P. nigripinnis; related congeners such as Pollimyrus isidori and Pollimyrus adspersus have documented discharges, but confirmation for this species is lacking. Mormyrids as a group carry one of the largest brain-to-body mass ratios of any vertebrate, with an enlarged cerebellum devoted to processing this electrosensory stream.
Habitat
The species is native to central Africa, recorded from the Democratic Republic of the Congo, the Republic of the Congo, and Cameroon, in the central and upper Congo River basin. Its type locality is Kutu, on Lake Leopold II — known today as Lac Mai-Ndombe — in the Upper Congo.
It is a freshwater, demersal fish, living on or near the bottom rather than in open water. FishBase reports water conditions of 75–79 °F and a pH near 7.0, with hardness of 15 dH or more — firmer water chemistry than is often assumed for Congo basin species, though it is unclear how many localities that figure is drawn from.
Feeding
No dietary study specific to Pollimyrus nigripinnis has been published. Mormyrids as a family are benthic invertebrate feeders, using their electric sense to locate insect larvae, worms, and small crustaceans hidden in mud, sand, and leaf litter, then taking them with a quick strike of the small mouth. Whether P. nigripinnis follows this pattern in the wild has not been directly confirmed, though it is the reasonable expectation for a small mormyrid of its build.
Mating
No study of courtship or mating behavior in Pollimyrus nigripinnis has been published. In mormyrids generally, the electric organ discharge is thought to carry information beyond navigation, including species and individual identity, and is presumed to play some role in courtship and shoal cohesion — but that broader pattern has not been documented for this species in particular. Sexual dimorphism in P. nigripinnis is likewise undocumented.
Breeding
Breeding has not been recorded for Pollimyrus nigripinnis, either in the wild or in captivity. As with the great majority of small Pollimyrus species, there is no published account of spawning behavior, egg deposition, or parental care, and none should be assumed from better-studied relatives such as Pollimyrus isidori.
In the aquarium
Pollimyrus nigripinnis has essentially no track record in the aquarium hobby; it is not a species that turns up in the trade, and no husbandry account specific to it has been published. What can be said comes from general mormyrid care practice rather than experience with this fish: a soft sand substrate for probing, dim lighting with ample cover, and live or frozen invertebrate foods such as bloodworm and brine shrimp, since mormyrids rarely accept dry foods.
Mormyrids as a group are known to be sensitive to poor water quality and to some common medications, so anyone attempting to keep a small Congo basin mormyrid such as this one should plan for gradual acclimation, stable water chemistry, and conservative dosing rather than treating it as a routine community fish.
Conservation
The IUCN Red List assesses Pollimyrus nigripinnis as Least Concern, based on a 2022 assessment. No major species-specific threats are documented. As with other small fish of the Congo basin, habitat degradation and water-quality pressures across the wider Congo River system are the kind of general, long-term concern that could affect it, but the current status does not indicate an active decline.