Taxonomy & naming
Pollimyrus marianne was described in 2003 by Bernd Kramer, Monique van der Bank, Nigel Flint, Hedi Sauer-Gürth and Michael Wink, part of a run of species-level splits within Pollimyrus that followed the discovery that outwardly near-identical "dwarf stonebashers" carry distinct electric organ discharge (EOD) waveforms. It belongs to the family Mormyridae within Osteoglossiformes, the ancient bonytongue lineage, and its closest relative is Pollimyrus castelnaui, from which it was separated on the combined evidence of EOD waveform, morphology and molecular genetics.
The type locality is a backwater of the Lisikili channel in the East Caprivi region of Namibia, at roughly 17°29'S, 24°26'E, on the upper Zambezi River system. Pollimyrus marianne and P. castelnaui meet in a parapatric contact zone around the Okavango system, where the two remain distinct species despite occurring close together — a pattern the describing authors linked to their electric signals acting as a barrier to interbreeding.
Morphology
Pollimyrus marianne is one of the smaller members of an already small-bodied genus, reaching a maximum recorded total length of about 3 in. Like other Pollimyrus, it has the compact, laterally compressed body and small mouth typical of dwarf mormyrids, a build suited to maneuvering through rock crevices and reed roots rather than open-water swimming.
As in all mormyrids, a weak electric organ near the base of the tail generates a pulse-type discharge that the fish reads through electroreceptors spread across its skin. In this species the discharge is central to its identity as a taxon: Pollimyrus marianne was defined in large part by its electric organ discharge waveform, which differs measurably in frequency and amplitude from that of its sibling species Pollimyrus castelnaui. In both species, EOD frequency and amplitude rise with water temperature, a rate-dependent effect typical of bioelectric signals in ectotherms.
Habitat
Pollimyrus marianne is endemic to the upper Zambezi River system of southern Africa, recorded from Namibia and Angola. Its type locality lies in a backwater of the Lisikili channel in Namibia's Zambezi (Caprivi) region.
Within the upper Zambezi it occupies two distinct settings: fast-flowing rapids over rocky substrate that offers crevices for shelter, and quieter reaches lined with dense reed beds over sandy bottoms. Specific water-chemistry figures — temperature and pH — have not been published for this species; the rapids and reed-fringed channels it inhabits are typical of the well-oxygenated, seasonally flooding rivers of the upper Zambezi basin.
Feeding
No dedicated dietary study of Pollimyrus marianne has been published. As in other mormyrids, it is presumed to forage on small benthic invertebrates — insect larvae, worms and tiny crustaceans — located with its electric sense among the crevices, sand and reed-root tangles of its rapids and backwater habitat.
General mormyrid care literature recommends live and frozen invertebrate foods such as bloodworm and brine shrimp, since dwarf mormyrids typically ignore dry foods, but no feeding regime specific to Pollimyrus marianne in captivity has been documented.
Mating
The original description ties species status in the Pollimyrus marianne / Pollimyrus castelnaui pair directly to differences in electric organ discharge waveform, and treats that difference as a likely barrier to interbreeding where the two meet in a parapatric contact zone around the Okavango system — a fish unable to recognize the "wrong" EOD pattern as a potential mate would be less likely to hybridize. That makes electric signalling a stronger candidate for a role in mate recognition in this species than in most Pollimyrus, though the courtship sequence itself — any specific display, timing, or pairing behavior — has not been documented.
Beyond this signalling context, nothing has been published on spawning behavior, seasonality, or sex-specific behavior in the wild for Pollimyrus marianne.
Breeding
No spawning of Pollimyrus marianne, in the wild or in captivity, has been documented in the literature available for this account. The species has no known aquarium-breeding record, and essentially nothing has been published on egg deposition, incubation, or parental care specific to it.
Some general mormyrid patterns — seasonal, flood-linked spawning triggered by rising water levels — are documented in better-studied genera, but extending that pattern to Pollimyrus marianne without direct evidence would be speculation rather than an established fact.
In the aquarium
Pollimyrus marianne is essentially absent from the aquarium trade and has no established husbandry record; general mormyrid care practice, rather than species-specific experience, is what would apply if it were ever kept. That practice calls for a tank of at least a meter in length, a soft substrate of fine sand or smooth gravel — mormyrids probe with sensitive facial skin that coarse gravel can damage — dim lighting, and ample cover such as driftwood, roots, or pipes to stand in for the crevices and reed beds of its native habitat.
Mormyrids as a group are notably intolerant of poor water quality and of many common medications, so stable, clean water and conservative dosing matter more than with most community fish. At under 3 in, Pollimyrus marianne would not need a large tank on size grounds alone, but the near-total absence of documented captive experience with this species means any care regime is an extrapolation from the wider family rather than a track record.
Conservation
Pollimyrus marianne is assessed by the IUCN Red List as Least Concern, per FishBase and iNaturalist records; the sources available for this account do not specify the assessment year, so none is given rather than an invented one. The species is known only from the upper Zambezi River system in Namibia and Angola, and no population decline has been documented.
No species-specific threats are recorded. General pressures on upper Zambezi and Okavango basin rivers — water abstraction, damming, and habitat alteration in rapids and reed-bed habitat — are the kind of long-term risk that could affect a narrow-range endemic like this one, though none is currently flagged against Pollimyrus marianne specifically.