Taxonomy & naming
Marcusenius caudisquamatus was formally described in 2014 by Nkosinathi Maake, Ofer Gon and Albert Swartz, one of three new Marcusenius species the authors split out of South African and Mozambican rivers in the same Zootaxa paper ("Descriptions of three new species of Marcusenius Gill, 1862 (Teleostei: Mormyridae) from South Africa and Mozambique", Zootaxa 3780(3):455–480). The type locality is the Mhlatuze River at the bridge on road R102, South Africa (28°50'44.2"S, 31°51'59.6"E), and the holotype is deposited at the South African Institute for Aquatic Biodiversity (SAIAB 88684).
The species sits in the family Mormyridae — the elephantnoses and mormyrids — within the order Osteoglossiformes, the bonytongues. Osteoglossiformes is one of the most ancient living lineages of bony fishes still swimming today, a scattered, deep-time radiation now found across Africa, South America, Southeast Asia and Australasia; the order's name refers to a toothed bony plate on the tongue that bites against opposing tooth plates on the roof of the mouth, an unusual dental arrangement inherited from very early in teleost evolution. The genus Marcusenius, erected by Theodore Gill in 1862, is one of the larger mormyrid genera in Africa; its own etymology is not clearly documented in the sources consulted here, so this account does not guess at it. The species epithet caudisquamatus is more straightforward — from Latin cauda ("tail") and squamatus ("scaled") — referring to the unusually high number of scales encircling the caudal peduncle that helped distinguish it from its closest South African relatives at description.
Morphology
Marcusenius caudisquamatus shows the general mormyrid body plan: a laterally compressed body, a single dorsal fin set well back over the anal fin, and a narrow caudal peduncle carrying a deeply forked tail. FishBase reports a maximum size of about 10 in standard length, which places it among the larger South African mormyrids rather than the smallest of the family, though still a modest-sized fish by the standards of the bonytongue order as a whole.
Unlike its far more famous relative the elephantnose, Gnathonemus petersii, this species does not carry an extended, trunk-like chin appendage (the schnauzenorgan); its mouth is small and unremarkable, suited to picking small prey items rather than probing deep into substrate. The feature that actually defines it taxonomically is meristic rather than visual — the elevated scale count around the tail that gives the species its name — which means confident field identification against other South African Marcusenius is a job for a specialist counting scales, not a snapshot.
As in all mormyrids, an electric organ located in the caudal peduncle generates a weak, pulse-type electric-organ discharge (EOD). The waveform of that discharge is species-specific and, together with an unusually large cerebellum, gives mormyrids as a family some of the highest brain-to-body mass ratios recorded in fish — the physiological basis for their reputation as unusually perceptive, sometimes nicknamed "thinking fish."
Habitat
The species is known only from the Nseleni and Mhlatuze river systems in KwaZulu-Natal Province, South Africa — a pair of short, independent coastal rivers draining toward the Indian Ocean near Richards Bay, well outside the Zambezi or any of the larger interior African drainages. FishBase describes it as freshwater and benthopelagic, recorded from stretches with moderate to fast water currents, at recorded temperatures of roughly 77–79 °F.
No pH or hardness data for the species' native water were found in the sources consulted, so this account does not assign one; readers should treat the water chemistry as unconfirmed rather than infer it from other African mormyrids. What is clear is that this is a lotic, flowing-water fish rather than a lake or floodplain species, and its entire known range is confined to a very small stretch of coastal South Africa — a genuinely narrow-range endemic even by the standards of a family that includes many single-river specialists.
Feeding
Detailed dietary data specific to Marcusenius caudisquamatus were not found in the sources consulted; this account draws on what is well established for the genus and family rather than inventing species-specific numbers. Mormyrids generally, and Marcusenius species in particular, carry a small, weak mouth suited to picking tiny invertebrates rather than tackling large prey, and they forage mostly after dark, using their electric sense to locate food in murky or fast-moving water where vision is of limited use.
Where Marcusenius species are kept in aquaria elsewhere, keepers offer live or frozen mosquito larvae, bloodworm, white worms, black worms, Daphnia, Tubifex and Cyclops — small, soft-bodied invertebrate foods that match the genus's weak-mouthed insectivory. There is no indication this particular species is feeding-specialised beyond that general pattern, but given how little has been published on it, "data sparse" is the honest summary.
Mating
No courtship or spawning behaviour has been documented for Marcusenius caudisquamatus in the sources consulted — FishBase lists its breeding simply as unknown. What can be said comes from the family in general: mormyrids use their species-specific electric-organ discharge as a recognition and courtship signal, allowing individuals to distinguish their own species (and potential mates) from the many other electric fish sharing the same water by waveform alone rather than by sight.
Given that this species inhabits rivers with moderate-to-fast currents, a seasonal, flow-linked spawning pattern — as seen in a number of riverine African mormyrids that time reproduction to rainy-season flow changes — is plausible, but this has not been confirmed for M. caudisquamatus specifically and should not be read as established fact.
Breeding
Breeding in Marcusenius caudisquamatus is poorly known and there are no confirmed captive-breeding records. This is typical of the mormyrid family as a whole: almost no species in Mormyridae have been bred with any regularity in aquaria, and the reproductive biology of most, including this one, has only been sketched in from field observation of related species rather than direct study.
Parental care has not been documented for this species. In mormyrids more broadly, where anything is known at all, some species are thought to scatter eggs among aquatic vegetation with little to no further care, but that pattern has not been confirmed here and is not asserted as fact for M. caudisquamatus. For a species this poorly studied, restraint is the correct posture — better to record the gap than to fill it with a guess.
In the aquarium
Marcusenius caudisquamatus is not a hobby fish. Given its narrow endemic range — confined to two small South African rivers — and its Endangered conservation status, it is effectively absent from the aquarium trade, and this account makes no attempt to dress it up as a species to shop for.
For context, where Marcusenius species do turn up in the trade, general care guidance for the genus calls for a tank of at least 39.4 in, soft and dimly lit water resembling tannin-stained African rivers, and company: mormyrids should not be kept alone, since a lone individual in a bright, featureless tank is both stressed and unable to use its electric sense normally. They are also considered relatively sensitive fish, doing poorly under harsh water conditions or heavy-handed medication, and can be territorial toward their own kind in cramped quarters. None of that guidance has been tested on M. caudisquamatus itself, and readers should not treat it as a substitute for real species-specific data that does not yet exist.
Conservation
The IUCN Red List assesses Marcusenius caudisquamatus as Endangered, under criteria B1ab(iii)+2ab(iii) — reflecting a very small extent of occurrence and area of occupancy, combined with continuing inferred decline in habitat quality. FishBase records the underlying assessment as dated December 2016; the IUCN's own listing carries a 2020 assessment cycle reference. Either way, the species has been consistently flagged as threatened since shortly after its 2014 description.
The basic driver of that status is straightforward: a species known from only two short coastal rivers has, by definition, almost no buffer against habitat degradation, water abstraction, pollution or any other localised pressure on the Nseleni or Mhlatuze systems. No population trend or specific ongoing threat beyond the restricted range itself was documented in the sources consulted, so this account does not speculate further — the narrow range is itself the conservation story.