Taxonomy & naming
Chiloglanis emarginatus was described by Rodney Jubb and Neels Le Roux in 1969. It belongs to the family Mochokidae, the African squeakers and upside-down catfishes, in the genus Chiloglanis, a group of small, sucker-mouthed "rock catlets" found across sub-Saharan Africa. The Catalog of Fishes recognises Chiloglanis emarginatus as the valid combination, and it has always sat in this genus rather than under an older name.
The genus name Chiloglanis combines Greek cheilos ("lip") and glanis (an old name for a catfish), a direct reference to the enlarged, sucker-like oral disc that defines the genus. The species epithet emarginatus is Latin for "notched" or "with the margin cut away", describing a distinguishing feature of the fin or oral disc margin noted in the original description.
Morphology
This is a small, flattened catfish built for clinging to rock in fast water. The mouth is modified into a broad, sucker-like disc on the underside of the head, used to grip cobbles and boulders against strong current — the same basic toolkit seen across the sucker-mouthed Chiloglanis. Like other members of the family Mochokidae it is scaleless, and it carries the stiff, serrated, locking spines typical of squeaker catfishes at the leading edge of the dorsal and pectoral fins.
Maximum recorded size is only about 2.5 in standard length (FishBase), making it one of the smaller catfishes in this atlas — but that size should not be mistaken for a delicate aquarium fish; it is a specialist of a demanding habitat, not a generalist community species.
Habitat
Chiloglanis emarginatus lives in shallow, clear, fast-flowing rocky runs and riffles, typically at depths of only 1 ft, over cobbled substrates at moderate elevation (roughly 900–1,656 ft). Its known range covers tributaries of the Phongolo and Komati–Incomati rivers in South Africa and Eswatini, plus the Pungwe and the middle-to-lower Zambezi system in Zimbabwe.
The species depends on current and clean, well-oxygenated water; it is a highveld and escarpment river specialist rather than a lowland or standing-water fish. Documented aquarium temperature and pH ranges are sparse, but a fast, clear, well-aerated highland river is not a soft, acidic blackwater habitat, and any aquarium approximation should prioritise strong flow and oxygenation over any particular water-chemistry extreme.
Feeding
In the wild, Chiloglanis emarginatus grazes invertebrates directly off rock surfaces — mayfly nymphs, caddisfly larvae, blackfly larvae and midge larvae are all recorded prey, gleaned from the same cobbles it clings to with its sucker mouth. This is a nocturnal benthic micro-predator/grazer in habit, foraging the rock biofilm and its invertebrate residents rather than taking food from open water.
An aquarium diet should mimic this: sinking pellets and frozen foods (bloodworm, mosquito larvae, brine shrimp) offered where the fish can graze them off hard surfaces, ideally after lights-out when it is naturally most active. It is not a fish that competes well for food in open water against faster community species.
Mating
FishBase records Chiloglanis emarginatus as oviparous with distinct pairing behaviour and a summer breeding season, rather than open, indiscriminate spawning in a shoal. Courtship and spawning details have not been documented in detail; the pairing behaviour suggests some degree of mate selection ahead of spawning, in keeping with its habit of holding a position on a particular rock in the current.
Breeding
The species is believed to be an interstitial gravel spawner, depositing eggs into the gaps between cobbles and gravel in its riffle habitat rather than scattering them in open water or building a bubble nest. This matches its wild habitat exactly — the same current-swept, cobbled riffles it grazes and clings to likely double as the spawning substrate.
Chiloglanis emarginatus is not a species with an established aquarium breeding record; its narrow habitat requirements (strong current, clean well-oxygenated water, cobble substrate) have not been reproduced in captivity as far as the cache of sources indicates, and there is no evidence of regular hobby breeding. Treat any account of home breeding with caution and prioritise conservation of wild populations over collection pressure.
In the aquarium
Chiloglanis emarginatus stays genuinely small at only 2.5 in SL, but that does not make it an easy community fish. It is a current specialist: it needs strong water flow, high dissolved oxygen and a bed of smooth cobbles or rounded gravel to grip and graze, essentially a rheophilic biotope setup rather than a standard planted or community tank. It is scaleless, like other Mochokidae, so it is medication-sensitive — dose copper-based and other treatments conservatively.
It also carries the stiff, locking pectoral and dorsal spines typical of squeaker catfishes, which can snag in a net and jab the handler; move it in a container rather than netting it. Because detailed aquarium water-chemistry data is sparse for this species, prioritise strong current and oxygenation, clean water, and a rocky substrate over guessing at a specific pH/hardness target. Given its Vulnerable status and narrow wild range, this is a fish best left to specialist keepers working from wild-collected or responsibly sourced stock, not a casual purchase.
Conservation
The IUCN Red List assesses Chiloglanis emarginatus as Vulnerable, assessed in November 2017 under criteria B1ab(iii,iv)+2ab(iii,iv). Its estimated extent of occurrence is only 16,412 mi² and its area of occupancy just 157 mi², with only about ten known locations (eight in Eswatini, two in South Africa) recorded at the time of assessment.
The main threats are coal-mining pollution, sedimentation and general habitat degradation in its home rivers, and a population decline has already been observed, particularly in South Africa, where the Usutu catchment population is now reduced to a single known locality. As a habitat specialist confined to short stretches of clear, fast-flowing river, it has very little resilience to water-quality decline, and its status is a direct signal of the health of the Phongolo, Komati–Incomati and Pungwe river systems.