Taxonomy & naming
Amphilius caudosignatus was described by Paul Skelton in 2007. It belongs to the family Amphiliidae — the loach catfishes of Africa — and to the genus Amphilius, a group of small, elongate, stream-adapted catfishes distributed across sub-Saharan Africa. The Catalog of Fishes treats Amphilius caudosignatus as the currently valid name, with no older combination in general use.
The genus name Amphilius is of Greek derivation, long applied to this lineage of African stream catfishes. The species epithet caudosignatus combines the Latin cauda ("tail") with signatus ("marked" or "signed"), referring to the diagnostic oblique white band across the caudal fin that distinguishes this species from its close relatives.
Morphology
Amphilius caudosignatus is a small, slender loach catfish, reaching a maximum recorded size of only about 2 in standard length — one of the smaller members of an already diminutive genus. Like other Amphilius it has a flattened head and a streamlined, elongate body suited to living against the current, with barbels used to feel out food on the streambed.
The skin is scaleless (naked), a trait shared across the family and one with real consequences for handling and medicating the fish (see "In the aquarium"). The species' most recognisable feature is the oblique white band crossing the caudal fin, which sets it apart from other small Amphilius species sharing similar habitat in Gabon.
Habitat
This species is endemic to a small number of southeastern tributary streams of the Ogowe (Ogooué) River system in Gabon, including Kiené Creek near the type locality. It has not been recorded outside this narrow catchment.
As a member of Amphiliidae, it is a fast-water, benthopelagic stream fish, typically found clinging to or foraging over stone and gravel substrate in flowing forest streams rather than still or sluggish water. Specific published data on temperature and pH for this exact population are not available from the sources consulted; treat any figures for this species as data sparse rather than assume the soft, warm blackwater conditions common to many other West-Central African streams.
Feeding
No species-specific feeding studies were found. Based on the ecology of Amphiliidae generally, Amphilius caudosignatus is best assumed to be a nocturnal benthic micro-predator/omnivore, foraging over the stream bottom for small invertebrates and detritus, likely most active after dark as in related Amphilius and other small African loach catfishes.
In the unlikely event it were kept, sinking foods offered after lights-out — small invertebrate-based pellets, frozen foods, and similar prepared diets — would suit this feeding style, though no aquarium feeding records exist for this species.
Mating
No courtship or spawning behaviour has been documented for Amphilius caudosignatus. The species is essentially unknown outside of taxonomic and conservation-assessment literature, and nothing about pairing, spawning site selection, or fecundity has been published.
Breeding
Breeding biology is unrecorded. Amphilius caudosignatus has never been reported bred in the aquarium, and there is no field literature describing its reproductive mode. Given the general pattern in Amphiliidae, egg-laying over stream substrate with limited or no parental care is plausible, but this is inference from the family rather than a confirmed fact for this species — it should not be stated as established.
In the aquarium
Amphilius caudosignatus is not a hobby fish. No specific aquarium care reports, imports, or breeding accounts were found for this species; it is effectively absent from the trade. If it were ever encountered, the size trap still applies in reverse here — at a genuine maximum of about 2 in SL, it stays small, but it would still need cool, well-oxygenated, flowing water to mimic its forest-stream habitat rather than a still community tank.
Two general Amphiliidae care points are worth stating even in the absence of direct records: the skin is scaleless, so this genus is presumed medication-sensitive and copper-based treatments should be dosed conservatively, as with other naked-skinned catfishes; and as a small stream fish it would be expected to appreciate current, oxygenation, and cover rather than open, still water. Given the total lack of husbandry data, anyone who did acquire this species would be working almost entirely from first principles.
Conservation
The IUCN Red List assesses Amphilius caudosignatus as Endangered (EN), under criteria B1ab(iii)+2ab(iii), in an assessment dated 16 February 2009. The listing reflects its extremely restricted range: the species is known only from a small number of tributary streams in the southeastern Ogowe River system of Gabon, making it vulnerable to any localised habitat disturbance.
Because the species has such a narrow known distribution and no active aquarium trade, its conservation outlook depends entirely on the condition of these Gabonese forest streams — factors such as deforestation, sedimentation, and water-quality change in the Ogowe catchment are the relevant long-term pressures, though detailed threat data specific to this species is sparse.