Taxonomy & naming
Akysis longifilis was described by Heok Hee Ng in 2006 in Zootaxa 1150(1):19-30, based on material from the Sittang (Sittaung) River drainage of Myanmar. It belongs to the family Akysidae, the stream catfishes of South and Southeast Asia, and to the genus Akysis, a large group of small, secretive hillstream species. Ng placed it within the Akysis variegatus species group, a cluster of similar-looking Akysis distinguished mainly by barbel length and body markings. The Catalog of Fishes treats Akysis longifilis as the currently valid name, and no older combination under a different genus is in general use.
The species epithet longifilis is descriptive rather than commemorative, referring to the fish's most obvious field character: unusually long, filamentous nasal and maxillary barbels compared to its close relatives. Two light, saddle-shaped markings on the back between the dorsal and caudal fins, together with a smooth-edged pectoral spine and a forked caudal fin, further separate it from other members of the variegatus group.
Morphology
This is a genuinely small catfish: the maximum recorded size is about 2 in SL, and adults do not grow appreciably larger than that in the wild or in the aquarium — there is no size trap here, but the flip side is a fish so small it needs correspondingly gentle tankmates. The body is elongated and somewhat flattened, in the typical akysid style built for hugging rocks in current, with a broad head tapering to a narrower caudal peduncle and a forked tail.
Barbels are the standout feature: the nasal and maxillary pairs are notably long and filamentous, used to feel out food and substrate in the dark. Like every Akysis, this species is scaleless, with naked skin rather than scales or bony plates, which makes it more sensitive to copper and many medications than a scaled fish. It carries stiff, sharp spines at the leading edge of the dorsal and pectoral fins, each fed by venom glands at its base — a defensive adaptation shared across the family. The pectoral spine itself has a smooth (not serrated) edge, one of the details used to identify the species. Colour pattern includes a pair of pale, saddle-shaped blotches on the back between the dorsal and caudal fins, set against a mottled, cryptic base colour suited to hiding among stream gravel.
Habitat
Akysis longifilis is endemic to the Sittaung (Sittang) River drainage of Myanmar; the type locality is the Pyu stream, a tributary of the Sittaung in Bago Region. This places it firmly in a fast-flowing, freshwater hillstream system rather than a lake or lowland floodplain.
Water at its native sites is cool to moderately warm and only mildly to moderately hard: reported readings run roughly 16.5-24 degrees C with pH about 6.0-7.5 and general hardness in the range of 36-215 ppm, spanning soft to moderately hard water rather than the extremes of either soft blackwater or hard alkaline conditions. In the stream it shelters among rocks, gravel and coarse substrate, using its cryptic pattern and small size to stay hidden through the day.
Feeding
Akysis longifilis is a nocturnal micro-predator, foraging over the stream bed after dark for tiny live invertebrates. Reports describe it as a picky feeder that strongly prefers live or frozen prey — brine shrimp (Artemia), Daphnia, bloodworm and glassworm — over dry or prepared foods, and bloodworm, chopped earthworm, whiteworm and daphnia are all noted as accepted foods, alongside sinking pellets taken less readily.
In the aquarium, food should be offered after lights-out so this small, shy species is not out-competed by more assertive tankmates at feeding time. Because of its size and prey preferences, it is best matched only with other small, peaceful fish that will not out-compete or predate it.
Mating
Breeding biology specific to Akysis longifilis is not documented in the available literature. Related Akysis species are reported to spawn in response to a drop in temperature, mimicking the onset of monsoon rains and rising, cooling stream flow in the wild, with eggs hatching after roughly four days — but this has not been confirmed for A. longifilis itself, and no courtship or spawning behaviour has been formally described for this species.
Breeding
There is no confirmed breeding record for Akysis longifilis in the aquarium. Some hobbyists have reported seeing eggs, but successful hatching and rearing of fry has not been documented, and captive-bred stock is not known to be available — any specimens in the trade are wild-collected. Given the pattern in the wider genus, egg-scattering is more plausible than nest-building or mouthbrooding for this species, but until it is actually documented for A. longifilis this should be treated as an informed guess rather than an established fact. This is honestly one of the many small stream catfishes about which very little is known; keepers should not expect to replicate a spawn without discovering new ground themselves.
In the aquarium
Akysis longifilis stays genuinely small (to about 2 in), so a modest, well-filtered aquarium with decent flow suits it, provided the flow is not so strong that it exhausts such a tiny fish. It needs cover: fine gravel or sand, smooth rocks, and pieces of pipe or driftwood to hide in during the day, since it is nocturnal and shy by nature; it will rarely be seen unless watched after dark.
Two care points follow directly from its biology. First, like all akysids it is scaleless, so it is more sensitive than scaled fish to copper and to many medications — dose conservatively and treat with caution. Second, it carries venomous spines at the base of the dorsal and pectoral fins; while not dangerous to a healthy adult, a sting is genuinely painful, so this fish should be moved in a container rather than netted, and handled with care when doing any tank maintenance around it. Feed live or frozen foods after dark, and keep tankmates small, peaceful and unlikely to bully or out-compete it — this is not a fish for a boisterous community tank.
Conservation
Akysis longifilis has not been formally assessed by the IUCN Red List and carries no status; it is Not Evaluated. It is known only from the Sittaung River drainage of Myanmar, and as a narrow-range stream endemic it would be vulnerable to habitat degradation, damming or pollution within that single drainage, but no population data or targeted conservation assessment exists to quantify the risk.
The species is essentially absent from mainstream aquarium trade, and any specimens that do appear are wild-collected rather than captive-bred, so there is no farmed-supply buffer protecting wild populations. Its conservation story is really one of data gaps rather than known decline: a small, poorly studied hillstream catfish that would benefit from basic population surveys within its home drainage.