Taxonomy & naming
Kryptopterus minor was described by the American ichthyologist Tyson R. Roberts in 1989. It belongs to the family Siluridae, the Old World sheatfishes, a family that also holds the giant Wallago and the European Silurus glanis, and to the glass catfish genus Kryptopterus, which is largely confined to the rivers of Sundaland and mainland Southeast Asia. The Catalog of Fishes treats Kryptopterus minor as the valid name.
For decades the common "glass catfish" of the aquarium trade was sold under the name Kryptopterus minor (or sometimes bicirrhis), but a taxonomic review clarified that the popular trade fish is a distinct, more common species, Kryptopterus vitreolus, described only in 2013. True K. minor is a Borneo endemic with a much narrower distribution, and the two are easily confused by eye — a case worth flagging for buyers who want the fish under this name specifically, since what is usually sold as "K. minor" in shops is very likely K. vitreolus.
Morphology
Kryptopterus minor is a small, laterally compressed, knife-shaped catfish that reaches only about 2.5 in standard length. Its most striking feature is transparency: the body lacks reflective scales and much of the flank musculature, so the vertebral column, ribs and swim bladder are visible through the living fish, along with a faint iridescent sheen that shifts with the light. A single long pair of maxillary barbels extends from the upper jaw, and the anal fin runs in a long, low ribbon along most of the belly, the fish's main means of propulsion — glass catfish swim with a gentle undulation of this fin while holding the body nearly still.
Like other Siluridae it is entirely scaleless, naked skin rather than the bony plating seen in some other catfish families, which makes it — like loaches, puffers and true eels — sensitive to copper-based and some other medications. There is no dorsal fin spine of the kind seen in many catfish groups; the small dorsal is reduced to a tiny rayed remnant, so the locking-spine hazard that applies to many catfish is much less pronounced in this genus.
Habitat
The species is native to the Kapuas River basin of western Borneo (Kalimantan Barat, Indonesia), a large blackwater and clearwater drainage system. It is a freshwater, benthopelagic fish, found hovering in loose groups over substrates of pebbles, sunken wood and leaf litter in stretches with gentle to moderate current and good oxygenation.
Water in its native reaches is warm and circumneutral to slightly alkaline: FishBase gives a temperature range of roughly 75–82 °F and pH 6.0–8.0. As with many Southeast Asian river fish, it does best with steady water quality, moderate flow and dim, filtered light rather than the harsh open conditions of a bare, brightly lit tank.
Feeding
Kryptopterus minor is a midwater micro-predator. In the wild it hangs in loose shoals in open water and picks off small aquatic invertebrates — insect larvae, tiny crustaceans and other zooplankton-sized prey — rather than foraging on the bottom.
In the aquarium it needs small live or frozen foods to start: bloodworm, daphnia and brine shrimp are readily taken, and once settled it can be weaned onto good-quality fine dry foods that stay suspended in the water column. It is a shy, slow, deliberate feeder that is easily out-competed by faster tankmates, so food should be offered in a way that reaches the whole shoal rather than being grabbed by more assertive fish.
Mating
Courtship and spawning in the wild have not been documented in detail for this species. Glass catfish in general are believed to be egg-scatterers, releasing eggs over vegetation or fine substrate in soft, still water without forming pairs or defending territory, but this is inferred from the wider genus and from close relatives rather than confirmed observation of K. minor itself.
Breeding
True Kryptopterus minor is essentially not bred in captivity, and the aquarium supply of glass catfish overwhelmingly consists of wild-caught (or captive-bred K. vitreolus) rather than farmed K. minor fry. Where hobbyist accounts describe breeding attempts under the "glass catfish" name, they report it as rare and poorly documented — soft, still, densely planted water is suggested as the closest approximation of natural spawning conditions, with live foods needed to raise any fry that do appear — but no reliable, repeatable home-breeding protocol exists for this species. Given how easily it is confused with K. vitreolus, some reported "breedings" of "K. minor" in the hobby literature may in fact refer to the other species. There is no parental care once eggs are scattered.
In the aquarium
Kryptopterus minor stays small — about 2.5 in SL at maximum — so tank size is not the size-trap concern it is for many other catfish in this group; the challenge here is instead correct identification, since most glass catfish in shops are K. vitreolus rather than the true, Borneo-only species. Whichever the identity, care needs are similar: it is an obligate shoaling fish that should be kept in groups of eight or more, since isolated or thinly grouped individuals become stressed, freeze in place, and often fail to feed. Dim lighting, dense planting for cover, gentle-to-moderate current and strong, well-oxygenating filtration (aquarium guides recommend turning over roughly 10–20 times the tank volume per hour) all mimic its native river habitat.
Because it is a fully scaleless catfish, it is medication-sensitive in the same way as loaches, puffers and eels — dose copper-based treatments and many other medications conservatively, often at reduced strength. It lacks the stout locking dorsal/pectoral spines of many catfish, so netting is less hazardous than with spined species, but it is still a delicate, easily stressed fish that is best moved gently. Being shy and a slow feeder, it should be kept with equally peaceful, non-boisterous tankmates that will not out-compete it at feeding time.
Conservation
The IUCN Red List assesses Kryptopterus minor as Near Threatened, based on an assessment dated 8 August 2019. Its range is narrow and specific — the Kapuas River basin of western Borneo — which leaves it more exposed than widespread river fish to habitat pressures such as deforestation, sedimentation and water-quality decline across Kalimantan.
Because true K. minor rarely enters the aquarium trade (most "glass catfish" sold commercially are the more widespread K. vitreolus), collection for the hobby is not considered a major driver of its conservation status; broader land-use change in its native Kapuas drainage is the more relevant long-term concern.