Taxonomy & naming
Kryptopterus vitreolus was formally described by Heok Hee Ng and Maurice Kottelat in 2013, in a revision that separated it from the similar Kryptopterus bicirrhis (which it had been confused with and sold under for many years) and established it as the species most commonly seen in the aquarium trade. The description resolved a long-standing misidentification: the 'glass catfish' in virtually every pet shop in the world is K. vitreolus, not K. bicirrhis, which is a larger and rarer fish.
The family is Siluridae, the sheatfishes — a primarily Asian family that ranges from Europe across to Southeast Asia and includes some of the largest freshwater fish on Earth (Silurus glanis, the wels) as well as the diminutive glass catfish. The Catalog of Fishes treats Kryptopterus vitreolus Ng & Kottelat, 2013 as the valid name and combination. Earlier aquarium literature and fish lists citing 'Kryptopterus bicirrhis' for the common glass catfish almost always refer to this species.
Morphology
The glass catfish is unmistakeable: the body is almost entirely transparent, with the internal organs confined to a small, silvery-green abdominal mass just behind the head, while the rest of the body reveals skeleton, musculature and a visible spine as if through glass. There are no scales — the skin is completely naked — and the body is laterally compressed and elongated. The dorsal fin is reduced to a tiny nub or absent, and the extremely long anal fin runs most of the body length. Two maxillary barbels project forward from the snout.
Maximum size is around 2 in standard length. This is a genuinely small catfish; there is no size trap in the sense of outgrowing a home aquarium — it will not. The trap instead is the social requirement: these fish must be kept in groups, and they are fragile, scaleless, and exquisitely sensitive to poor water and aggressive tankmates.
Habitat
Kryptopterus vitreolus occurs in river drainages of Thailand and Myanmar, including systems draining to the Gulf of Thailand and in the Salween River drainage. It inhabits slower-moving rivers, streams and floodplain waters with clear to slightly tannin-stained water, often in mid-water over sandy or muddy substrates where it hovers in aggregations.
Water conditions in its native rivers are soft and slightly acidic to neutral: temperatures of roughly 75–82 °F, pH in the range of 6.0–7.0, and low to moderate hardness. The species is not a blackwater extreme; it frequents clear or mildly soft river water rather than deeply acidic peat-swamp conditions. Strong current is not required and it is typically found in calmer stretches or the lee of marginal vegetation.
Feeding
Kryptopterus vitreolus is a midwater micro-predator that takes small live invertebrates in the wild — copepods, small insect larvae, daphnia and similar zooplankton-sized prey. It hunts in a characteristic posture, hovering almost stationary in the water column with the body angled slightly downward, and snaps at passing prey items.
In the aquarium it will accept small frozen foods such as bloodworm, daphnia, brine shrimp and cyclops, and patient keepers can wean it onto high-quality micro-pellets or flake crumbled fine enough to be taken at mid-water. It is a shy feeder that is easily out-competed by faster or more aggressive tankmates; food must reach it at its preferred depth and it should not be housed with boisterous species that race for every morsel. Feeding after lights-dim can help in a community context.
Mating
Nothing is known of the mating behaviour of Kryptopterus vitreolus in either the wild or captivity. No documented natural spawning observations exist in the ichthyological literature, and the species has not been induced to breed under aquarium conditions. It is thought to be a free-spawning fish — eggs shed into open water or over vegetation — but this is inferred from family-level biology rather than direct observation of this species.
All glass catfish in the trade are wild-collected, and there is no captive breeding stock or established method. Until a reliable breeding protocol is documented, any account of its mating behaviour would be speculative.
Breeding
Kryptopterus vitreolus has not been bred in captivity. No reproducible home or commercial breeding method exists for this species, and every specimen sold in the aquarium trade is wild-caught from its native rivers in Thailand and Myanmar. Occasional anecdotal reports of apparent spawning in aquaria have circulated in the hobby but none have produced documented, independently raised offspring.
The contrast with the callichthyid catfishes (which build floating bubble-nests and breed freely) or with Synodontis (some of which can be spawned using mouthbrooding cichlids) is stark: glass catfish remain one of the groups where keeping the fish alive and thriving is the ambition, not breeding it. Keepers should assume wild-caught origin and purchase only from reputable suppliers who can confirm the fish were handled with care in the supply chain.
In the aquarium
Glass catfish are demanding despite their small adult size of around 2 in. The non-negotiable requirement is a group: fewer than six fish typically results in refusal to feed, chronic stress, loss of the characteristic transparency and early death. Ten or more allows natural shoaling behaviour, with the fish hovering together in a loose mid-water formation. A tank of at least 20 US gal is appropriate for a proper group, with gentle to moderate flow, open swimming space at mid-water, and shaded areas with plants or floating cover.
Because the skin is entirely scaleless, K. vitreolus is notably sensitive to copper-based medications and many other chemical treatments. Half-dose protocols are advised as a starting point, and copper should be avoided entirely if alternatives exist. Water quality must be excellent: the species is intolerant of elevated ammonia or nitrite, and even moderate nitrate accumulation degrades condition. Temperature should be maintained at 75–82 °F with pH 6.0–7.0 and low to moderate hardness.
Compatible tankmates are small, peaceful fish of similar size that will not compete aggressively for food: small rasboras, tetras, dwarf corydoras and other gentle community fish are appropriate. Avoid nippy species, large or fast-moving fish, and anything that will monopolise food. Glass catfish carry no locking spines worth noting and no venom — the danger runs the other way, toward the catfish rather than from it.
Conservation
Kryptopterus vitreolus has not been assessed by the IUCN Red List; it carries a status of Not Evaluated (NE). The broader genus Kryptopterus is largely unevaluated, and the 2013 taxonomic revision separating K. vitreolus from K. bicirrhis is recent enough that range-specific data are still being assembled.
The species is endemic to a portion of mainland Southeast Asia — principally Thailand and the Salween drainage into Myanmar — and the aquarium trade depends entirely on wild collection. Pressures on these river systems include agricultural runoff, damming, water extraction and deforestation, all of which degrade the clear, soft, moderate-temperature water the species requires. Given that no captive breeding supply exists, continued availability in the trade is directly tied to wild population health. Responsible sourcing from reputable importers matters more for this species than for groups with established captive production.