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FACTSHEETS: May 2026 - no. 359

Kryptopterus cryptopterus (Bleeker, 1851)

ike the Schilbeidae, the family Siluridae is known as "glass catfishes" or "sheathfishes." Their dorsal fin usually has fewer than seven rays, is sometimes absent, and is not preceded by a spine. The adipose fin is absent. Pelvic fins are small or sometimes absent, while the anal fin base is very elongate with 41-110 rays. Nasal barbels are absent. One or two pairs of barbels are found on the lower jaw (mandibular barbels), and maxillary barbels, located at the corners of the mouth, are usually elongate.

Kryptopterus cryptopterus

This is quite a diverse family, from the midwater shoaling Krytopterus to the predatory Wallago and the European wels, Silurus glanis. The difference between the families is quite straightforward: the Silurids do not possess an adipose fin, and most of the Shilbids do. The Silurids also have a small notch between the anal and caudal fin, whereas the Shilbids have this joined. Found in rivers, canals and also in the Great Lakes.

Kryptopterus cryptopterus

Members of the silurid catfish genus Kryptopterus Bleeker, 1858, are small-to-medium-sized fishes found in inland waters throughout Southeast Asia. Kryptopterus, as currently understood, is known to be paraphyletic and shown to consist of at least two distinct clades (Bornbusch, 1995): one characterised by higher branchiostegal-ray counts (14–17), and the other with lower counts (8–13). This distinction is reflected in the recent taxonomy of the group, in which the large species with elevated branchiostegal-ray counts are reassigned to the genus Micronema (e.g. Rainboth, 1996; Kottelat, 2001). The distinctive type species of Kryptopterus, K. cryptopterus (Bleeker 1851), is widely distributed throughout Southeast Asia and is easily identified by its dorsal profile (horizontal or very gently convex, lacking a nuchal concavity) and short maxillary barbels.

The differences noted between K. cryptopterus and K. geminus are not due to ontogeny. Bivariate analyses (ANCOVA) of the regression lines of anal-fin length, head width, and snout length on SL for both species are significantly different (Ng, H. H., 2003).

South Kalimantan

South Kalimantan

Indonesia

Indonesia

Asia: Mekong and Chao Phraya basins; also from the Malay Peninsula, Sumatra and Borneo. Type locality: Banjarmasin, South Kalimantan, Borneo, Indonesia.

South Kalimantan, known as the Land of Lambung Mangkurat, is a province on the island of Borneo with a rich history and diverse culture. Home to over 4.2 million people, it’s traditionally the homeland of the Banjar people and was once part of ancient kingdoms with connections reaching as far as Madagascar. The province experienced periods of trade, colonisation, and ultimately Indonesian independence, with its capital moving from Banjarmasin to Banjarbaru in 2022. Today, South Kalimantan offers a blend of Banjarese, Dayak, and Javanese influences and is known for its historical Sultanate of Banjar, which flourished through trade, particularly pepper, and faced conflicts with Java and Dutch colonial powers.

Common Name

Blue Sheathfish

Synonyms

Silurus cryptopterus, Kryptopterus micropus

Family

Siluridae

Subfamily

Habitat

Endemic from the Congo basin, where it has been collected in the Lower Basin, Pool Malebo, the Kasai Subsystem, the middle Congo and the Uele Ubangui System, as well as in the Lualaba (including the Upemba System).

Distribution

Asia: Mekong and Chao Phraya basins; also from the Malay Peninsula, Sumatra and Borneo. Type locality: Banjarmasin, South Kalimantan, Borneo, Indonesia.

Size

20.0cm. (8ins)

Temp.

22-25°C (71-77°F)

p.H.

6.0-7.0.

Characteristics

Maxillary barbels reaching to pectoral base. Rudimentary dorsal fin (one ray) present. Nearly straight dorsal profile with no nuchal concavity. 4-6 pelvic fin rays. The pectoral fin lengths greater than head length. 64-78 anal fin rays.

Colouration

Silvery opaque body, some olive hue dorsally, fins hyaline. Dark pectoral, caudal and anal fin margins.

Aquarium Care & Compatibility

Quite a peaceful species that is best kept in a group, which needs a lot of swimming space. Will consider smaller fish (less than 4cm) as prey. Active during the day in a tank 4ft (120cm) or over with quiet tank mates. Provide a planted tank with overhanging or floating plants.

Reproduction

Spawns at the early part of the rainy season. The young move into seasonally flooded habitats and are first seen in August.

Sexual differences

Males are slimmer than the females.

Diet

Small live foods and good quality flake. Frozen and tablet foods and small earthworms.

Glossary of Terms

Anal fin: The median, unpaired, ventrally located fin that lies behind the anus, usually on the posterior half of the fish.
Barbels: Whisker-like structure on the heads of most catfish.
Dorsal fin: The primary rayed fin(s) on top of the body.
Hyaline: Transparent or clear without pigment.
Maxillary barbels: Pertaining to the upper jaw. (maxillary barbels).
Nuchal: Area between the skull and dorsal fin.
Paraphyletic: Of a group of organisms, descended from a common evolutionary ancestor or ancestral group, but not including all the descendant groups.
Pectoral fin: The paired fins just behind the head.
Pelvic fin: The paired fins, between the pectorals and the anal fins (also referred to as ventrals).

Etymology

Kryptopterus: Krypto = hidden; pterus = fin, (a reference to the almost invisible one-rayed dorsal fin).
cryptopterus: cryptos, from krypt, hidden; pterus, from pterón or ptéryx, fin, referring to its dorsal fin, described as a “short slender thread” (translation).

IUCN Red List

Although there is no detailed information on the population size and trend of this species, it is still abundant throughout its known distribution and the population trend is thus suspected to be stable or declining at a rate that precludes it from a threatened catgory. While there may be localised or regional threats, they are unlikely to affect this species on a range-wide scale, and it is likely found within several protected areas. Therefore, it is assessed as Least Concern (IUCN 2019).

References

Baensch, H.A. and R. Riehl, 1985. Aquarien atlas. Band 2. Mergus, Verlag für Natur-und Heimtierkunde GmbH, Melle, Germany. 1216 p.
Froese, R. and D. Pauly. Editors. 2021. FishBase. World Wide Web electronic publication. www.fishbase.org, ( 02/2021 ).
Kottelat, M. 2001 Fishes of Laos. WHT Publications Ltd., Colombo 5, Sri Lanka. 198 p.
Ng, H.H. (2003) Kryptopterus geminus, a new species of silurid catfish (Teleostei: Siluridae) from mainland Southeast Asia. Zootaxa, 305 (1), 1–11.
Ng, H.H. 2019. Kryptopterus cryptopterus. The IUCN Red List of Threatened Species 2019.
Rainboth, W.J. 1996 Fishes of the Cambodian Mekong. FAO Species Identification Field Guide for Fishery Purposes. FAO, Rome, 265 p.
Roberts, T.R., 1989. The freshwater fishes of Western Borneo (Kalimantan Barat, Indones
The ETYFish Project Fish Name Etymology Database © Christopher Scharpf.

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ScotCat Sources

Etymology-genus name

Etymology-specific name

Other Sources

Fishbase

Wikipedia

Catalog of Fishes

GBIF

FishNet2

iNaturalist

IUCN