Kryptopterus cryptopterus (BLEEKER, 1851)

Blue Sheatfish

SynonymsTop ↑

Silurus cryptopterus Bleeker, 1851; Kryptopterus micropus Bleeker, 1858

Etymology

Kryptopterus: from the Greek kryptos, meaning ‘hidden’, and pterýgio, meaning ‘fin’, in reference to the reduced or absent dorsal-fin in members of this genus.

cryptopterus: from the Greek kryptos, meaning ‘hidden’, and pterýgio, meaning ‘fin’, in reference to the reduced or absent dorsal-fin.

Classification

Order: Siluriformes Family: Siluridae

Distribution

Known from the Malay Peninsula and Singapore plus Greater Sunda Islands of Sumatra, Borneo and Java with populati0ns from Thailand, Cambodia, Laos and Vietnam which had formerly been considered conspecific  now referred to K. geminus (Ng, 2003).

Type locality is given as ‘Bandjarmassing’ which corresponds to a town now more commonly referred to as ‘Banjarmasin’ in South Kalimantan (Kalimantan Selatan) province, Indonesia (Borneo).

Habitat

Inhabits flowing rivers and larger streams typified by turbid water with a lot of suspended sediment.

Maximum Standard Length

The largest officially-recorded specimen measured 147 mm.

Aquarium SizeTop ↑

An aquarium with base dimensions of 120 ∗ 45 cm or equivalent should be the smallest considered.

Maintenance

Décor is relatively unimportant although this species prefers weakly-lit conditions and may become skittish in the absence of cover.

Do not add introduce it to a biologically immature aquarium as it can be susceptible to swings in water chemistry.

Water Conditions

Temperature: 20 – 27 °C

pH: 6.0 – 7.5

Hardness: 36 – 268 ppm

Diet

Probably a predator feeding on crustaceans, invertebrates and smaller fishes in nature, although there should be no need to use such live foods in captivity.

Offer a varied diet comprising sinking dried foods, live and frozen bloodworm, Tubifex, etc., and perhaps the occasional small earthworm.

Behaviour and CompatibilityTop ↑

Generally peaceful though it may predate on smaller fishes and is somewhat timid so does not compete well with much larger, robust or otherwise boisterous species.

Peaceful, comparably-sized cyprinids, loaches and other catfishes perhaps constitute the best options but be sure to research your choices thoroughly prior to purchase.

K. cryptopterus is gregarious and tends to form schools so ideally four or more specimens should be purchased.

Sexual Dimorphism

Adult males are noticeably slimmer than females but additional information is contradictory with some sources stating that the posterior edge of the pectoral-fin spine is serrated in males (vs. smooth in females) and others that there is no such difference.

Reproduction

Unrecorded. In nature the closely-related congener K. geminus (see ‘Notes’) spawns at the onset of the wet season with young specimens common in seasonally-inundated areas.

NotesTop ↑

This species is sometimes traded as ‘smokey glass catfish’.

Its closest relative is K. geminus, populations of which were formerly considered to represent K. cryptopterus, and these two can be distinguished from congeners by the dorsal profile lacking a nuchal concavity (vs. possessing a nuchal concavity) and possessing short maxillary barbels (extending to the pectoral-fin base vs. extending beyond tip of pectoral-fin).

K. cryptopterus can be distinguished from K. geminus by possessing a wider head (12.2-14.2 % SL vs. 9.5–12.0), shorter anal-fin (57.2-62.9 % SL vs. 62.2–72.7) and snout (35.1-39.8 % HL vs. 39.5–45.3), and less laterally-placed eyes (ventral two-thirds of the orbital margin visible when the head is viewed ventrally vs. only the ventral half).

K. cryptopterus and K. geminus can be further told apart from all other silurid catfishes by possession of an anteriorly truncated supralabial fold with the lower edge extending beyond the base of the maxillary barbel and an elongate antorbital process of the lateral ethmoid that is not anteroposteriorly compressed.

Kryptopterus species are found only in Southeast Asia and the genus has been considered polyphyletic since Bornbusch (1995) with some former species already moved to the genera Phalacronotus and Micronema.

Those still contained within the genus are assigned to a number of putative species groups as follows:

K. bicirrhis group: K. bicirrhis, K. lais, K. palembangensis, K. macrocephalus, K. minor, K. piperatus, K. vitreolus
K. cryptopterus group: K. cryptopterus, K. geminus
K. limpok group: K. limpok, K. mononema, K. dissitus, K. baramensis, K. hesperius
K. schilbeides group: K. schilbeides, K. paraschilbeides

Bombusch (1995) identified the K. bicirrhis group as a distinct clade although he didn’t propose any synapomorphy to diagnose it.

Ng and Kottelat (2013) later noted that members normally have fewer anal-fin rays (46–67 vs. 64–85) than other congeners and placed K. piperatus and K. vitreolus within the group based on this character.

References

1. Bleeker, P., 1851 - Natuurkundig Tijdschrift voor Nederlandsch Indië v. 1: 259-275
   Nieuwe bijdrage tot de kennis der ichthyologische fauna van Borneo met beschrijving van eenige nieuwe soorten van zoetwatervisschen.
2. Bornbusch, A. H., 1995 - Zoological Journal of the Linnean Society 115: 1-46
   Phylogenetic relationships within the Eurasian catfish family Siluridae (Pisces: Siluriformes), with comments on generic validities and biogeography.
3. Ferraris, C. J., Jr., 2007 - Zootaxa 1418: 1-628
   Checklist of catfishes, recent and fossil (Osteichthyes: Siluriformes), and catalogue of siluriform primary types.
4. Kottelat, M. and E. Widjanarti, 2005 - Raffles Bulletin of Zoology Supplement 13: 139-173
   The fishes of Danau Sentarum National Park and the Kapuas Lakes area, Kalimantan Barat, Indonesia.
5. Ng, H-H. and M. Kottelat, 2013 - Zootaxa 3630: 308-316
   After eighty years of misidentification, a name for the glass catfish (Teleostei: Siluridae).
6. Ng, H. H., 2003 - Zootaxa 305: 1-11
   Kryptopterus geminus, a new species of silurid catfish (Teleostei: Siluridae) from mainland Southeast Asia.
7. Parenti, L. R. and K. K. P. Lim, 2005 - Raffles Bulletin of Zoology Supplement 13: 175-208
   Fishes of the Rajang Basin, Sarawak, Malaysia.
8. Rainboth, W. J., 1996 - FAO, Rome: 1-265
   FAO species identification field guide for fishery purposes. Fishes of the Cambodian Mekong.
9. Roberts, T. R., 1989 - Memoirs of the California Academy of Sciences No. 14: i-xii + 1-210
   The freshwater fishes of western Borneo (Kalimantan Barat, Indonesia).
10. Tan, H. H. and H. H. Ng, 2000 - Journal of Natural History 34(2): 267-303
    The catfishes (Teleostei: Siluriformes) of central Sumatra.