Kryptopterus geminus

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.

geminus: from the Latin geminus, meaning 'twin-born', in allusion to this species' close morphological similarity to K. cryptopterus.

Known from the lower and middle Mekong river system in Thailand, Laos, Cambodia and Vietnam at least as far upstream as Vientiane, capital of Laos, and the lower Chao Phraya drainage in Thailand.

Type locality is ' Stung Treng, Mekong River 2 kilometers downstream from mouth of Tonle Sap on sandbars, Mekong River drainage, Cambodia, 13°31'N, 105°56'E'.

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

An aquarium with base dimensions of 150 ∗ 45 cm60 ∗ 18 in or equivalent should be the smallest considered.

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.

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.

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

Unrecorded in aquaria. In nature it spawns at the onset of the wet season with young specimens common in seasonally-inundated areas.

This species is likely to be traded for aquaria but probably misidentified as the very similar-looking K. cyrptopterus with which wild populations were formerly considered conspecific.

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

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)[5] 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.