Macrochirichthys macrochirus

Macrochirichthys: from the Ancient Greek μακρός (makrós), meaning 'long', and ἰχθύς (ikhthús), meaning ‘fish’, in allusion to the long pectoral fins in this genus.

macrochirus: as above.

Widespread in Southeast Asia, including the Mekong basin in southern China, Laos, Thailand, Cambodia, and Vietnam, the Chao Phraya and Mae Klong systems in central and western Thailand, various smaller watersheds in southern Thailand and Peninsular Malaysia, and the Greater Sunda Islands of Borneo, Sumatra, and Java.

Type locality is 'Java, Indonesia'.

It is thought to have been extirpated from the Chao Phraya and Mae Klong rivers, Lake Songkhla, and the entire island of Java due to a variety of anthropogenic factors, and the Mekong populations have also been drastically reduced. In particular, it is sensitive to pollution and gillnetting, and is heavily overfished.

A pelagic species displaying a preference for large lakes, main river channels and major tributaries, but moves into flooded forests and other inundated zones during the wet season.

Suitable only for public installations or the very largest private aquaria.

The aquarium should ideally be designed to resemble a flowing stream or river with a substrate of variably-sized rocks, sand, fine gravel, and some larger water-worn boulders. This can be further furnished with driftwood roots and branches if you wish, but be sure to leave plenty of open swimming space.

Like many fishes that naturally inhabit running waters it’s intolerant to the accumulation of organic wastes and requires spotless water at all times in order to thrive.

It also does best if there is a high proportion of dissolved oxygen and moderate degree of water movement so external filters, powerheads, etc., should be employed as necessary.

As stable water conditions are obligatory for its well-being this fish should never be added to biologically-immature aquaria and weekly water changes of 30-50% aquarium volume should be considered mandatory.

A tightly-fitting cover is essential as this species is a prodigious jumper, and it may also prove beneficial to cover the back and sides of the aquarium in order to reduce the chances of it swimming into the glass since it can be skittish, especially in confined surroundings.

An obligate carnivore with juveniles feeding on aquatic and terrestrial invertebrates but becoming increasingly piscivorous as they grow.

Best kept alone, or with similarly-sized, non-aggressive fishes it cannot fit into its mouth since it’s otherwise quite peaceful and easily-dominated.

It can also be maintained in a group in a suitably-sized aquarium but the purchase of at least three specimens is advisable.

This species is unsuitable for the majority of private aquaria although juveniles are traded on occasion.

It is the only member of its genus, although there is a possibility that Indochinese and Sundaic populations may represent distinct species.

It can be distinguished from all other Southeast Asian cyprinids by the following combination of characters: head upturned; 108-130 + 3-4 lateral line scales; no barbels; body compressed with a sharp ventral keel extending from throat to anus; mouth cleft almost vertical; a black blotch on the caudal-fin base; pectoral fins elongated.