G. cornusaccus can be distinguished from congeners by the following combination of characters: secondary rostrum present; incomplete postoral pouch present reduced to pockets located posterior to mouth corners; sublacrymal groove present and visible when viewed laterally; juveniles with thick, cream-coloured bars and blotches on body, adults uniformly-coloured; head dorsum plain; subopercular groove absent; gill slit vertical; snout truncate when viewed dorsally; no scales on abdomen; 55-61 lateral line scale…

One of the more commonly-traded members of the genus and often found in mixed shipments which may contain other Gastromyzon spp. or related fishes like Beaufortia kweichowensis, these often labelled collectively as ‘Borneo sucker’, ‘Hong Kong pleco’, ‘butterfly loach’, etc. It’s sometimes misidentified as G. punctulatus, a species not currently traded which possesses yellow finnage and a lighter-coloured, less-intensely spotted body.

This species is one of several traded variously as 'butterfly loach', 'butterfly plec', 'Hong Kong plec(o)', 'Chinese hillstream loach' or simply 'hill stream loach'. In many countries it's the most common balitorid in the shops but is also often found in mixed shipments containing members of other genera.

Like all balitorids it's an obligate bottom-dweller with specialised morphology adapted to life in fast-flowing water. The paire…

Field observations have revealed that individuals almost always position themselves facing into the flow, either along the sides, behind or under rocks, their specialised morphology (see ‘Notes’) allowing them to feed and maintain position without being swept away.

Not many fishes have been able to successfully colonise this narrow ecological niche, but syntopic species in nature include Gastromyzon extrorsus (Petagas River), G. introrsus, G. lepidogaster (Pad…

Annamia spp. may be confused with related genera such as those of the genus Balitoropsis. They can be identified by their more depressed body shape, elongate lower caudal-fin lobe, and the presence of a single unbranched ray in the pectoral and pelvic fins. At least one undescribed member of the genus is thought to exist.

Traditionally considered to be a micropredator feeding on insect larvae and suchlike (Rainboth, 1996), but a study by Herder and Freyhof (2006) revealed adult A. normani inhabiting the Duc My River in central Vietnam to be specialised grazers of cyanobacteria. In rapids the latter form hard encrustations on rock surfaces from which adults are able to bite chunks.