It is included in a group often referred to as ‘red-eyed puffers’, which currently contains four recognised species distributed in Indochina and the Greater Sunda Islands. It can be distinguished from C. borneensis, C. irrubesco, and C. lorteti, the remaining members of this group, by the following combination of characters: 11 dorsal-fin rays; 16 pectoral-fin rays; 11-13 anal-fin rays; 11 caudal-fin rays; eyes not bulging above the head; in males dorsal-fin hyaline, black spot on dorsal-fin base present, pectoral-fin base hyaline, anal-fin hyaline with no black spot at base…

It is distinguished from congeners by the following combination of characters: anal-fin with 6-7 basal pterygiophores and 9 rays (vs. 10-11 rays in C. asellus and C. psittacus; dorsal-fin with 10 bas…

Although it does penetrate the lower basins of rivers, particularly the Amazon where it has been collected from the rio Xingu several hundred kilometres from its mouth, this species is predominantly an inhabitant of mangrove swamps, estuaries, and other such saline habitats.

It is particularly common in tidal channels, shallow inshore lagoons, and the lower reaches of rivers.

This species is relatively uncommon in the aquarium hobby but is available on occasion, sometimes mixed in among shipments of the congener C. salivator.

These two can be told apart by the fact that C. salivator possesses a series of distinct dark bars on the head and body in both sexes, a colour pattern unique within the genus.

It is also similar t…

This species is also referred to as ‘South American puffer’, ‘SAP’, ‘Amazonian puffer’, ‘Peruvian puffer’, or ‘Brazilian puffer’ in the ornamental trade.

Within the genus Colomesus, C. asellus can be immediately identified by possessing a unique transverse row of dermal flaps across the chin which is absent in its congeners C. psittacus and C. tocantinensis.

This species is uncommon in the aquarium hobby. It is similar to the congeners C. borneensis and C. lorteti but can be told apart by males possessing a red (vs. bluish to greyish with black and white distal bands in C. lorteti) caudal-fin and lacking (vs. possessing) a black blotch at the base of the dorsal-fin.

Known from the lower Mekong basin in Thailand, Vietnam, and Cambodia, the Chao Phraya watershed in central Thailand, and may occur in smaller river systems between.

Type locality is ‘Thu-dâu-môt, Vietnam’.