Opsarius caudiocellatus

Overview

Fast swimming and vigorous feeding distinguish the riverine Opsarius caudiocellatus. A round black tail-base spot and dark dorsal rays assist identification. It needs spacious, clean, oxygenated mature accommodation, not simply a quiet community chosen by body length.

Distribution & habitat

Records span the Salween system in China, Myanmar, and western Thailand and the upper Mekong in Yunnan. Mengding in Yunnan is the type locality.

Moderate to swift rivers and streams of low or intermediate gradient, over gravel, cobbles, boulders, and bedrock, are the suggested habitat. A January 2010 Beiqiaohe site in Yunxian had turbid water measured at about 22 °C, pH 7.6, and 70 µS/cm conductivity at 20 cm depth. This is one field observation, not a replacement aquarium target.

Aquarium setup

Arrange sand, gravel, stones, and optional roots as a stream layout, retaining extensive swimming space. Hardy attached ferns or Anubias can be used.

Avoid organic waste accumulation and maintain stable clean water with plentiful oxygen and moderate circulation. Filters, additional pumps, or air stones can be used as needed. Use only a mature aquarium, change roughly 30–50% weekly, and secure the lid against jumping.

Diet & feeding

Members of the genus feed largely near the surface on aquatic and terrestrial insects, possibly also taking small fishes and bottom invertebrates. This general account is not a confirmed complete species-specific menu.

Good dry preparations should be supplemented with live or frozen bloodworms, Artemia, chopped earthworms, and similar foods. Fruit flies and small crickets are options after appropriate gut-loading.

Behaviour & compatibility

A standard community is usually unsuitable. Speed and assertive feeding may overwhelm slow or timid fishes, while very small companions face possible predation. Robust similar-sized open-water cyprinids and suitable bottom dwellers sharing its environmental requirements are better candidates.

It forms a loose aggregation with a hierarchy rather than a continuously coordinated school. Keep at least five. With only two or three, subordinates may suffer persistent harassment; solitary fish may attack similar-looking companions.

Sexual dimorphism

Adult females may be larger, deeper-bodied, and less colorful, especially when ripe. Breeding males may show stronger color and tubercles as in related fishes, but these tendencies need cautious interpretation.

Breeding

No practical aquarium breeding record is available.

Notes

Black dorsal rays separated by clear membranes and the round tail-base spot form useful recognition clues. Trade appearances may have occurred under incorrect names, and the older genus Barilius can still appear in references. A sales label alone cannot settle identity.