Rasbora rubrodorsalis

Overview

Rasbora rubrodorsalis is a tiny, peaceful rasbora with a vivid red dorsal-fin patch. Gentle flow, planting, and company suit it. The dorsal mark is especially useful in separating it from a similar fish with a clear dorsal fin.

Distribution & habitat

Confirmed records center on northeastern Thailand's lower Mekong region, including wetlands around Nong Khai. Claims of broader central Thai or cross-border distribution lack equally definite locality support and should remain qualified.

It occupies shallow margins of still or slowly moving swamps, reservoirs, and floodplain waters. Clear water with fine vegetation appears preferred, with movement into temporarily flooded areas during the rains.

Aquarium setup

A footprint of at least around 45 × 30 cm accommodates a small group. Dense plants and a dark substrate improve the display, while floating vegetation, roots, and branches diffuse the light.

Keep filtration gentle. Strong current can overwhelm this fish, so a torrent-style circulation scheme is inappropriate.

Diet & feeding

Natural feeding is presumed similar to related rasboras, involving minute worms, crustaceans, and other animal prey. In captivity, use suitably small dry foods alongside daily live or frozen Daphnia, brine shrimp, and comparable items.

Behaviour & compatibility

Its very peaceful nature requires companions that will not swallow or continually dominate it. Maintain eight to ten or more to reduce anxiety and allow males to display courtship color.

Sexual dimorphism

Males are noticeably smaller and slimmer, with stronger color especially during breeding.

Breeding

It repeatedly scatters eggs without parental care. Some fry may appear in an established planted tank, but a separate dim breeding container with mesh or plastic grass separating eggs from adults can improve yield.

A successful approach used softer acidic water and two males with one female. Spawning took place in the morning, and a female may produce about 250 eggs. General rasbora nursery guidance suggests roughly a day to hatch and three further days before free swimming, with timing affected by temperature and other conditions.

Offer Paramecium or equivalent microscopic food first. Introduce brine shrimp nauplii or microworms only once the fry can swallow them; adult pellets are not a direct substitute.

Notes

The red dorsal patch distinguishes it from Rasbora borapetensis, which has a clear dorsal fin and red mainly at the tail base. It has also been mislabeled Rasbora beauforti, making examination of living fish more useful than the label alone.