Blue Cardinal Rasbora Care Guide - Aquarium Tips, Diet & Breeding

The Blue Cardinal Rasbora is a small, elegant schooling fish with a slender body and a striking blue to blue-green sheen along its flanks. Depending on mood and lighting, the colour may appear more silvery or iridescent, with subtle darker markings adding definition to the body. Its compact size makes it an appealing choice for carefully planned nano and planted aquariums.

This rasbora is an active but generally peaceful swimmer. It feels most secure in a group, where the fish display natural shoaling behaviour and move together through the middle and upper levels of the aquarium. A larger group usually produces bolder behaviour and more impressive colour than keeping only a few individuals.

In the wild, Rasbora rutteni comes from tropical freshwater habitats in Sumatra. Its association with the Lake Toba area gives it a particularly interesting regional background, as the lake and surrounding waters support a distinctive fish community. Like many small rasboras, it is adapted to environments with cover, submerged vegetation and relatively gentle water movement.

Blue Cardinal Rasboras are best appreciated as a group rather than as solitary feature fish. Their small size and calm nature allow them to complement planted community aquariums, while their shimmering colour becomes especially noticeable against darker substrate and dense green vegetation.

The Blue Cardinal Rasbora, Rasbora rutteni, is native to Sumatra in Indonesia, in Southeast Asia. It is associated with the Lake Toba region and its connected freshwater habitats, although aquarium-trade identification can occasionally be complicated by the use of similar common names.

A group should have at least a 60-litre aquarium, ideally measuring around 60 x 30 x 30 cm or larger, with extra length providing useful swimming space. Use a mature, stable setup with gentle filtration, subdued lighting and plenty of plants, including fine-leaved varieties, floating cover and open areas for schooling. Dark sand or fine gravel can enhance their colour, while wood, leaf litter and shaded retreats help recreate the sheltered character of their natural habitat. Keep the water clean and well oxygenated without creating excessively strong flow.

Up to about 3.5 cm (1.4 in) in total length. Females are usually slightly larger and deeper-bodied than males, while males tend to remain slimmer and may show stronger colour.

Blue Cardinal Rasboras are small omnivores and should receive a varied diet of quality nano pellets or finely crushed flakes, supplemented with frozen or live foods such as baby brine shrimp, daphnia, cyclops and finely sized mosquito larvae. Offer small portions once or twice daily, using foods that can be eaten quickly without leaving excessive waste. A varied diet helps maintain their colour, energy and breeding condition.

Blue Cardinal Rasboras are peaceful community fish and suit other similarly small, calm species. Good tankmates include small peaceful tetras, celestial pearl danios, ember tetras, pygmy Corydoras, otocinclus and other gentle rasboras. Avoid large cichlids, predatory fish, boisterous barbs and fin-nipping species, which may harass or eat them. They should also not be housed with considerably larger or aggressive fish that prevent them from feeding confidently.

Blue Cardinal Rasboras are egg-scattering fish that can breed in a mature, well-planted aquarium. Condition a group with small live or frozen foods, then provide fine-leaved plants or a spawning mop for the eggs. Adults may eat the eggs, so remove the parents after spawning or protect the eggs with a breeding grid. The eggs usually hatch within a day or two, and the tiny fry need infusoria or another suitably microscopic first food before moving on to newly hatched brine shrimp.

Females are generally fuller through the abdomen, particularly when carrying eggs, and are often marginally larger. Males are slimmer and may display more intense blue coloration, especially when courting or competing with one another.