Fish
Rasbora
Rasbora and Trigonostigma · also called rasboras
A rasbora is a small, calm, schooling fish from the blackwater streams and peat swamp forests of Southeast Asia, and one member, the harlequin rasbora with its bold orange body and black wedge of colour, has become one of the most instantly recognisable fish in the aquarium hobby.
Overview
Rasboras are small cyprinid fish, spread across the related genera Rasbora, Trigonostigma, and Boraras, from streams, peat swamp forests, and rice paddies across South and Southeast Asia. They eat small invertebrates and fine plant matter, and many species come from soft, acidic blackwater stained by tannins from fallen leaves.
Peaceful schoolers
Rasboras are undemanding, peaceful egg-scatterers with no parental care — the harlequin rasbora notably turns upside down to lay its eggs on the underside of a leaf. Kept in a school of six or more, they mix easily with other calm community fish like small tetras, corydoras, and dwarf gouramis, making them a classic beginner recommendation.
Status
Least Concern for the popular, widely farmed species like the harlequin rasbora, but many smaller rasboras are confined to specific blackwater streams and peat swamp forest in Borneo, Sumatra, and the Malay Peninsula, and a number are Vulnerable or Endangered as that habitat is drained and converted to plantations.
Rasbora: common questions
Are rasboras good fish for a beginner aquarium?
Yes, the popular species such as the harlequin rasbora are widely recommended for beginners, since they are hardy, peaceful, tolerant of a reasonable range of water conditions once the tank is established, and readily available as captive-bred stock. Like most small schooling fish they do best kept in a group of six or more, which makes them feel secure, brings out their natural schooling behaviour, and produces a much more attractive, active display than a single fish or a small pair, so a beginner should plan for a proper school rather than just one or two individuals.
What is the difference between a rasbora and a tetra?
Both are small, popular, schooling aquarium fish of similar size and temperament, but they come from different families and different continents. Rasboras are cyprinids from Asia, the same broad family as barbs, carp, and goldfish, and generally lack the small adipose fin found on many tetras. Tetras are characins from Africa and the Americas, the family that also includes piranhas, and often show a small extra fin between the dorsal fin and the tail. In the aquarium the two groups have broadly similar care requirements, and both are frequently kept together in the same community tank without any issue.
Why do harlequin rasboras lay their eggs upside down?
During spawning, a pair positions itself under a broad, flat leaf, and the female turns upside down against the underside of the leaf to release her eggs there while the male fertilises them, a behaviour that sticks the adhesive eggs to a sheltered surface out of the main current and away from some bottom-dwelling egg predators, rather than scattering them loosely over the substrate the way many other small egg-laying fish do. Even so, the adults provide no further care and will eat the eggs or newly hatched fry if they are not removed or if the fry cannot find cover, so successful breeding in a home aquarium usually requires providing suitable broad-leaved plants and separating the eggs or fry from the adults.
Do rasboras need soft, acidic water?
Many rasboras, especially those from blackwater and peat swamp habitats such as the harlequin rasbora, naturally prefer soft, slightly acidic water and often show their best colour and breed most readily under those conditions, closer to their native streams. That said, captive-bred harlequin rasboras and several other popular species have proven fairly adaptable and can live well in moderately hard, near-neutral water typical of many household taps, so soft acidic water is more important for achieving peak colour and successful breeding than for simply keeping the fish alive and healthy.