Exclamation Point Rasbora (Boraras urophthalmoides) Care Guide
One of the tiniest aquarium fish, this micro rasbora features a warm reddish body with a distinctive dark spot near the tail base followed by a thin line — resembling an exclamation mark.
Compiled by Aquairi from published sources · Published · Updated
Overview
Boraras urophthalmoides is a species in the family Cyprinidae. One of the tiniest aquarium fish, this micro rasbora features a warm reddish body with a distinctive dark spot near the tail base followed by a thin line — resembling an exclamation mark. Perfect for densely planted nano tanks, it is a peaceful schooling fish that thrives in soft, acidic water with minimal flow.
Taxonomy
- Family: Cyprinidae
- Genus: Boraras
- Scientific name: Boraras urophthalmoides
- Other names: Least Rasbora, Boraras urophthalmoides
- Origin: Southeast Asia
Habitat
Native to shallow, still and slow-moving waters of Thailand, Cambodia and Vietnam, including rice paddies and roadside ditches. Inhabits soft, slightly acidic water with dense vegetation. A nano-sized species of the genus Boraras named for the mark on its caudal peduncle.
Tank requirements
- Minimum tank volume: 20 L
- Temperature: 22-28 °C
- pH: 5-7
- GH: 1-8 °dGH
- Water flow: low
- Adult size: 1.5-2 cm
- Lifespan: 2-4 years
- Recommended group size: ≥ 10
- Difficulty: beginner
Diet
Classified as omnivore. Recommended feeding frequency: 2x daily. In captivity, offer a varied diet appropriate to the species — quality prepared foods supplemented with frozen or live items of suitable size.
Compatibility
- Temperament: peaceful
- Swimming level: middle
- Compatible tank mates: Chili Rasbora, Ember Tetra, Pygmy Corydoras, Cherry Shrimp, Otocinclus
- Avoid with: Any fish large enough to eat them, Aggressive species
Breeding
- Breeding strategy: egg-scatterer
- Breeding difficulty: intermediate
Exclamation Point Rasbora (Boraras urophthalmoides) Breeding Guide
Overview
Boraras urophthalmoides is an egg-scattering, continuous spawner that exhibits no parental care. In a well-established, densely planted aquarium small numbers of fry may appear naturally without intervention; for higher yields a dedicated spawning setup is used.
Sexing
Mature females are noticeably rounder-bodied and often a little larger than the slightly more colourful males. This difference is the most practical way to select spawning groups.
Conditioning
Condition adults well, then introduce two to three pairs to the spawning container; if conditions suit them, spawning typically begins the following morning. Although this species will eat its eggs, it does not appear to actively hunt for them.
Breeding Setup
Use a small 10-15 litre container with dim lighting and either a bare base or a mesh that lets eggs fall through but keeps adults away from them. Fill roughly half the space with java moss or other fine-leaved plants, and add a small air-powered sponge filter. Spawning water is soft and acidic: pH 5.0-6.5, hardness 1-5 °H, with temperature toward the upper end of the normal range (around 28 °C).
Spawning Behavior & Trigger
As a continuous spawner the species scatters small batches of eggs among the moss and fine plants. The adults should be left in place for no more than a couple of days, then removed before they eat significant numbers of eggs.
Egg & Fry Care
Eggs hatch within about two days, and the fry then subsist on their yolk sacs for roughly 24 hours. Their first food must be very small, such as Paramecium or other microscopic organisms; after 7-10 days they can take Artemia (brine shrimp) nauplii and microworms. Delay water changes for the first one to two weeks to avoid shocking the tiny fry.
Common Challenges
The main hurdles are providing first foods small enough for the extremely tiny fry and avoiding losses from premature water changes. A mesh or bare base, plus prompt removal of adults, limits egg predation.