Exclamation-point Rasbora
Boraras urophthalmoides
The Exclamation-point Rasbora (Boraras urophthalmoides) is one of the smallest aquarium fishes. Its common name refers to the dark lateral mark and round spot near the tail base, which together resemble an exclamation point. It inhabits shallow, vegetated wetlands in Thailand, Cambodia and Vietnam. The fish is peaceful, but its tiny size and timid nature make it vulnerable in a busy community tank. Keep a species group in a mature, stable aquarium, provide finely sized food and do not mix it with other Boraras species, as hybridisation may occur.
Plan your aquarium →At a glance
- Temperature
- 20–28 °C
- pH
- 6.0–7.0
- GH
- 1–10 °dGH
- Aquarium length
- At least 45 cm
- Minimum aquarium volume
- At least 41 L
- Adult size
- At least 1.6 cm
- Group size
- At least 8–10 individuals
- Temperament
- Peaceful
About this species
Seriously Fish reports about 16 mm standard length, excluding the caudal fin. A distinct lateral stripe and round dark blotch on the caudal peduncle are characteristic. Orange to red colour varies by locality, so confusion with Boraras brigittae is possible. FishBase displays an outlying maximum of 4 cm total length; because this conflicts sharply with the species-specific profile and other evidence, that figure is not used as the care size.Natural habitat
The species was described from a swamp near the Sai Buri River in Thailand’s Pattani province. Records also include other parts of Thailand, Cambodia and Vietnam, including moats and ponds around Angkor. It lives in shallow swamps, floodplains, rice fields and pools with abundant submerged vegetation, usually in clear water. During the wet season it may use temporarily inundated areas. It should not be described as exclusively a blackwater peat-swamp species.Aquarium and layout
Seriously Fish gives a minimum base of 45 × 30 cm and about 41 litres for a group. This allows swimming and helps accommodate temporary male territories around spawning. Use dense fine-leaved planting, floating plants and calm refuges while retaining open swimming space. Keep the current gentle and introduce the fish only to a biologically mature aquarium. For such a small fish, stable water quality matters more than high flow or a crowded stock list.Water conditions
The care profile gives 20–28°C, pH 6.0–7.0 and GH 1–10 dGH. These differ from the narrower range the same specialist describes for a dedicated breeding setup; those breeding values are not treated as routine maintenance limits. Do not adjust pH abruptly to chase a number. Test regularly, prevent ammonia and nitrite and keep conditions steady. Acclimate new fish gradually, allowing for differences between shipping water and the aquarium.Behaviour and group size
This species is peaceful but very small and reserved. Keep at least 8–10 conspecifics so the fish can shoal naturally and may be less nervous. A species-only aquarium is a safe choice. One important warning: Seriously Fish advises against keeping it with other Boraras because hybridisation may occur. Keep the species separate even where water ranges overlap. Larger or faster fish may also outcompete it or treat it as prey.Feeding
Boraras urophthalmoides is a micropredator of small insects, worms, crustaceans and zooplankton. Offer suitably tiny live or frozen foods such as Daphnia and Artemia alongside quality dried food. Crumble flakes and feed small portions that the fish can actually swallow. Larger worms or coarse granules are unsuitable if they do not fit the mouth. Watch the entire group while feeding, as timid individuals may otherwise receive too little. Remove leftovers to protect water quality.Breeding
The fish scatters eggs among plants and provides no parental care. Fry may occasionally appear in a mature, densely planted aquarium, but eggs and larvae are not protected from adults. A separate breeding setup offers more control; the specialist gives softer, more acidic water for breeding than for routine care, so do not confuse those ranges. Larvae are minute and initially need microscopic food. Do not breed or house it with other Boraras species because of hybridisation risk.Suitable products
Recommended staple foods
Tropical Supervit Basic 100ml
Complete flake food for animal-eating fish. Crumble it very finely for this tiny mouth and check that shy fish feed.
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Tropical Dafnia 100ml
Dried Daphnia as an occasional supplement. Break it into tiny pieces and continue to provide a complete staple food.
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Sources & review
This care guide draws on several specialist sources and was last checked on .