Exclamation-point rasbora

Boraras urophthalmoides

FreshwaterFish

Care at a glance

Temperature: 73–81°F (23–27°C)
pH: 6.0–7.0
Adult size: 0.6 in (1.6 cm)
Minimum tank: 11 gal (40 L)
Temperament: Peaceful
Social behavior: Schooling
Swim level: Middle
Difficulty: Easy
Breeding: Medium
Rarity: Common
Origin: Southeast Asia (Thailand, Cambodia, Vietnam)
Family: Cyprinidae

Overview

Keep them in a school of 8 to 10 or more in a tank of at least 40 liters, since a small group hides and loses its color. They are peaceful mid-water shoalers that drift through open space near the plants and warm up to a tank as they settle in. Hold the water at 23 to 27 C with a pH of 6 to 7, soft and slightly acidic. Feed tiny foods their small mouths can manage, like crushed micro pellets, baby brine shrimp, and microworms. They are shrimp-safe, so pair them only with other small, calm species and skip anything big enough to bully or eat them.

In the wild

Exclamation-point rasboras come from slow, shallow blackwater in Thailand, Cambodia, and Vietnam, the kind of forest pools and ditches stained dark with tannins and packed with plants. To match that, give them a mature, heavily planted tank with driftwood and a few catappa leaves to tint the water and soften it, gentle flow, and dim light. Keep the water warm at 23 to 27 C and on the soft, acidic side, with a pH of 6 to 7. They hold their best color over dark substrate in low light.

Good to know

This is a tiny cyprinid in the family Cyprinidae, one of the smallest fish in the trade at about 1.6 cm full grown. It is an egg scatterer with no parental care, and breeding is doable but takes patience, so it lands at medium difficulty. Most are wild caught, and they are often sold mixed in with or mislabeled as the chili rasbora, Boraras brigittae.

Did you know

The name comes from the marking near the tail, a dark spot under a short horizontal stripe that together look like an upside-down exclamation point. The fish is so small and so often shipped alongside chili rasboras that mixed groups of the two are common in stores, and you sometimes only sort out which is which once they color up at home.