Boraras urophthalmoides (Tail Stripe Rasbora)

28 March 2026

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The Tail Stripe Rasbora (Boraras urophthalmoides) is a captivating, nano-sized cyprinid native to the blackwater swamps of Southeast Asia. Renowned for its striking lateral stripes and peaceful demeanor, this miniature jewel is highly popular among aquascapers looking to bring vibrant life and schooling behavior to heavily planted nano aquariums.

Boraras urophthalmoides (Tail Stripe Rasbora)

Overview

The Tail Stripe Rasbora, scientifically known as Boraras urophthalmoides, is one of the smallest species in the aquarium trade. Despite its diminutive size, it packs a visual punch with its distinctive lateral striping. It is a fantastic choice for nano aquariums and aquascapes, where a school of these tiny fish can swim harmoniously among dense vegetation without disrupting the layout.

Image of tail stripe rasbora boraras urophthalmoides

Distribution and Habitat

This species is native to Southeast Asia, specifically found in the swamps, marshes, and slow-moving blackwater streams of Thailand, Cambodia, and Vietnam. Their natural habitat is heavily shaded by forest canopies and densely choked with aquatic vegetation, submerged roots, and leaf litter, which releases tannins into the water, making it soft and slightly acidic.

Description of Tail Stripe Rasbora

Body shape:

They possess a highly streamlined, torpedo-like body that is extremely slender, allowing them to navigate effortlessly through dense aquatic vegetation.

Color:

Their coloration is their most striking feature. They exhibit a dark, often black or deep blue-iridescent lateral stripe running from the gills to the tail, bordered just above by a vibrant orange or gold stripe. The belly is usually a pale silver or clear.

Barbels:

Like other members of the Boraras genus, they completely lack barbels.

Snout:

The snout is relatively short and slightly pointed, adapted for picking tiny micro-organisms from the water column.

Eyes:

Their eyes are noticeably large in proportion to their tiny head and overall body size, aiding them in low-light environments.

Fins:

The fins are mostly translucent or clear. The dorsal fin often features a dark leading edge or a subtle dark blotch, sometimes accented with a hint of red or orange.

The Tail:

The caudal fin (tail) is distinctly forked and clear, featuring a prominent dark spot right at the base of the caudal peduncle, which gives the fish its common name.

Temper

The Tail Stripe Rasbora is an exceptionally peaceful species. They are timid and easily intimidated by larger, more boisterous tank mates, making them ideal for dedicated nano setups or tanks with other similarly sized, gentle species.

Sociality

They are highly social, schooling fish that rely on numbers for a sense of security. They should always be kept in groups of at least 8 to 10 individuals. In larger groups, their colors become more vibrant, and they display fascinating natural schooling behaviors.

Activity

These rasboras are active mid-level swimmers. During the day, they will constantly dart around the middle and upper levels of the aquarium, especially if the lighting is kept subdued and there is plenty of cover.

Keeping and Caring for Tail Stripe Rasbora

Tank size:

Due to their tiny footprint, a small group can be housed in a tank as small as 5 gallons. However, a 10-gallon aquarium is much preferred to provide adequate swimming space for a proper school and to maintain stable water parameters.

Water Parameters:

Temperature

They thrive in tropical temperatures ranging from 20-28°C (68-82°F).

pH

A slightly acidic to neutral pH between 6.0 and 7.0 is ideal, closely mimicking their natural blackwater habitats.

Hardness

They require very soft water, typically between 2 and 10 dGH.

Ammonia, Nitrite, Nitrate

Ammonia and Nitrite must always remain at 0 ppm. Nitrates should be kept as low as possible, ideally below 20 ppm, through regular water changes and live plants.

Lighting

Dim to moderate lighting is best. Bright lights can wash out their colors and cause them stress unless the tank is heavily shaded by floating plants.

Water flow

The water flow should be gentle. They come from slow-moving swamps and will struggle against strong currents generated by oversized filters.

Decorations and Plants

A heavily planted tank is a must. Fine-leaved plants, mosses, and floating plants are excellent choices. Adding driftwood and dried leaf litter (like Indian Almond leaves) will release beneficial tannins and provide a natural, comforting environment.

Diet

In the wild, they are micropredators feeding on tiny insects, worms, and zooplankton. In the aquarium, their tiny mouths require appropriately sized foods. Offer them crushed high-quality flakes, micro-pellets, and small live or frozen foods such as baby brine shrimp, daphnia, and microworms.

Some Feeding Tips

Feed them very small amounts 2 to 3 times a day. Since they are mid-water feeders, ensure the food sinks slowly so they have time to catch it before it reaches the bottom.

Breeding

Breeding the Tail Stripe Rasbora is possible but challenging due to the tiny size of the fry. They are continuous egg scatterers that show no parental care. To yield fry, set up a separate, dimly lit breeding tank with very soft, acidic water and a bottom covered in dense moss or a spawning mop. Once eggs are laid, remove the adults to prevent predation. The microscopic fry will initially require infusoria before graduating to baby brine shrimp.

Conclusion

The Tail Stripe Rasbora is a magnificent, peaceful addition to any blackwater or heavily planted nano aquarium. While they require stable water conditions and careful consideration of tank mates, their vibrant stripes and active schooling behavior make them a deeply rewarding species for intermediate and dedicated aquarists.

Fish info

Care level: Moderate
Temperament: Peaceful
Adult size: 1.5-2 cm
Life expectancy: 3-5 years
Fish type: Cyprinid
Temperature : 20-28°C
pH: 6.0-7.0
Color Form: Black, Clear, Orange, Silver

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