Rasbora trilineata (Scissortail Rasbora)

Overview

The Scissortail Rasbora (Rasbora trilineata), sometimes traded under names like Flag Tail Glass Danio, is a sleek, energetic schooling fish. Known for the distinctive twitching motion of its tail that resembles a pair of scissors opening and closing, this species brings continuous movement and a shimmering presence to the mid-to-upper levels of the aquarium.

Distribution and Habitat

This species is widely distributed across Southeast Asia, with native populations found in the Mekong basin, the Malay Peninsula, Sumatra, and Borneo. They primarily inhabit flowing rivers, streams, and flooded forest areas where the water is well-oxygenated and shaded by dense canopy cover.

Description of Scissortail Rasbora

Body shape:

They possess an elongated, torpedo-shaped body that is highly streamlined, allowing them to swim swiftly against river currents.

Color:

The body is predominantly silver with a semi-transparent or clear quality, highlighted by a subtle horizontal black line stretching from the mid-body to the caudal peduncle.

Barbels:

Unlike some other cyprinids, they lack prominent barbels.

Snout:

They have a pointed snout with a terminal mouth that is perfectly adapted for grabbing insects and food particles from the water column and surface.

Eyes:

Their eyes are relatively large, aiding them in detecting both predators and prey in dimly lit, tannin-stained waters.

Fins:

The dorsal, pectoral, pelvic, and anal fins are mostly clear and transparent, blending seamlessly into their sleek profile.

The Tail:

The deeply forked caudal fin is their most famous feature. It is boldly marked with distinct black and white horizontal bands. As the fish swims, it twitches this fin, creating a mesmerizing scissor-like effect.

Temper

They are incredibly peaceful and pose no threat to other tank mates, making them an ideal resident for a community aquarium.

Sociality

Highly social by nature, the Scissortail Rasbora is a schooling fish that must be kept in groups of at least six individuals, though groups of eight to twelve are highly recommended to reduce stress and encourage natural behaviors.

Activity

They are extremely active swimmers, constantly darting back and forth in the middle and upper strata of the aquarium water.

Keeping and Caring for Scissortail Rasbora

Tank size:

Due to their active swimming habits and potential adult size of up to 15 cm, a minimum tank size of 30 gallons (114 liters) is required, though a longer tank (like a 40-gallon breeder) is preferable to provide ample horizontal swimming space.

Water Parameters:

Temperature

Maintain a stable temperature between 22-26°C (72-79°F).

pH

They thrive in slightly acidic to neutral water, with a pH range of 6.0 to 7.5.

Hardness

Keep water hardness between 2 and 12 dGH.

Ammonia, Nitrite, Nitrate

Ammonia and Nitrite must always be at 0 ppm. Nitrates should be kept below 20 ppm through regular water changes.

Lighting

Moderate lighting is ideal. Too bright of a light can wash out their colors and cause stress unless mitigated by floating plants.

Water flow

A moderate water flow is recommended to replicate their natural riverine habitats and encourage their active swimming behaviors.

Decorations and Plants

Provide plenty of open swimming space in the center of the tank. Plant the perimeters densely with robust aquatic plants and add some driftwood or floating plants to offer shaded, secure areas.

Diet

Scissortail Rasboras are omnivorous and not fussy eaters. In the aquarium, they will readily accept high-quality flakes and micro-pellets. To ensure optimal health and coloration, supplement their diet with live or frozen foods such as daphnia, bloodworms, and brine shrimp.

Some Feeding Tips

Feed them small amounts once or twice a day, only offering what they can consume within a few minutes. Since they are mid-to-top water feeders, use slowly sinking or floating foods.

Breeding

They are egg scatterers that provide no parental care. To breed them, set up a separate, dimly lit breeding tank with soft, slightly acidic water and line the bottom with a spawning mop, mesh, or fine-leaved plants like Java Moss. Condition the adults with live foods, introduce them to the breeding tank, and remove them immediately after spawning to prevent them from eating their own eggs. The fry typically hatch in 24 to 48 hours and will need infusoria before graduating to baby brine shrimp.

Conclusion

The Scissortail Rasbora is a hardy, dynamic, and exceptionally peaceful fish that brings a wonderful sense of motion to the freshwater aquarium. Their unique tail markings and schooling behavior make them a rewarding species for both beginner and experienced aquarists alike.