Harlequin Rasbora

Species NameTrigonostigma heteromorpha
Common NameHarlequin Rasbora
Care LevelEasy
Lifespan5-8 years
Adult Size1.5-2 inches (4-5 cm)
Minimum Tank Size10 gallons (38 liters)
Temperature74°F – 80°F (23°C – 27°C)
Water ConditionspH 5.5-7.5, Soft to moderately hard water

About the Harlequin Rasbora – Species Summary

Harlequin Rasboras are small, vibrantly colored fish that have become increasingly popular in the aquarium hobby, primarily because of their easy care, peaceful nature, and captivating appearance. Originating from the soft, acidic waters of Malaysia, Singapore, Sumatra, and southern Thailand, these fish belong to the Cyprinidae family. Their distinct coloration, combined with their schooling behavior, makes them a beautiful addition to community tanks.

Harlequin Rasbora Lifespan

A well-cared-for Harlequin Rasbora can live between 5 to 8 years. Their lifespan can be influenced by various factors, including diet, water quality, and overall care. Providing an optimal environment and regular care routines can ensure that these fish live to their full potential.


One of the defining features of the Harlequin Rasbora is its black, triangular patch that begins near the dorsal fin and tapers off towards the caudal peduncle. This patch is set against a vivid orange or coppery body, making it stand out distinctly. Their bodies are slightly compressed laterally, and they exhibit a streamlined shape, ideal for their active swimming habits.

Average Size

Typically, adult Harlequin Rasboras will grow to a size of about 1.5 to 2 inches (4-5 cm). Females might appear slightly plumper, especially during breeding seasons, while males tend to be slimmer.

Harlequin Rasbora Care

Tank Size

A minimum tank size of 10 gallons (38 liters) is recommended for Harlequin Rasboras. While this might seem spacious for such small fish, they are active swimmers and will benefit from the extra room. If you’re planning to keep a school, which is recommended, a larger tank would be ideal.

How To Set Up Their Tank

Recreate the rasbora’s natural environment by using soft, slightly acidic water and a dark substrate to mimic the tannin-stained waters of their natural habitats. Live plants, particularly those that offer dense foliage like Java moss or Java fern, provide the fish with hiding spots and replicate their natural environment. Driftwood and leaf litter can also enhance the naturalistic feel and provide additional shelter.

Lighting Requirements

Harlequin Rasboras don’t have specific lighting needs, but they do appreciate dimmer, more subdued lighting which mirrors the shaded waters they come from. Floating plants can help diffuse overhead lighting and provide the desired environment.


The ideal pH range for Harlequin Rasboras is between 5.5 and 7.5. These fish are known to adapt to various water conditions, but as always, stability is key, and sudden fluctuations should be avoided.


Maintaining a temperature between 74°F and 80°F (23°C – 27°C) is crucial for Harlequin Rasboras. Consistency within this range ensures their comfort and health.

Water Parameters

Soft to moderately hard water is best for Harlequin Rasboras. A routine weekly water change, comprising 25% of the tank’s volume, can help in keeping the water parameters stable and removing potential contaminants.

Disease Potential

Harlequin Rasboras, like many other aquarium species, are susceptible to common fish diseases like ich, fin rot, and various parasitic infections. Quarantining new additions and maintaining water quality are essential steps in disease prevention.

Food & Diet

Being omnivorous, Harlequin Rasboras enjoy a varied diet. High-quality flake food can serve as a staple, but for a balanced diet, it’s beneficial to provide live or frozen foods like brine shrimp, daphnia, or micro-worms. Occasional vegetable supplements can also be included.

Behavior and Temperament

These fish are peaceful by nature and thrive in schools of six or more. Their schooling behavior, combined with their bright coloration, makes them a visually pleasing addition to tanks. They mostly occupy the middle layers of the water column, often swimming in unison.

Tank Mates

Harlequin Rasboras are compatible with many other peaceful fish species. Suitable tank mates include tetras, guppies, mollies, and non-aggressive catfish. As always, it’s essential to monitor any new introductions to ensure harmony within the tank.


Breeding Harlequin Rasboras can be a rewarding experience for aquarists. They are egg scatterers, usually laying their eggs on the undersides of broad-leaved plants. Slight drops in temperature, combined with a protein-rich diet, can often induce spawning. Once eggs are laid, it’s a good practice to remove the parents to a separate tank to prevent them from eating the eggs. The eggs typically hatch within a day or two, and the fry can be fed infusoria or finely ground flake food.

Harlequin Rasbora FAQs (Frequently Asked Questions)