Harlequin Rasbora
Trigonostigma heteromorpha
Description
The Harlequin Rasbora is a small, active, and colorful fish known for its bright orange to reddish body and the black triangular patch on its back near the tail, which resembles a harlequin mask. These fish are peaceful, schooling species that do well in groups and add vibrant color to any aquarium. They are often seen swimming in mid to upper tank levels and are highly social, making them a great choice for community tanks. Their small size and attractive color make them ideal for aquascaping setups.
Habitat Origin
Native to Southeast Asia, specifically found in slow-moving streams and rivers in Malaysia, Thailand, and Sumatra.
Aquarium
Ideal Number in Aquarium: At least 6 individuals for natural schooling behavior.
Favorite Food
Harlequin Rasboras are omnivores and enjoy a varied diet, including high-quality flake food, pellets, and live or frozen foods like brine shrimp, daphnia, and bloodworms. They also appreciate the occasional vegetable matter, such as blanched spinach or zucchini.
Behavior:
Harlequin Rasboras are peaceful, non-aggressive fish that do well in community tanks. They are best kept in schools of 6 or more to feel secure and to display natural schooling behavior. These fish are generally active, often swimming in the middle and upper levels of the aquarium. They are not fin-nippers, and their small size makes them ideal tank mates for other peaceful species.
Special Care:
Harlequin Rasboras thrive in a well-planted tank with plenty of hiding spots, such as plants, driftwood, and caves. While they are relatively hardy, they do best in stable water conditions, so regular water changes and good filtration are important. A gentle water flow is ideal, as they prefer calm waters.
Compatibility with Other Fish:
Yes, they are excellent for community tanks with other small, peaceful fish, such as tetras, small barbs, and shrimp. Avoid keeping them with larger, aggressive fish that may view them as food. They are especially suited for tanks with other schooling species, as they feel more secure in groups.
Breeding Tank Setup
Using a separate breeding tank is highly recommended for Harlequin Rasboras to prevent egg predation and to maintain ideal water conditions. A 10-gallon (38-liter) tank is suitable for a breeding pair or small group, while a 20-gallon setup works better for multiple pairs. Maintain soft, slightly acidic water with a pH of 6.0–7.0, temperature between 24–28°C (75–82°F), and hardness of 4–8 dGH. Use a gentle sponge filter or small internal filter to ensure calm water flow. Include soft-leaved plants like Java moss, Java fern, or Anubias for egg-laying surfaces, and optionally add floating plants such as Water Sprite or Hornwort to offer shade and additional protection. Moderate, subdued lighting on a 10–12 hour light cycle will help mimic their natural habitat.
Conditioning the Breeders
To prepare Harlequin Rasboras for breeding, feed a nutrient-rich and varied diet for 1–2 weeks. Include high-quality tropical flakes or pellets, supplemented with live or frozen foods like brine shrimp, daphnia, and bloodworms, and occasional vegetable-based foods such as blanched peas or chopped spinach. Perform 25–30% weekly water changes to maintain water quality. A larger water change (~50%) and a slight temperature increase just before the breeding attempt can act as a spawning trigger.
Spawning Process
Spawning usually occurs in the early morning, often after a change in water conditions. Harlequin Rasboras are egg scatterers; females deposit 30–50 sticky eggs onto plants or tank surfaces, and males fertilize them immediately. Males will often display brighter colors during courtship. After spawning, remove the adults immediately to prevent them from eating the eggs. Leaving the eggs in a quiet, undisturbed tank improves hatching success.
Fry Development
Eggs hatch within 24–36 hours, depending on temperature. Fry are tiny and fragile, initially surviving on their yolk sacs. After absorption, begin feeding infusoria or liquid fry food. As they grow, gradually introduce baby brine shrimp, microworms, or finely crushed flakes. Perform daily 10–20% water changes to maintain cleanliness and stable conditions. Avoid overfeeding, which can quickly foul the water and endanger fry.
Breeding Tips
Harlequin Rasboras reach sexual maturity at 6–12 months, but the best breeding results come from fully mature, well-conditioned adults. Males are smaller, slimmer, and more vividly colored, while females are rounder, particularly when gravid. Avoid stressing the fish with sudden water changes, aggressive tank mates, or poor tank hygiene. A calm, planted, and consistently maintained environment gives the highest chance of successful breeding and healthy fry development.