Copper Harlequin Care Guide – Aquarium Setup, Diet & Breeding

The Copper Harlequin is a small, elegant rasbora with a warm copper-orange body and a distinctive dark, wedge-shaped marking along the rear half of its flanks. Its compact shape, translucent fins and lively colour make it a popular choice for planted nano and community aquariums.

Unlike the larger Harlequin Rasbora, Trigonostigma espei has a slimmer profile and a more coppery overall appearance. When settled and viewed in a coordinated shoal, the fish display an attractive contrast between their glowing bodies and bold black lateral markings.

Copper Harlequins are peaceful, active swimmers that spend much of their time in the middle and upper areas of the aquarium. They are naturally social and become more confident, colourful and behaviourally interesting when kept in a proper group.

In the wild, this species is associated with quiet, shallow habitats containing dense aquatic vegetation, submerged roots and leaf litter. Its distribution overlaps with other small Southeast Asian fishes, and its subdued natural surroundings help accentuate its copper colouring.

Copper Harlequins are native to mainland Southeast Asia, particularly Cambodia and eastern Thailand, with populations associated with the Mekong basin and nearby lowland waters. They inhabit slow-moving streams, marshes, flooded forests and peat-influenced pools with soft, often tannin-stained water.

A group of Copper Harlequins should have at least 45 litres, with a footprint of approximately 60 by 30 cm or larger. Use a dark, fine-grained substrate with dense planting around the sides and rear, leaving open swimming space through the middle. Driftwood, roots, leaf litter and floating plants provide shelter and help create the subdued, blackwater-style surroundings they favour. Gentle filtration, subdued lighting and some water movement are suitable, provided the fish are not forced to swim against a strong current.

Up to 3.5 cm (1.4 inches); females are usually slightly larger and deeper-bodied than males.

Copper Harlequins are omnivores and thrive on a varied diet of high-quality micro pellets and finely crushed flakes supplemented with small live or frozen foods. Baby brine shrimp, daphnia, cyclops and mosquito larvae are especially useful for encouraging strong colour and breeding condition. Their small mouths require appropriately sized food, offered in small portions that they can consume quickly.

Copper Harlequins are peaceful community fish and can be kept with similarly gentle species such as small tetras, celestial pearl danios, chilli rasboras, other small rasboras, pygmy Corydoras, Otocinclus and peaceful freshwater shrimp. Avoid large, predatory or boisterous fish, including larger cichlids, aggressive barbs and many gouramis, which may intimidate or eat them. They should not be housed with fin-nipping or highly competitive tankmates.

Copper Harlequins are egg-scattering fish that can breed in a mature, densely planted aquarium with soft, slightly acidic water. Condition the adults with plenty of small live or frozen foods, then provide fine-leaved plants or broad leaves such as Anubias for spawning. The pair scatters adhesive eggs among the leaves, after which the adults should be removed because they may eat the eggs. Eggs usually hatch within a day or two, and the tiny fry initially need infusoria or another suitably fine food before progressing to newly hatched brine shrimp.

Females are generally fuller through the abdomen and slightly larger overall. Males tend to be slimmer, with a more intensely coppery colour and a sharper, more vividly defined dark flank marking, particularly when displaying.