The harlequin rasbora (Trigonostigma heteromorpha) is a small fish in the family Cyprinidae. The species became an instant favorite among aquarists after its introduction in the early 1900s and is the best known and most widely kept species among the rasboras. The species was originally classified into the genus Rasbora, and given the specific name heteromorpha (Greek, "differently shaped") to alludes to the fact that its body shape differed from other members of that genus. The common name alludes to the black triangular patch on the body, reminiscent of the patterns found on the costume of a harlequin.
Harlequin Rasboras are a beautiful freshwater fish that can be found in plenty of tanks all over the world. This species is loved by aquarists because of their ease of care and stunning appearance. Watching a school of them swimming around just never gets old.
The harlequin rasbora is a native of Malaysia, Singapore, Sumatra, and southern Thailand. It inhabits streams and waters that are characterized principally by their low mineral content and high concentrations of dissolved humic acids, which is typical of water that flows through swamped forests. The waterlogged soils of these forests inhibit the complete decay of leaf litter, resulting in the formation of peat, which leaches humic acids. These conditions resemble those found in the blackwater habitats of South America.
Male harlequins are more slender and a bit smaller than females. Although they share similar colors and patterns, the males tend to be more brightly colored than the females. In addition, the distinctive black wedge covering the posterior of the fish may be more rounded in males and more angular in females.
The harlequin rasbora is a small fish with an elongated and laterally compressed body, a small terminal mouth, and a deeply forked caudal fin. These rasboras are very similar to their cousins, the lambchop rasbora and glowlight rasbora, but are much stockier with a convex belly area.
Like all other cyprinids, the harlequin rasbora’s pectoral fins are behind the gill cover. The pelvic fins are located further back, along the ventral portion of the body. The dorsal, pelvic, anal, and caudal fins of the fish are tinted red. The inner section of the forked caudal is crystal clear, with the red color concentrated in the outer areas of the tail. The bodies of these fish can vary in color from a pale pink or bright red to copper orange. The harlequin rasbora’s body is adorned by a black triangular marking that covers the back half of the fish’s side, parallel to the gills. The distinctive wedge-shaped marking stretches from the dorsal fin and comes to a point near the base of the caudal fin. Both male and female harlequin rasboras have a black wedge-shaped marking on the back half of their bodies. This patch is larger in male fish and has a rounded extension at the bottom edge. On females, the black wedge is completely straight. There are several color morphs of the harlequin rasbora. Fish with copper or golden-colored bodies are called golden harlequin rasboras. Black harlequin rasboras have mostly black bodies and a black triangular patch. Fish with a strong bluish hue are referred to as blue harlequin rasboras.
The active and fast-moving harlequin rasboras are peaceful community fish. These schooling fish do best in groups of 10 or more individuals. Harlequin rasboras get along with most fish. But some less active fish species may not tolerate the rasbora’s active lifestyle.
The harlequin rasbora is a shoaling fish; it should be kept in schools of eight to 10 individuals. Schools of even larger numbers make for a beautiful display. You can keep harlequins with any fish as long it’s not large and predatory. It will not nip at or quarrel with any other species. Some potentially good tankmates may include cardinal tetras, one betta, neon tetras, small barbs, dwarf gouramis, danios, other small rasboras, and cory catfish.
An aquarium intended to house harlequin rasboras should be planted with live plants. Create open areas for swimming between stands of plants such as Cryptocoryne species, these being among the plants that inhabit the harlequin rasbora's native waters.
Harlequins readily accept all foods but prefer to eat live foods whenever possible. In nature, their diet consists primarily of insects. However, they will accept frozen foods and freeze-dried foods as well as flake foods. A varied diet will ensure that digestive problems or susceptibility to disease do not occur. Brine shrimp, daphnia, and any type of worm are excellent supplemental foods, particularly when conditioning beforeb reeding.
