|Genus & Species: Trigonostigma Heteromorpha|
|Common Names: Harlequin Rasbora|
|Temperature: 72º – 81ºF (22º – 27ºC)|
|pH: 5.0 – 7.5|
|GH: 1.0 – 12 dGH|
|Max Size: 3.5 – 4.5 cm (1.38 – 1.77 inches) in length|
|Lifespan: 5 – 8 years|
|Depth Preference: Mid dweller|
|Tank Size: 10 gallons|
Since their introduction in the early 1900s, the harlequin rasbora has become the most common species of rasbora kept within the aquarium hobby. Their scientific name Heteromorpha actually refers to its rather distinctive color pattern, which is undoubtedly the reason this species gained so much popularity.
Since then there have been a number of ornamental strains that have been selectively bred including purple, black, and golden varieties.
Origin & Habitat
Harlequin rasboras are a freshwater species of fish deriving from Malaysia, Singapore, Sumatra, Indonesia, Sumatra, and Thailand.
Thai inhabitants appear to be confined to the Narathiwat district in the states of Johor, Terengganu, Pahang, Selangor, and Kelantan. Additionally, they can be found in Nee Soon Swamp, one of the island’s last remaining freshwater forest swamps.
Its natural habitat consists of areas with calm streams and tributaries, where there are abundant populations of submerged aquatic plants, as well as forest cover above. Runoff from heavy rains into waterways litter the substrate with fallen leaves, twigs, branches, and other debris. The water turns brown occasionally as a result of increased tannins and decomposing organic debris.
Harlequin Rasbora Care
Harlequin rasboras require clean water in order to ensure that they live long and healthy lives because of their smaller size and susceptibility to poor water quality. Although very adaptable to changing water parameters, water should maintain an acidic-neutral pH and contain low levels of dissolved mineral content.
A water filtration system should be effective enough to cycle through roughly three times the volume of water in your aquarium per hour while still being mild enough to avoid producing a strong current.
Weekly water changes and routine tank maintenance are required for the fish’s health and will aid in the reduction of ammonia, nitrite, and nitrate buildup. If you don’t have any live aquatic plants, air stones are an excellent alternative to promote water oxygenation.
When kept in an aquarium with a variety of decorations, several plants, both submerged and floating, and a dark substrate, they often display more vivid colors. Numerous hiding places will make harlequin rasboras feel a little more at ease because they tend to hide when they’re stressed, while also offering some relief from intense lighting.
Harlequin Rasbora Diet & Feeding
By examining the stomach contents of wild specimens, it has been discovered that harlequin rasboras are micropredators. Their main sources of food were found to include insects, worms, crustaceans, and other zooplankton.
The harlequin rasbora will readily accept live, frozen, flake, or pelleted food without hesitation. Despite being omnivores, they nevertheless favor foods that are high in protein or designed primarily for carnivores.
In fact, one of the key factors contributing to a shortened lifespan is inadequate food sources, which include diets of poor quality with low protein content, excessive amounts of ash, and other fillers.
Foods consisting of high-quality ingredients that include blood worms, brine shrimp, insect larvae, daphnia, artemia, and other microworms should make up the bulk of their diet.
They shouldn’t receive more than two scheduled feedings each day because they are vulnerable to health problems associated with overfeeding. Give them as much food as they can finish in a short period of time.
Tank Mates & Temperament
Harlequin rasboras are social yet peaceful fish, and they are most active when they are with other fish of their own kind. As a schooling species of fish, they thrive when kept in schools of six to eight fish or more. They frequently exhibit signs of timid or stressed behavior in smaller schools, whereas they display their color more naturally in larger groups.
Ideal tank mates for harlequin rasboras are barbs, rasboras, danios, tetras, discus, livebearers, corydoras, catfish, plecos, and labyrinth fish. Almost any species of fish that require similar water conditions, aren’t extremely aggressive, and don’t consume smaller fish will make excellent tank companions.
The subject of whether angelfish and harlequin rasboras can coexist in the same tank is one that is frequently asked, but there are proper and improper methods for doing so. Although fully mature angelfish could mistake a smaller harlequin rasbora for food, if they are kept together initially without a significant size difference, they can safely coexist.
Male & Female Differences
Mature females are often larger and have fuller bellies than the more colorful, leaner males. Examining the contour of the black triangular marking on the side of the fish can also be used to determine the gender of the fish; this marking typically appears more rounded on females than it does on males, who tend to have a sharper, more defined shape.
Breeding & Spawning
Harlequin rasboras are an egg-scattering species of fish that spawn during dawn and do not display any signs of parental care; instead, they often consume any eggs that they come across shortly after spawning.
However, they differ from most other species in that the female will invert herself to attach eggs to the underside of broad-leaved plants rather than disperse them at random. The males then fertilize those eggs, and the cycle continues until the female has exhausted all of her eggs. Which normally hatch between 36 and 48 hours after fertilization; 4 to 6 days later, the fish fry are free-swimming.
If kept in a mature aquarium with plenty of aquatic plants and regular water changes, they may regularly spawn.
The most efficient method is to set up a smaller 5 to 10-gallon breeding tank, which allows you to remove the adults as soon as eggs are visible, preventing them from preying on the eggs shortly after they spawn.
Small schools of 6 to 8 fish that have a slightly higher male-to-female ratio of about 2:1 are ideal for a 5-gallon tank. An appropriate male-to-female ratio is necessary because females will invert themselves under broad leaves and waits to deposit eggs until a male comes along to assist in fertilizing the eggs.
For harlequin rasboras to successfully spawn, waters must have a pH of 6.0, which can be attained, among other things, by using rainwater or almond leaves. The water’s temperature should be near the top of its range, or about 81° Fahrenheit (27° Celsius), with a lower mineral concentration of 1 – 5 dH.
Low-wattage lighting, dimmers, or light switch timers should be used to provide dim lighting for the aquarium. You can create a few separate spawning areas inside the tank that are needed by planting various broad-leaved plants like anubias, amazon swords, or others.
Condition the adults with live foods such as blood worms, artemia, brine shrimp, and daphnia prior to relocating them into the breeding tank, this will ensure that the females produce plenty of eggs.
Once the females appear gravid, properly acclimate the adults and then relocate them into the spawning tank. Continue feeding them live foods as usual, and check the tank each morning for any obvious signs of eggs because the adults will then need to be taken out if there are any. Breeding typically happens soon after, although it could take a few weeks.
Another great way to encourage spawning is to perform significant water changes and replace roughly 50% of the tank’s volume with slightly cooler rainwater once a week. Wait a day or two if you’ve just recently moved the adults into the spawning tank before doing so.
Newly hatched fry must be fed with appropriate-sized foods because they will be too little to consume most commercially available foods. Although there are various powdered feeds available for the newly hatched fish fry, feeding them live cultured infusoria is the healthiest alternative to promote rapid development.
W. Duncker first identified Trigonostigma Heteromorpha in 1904; the original specimens were from a pond in the Singapore Botanical Garden. There are now 5 species of Trigonostigma: Trigonostigma Truncata, Trigonostigma Heteromorpha, Trigonostigma Hengeli, and Trigonostigma Somphongsi.
There are three other species within the Trigonostigma genus that look rather similar to the harlequin rasbora (T. Heteromorpha), being the most resemblant in appearance to T. Espei. The two are easily distinguished by T. Espei’s slimmer appearance and T. Heromorpha’s distinct, triangular-shaped black tail marking, which is less pronounced in T. Espei.
The genus Trigonostigma was established by Kottelat and Witte in 1999, to distinguish individuals from the larger rasbora grouping based on the following combination of characteristics: Color pattern features a reddish, pinkish, or orange body with a prominent black stripe extending from below the dorsal-fin origin to the middle of the caudal-fin base that broadens to have a triangular shape. With the exception of T. Somphongsi, which has a stripe that is only slightly broader anteriorly. The reproductive strategy involves the laying of eggs on the underside of broad leaves or other similar structures.
Additional characteristics that set the genus apart but are not unique to it include their miniature size with a maximum length of 32 mm in nature (captive specimens may grow slightly longer), an incomplete lateral line reduced to 6 to 9 pores, the absence of barbels, five branched anal-fin rays, and a relatively deep body.
Heok Hui Tan. Trigonostigma truncata, a new species of harlequin rasbora from Malay Peninsula (Teleostei: Danionidae). 2020
Maurice Kottelat and Kai-Erik Witte. Two new species of Microrasbora from Thailand and Myanmar, with two new generic names for small Southeast Asian cyprinid fishes (Teleostei: Cyprinidae). 1999