Harlequin Rasbora Stats
Minimum Tank Size: 10 Gallons
Care Level: Very Easy
Water Conditions: 6.0-7.8 and Very Soft to Moderately Hard
Temperature: 22–27 °C (71.5–80.5 °F)
Maximum Size: 1.5 inches (4cm)
The Harlequin Rasbora (originally named Rasbora heteromorpha, but recently changed to Trigonostigma heteromorpha) is a small fish native to Southeast Asia. It mainly inhabits streams and small bodies of water, most of which are located in the unique peat swamp forests. The peat swamps forests have very low dissolved mineral content, and high concentrations of humic acid which results in very soft water.
While their habitat in the wild does consist of very soft water, the majority of harlequin rasboras available for sale have been raised in fish farms, and can adapt to a wide array of water types. If given enough time to acclimate, they will even do well in hard water aquariums, though they generally won’t successfully breed.
Harlequin rasboras are not a large fish, and will usually grow to a maximum of 1.5 inches (4cm) in the home aquarium. But don’t let their small size fool you – these fish have remained a staple of the fish trade since the 1930’s for a reason. Upon reaching adulthood, they develop a stunning gold coloration, and they maintain tight schooling formations in the aquarium. They also have a personality that is out of proportion with their size, and are both inquisitive and playful with each other.
Harlequin rasboras are a hardy fish, and will thrive in smaller aquariums with less than perfect water quality. Because of this, they make an excellent beginner fish, and can be kept quite happily in a well filtered 10 gallon fish tank. They should always be kept in groups of at least 5, as they are a schooling fish, and will become stressed if kept in smaller groups.
Harlequin rasboras don’t have any special substrate requirements, and the substrate should be tailored to whether or not live plants are going to be added to the tank. If you are planning to add live plants, then gravel is the best choice, since it allows plants to easily root. If there are no immediate plans to add plants, then play sand or river rocks are cheaper options. (Make sure that it’s play sand, and not construction sand). Play sand has the added benefit of being the cheapest of the three, and can look stunning under the proper lighting.
When choosing a filter for harlequin rasboras, the best choice is usually a high quality hang-on-back filter. These combine excellent filtration with an economical price and can be combined with a sponge filter if you want to keep you water absolutely pristine.
I would strongly recommend choosing an Aquaclear Power Filter for a harlequin rasbora tank. This filter combines excellent filtration with a durable design, and it will keep your tank sparkling clear for years to come. You can also read the Aquarium Tidings Aquaclear Filter Review here.
Harlequin rasboras are omnivores in the wild, and need to be provided with a diet that reflects that in the home aquarium. The best way to recreate their diet is too provide herbivore fish food (Spriulina, Algae Wafers), regular fish flakes, and occasionally provide them with frozen foods or live foods. One of the best prepared foods available is Hikari Micro Wafers and I have used it for the numerous small fish that I keep.
When choosing live foods, their favorites are daphnia, mosquito larvae and brine shrimp. They tend to be too small to properly eat bloodworms, and will often swim around with what looks like little blood worm cigars in their mouths, unable to eat them.
They have very similar tastes with frozen food, and greedily accept frozen daphnia and brine shrimp. They can even be fed larger frozen foods like blackworms and blood worms, and they will usually figure out how to eat them after a few minutes of struggling. (You can expect more blood worms being held like cigars until they figure out how to eat them.)
The harlequin rasboras are notoriously difficult to breed in home aquariums, mainly due to the fact that they have very specific water requirements. They must be kept in soft, acidic water with a temperature of 28C (82.5F) to have any hope of breeding. This mimics their natural environment, and the water softness has been shown to have a major impact on the fertility of their eggs.
They also need to be provided with live plants, since the females deposits adhesive eggs on the underside of leaves. If there are no live plants available, the fish will rarely spawn. Though most of the commonly available leaved plants will work, some aquarists have reported the best success with Cryptocoryne and Aponogetonplants.
Once all these conditions have been met, the next step is to get the harlequin rasboras into breeding condition. This can be accomplished through feeding them a mix of high quality flake food and live/frozen foods. Live or frozen foods should be fed every day for a week to condition them for breeding, and the females should plump up noticeably.
Once they are ready to spawn, the female will position herself vertically next to a chosen leaf, with her head pointing down. A male will then be enticed over and assume the same position, fertilizing the eggs as she releases them on the leaf.
After the eggs have been deposited, they will hatch in approximately 18-24 hours, and will cling to the leaf for another day, until their egg sacks have been absorbed. At this point they will become free swimming, and because of their tiny size, can only be fed infusoria for the first week or two.
Sometime during the second week, they can be introduced to larger foods, with baby brine shrimp being the standard choice. If baby brine shrimp aren’t available, there are also many commercially available fry foods, and some fry will also accept finely powdered flake food.