The Harlequin Rasbora (Trigonostigma heteromorpha) is a small tropical freshwater fish that is extremely popular and well known in the aquarist hobby.
These are energetic little fish that make up for their size with tons of personality and extra zing for your tank.
Native to Asia, they are usually found in the wild in the streams, rivers, and swampy waters of Thailand, Singapore, and Malaysia. Most of these waters bear a resemblance to the black water conditions rich with tannins, as can be found in South America.
With striking good looks, Harlequins are easy-breezy, peaceful shoaling fish that don’t cause any trouble in a tank community. Ideal for the beginner in the hobby, they are straightforward to care for, have a long lifespan for such a little fish, and they add some vibrant good looks to the tank too.
They feature iconic markings making them instantly identifiable in a tank, and with their schooling and shoaling behaviors, they can put on a dramatic display worthy of inclusion in even the more experienced aquarists tank.
Harlequin Rasbora Behavior
Harlequin Rasboras enjoy spending the majority of their time in the middle stratum of the water column. They are rarely spotted swimming near the surface or around the substrate of the tank, so make ideal tank companions for tank setups that have fish who prefer those layers.
These fish are super peaceful and don’t pick a fight or squabble with anyone! They are not known to be fin-nippers either, so this is a great choice of species for those who want to introduce more color into the tank without affecting the overall community too much.
Rasboras are well known for being kept in a species-only tank, but they needn’t be. With low to nonexistent levels of aggression, they are very adaptable for many tank communities. The bigger issue with why they aren’t included in more tank communities is because of their reluctance to defend themselves! They are easily targeted by more aggressive fish, which renders them susceptible to injury or fatal catastrophes.
These fish love to be in a large group of their own kind; in fact, it’s essential that they are within a large group in your tank as they would otherwise not survive well. They almost never dwell on their own and require accompaniment to prevent anxiety or stress.
Ideally, you should keep a group of at least 8 – 10, which is reasonable for a 10-gallon tank but the minimum you should consider.
Since they enjoy interaction with fellow Harlequin Rasboras, it is ideal for keeping a relatively large group, but we will discuss more on those numbers later.
When you do keep a shoal of Harlequin Rasboras, they are more likely to show off their vibrant coloring and personable behaviors in larger groups. Basically, you want to think of these fish as better in bigger numbers.
Harlequin Rasbora Lifespan
If you cater to the needs of your Harlequin Rasboras, you could expect them to live for around 5 – 8 years. The quality of their tank conditions will impact their lifespan, as always, so you can expect a longer life if you meet their requirements meticulously.
We will discuss more on tank requirements a little later in this article.
Harlequin Rasbora Appearance
These fish are not only visually stunning, but they evoke a half and half coloration that is reminiscent of a Joker or Jester. They literally look like they are marked in half, and they have an outline on their darker half that truly highlights their shaping and color.
They have small fins with the exception of their caudal tail, which is sharply forked and is nearly transparent except for fiery orange-red pieces on the top and lower trim. In terms of body shape, they are slightly diamond-shaped, which is to say that they are longer in the mid-section and tapered to smaller points at the front and back.
The forefronts of their bodies are reddish-orange with silver overtones. Just after their dorsal fin begins, their latter half of the torso is black, formed from a triangulated patch that makes it stand out sharply in the tank. It literally looks like a vertical line divides the front and back half of this fish. The rear portion that is black has a silvery perimeter which makes the latter half stand out even more.
In terms of length, you can expect them to reach up to 2 inches in length at a maximum, so they are not nano-fish, but they are not large specimens either.
The triangular patch of black on the rear body of this fish is what gives it its moniker ‘Harlequin .’It gives this little fish a striking appearance that looks spectacular when viewed in a school or shoal for the observer.
Males often have larger black, or ‘harlequin’ triangulated patches on their bodies, and they are usually smaller than the females in terms of midsection girth as well.
If you’re looking for a smart fish that will stand out in the tank, this might be the ideal species for you!
Harlequin Rasbora Habitat And Tank Requirements
In the wild, these fish are found in predominantly blackwater, meaning that the water is clear but brown. This does not mean these fish like dirty water! The brown coloring comes from the tannins leaching into the river from all of the debris and rainforest wood that falls into the riverbed.
Blackwater usually involves a lot of tangled root systems in the water from the riverbanks as the vegetation is so lush. You can add tannins to the water by adding dried leaves, but they need replacing every few weeks. Your stockist can provide the right types of leaves to do this, so do not collect your own and think they will be okay!
Having the correct tannins in your tank will help keep the water slightly acidic, which is what these fish prefer.
Harlequin Rasbora Tank Conditions
The ideal setup for these fish is something that has a natural look to it that has a stable temperature and parameters. Fluctuations are the bane of most fish, even though the conditions may be tolerable.
Darker substrates are preferable for these fish, and they will also adore areas of thicker and more densely planted areas for their use to shelter.
Dense vegetation is ideal for these fish, so including species like Camboba, Crytocoryne, and Aponogeton would sit well alongside driftwood which mimics their natural habitat. Add in some rocky formations but do allow for space, providing plenty of open swimming for these schoolers!
Filtration should be subtle as they prefer slow-moving waters, and a mild current is ideal for these guys.
Water changes need to be done weekly of at least 10 – 20% to keep optimum water quality.
Water conditions should be noted and maintained as follows:
- pH of 5.5 – 7.0
- Water hardness between 5 – 12 dKH
- Temperature between 72 – 80ºF (23 – 28ºC)
- Lighting conditions should be subdued
Harlequin Rasbora Tank Size
The minimum tank size for a small group of Harlequin Rasbora would be 10 gallons.
Since we don’t advocate that you keep one solo and they enjoy a group, you should ideally aim for 20 – 30 for extra space as these are not nano-fish. Two fish per gallon is a good guide but upsize a tank whenever possible for the happiest of homes.
Choosing Tank Mates For Harlequin Rasboras
When it comes to finding species appropriate for your Harlequin Rasboras, you need to consider peaceful and slow-moving tankmates.
A similar-sized fish is what makes these guys feel most comfortable, and you should ideally have a minimum group of 8 – 10 of them settled in a tank before adding more species if possible.
Being peaceful and not known for fin-nipping, these make excellent community fish, and can you can mix them up with other water level dwellers.
Some excellent tank mate pairings for your Harlequin Rasboras that would work well include:
- Neon Tetras
- Danios
- Guppies
- Platies
- Mollies
- Bolivian Ram
- Dwarf Gourami
- Kuhli Loaches
- Smaller catfish species
- Dwarf Cichlids
- Cherry Barbs
- Amano Shrimp
- Cherry Shrimp
- Zebra Loaches
- Yoyo Loaches
- Otocinclus
- Mystery Snails
Avoid anything aggressive like larger Cichlids or anything that is about twice the size of your Harlequin Rasboras, or they may try to make a meal out of your school.
How To Feed Harlequin Rasboras
Harlequin Rasboras are omnivores who are not fussy and will eat everything from flake and pellet foods to live or frozen diet sources.
Higher quality foods will impact the coloring of your Harlequin Rasboras too!
It’s important to focus on food size as they have small, pinched mouths, so some items may need to be chopped up for them to consume what is on offer.
Quality flaked foods are usually accepted from the top of the tank, but be sure to add in quality live or frozen foods that are suitable for extra hits of protein and to vary their diet.
Blanched and finely chopped vegetables are also ideal to offer regularly to mix things up, but take to remove anything they don’t eat to avoid fouling the water.
Aim for a meal at least twice per day, and ideally in quantities that amount to what they can consume in a few minutes. Any longer than that and your fish will likely be guilty of overeating which is never a good idea.
Harlequin Rasbora Common Diseases And Illness
Luckily, Harlequin Rasboras are not known to be susceptible to much in the way of illness and disease.
However, the typical well-known freshwater afflictions could potentially impact Harlequin Rasboras too. Things like Ich, Fin Rot, and Dropsy are commonly spotted but are more easily treated when caught early.
Consistent monitoring of water quality is the most important factor for keeping your fish healthy, but so is quarantining any new tank additions, whether they are alive or decor.
How To Breed Harlequin Rasboras
In captivity, Harlequin Rasboras are not as straightforward to breed. They are egg layers, and the female will deposit eggs on the underside of broad leaves, after which the male will fertilize them.
In order to attempt to encourage breeding, it is recommended to separate out your selected fish into a breeding tank in a ratio of two males for every female and begin to condition the group with live foods.
This helps provide the necessary extra energy to reproduce.
Broadleaf plants must be in the tank as they use it to lay their eggs, and breeding will happen in the early hours of the morning.
Slightly elevated water temperatures than your main tank and a hardness no higher than 4 dGH is essential to help things along. Your breeding tank pH should be around the 6.4 mark.
Before the eggs hatch in around 18 – 24 hours, you should remove the adults from the breeding tank to give the newly hatched fry a chance for survival. They will need to wait until around 6 – 9 months of age to be relocated to the community tank, so ensure you are able to keep up with the cleaning regime for two tanks!
Conclusion
Should you go for this ‘diamond’ of the aquarium, or is the joke on you?
Being beautiful, hardy, peaceful fish without anything too exceptional needed in the care department, it’s easy to see why we think Harlequin Rasboras make an ideal starter fish. And that is definitely no joke!
Dazzling displays of schooling and shoaling behaviors will reward every hobbyist who decides to take them in.
And if breeding is not your goal, they are ideal for reducing the hassle of what to do with unexpected fry counts from becoming an issue since they are harder to cajole into doing so in the first place.
They are definitely an ace up the aquarist’s sleeve and a species to consider.
