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.
Housing
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
Feeding
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.)
Breeding
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.
How long can they live max? Up to how many years?
Usually around 3-5 years.
My last two are almost 7 yo and just had fry for the second time (without me doing any of the above).
It’s always exciting when fish breed without trying to trigger it, though you’re obviously doing something right with your aquarium. Hopefully you end up with a few generations in your fish tank.
is it possible to put a small school of rasboras in a 20 gallon tank with a 4 cory cats and a male betta, or would that be pushing the bio load?
I think you would be fine with that. They don’t have a very large bio-load, though you may end up with aggression from the betta – though I think they will be alright.
I have 8 Rasboras with my extravagent male betta. Because the rasboras school, they are able to protect themselves by employing confusing defensive tactics against the betta fish. For the first day, the betta fish attempted to get the little guys, but he become frustrated and learned that they were too much for him to handle, so now he just hangs out throughout the aquarium, frequently making appearances, but gives the rasboras all the space they need. I keep live plants and rock structures for a place for the betta to hide if the rasboras get too annoying. I also have a nice empty part of the tank above the grasses where the rasboras love to school. I think that the combo will work for ya! Have a nice day.
That sounds like a really interesting tank. It’s always to great to hear about these oddball tanks that work well.
I have just set up an aquarian Home25 and bought 6 Harlequins yesterday but to my dismay 3 Harlequins jumped out of the tank in the night. The lid doesn,t cover the tank completely. Are there any small fish that I could buy that won,t escape in that way
Usually, but not always, fish jump out when there’s something wrong with the water. Have you checked the water parameters?
As for fish for an aquarium that size, you don’t have a lot of options. One of my favorites is a betta with some shrimp. But dwarf puffer fish would also work (though they are very difficult to keep, with special food requirements), guppies and endler’s livebearers (you’d have to keep the population under control), African dwarf frogs, or an all invertebrate tank with shrimps or snails would all be good choices. Small tetras may also work, but you’d really have to keep an eye on the water parameters.
these guys are some of the most underrated fish in the hobby! Don’t understand why they aren’t kept as much
Thank you for this information. Very helpful.
I’m always happy to help out.
My rasbora fish just produced 6 new babies. the babies are with some other freshwater fish Should we keep them in the tank or not? We are afraid if the other fish May eat the babies. Thank u for this info.
Most of the time fish fry will get eaten by other fish in a community tank. If you have another filtered aquarium ready to go, then you can use that, or even a breeder net or box until they grow older.
I enjoyed reading your article. I like the way you wrote about Harlequin Rasbora in detail. I have been keeping harlequin rasbora for over a month now and watch them daily. I love watching them swim in a group. Since it was a tank for harlequin rasbora only I wanted to keep a compatible fish and found out that betta does great as a tank mate. I read an article on a website about Betta tank mates
I agree with your word that they are best for beginner and quite happy fish. I found this article very helpful.
Thanks for sharing the article with us.
My harlequins have just started breeding, thats all i have in the tank, have isolated the female in question, but the males seem to be protective over the little ones in the tank i cant catch to put in the hatchery, so im in two minds is it best to use the hatchery or better to let nature take its corse?
What’s the tank setup like? Are there many fine leaved plants or mosses in the tank?
Generally speaking, harlequin rasboras aren’t especially deadly to their fry. They will sometimes pick off some of them, but they aren’t like zebrafish where it would be a miracle for any of the babies to reach adulthood in the same tank as the parents.
Thanks for advice rob, my set up is a 30ltr biorb cylindrical tank, no organic plants, as yet as i have a little algae problem, which does raise issues on vacuuming the subtrate over fear of sucking up the fry. Have treatment, but nothing works better than physical removal of the problem. They seem pretty passive towards the fry so i released the female to the group yesturday eve, but i think i may have shocked a fry and it sadly died :(, my temps are 25 -27c, which are low for breeding, but ive also had the light on 8hrs a day, however have turned off light because of algae issues, anything you think i should know or guidance would be much appreciated just want all my fish to get the best in life.
have a school of harlequins , neon tetras, mixed platys, albino corys and a male betta they all get on great. introduced betta last to avoid terratorial issues.
That’s great it worked out for you. It can sometimes be hit or miss with bettas, but I think you chose good fish to avoid most problems.
Hi. So my harlequin just had fry which was totally unexpected and unplanned for. Supposedly we purchased only “males”! 😱🙄. And, our tank, well, is less than perfect. I just noticed them swimming around in the tank this morning, so now what? Do I need to separate them from the adults? Buy special food? Etc. any help would be appreciated. Thank you!
If it’s feasible, you should consider buying a breeding net. The fish are so small they are easy target for other fish in the tank. As for taking care of the fry, you should buy some fry food for them. Most pet stores will sell it. While there is some microscopic food in aquariums for fry to eat, there isn’t nearly enough to support them all. Also, if you place them in a breeding net, it’s easier to target feeding to them. But once the fry are born, it’s very hard to capture them, so do whatever you can at this point.
Thanks, Robert. I did get a net and captured some of the small fish. Our local pet store suggested that i feed them crushed up micro pellets. Do you think that would suffice? Or, should I try something different? Thank you for your help.
TM
It might work if you crush them finely enough and depending on the size of the micro pellets. Just make sure they’re incredibly fine when you’re done, since harelquin rasboras have very tiny mouths.
Thanks, Robert. I did get a net and captured some of the small fish. Our local pet store suggested that i feed them crushed up micro pellets. Do you think that would suffice? Or, should I try something different? Thank you for your help.
TM
Do I have to take my fish out of the main ank to lay?