Coming in at under an inch, but bringing big color to the table, the Chili Rasbora is an amazing fish for those interested in nano tanks. Their small size and relatively easy care make them a great choice for beginners as well.
So, let’s dive straight into the world of Chili Rasbora care so that you can make these fish thrive in your home aquarium!
Chili Rasbora Quick Care Sheet
- Common Name: Chili Rasbora
- Alternate Common Name(s): Mosquito Rasbora
- Latin Name: Boraras brigittae
- Care Level: Beginner
- Tank Size: 5+ Gallons
- Size: ½” to ¾”
- Diet: Omnivorous
- Behavior: Peaceful Schooling Fish
- Lifespan: 4-8 years
- Reproduction Type: Egg Scattering
- Water Temperature: 77° -82°F (25°-28°C)
- pH: 6.0-7.0
- Water Hardness: 3–12 dKH
Origins of the Chili Rasbora
The Chili Rasbora is a micro fish native to Southwestern Borneo. These fish school in large numbers in the wild, and inhabit slow-moving, shallow streams and small ponds in the swamps there.
These swamps are considered black water. The water system has a large amount of peat in the substrate which stains the water, giving it a characteristic opacity. The peat also lowers the pH of the water, and these streams can go as low as 4.0 pH.
The substrate in these areas is often dotted with dense vegetation and rotting woody plants, providing dense cover for these small fish. That cover is necessary after all the males are bright red but less than an inch long.
Fortunately, their environment is easy to replicate at home. You don’t have to go as far as making a blackwater tank for them, captive-bred specimens seem to do well with hardness and pH outside the range described in our Quick Facts.
What does matter is keeping your nitrates low.
Chili Rasbora can be sensitive to nitrates. If they’re too high for your fish, they will most often appear sluggish and lose some of their bright colors.
In the wild, these fish are micro predators. They hunt down and eat small critters like daphnia, worms, and small insects. You’ll find they eat just about anything that you drop in the tank, usually eating at the surface.
Red fish, in particular, benefit from some foods for coloration. Bloodworms are a good treat, but any color-enhancing flake will help bring out the crimson colors that make these fish a favorite.
So, the takeaways to remember are:
- Chili Rasboras come from blackwater environments. Low pH and water hardness are the defining features of their native habitat.
- Tank-bred specimens tend to be hardy and don’t mind higher pH or dKH in most cases.
- They’re sensitive to nitrates, so heavy planting is advised. It also means they usually don’t survive a fish-in cycle. Cycle the tank first.
- They’re not picky eaters, and naturally eat very small crustaceans, arthropods, and zooplankton in the wild. They’ll take almost anything given in captivity.
- Too much current is bad for these fish. It doesn’t take much to bat them around due to their small size.
Ideal Tank Setup
While Chili Rasbora do well in most planted tanks, the ideal tank is going to be a blackwater setup. Fortunately, the rest of the advice will hold regardless of what you’re planning to do.
Chili Rasboras do well in small aquaria and are one of the most common nano fishes for desktop aquaria. Their very small size leads to low bioload, and you can fit quite a few in a relatively small area.
They also like low current, which means you’ll need extra plants to make up for the lower amount of water circulation. The following should be sufficient to keep your fish happy:
- HOB or Internal Filter Sized for Tank (No activated carbon for blackwater tanks)
- 5+ Gallon Aquarium
- Heater Sized for Tank
- Nutritious Substrate
Chili Rasboras do well in low light conditions, as dim lights mimic the Indonesian swamps they come from. That makes them a viable fish for low-tech planted tanks, where equipment is often kept to an absolute minimum.
You can also go down the other route, with high lighting and CO2. These fish will enjoy the lower pH a CO2-rich environment brings in.
If you do go with high lighting, you may need to pick plants carefully to allow for dark areas in the tank. Chili Rasboras often feel safer when they can retreat to a dim, densely planted area.
There’s no need for specialized equipment beyond a normal planted tank.
If you choose to go with a tank without plants, then you’ll need to be more careful about water quality. If you don’t have an aquatic green thumb, consider just tossing in a couple of handfuls of Java Moss and trimming them back to a manageable bush.
While a blackwater tank is ideal, Chili Rasbora will do well in any basic planted tank.
If you still want the benefits of a blackwater tank without the extra work in setup, you can also add Indian Almond Leaves to the tank on a regular basis. These don’t color the water, but instead, add many of the “invisible” components of a blackwater system.
Blackwater Biotope Setup
Let’s cover two points first:
- Chili Rasboras don’t require a blackwater biotope, even if you want to breed them. It’s just closer to their natural environment.
- Blackwater tanks aren’t beginner-friendly, but Chili Rasboras are a good fish to use in your first attempt. Make sure you’re a competent aquarist before you go down this road.
That said, don’t let it discourage you from giving it a shot. I’d personally put them on par with basic marine tanks, but they’re not nearly as intense as running a reef tank.
You’ll benefit from a larger tank to make a blackwater biotope. For Chili Rasbora you may not want to go with an exceptionally large tank, they’re not a great fish for community tanks. Instead, consider sizing up to 10-20 gallons. It’s not the most stable size, but these tanks don’t swing as rapidly as smaller aquaria.
So here’s the basic rundown on blackwater: blackwater occurs in areas where freshwater flows from mineral-poor areas into those with a lot of woody vegetation. The water column absorbs tannin, mainly from fallen branches and rotting vegetation, which lowers the pH and creates the characteristic tint of blackwater.
It’s fairly easy to set up in a home aquarium:
- Start with RO or distilled water.
- Add tannins to the water from one of the commercial preparations available. Some contain only the “good bits” and change water chemistry without changing the water’s color.
- Use only a pH-neutral substrate in the tank. ½”-1” of sand capping peat is a common method to slowly release tannins and keep the water acidic.
- Add driftwood to the tank to slowly release tannins over time.
Blackwater can be a pain to get just right initially, there’s a lot of room for experimentation.
The big thing is to not add any activated carbon to your filters. Carbon strips out the tannins that color the water and lower the pH… which is the exact opposite of what we want.
Instead, you can opt to use peat to help replenish tannin levels in the water column and provide a spot for bacteria to live. Blackwater tanks rely a lot on their bacteria and plants to keep the water within acceptable levels.
Using RO or distilled water to start is important. Most household water is alkaline and hard. Neither of those helps out when creating a blackwater environment.
That includes topping off the tank.
Be careful with substrates and stones as well. The acidic waters in the tank will hungrily take in any minerals that end up in the tank, and mess up your chemistry.
The thing that makes blackwater tanks harder to run is that they can “crash” their cycle.
The main cause of this is an overly low pH, which inhibits the bacteria from doing their stuff. Keep an eye on the pH of the tank, if it begins to go too low you may need to take action. This ultra-low pH is sometimes caused by having too many tannin sources.
The other cause comes from extra high nitrates. Without plants and filters uptaking the nitrate compounds they will resolve spontaneously into nitric acid in the water. In a normal aquarium, this isn’t a problem, the nitric acid is immediately salted out by the mineral “buffer” in the tank. In a blackwater tank, this can cause a runaway chemistry reaction.
In many cases you can counteract this by adding a little bit of tap water to create a buffer, just remove 5-10% of the tank’s volume and replace it with dechlorinated tap water.
The latter scenario very rarely occurs in blackwater tanks with even a moderate amount of plants.
The takeaway is just to regularly measure the pH of a blackwater tank.
I also suggest being very careful about chemicals that rapidly alter pH in either direction. Fish generally don’t fare well with broad, fast changes in the pH level of the water column.
An actual biotope is different than a simple blackwater tank but requires more research. In this case, you should delve into the blackwater environments of southeast Asia to find which plants are native to the area that houses wild Chili Rasboras.
Boraras brigittae is a common fish in small planted tanks, and they do well with most types of plants, so there aren’t many special considerations to take into account.
Beginners shouldn’t experiment with new plants in a tank with Chili Rasbora, but if you know the basics you’re free to grow most plants. I do recommend using plants to produce extensive cover in at least one section of the tank. These small fish are easily spooked, and the plants add security to their environment.
Since they’re a bit sensitive to water cleanliness, you may want to avoid plants that drop a lot of foliage. Hornwort, for instance, sheds needles constantly and can create problems if the needles gather and rot in an unseen place.
Blackwater biotopes require a little bit more care in plant selection, but they’re perfectly capable of having thriving plants inside. The acidic conditions and low light created by the absorbed tannins make some plants much harder to grow.
In particular, it’s often not possible to grow carpet plants in blackwater tanks. Most of these are relatively sparse in the wild and are used to create a carpeted substrate by artificially high lights and carbon dioxide content in the water.
In that case, the following plants are a good option:
- Anubias sp.– These long-lived plants do well in dim light and they’re easy to attach to driftwood or rocks in the hardscape of the tank.
- Java Fern- Likewise with Java Fern. You can find a surprising amount of different cultivars if you look online.
- Amazon Swords- Any Echinodorus sp. is a good choice, but Amazon Swords actually hail from blackwater systems.
- Bucephalandra sp.– These plants are similar to Anubias and can be treated the same way. They also hail from acidic, darkened environments.
- Cryptocoryne sp.– Cryptocorynes are another native to these kinds of water. Just be aware that your crypts will almost always go through a melt when switched from “normal” aquaria to blackwater tanks.
The key here is to do some extra research before picking up plants. Not all of them are suitable for a blackwater environment.
For the rest of us, Chili Rasbora pair well with most plants. Most of them will spend their lives in basic planted nano tanks, where the only limits are your skill as an aquatic botanist.
All wood, all the time when it comes to a tank that’s housing Chili Rasbora.
Or, more accurately, use only chemically stable types of stone to decorate a blackwater tank. Otherwise, you may end up altering your water chemistry.
Even in non-blackwater aquaria, you may want to give some careful consideration to driftwood. In a tap water tank, it’s unlikely to change the pH much due to calcium buffering, but driftwood still leaches tannins.
These chemicals are good for fish across the board. Some rare exceptions exist, but they’re outside of the realm of the usual fishkeeper’s priorities.
The best types of wood for tannin content are Mopani or Malaysian driftwood. Both are readily available online and should be considered, especially if you’re working hard at creating an acidic environment for these fish.
Chili Rasboras are very small compared to most aquarium fish. The only other common fish close in size are Galaxy Danios and Endler’s Livebearers. Their small size is enormous as a matter of scale when you compare them to fish 1 ½” to 2” long.
Because of that simple fact, people tend to overfeed them. A small amount of flake should be supplied once per day at most, and only that which is eaten in a couple of minutes. Otherwise, the rotting food can get down in the substrate.
On the other hand, shrimp or small bottom-feeders like Corydoras sp. will eat anything they miss. I consider bottom feeders essential, but overfeeding is a big concern for those who don’t.
Chili Rasboras require a cycled tank. We’ll remind you at every opportunity that a fish-in cycle is a bad husbandry practice, but in this case you’ll just end up losing the fish. They’re not overly sensitive, but they’re not as hardy as most of the common small fish either.
Cycling your tank is a simple process:
- Setup your tank, including hardscape and equipment.
- Add a small amount of food to the tank daily, a little pinch will do it.
- Test each day for ammonia until ammonia levels reach 0.
- Test each day for nitrites until the nitrite levels are.
- Test each day for nitrates until they’re less than 10ppm, which is a safe level to add your Chili Rasbora.
In blackwater tanks you’ll also need to keep an eye on the pH. Before you’ve established the right level of tannin leaching material for your tank you can cause a crash in your bacteria levels.
The pH should stay above 4.0 at all times during the cycle to avoid collapsing the beneficial bacteria you’re working with.
Chili Rasbora Behavior
Chili Rasboras are quite lively when they’re in a secure environment. If they’re acting overly shy then you may have a problem in your tank’s setup. Most often it’s simply a lack of good cover.
These fish prefer to stay on the top and in the middle of the water, rarely venturing to the bottom of the tank. Try to provide them cover with stem plants or other mid-growing plants. Vallisneria is a good option, allow them to grow along the top of the tank and you’ll instantly create a floating cover.
The other major part of their behavior is schooling. Chili Rasboras dwell in large schools, so you can’t just buy two or three of them. While most schooling fish have a recommendation of 6 fish, I strongly advise getting at least 8 Chili Rasbora.
A school that size can do well in a cycled and heavily planted 5-gallon tank due to the small size of the fish. Just make sure it’s cycled first. In larger tanks with extensive planting 1-2 per gallon is a reasonable stocking density.
Chili Rasboras are peaceful and shy around larger fish. They’re not fin-nippers or aggressive, preferring to simply school and avoid larger fish.
Males can get territorial when breeding. Usually, a larger male will begin to chase off the other Chili Rasboras in the tank when they get close.
In nano tanks, this can cause the other fish to remain in hiding semi-permanently.
If you have trouble with a male becoming overly territorial you may have too many fish in the tank. Chili Rasboras don’t claim a lot of territories and it’s less of an issue in a 10 gallon or more tank.
In smaller tanks, you may need to either remove the male or upgrade to a larger tank. Nano tanks in the 5-gallon range can be disrupted entirely by just one male, but the same male wouldn’t cause a real problem in a 20 gallon or larger tank.
When I see errors in care for Chili Rasbora, it’s usually a problem of tankmates. Their tiny size and preference for calm conditions make them vulnerable to fish that would normally be considered “safe.”
Chili Rasboras are not a good choice for “general” community tanks. The common clown-puke gravel with a variety of gourami, goldfish, and livebearers can be a fatal environment for these little guys.
Ideal tank mates will have the following qualities:
- Small Size- Very small for the most part. With few exceptions, any fish 2” or over should be considered very carefully before being added to the tank.
- Non-aggressive- Chili Rasbora are very peaceful, and fish that chase them constantly will create a lot of stress. They may even harass the Chilis until they’re dead.
- Bottom Dwellers- Fish that dwell on the bottom will rarely interact with your Chili Rasbora.
There’s not a lot of wiggle room in size: Chili Rasbora are tiny and that means they’ll be eaten by any fish significantly larger than themselves. It’s just the fishy way.
I’ve had success mixing them with Endler’s Livebearers in the past, creating a very colorful planted nano tank. Some of the following are also good options:
- Neon Tetra
- Cherry Barb
- Pygmy/Dwarf Corydoras
- Galaxy Danio
- Otocinclus Catfish
Some people report that they do well with active fish such as Zebra Danio, but in my experience, the school tends to remain shy if you have very active fish in the tank.
For the most part, Chili Rasboras do best with a single bottom-dwelling species such as a trio of Cory catfish.
If you want to keep a single species tank then be sure to take a look at our invertebrate subsection below.
Betta or Dwarf Gourami
So here’s the deal: Chili Rasboras pair very well with small Gourami species and Betta. Their mouths tend to be small enough they won’t eat them. Betta may have a big enough mouth but most have such voluminous fins it’s hard for them to swim fast enough to be a real threat.
The problem is this: not every Dwarf Gourami or Betta is compatible with small fish. I’ve owned very aggressive Betta that would endlessly harass smaller fish before, but the majority are actually timid fish.
I’ve never seen an aggressive Dwarf Gourami in person, but there are the occasional tales on old message boards. They’re just as intelligent and variable in personality as Betta so it’s a possibility.
They’re great tankmates for these fish, as long as the Betta or Gourami has the right personality for it.
African Dwarf Frogs
For those willing to take a walk outside of the usual aquatic fare, African Dwarf Frogs are another great companion for Chili Rasbora. The only drawback is that you’ll have to hand-feed your ADF with a turkey baster or equivalent, otherwise they won’t be able to compete for food.
It’s only African Dwarf Frogs that are good with these tiny fish. They’re sedentary, mostly blind, and remain small for their entire lifespan. They may be able to catch and eat an injured or sick Rasbora, but it’s unlikely.
African Clawed Frogs are sometimes sold as ADF in pet stores and aren’t suitable companions. It’s not as common as it was even a decade ago, but I still seem to run into it once every couple of years. They get quite large in comparison, and even at a smaller size tend to be more active and predatory.
Take a look at the feet of the supposed ADF before you buy them. A true African Dwarf Frog has four webbed feet, the African Clawed Frog has no webbing on the front.
ADF are entirely aquatic, and apart from feeding need no special considerations in care.
Invertebrates and Chili Rasbora
Since Chilli Rasboras do best in planted tanks, they mesh well with many invertebrates.
In particular, Chili Rasbora fit in well with dwarf shrimp. Cherry Red shrimp, or one of their endless color morphs, do well alongside these fish. Bee Shrimp have similar requirements to these fish, which is great if you’re already keeping Crystal Reds or another variation of the species.
Acidic tanks, especially blackwater tanks, usually make keeping snails hard or impossible. If you’re running a standard tank then use whichever snails you would normally keep in the tank, even if they’re just pond snails that hitchhiked with plants from elsewhere.
Bamboo Shrimp are an option for advanced aquarists. Their filter-feeding mechanism takes special consideration on your part and their care is more advanced than we can go into here. The truth is that most Bamboo Shrimp end up starving in captivity, so do your research if you go down this route.
Avoid predatory crustaceans like crayfish or crabs, as they can sometimes kill Chilis and usually require hard water for optimal health.
Breeding Chili Rasbora
Breeding Chili Rasbora is a simple process for the most part. If you’ve bred other egg-scattering fish then you’ll be on familiar ground. They’re only marginally more complicated than livebearers to breed successfully.
Chili Rasboras aren’t radically different between the sexes, but you can usually tell which are male or female.
The females will be plumper and often have less bold coloration. They may also be a bit longer than the males on average. Essentially, the big ones are usually going to be girls.
The males usually have bolder coloration, and the difference in color is more apparent with very healthy fish.
Chili Rasboras are continuous spawners, meaning they breed all the time. In a mature tank with enough cover, you may not need to do anything special to have a population increase.
On the other hand, they also eat their spawn and people tend to keep them with a high population density. That leads to declining numbers over time since none of the fry get a chance to cover up.
Your best bet is to either keep them in a tank with heavy low-level vegetation or to have a separate breeding tank. Breeding tanks can be bare-bottomed with a handful or two of Java Moss thrown in, but the water should be similar in chemistry to the main tank.
You can then place your breeding pair in the breeding tank for roughly 48 hours. After two days the eggs begin to hatch, and the adults should be removed before that happens.
If your fish aren’t breeding, then you most likely have a pH problem. In some cases, Chili Rasboras will refuse to spawn at a high pH or in very hard water. In that case, you should control those parameters.
Dimmer lighting can also trigger spawning in fish that are reluctant to breed.
Chili Rasbora fry are easy to take care of. They’ll still have the yolk to eat for 24-48 hours after spawning and then begin their life as micro predators.
You may need to find some even smaller foods than you feed the adults, but finely ground flake still works. You can also feed microworms, daphnia, or baby brine shrimp to help them get a high protein intake.
Avoid doing any water changes for 10-14 days after removing the spawning pair. The fry are very small and physically delicate, so give them some time to grow out before you begin changing the water out. The tank should be cycled and stable before adding the new fry.
The Lovely and Lively Chili Rasbora
These enchanting micro fish are becoming more common and with good reason! They’re beautiful, lively fish that make for great accents in planted tanks. Their schooling behavior and bold coloration have made them a staple for aquatic garden keepers.
They’re easy to care for and even offer an exciting start to blackwater tanks for those interested in the next level of the hobby!