The Chili rasbora (Boraras brigittae), also known as the mosquito rasbora, is one of the smallest tropical fish in the aquarium hobby. The fish are not true rasboras and were put in the Boraras genus in 1993.
Dieter Vogt originally described the fish in 1978. He named it Rasbora urophthalma brigittae, in dedication to his wife Brigitte. The common term mosquito rasbora was chosen because the habitat was full of annoying mosquitos.
There are several Boraras species imported for the aquarium trade. These include B. maculatus, B. merah, B. urophthalmoides and B. micros. Tropical fish hobbyists have rated Boraras brigittae the best-looking of all the Boraras species so far.
The Chili rasbora has a reddish body with a dark stripe along its side. An intense red strip sits above the dark stripe and creates a beautiful contrast.
If you look closely, you’ll see small dark spots at base of the tail fin and anal fin. Male Chili rasbora have red highlights on their dorsal and anal fins.
Boraras uropthalmoides are often mislabeled as chili rasboras in the aquarium trade. B. uropthalmoides has a dark spot at the base of the tail fin (peduncle). It is more orange in color that Chili rasbora.
Chili rasboras are “nano” fish, growing to just .7 -inches (18 mm) in length.
Natural habitat
Chili rasboras are native to Southwestern Borneo, Indonesian province of Kalimantan Selatan (South Kalimantan) and Kalimantan Tengah.
Boraras brigittae was first found in Banjarmasin in the South of Borneo. They live in “blackwater” streams and pools.
These quiet, peat-stained waters are very low in salts and minerals. The water is naturally soft with a pH as low as 4.0.
Decaying vegetation scattered on the substrate in addition to aquatic plants give the fish plenty of cover. Submerged roots and branches are common in their habitat. Overhanging vegetation and trees reduce the light penetrating the water.
Aquarium requirements
While the Chili rasbora is not considered difficult to keep, care should be taken when setting up the aquarium. The ideal tank is a dedicated species aquarium where these are the only fish.
This nano Cyprinid can be kept in an aquarium as small as 5-gallons (20L). But they make a great addition to larger tanks as a massive school of moving color.
Experienced aquarists recommend a fine-sized gravel, preferably darker in color.
Chili rasbora is a schooling fish and likes to swim in the middle and upper portion of the aquarium. They will also explore the lower level of the aquarium when looking for food.
Live aquatic plants are a welcome addition to the Chili aquarium. The fish are small and enjoy investigating the micro-environments created by plant cover.
Live plants also provide a habitat for live foods like worms and plankton, which are perfect for the small mouths of Chili rasboras.
Water conditions
Chili rasboras thrive under the right conditions. These fish prefer very soft water. A general hardness (GH) range of 1 to 2 degrees is ideal.
Carbonate hardness (KH) would need to be from 0 to 1 degree to maintain a pH of 5.0 or below. This low level of pH and alkalinity requires careful monitoring with test kits.
But don’t think you must run your aquarium this low in minerals and pH. The fish will thrive water with a little higher pH and water hardness levels.
Reverse osmosis or distilled water can be used to create these water conditions. These zero-mineral water sources can be used to dilute your tap water.
The addition of peat moss, peat pellets or almond leaves will lower the pH naturally. The peat will tint the water as natural tannins are released. Peat will also soften the water. But don’t confuse tannin-tinted water with “dirty” aquarium water.
The fish’s habitat is slow-moving water with beneficial tannins that promote fish coloration and health. The tea-stained water is clear, without sediment that clouds the water. The water is clear yet tinted.
The combination of low pH and tannins reduces the pathogen level in the water, so the fish don’t get sick. The Chili rasbora tank should never have gravel packed with sludge.
Over-feeding causes fish to process needless food and create solid waste. Excess nutrients from the food stimulate algae growth in the water, even if you can’t see it. The combination of dead algae and fish waste accumulates in the gravel, creating the perfect conditions for fish pathogens to thrive.
The Chili rasbora tank must be kept clean through partial water changes and occasional gravel cleaning with a siphon.
Chili rasbora and water chemistry parameters
| pH: | 6.0 – 7.0 (4.0-5.0 expert) |
|---|---|
| General or Total hardness: | 2 – 3 degrees |
| Alkalinity or carbonate hardness: | 1 – 3 degrees |
| Water temperature: | 74 – 82°F (22 – 28°C) |
| Ammonia & Nitrite: | 0.0 |
Chili rasboras and water temperature
Like other tropical fish, Boraras brigittae can live in range of temperatures. For captive aquarium fish temperature stability is important.
Novice aquarists sometimes believe a nano aquarium does not require an aquarium heater. Room temperature can vary due to heating and air conditioning cycles.
Chilled aquarium water is especially stressful to tropical fish. Use a submersible aquarium heater to maintain a stable water temperature. Set the heater thermostat to 74 – 82°F (22-28°C).
Be aware that sunny locations can cause the aquarium to over-heat. If in direct sunlight for more than 30 minutes, monitor the water temperature to make sure the tank is not getting too warm.
Curtain-filtered sunlight or periodic exposure to sunlight should not adversely affect the water temperature.
Using tap water in a Chili rasbora aquarium
The ideal Chili rasbora aquarium requires specialized water chemistry to duplicate the fish’s natural habitat. You won’t be able to use tap water alone to recreate the ultra-low water hardness and pH. It will be necessary to blend tap water with reverse osmosis or distilled water to achieve the ideal water conditions.
If you have a water softener on your home water supply, there are some facts you need to know.
Water softeners are filled with ion-exchange resin beads. The beads are “charged” with sodium ions. As water flows through the water softener, the resin beads trade sodium in exchange for the calcium and magnesium in the water. This is the ion exchange process.
Water hardness is removed, and sodium is added to the water. Soft water is great for reducing mineral scale on glassware and making your hair silky smooth. But is not the same as the soft water found in natural streams and bogs.
The Chili rasbora’ s water is low in all minerals and salts. Water from a water softener is low in calcium and magnesium but “high” in sodium. The carbonates, if high, will still be high in softened water. The solution to this problem is to blend tap water with RO or distilled water.
Use aquarium test kits to determine the GH, KH and pH of the blended water. You’ll be able to determine how much tap water should be blended with RO or distilled water to achieve the desired water chemistry.
Conditioning tap water for the Chili rasbora aquarium
While distilled and reverse osmosis water are free of chlorine disinfectants, most tap water supplies are not. Chlorine disinfectants, like chlorine and chloramine, are oxidizing chemicals that kill bacteria and parasites in the water.
These disinfectants are highly toxic to aquatic life. It only takes a small amount of chlorine to damage delicate gill tissue. Use an aquarium water conditioner to remove chlorine and chloramine. Heavy metals are another problem, especially in “soft water” aquariums.
Copper water pipes release copper into the water. In trace amounts copper is an essential nutrient. But too much can cause toxicity to fish, shrimp and snails. Metals are more toxic is low-mineral water.
Many water conditioners will detoxify a small amount of copper. But some water sources have high copper levels.
Before using your tap water, flush the faucet for a minute or two. This drains the pipes of water and reduces the level of copper coming out of the faucet.
When making water changes, make sure the water is neither too hot or cold, so it does not shock the fish.
Water filtration for Chili Rasboras
Boraras brigittae are small, delicate fish. They aren’t powerfully built and cannot swim against strong water currents. These schooling fish like slow-moving water, not rushing rivers of current. It’s OK to filter a lot of water, but the water flow should be dispersed evenly through the tank.
Driftwood, resin logs, branches and other structures will break up the currents, just like in nature. Another benefit of a heavily planted tank is that the plants slow the water movement caused by the aquarium filter.
The plants need water to flow over their leaves for nutrient and gas exchange. They also redirect strong water flow into milder currents and eddies in the tank. Smaller hang-on-back power filters usually have a flow adjustment knob. But larger aquariums will require a canister filter.
Some canister filters have adjustable nozzles, so you can create a river-like water flow pattern in the tank. Plants and structure will even out the currents and provide a place for the fish to rest.
If you choose to use peat to acidify the water and add tannins, activated carbon will remove some of the natural acids and organics. You can remove the activated carbon or use it a few days out of the month to keep the organics under control.
Partial water changes are also an important part of maintaining water quality, especially if you don’t use activated carbon all the time.
Mechanical filtration material should be changed or cleaned every few weeks. Even though the filter is pumping adequate water, it is not a signal that the filter is clean.
Organic matter captured in filter pads, sponges and other mechanical media will decay if left inside the filter. Decaying organics release algae promoting nutrients. The decay process uses oxygen and is also a breeding ground for pathogens. Chili rasboras like very clean water, so service the filter often.
Aquarium lighting
Chili rasboras come from an aquatic habitat that is peat-stained and under partial tree cover. This does not mean you have to keep the fish in the dark.
But experience shows that the fish’s colors seem to intensify when they’re kept in slightly subdued lighting. A modern LED aquarium light with a dimming feature gives you the most flexibility for controlling light levels.
The addition of live or plastic plants will create some shade and bright spots, much like their natural environment. A lighting period of 8 to 12 hours is recommended.
Aquascaping for Chili rasbora
Boraras brigittae like to school in mid to upper water levels. This means they like open water for swimming. But they also like partial plant cover. The fish’s color appears most intense when the gravel is darker.
The ideal aquascape would include a dark substrate using small-sized gravel. Some aquarists have used sand. Pebbles or rocks along with driftwood or logs create a natural-looking stream tank. Live plants are always a good idea from an aesthetic and biological standpoint.
Live plants look great plus they remove nutrients and produce oxygen. The fish love swimming through the leaves and stems. The upright plants also buffer the water flow if you’ve got a strong aquarium filter. Low-light plants, like Java moss, Anubias and Java fern are easy to grow low-light plants. If you’ve got brighter lighting, try some swords and Valisneria.
If your growing live plants, do not use an air stone or heavy surface agitation. This will drive off carbon dioxide and inhibit plant growth. Even if you’re using plastic plants, the dark substrate will help bring out the fish’s colors.
Experts sometimes add a couple of almond leaves to the aquarium. The dried leaves sit on the bottom but don’t rapidly decay. Instead, they release tannins and other beneficial organics believed to stimulate color and health.
Aquascaping essentials for the Chili rasbora aquarium:
- Fine, dark gravel-brown or black
- Driftwood for cover
- Smooth decorative pebble or rocks
- Live or plastic plants
Feeding requirements of Chili rasboras
Boraras brigittae is not a picky eater but the fish do require tiny food particles. A varied diet is recommended. You can pulverize flake food and feed it as a powder.
Sinking or slow-sinking micropellets are also a good choice. Live or frozen baby brine shrimp (Artemia), microworms, Tubifex, and finely chopped bloodworms are all favorite foods.
Chili rasbora compatibility
The following recommendations apply when keeping Chilis.
- Chili rasboras are very small, shy and gentle
- They get along with their own kind (schooling)
- They must be kept with very small, peaceful fish
Good tank-mates include small species Chocolate and Sparkling Gourami, neons, cory cats, celestial pearl danios and other small, non-aggressive tropicals.
Chili rasboras and dwarf shrimp
The good news is this fish is friendly toward dwarf shrimp. Chilis are completely compatible with Cherry shrimp, Wood shrimp and Amano to name a few.
Breeding Chili rasboras
It is fairly easy to identify males and females. Males Chili rasboras, when ready to breed, develop a brighter red coloration compared to the females. The males also develop darker black and red highlights on dorsal and tail fins. Females will look plumper, due to being ripe with eggs.
Males may become a little territorial as they showoff for the females. Females lay small numbers of very small eggs, which are scattered on the bottom of the tank. The fish do not care for the eggs. In some cases, parents have eaten the eggs.
In a well-planted tank, the fry may be able to survive on their own, even with other fish in the tank. If your serious about saving the fry, a separate breeding tank will be necessary. The very small fry require live food, like infusoria and paramecium, until they can take larger prepared foods.
Final thoughts
The Chili rasbora is tiny gem of a fish. It is beautiful, especially in groups of six or more. They’re ideal for nano and shrimp aquariums due to their gentle nature. Another bonus is their low price and relatively easy care.