Dwarf Rasbora

Pygmy Rasbora, Spotted Rasbora, Dwarf Spotted Rasbora

Family: Cyprinidae Dwarf Rasbora, Boraras maculatus, Pygmy Rasbora, Spotted RasboraBoraras maculatusPhoto © Animal-World: Courtesy Ken Childs

The Dwarf Rasbora is a tiny but magnificent sight to be had, especially as a school in top condition!

The Dwarf Rasbora Boraras maculatus (previously Rasbora maculata) is very tiny, reaching a total length of not quite an inch (2.5 cm). It is one of the smallest known members of the Cyprinid family, Cyprinidae. Although it has been ousted by recent discoveries as being the smallest, it once claimed the title of the tenth smallest known vertebrate.

The smallest known cyprinid is the Micro Glassfish Danionella translucida that reaches less than 1/2 inch (1.1 cm). But that little guy isn't nearly as attractive as this lively cyprinid. Until recently the Dwarf was also believed to be a juvenile of the Clown Rasboras Rasbora kalochroma, but is now determined to be a species of its own.

A school of these dynamic little fish makes a lively display in the aquarium. Even with such a small body, they sure have a high concentration of color. The slender body is reddish colored, varying in intensity depending on where its from, and is decorated with three black spots on the sides. The males are more brightly colored ranging from intense cherry reds to oranges with the females usually being a little more pink in color.

Along with their intriguing colors, they are friendly and peaceful. The companionship of their own species is absolutely essential for their well being. They need to be kept in a groups of at least 8 - 10 individuals. They could be considered a community fish because they are so peaceful, but on the other had they can be easily intimidated so really can only be kept with certain fish. Be carefully to select other tank mates that can be trusted with the Dwarf Rasbora. A lot of other fish can be scary companions when your only 3/4 of an inch long, and confronted with much larger or highly rambunctious companions. Choose tankmates that are of a similar size and personality, and not overly hyper.

These fish are rather sensitive to their environment, so are suggested for aquarists with some experience. To thrive they need very good water conditions, but above all a consistent water quality. Because of their small size a school can be housed in a 5 gallon tank just fine, but a bit larger aquarium can also work well and is easier to maintain. They will show their colors best and be happiest in a carefully aquascaped tank. Provide plenty of plants for them to hide in and some floating plants to help subdue the light, and you will be rewarded with a dynamic display.

For Information on keeping freshwater fish, see:
Freshwater Aquarium Guide: Aquarium Setup and Care


  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Actinopterygii
  • Order: Cypriniformes
  • Family: Cyprinidae
  • Genus: Boraras
  • Species: maculatus
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  • Temperament: Peaceful
  • Aquarium Hardiness: Moderately Difficult
  • Aquarist Experience Level: Intermediate
  • Diet Type: Omnivore
  • Minimum Tank Size: 5 gal (19 L)
  • Temperature: 74.0 to 79.0° F (23.3 to 26.1° C)
  • Range ph: 6.0-6.8
  • Hardness Range: 1 - 12 dGH
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Habitat: Distribution / Background

The Dwarf Rasbora Boraras maculatus (previously Rasbora maculata) was described by Duncker in 1904. They are found in South East Asia on the Malay Peninsula onto southern Thailand, eastern Sumatra, Singapore and the island of Bintan in Riau Islands province, Indonesia.

This species is listed on the IUCN Red List as Least Concern (LC). It is widespread across its range and although there has been habitat destruction, there have been no reports of significant declines in populations. Other common names they are known by include Pygmy Rasbora, Spotted Rasbora, Dwarf Spotted Rasbora, and Dwarf.

There are currently six distinct members in the Boraras genus. These fish were previously contained in the Rasbora genus but were reclassified in 1993 into their own genus by Kottelat and Vidthayanon. This small group of species was separated based on differences in morphology and in their reproductive methods. Some experts have more recently begun to refer to these two genera as being synonymous. so the Boraras genus will undoubtedly be scrutinized further to confirm its validity.

In nature these fish inhabit slow-flowing black water forest streams and rivers connected to peat swamps as well as ponds and ditches. They can be found hiding among fallen leaves and branches where the water is soft and acidic. The forest canopies often keep it heavily shaded as well. These fish swim in schools and are known as micropredators, feeding on small insects, worms, and zooplankton.

  • Scientific Name: Boraras maculatus
  • Social Grouping: Groups
  • IUCN Red List: LC - Least Concern

Description

This is a slender fish with no exaggerated features. The average Dwarf Rasbora will reach .75 inches (2.5 cm), with the largest individuals reaching 1 inch (2.5 cm). They have an average lifespan of 3 to 5 years with good care.

The body has a reddish background with 3 roundish black or dark brown spots on the sides. One is in the center at the shoulder area, a second is at the start of the anal fin, and a third is at the base of the tail fin or caudal peduncle. They vary somewhat in color patterning depending on the population they originate from. Some are more intensely red than others, They also vary depending on whether they are male or female. Males can be anywhere from cherry red to orange, which is affected by both diet and lighting, and the females are usually a little more pink in color.

  • Size of fish - inches: 1.0 inches (2.49 cm) - On average they reach .75" (2.5 cm), with the largest individuals reaching 1" (2.5 cm).
  • Lifespan: 3 years - They have a lifespan of about 3 - 5 years with proper care.

Fish Keeping Difficulty

These fish are suggested for an intermediate aquarist. They are quite sensitive to their environment and any sudden changes in the water quality will weaken them significantly. They also don’t respond well to medications. If medicines are necessary, be sure to introduce them a little at a time by diluting the medicine with tank water before adding it.

  • Aquarium Hardiness: Moderately Difficult - This fish requires consistency in water conditions and proper tankmates, or it will stress.
  • Aquarist Experience Level: Intermediate

Foods and Feeding

The Dwarf Rasboras are omnivores. In the wild they feed on small insects, worms, and zooplankton. In the aquarium they need a varied diet. Flake or tablet foods with natural pigment enhancers benefit this fish a lot. Some good ingredients to look for in commercial foods are those that contain spirulina algae and carotenoids. They can only handle the smallest live foods, like daphnia or baby brine shrimp. These fish will do best when offered food several times a day, but only offer what they can eat in 3 minutes or less at each feeding. If you feed only once per day, provide what they can eat in about 5 minutes.

  • Diet Type: Omnivore
  • Flake Food: Yes
  • Tablet Pellet: Yes
  • Live foods (fishes, shrimps, worms): Some of Diet
  • Vegetable Food: Some of Diet
  • Meaty Food: Some of Diet
  • Feeding Frequency: Several feedings per day - Offer only what they can consume in 3 minutes or less with multiple feedings per day.

Aquarium Care

These fish needs consistent quality conditions, and their water to be kept clean. At least 25 - 50% of the tank water should be replaced once a month. If the tank is densely stocked 20 - 25% should be replaced weekly or every other week. The substrate should also be vacuumed during water changes to avoid accumulation of waste.

  • Water Changes: Monthly - It the tank is densely stocked the water changes should be done every other week.

Aquarium Setup

The Dwarf Rasboras are a schooling species that will swim in all regions of the aquarium. Since they are so small, a school can be housed in as small an aquarium as five gallons. However that little water is more difficult to maintain, and a larger aquarium can work fine too. As they require very stable water conditions, these fish should be introduced to a mature aquarium with an established biological filter. Additionally, the tank should be securely covered as these fish are liable to jump if startled or excited.

A carefully aquascaped aquarium is an excellent choice for the fish. Their colors can be quite stunning and will show best in soft, acidic water conditions. For this, peat filtration is a worthy investment. Bogwood is also a great addition as the tannins help maintain water parameters more closely to their natural environment.

Provide a dark substrate and some dense thickets of stem plants, and as they resent overly harsh lighting add a few broad leaved rosette plants for cover and shadowy areas. The addition of some floating plants and driftwood roots or branches will also diffuse the light entering the tank. To create a natural feel and encourage the growth of microbe colonies add dried leaves to the tank. The microbe colonies will also act as a secondary food source.

  • Minimum Tank Size: 5 gal (19 L) - Due to its small size it can be kept in a five gallon tank, however the water quality must be diligently maintained.
  • Suitable for Nano Tank: Yes
  • Substrate Type: Any
  • Lighting Needs: Low - subdued lighting - This fish doesn't like harsh lighting and will not show good coloration under such circumstances.
  • Temperature: 74.0 to 79.0° F (23.3 to 26.1° C)
  • Breeding Temperature: 79.0° F - Breeding temperatures need to be at the upper end of it's normal tank requirements.
  • Range ph: 6.0-6.8
  • Hardness Range: 1 - 12 dGH
  • Brackish: No
  • Water Movement: Moderate
  • Water Region: All - They will swim in all regions of the tank.

Social Behaviors

The companionship of their own species is absolutely essential for their well being. A school of eight or more individuals is a must for then to feel comfortable. They could be considered a community fish because they are so peaceful, but on the other had they can be easily stressed. If kept with too few companions or with significantly larger fish, they tend to be high strung and constantly in hiding. Companion fish should be similar in size, peaceful, and not too active. A good sized school can happily be kept in a species only tank.

If keeping them with other fish, companions should be similar in size and personality, and not too active. Good selections can include some of the other cyprinids species like those of the Trigonostigma, Eirmotus, and Microdevario genera. A couple good ones are the Harlequin Rasbora Trigonostigma heteromorpha and the Espe’s RasboraTrigonostigma espei, but do watch other rasboras closely and remove any misbehavers. Its best to avoid most members of the Danio group as they are generally too active. Small catfish like the pygmy Corydoras catfish and Otocinclus also work well.

  • Temperament: Peaceful - They are peaceful fish but are quite timid and easily stressed by other fish.
  • Compatible with:
    • Same species - conspecifics: Yes - It is essential that they be kept in a school of at least 8 - 10 individuals.
    • Peaceful fish (): Safe - Only combine other similarly sized peaceful fish that are not overly hyper.
    • Semi-Aggressive (): Threat - Because they are so small, dwarf rasboras are easy targets for even mildly aggressive fish or fish that are bigger.
    • Aggressive (): Threat
    • Large Semi-Aggressive (): Threat
    • Slow Swimmers & Eaters (): Monitor
    • Shrimps, Crabs, Snails: Safe - not aggressive
    • Plants: Safe

Sex: Sexual differences

The females have rounder bellies and are normally larger than males. The males show more intense coloring during breeding. This is especially true for dominant males.

Breeding / Reproduction

The Dwarf Rasboras are moderately difficult to breed, though if kept in a well maintained aquarium with dense planting, you may see some young fish showing up. Like  other cyprinids they are open water egg scatterers and exhibit no parental care for the young. In a controlled spawning, two or three pairs need be well conditioned with small offerings of live foods several times a day, usually for about 4 weeks. Conditioning well with live foods will also bring out the males color. When well fed, mature females should begin filling out with eggs.

It is best to provide a dimly lit breeding tank with a water level low, at about 6" (15 cm) deep. The water should be very soft at about 2-3° dGH, slightly acidic with a pH of 5.8 - 6.3, and a temperature towards the upper end of the range for their normal aquarium. Filtration isn't really necessary, but you can add a small air-powered sponge filter or some peat filtration. The tank should be planted densely with fine leaved plants such as Cabomba or Milfoil, or with artificial plants. A substrate of marbles will save any eggs that fall from the plants, or a spawning mop like the plastic ‘grass’-type matting works very well.

Place two or three pairs in the breeding tank. Parents will usually need to adjust to the tank for a week or two before anything happens. The dominant males will form temporary territories when spawning. Spawning will usually occur in the morning hours after a strong ritual display. Then the parents will deposit eggs among plants. Though they are not very productive, they are continuous spawners. They will deposit a few eggs at a time until there are about 50 eggs deposited in all. The parents should be constantly well fed during spawning and then removed.

The fry will hatch in about 24 - 36 hours and they are extremely small. They will survive in their yolk sac for about 24 more hours and then be free-swimming. Feed the free swimming fry starter foods like infusoria or other liquid fry food until large enough to eat crushed flake food or just hatched brine shrimp. See Fish Food for Fry for information about types of foods for raising the young.

  • Ease of Breeding: Moderate

Fish Diseases

For the Dwarf Rasbora disease is not usually a problem in a well maintained aquarium. Still they get stressed very easily which makes them prone to many common aquarium diseases. They are also very sensitive to medications and normally require medicines be introduced very slowly to the aquarium. Dilute medications with tank water before adding and then introduce it a little at a time. With any additions to the tank such as new fish, plants, substrates, and decorations there is a risk of introducing disease. It's advisable to properly clean or quarantine anything that you want to add to an established tank prior to introduction, so as not to upset the balance.

A good thing about these fish is that due to their resilience, an outbreak of disease can often be limited to just one or a few fishes if you deal with it at an early stage. The closer to their natural habitat the less stress the fish will have, making them healthier and happy. Stressed fish are more likely to acquire disease. For information about freshwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.

Availability

The Dwarf Rasbora is not widely available due to its size and sensitivity during transport, and is moderate to moderately expensive in price.

References

Author: Barbara Roth, Clarice Brough CFS, Jeremy Roche

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