Slender Rasbora

Striped Rasbora, Black Line Rasbora, Gold Line Rasbora

Family: Cyprinidae Slender Rasbora, Rasbora daniconius, Striped Rasbora, Black Line Rasbora, Gold Line RasboraRasbora daniconiusPhoto © Animal-World: Courtesy Ken Childs
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I have 32 of these fish in my community tank and they are my cheapest and most favorite fish I have.  They keep my tank from being boring, they all group... (more)  kris

The Slender Rasbora is a great fish for the aquarist looking for a less common species to add interest to their tank!

The Slender Rasbora Rasbora daniconius isn't as colorful but is just as attractive as its flashier cousins. It is a good sized cyprinid in the wild, usually reaching just shy of 6 inches (15 cm) in length. Some reports even say an occasional individual can reach almost 8 inches (20 cm), but in captivity it doesn't reach either of those sizes. An aquarium specimen will usually only reach a length of about 3 1/2 inches (8 - 9 cm).

To delightfully liven up the middle of an aquarium display, add a school of these subtle beauties. Overall they have a silver body with olive colored undertones, but the scales are large and highly reflective, giving a sparkling effect. The belly of the males will be yellow or reddish while the female's will be whiter. However their most prominent feature is a blue-black line that runs the body length. This line is finely outlined in a bright gold. It is this feature that has inspired several rather descriptive names including Striped Rasbora, Black Line Rasbora, Gold Line Rasbora, and Golden Striped Rasbora.

In the wild they may be found swimming the rivers in schools with hundreds of individuals. So in the aquarium a school is a must. The companionship of their own species is absolutely essential to their well being. Never keep less than 6 - 10 individuals, with more being even better. If this fish is kept singly it will waste away. These fish do fine in community tanks but will suffer in the company of aggressive fish. It is recommended to keep them with fish of similar size and temperament.

For beginners that want to have a tank of peaceful schooling fish this is a good choice. It is robust and will readily accept aquarium foods. However keeping this cyprinid does require providing good quality water and regular maintenance. Fluctuations in water quality leave this fish weak and prone to disease.

They really look beautiful in a tank that simulates their habitat with plants, rocks, wood and substrate. An aquarium best suited to this fish would be large and roomy, with a fine gravel bottom and dense plantings along the edges. A school of these fish can be kept in a 20 gallon size aquarium, but a larger tank is better for these lively fish and easier to maintain. They can jump with surprising gusto so keep a tight covering on your aquarium.

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

Geographic Distribution
Rasbora daniconius
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  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Actinopterygii
  • Order: Cypriniformes
  • Family: Cyprinidae
  • Genus: Rasbora
  • Species: daniconius
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Slender Rasbora - Quick Aquarium Care
  • Aquarist Experience Level: Beginner
  • Size of fish - inches: 5.9 inches (15.01 cm)
  • Minimum Tank Size: 20 gal (76 L)
  • Temperament: Peaceful
  • Aquarium Hardiness: Moderately hardy
  • Temperature: 71.0 to 80.0° F (21.7 to 26.7° C)
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Habitat: Distribution / Background

The Slender Rasbora Rasbora daniconius was described by Hamilton in 1822. They are found in South East Asia in the Mekong, Chao Phraya and Salween basins and the northern Malay Peninsula, and to the west in the Indus River of Pakistan and south in Sri Lanka. It is also known from Borneo and Sumatra.

This species is listed on the IUCN Red List as Least Concern (LC). It has a wide distribution, is adaptable to a variety of habitats, and lacks any known major widespread threats. Other common names it is known by include Striped Rasbora, Black Line Rasbora, Gold Line Rasbora, Blackline Rasbora, Common Rasbora, Golden Striped Rasbora, Slender Barb, and Striped Barb.

This fish is very similar in appearance to its close cousin Rasbora labiosa, that is also called a Slender rasbora. The R. labiosa was once considered to be a subspecies of R. daniconius though now is recognized as a distinct species. In earlier times R. labiosa probably became more readily available to the trade as it was first cultivated in captivity in 1935. Though these two resemble each other closely, R. labiosa is actually only about half the size of R. labiosa. Its total length is about 3 3/4 inches (8.5 cm). There are some other distinctions too. It is much more slender, almost cylindrical in shape, and the lateral line is reduced. It also has smaller fins and fat, fleshy lips.

These fish inhabit all sorts of waterways from ditches, canals, brooks, and streams to medium and large rivers as well as ponds and flooded fields. They are also found in brackish waters. But they are primarily found in sandy streams and rivers with slow moving, muddy waters. They sometimes form large schools and feed on small aquatic insects and detritus.

  • Scientific Name: Rasbora daniconius
  • Social Grouping: Groups
  • IUCN Red List: LC - Least Concern


The Slender rasbora is a slim fish, as the common name implies. It can reach a total length of just under 6 inches (15 cm) in length, with some reported at close to 8 inches (20 cm), but in the aquarium it will commonly reach a about 3 1/2 inches (8 - 9 cm) in length. They have a typical lifespan of 5 to 8 years with good care.

The general body color is silver, with olive colored undertones. The belly will be whiter on males and yellow or reddish on females. These fish have a striking blue-black line that runs the whole body length, right through the tail. This line is finely outlined with gold. Scales are large and highly reflective. Fins are small and yellow.

  • Size of fish - inches: 5.9 inches (15.01 cm) - It can reach up to 6" (14 cm) in the wild but usually only reaches 3.5 inches (9 cm) in the home aquarium. An occasional specimen has also been reported at up to almost 8" (20) in the wild.
  • Lifespan: 5 years - They have an average lifespan of about 5 to 8 years years with proper care.

Fish Keeping Difficulty

This fish is a great choice for the beginner as it is robust and fairly hardy, but it must be kept in a school. With well filtered water and regular maintenance these fish will do very well. They are usually not very picky eaters and will accept and thrive on quality flake foods, with the addition of occasional live foods.

  • Aquarium Hardiness: Moderately hardy
  • Aquarist Experience Level: Beginner

Foods and Feeding

The Slender Rasboras are omnivores. In the wild they feed on small aquatic insects and detritus. In the aquarium their diet should be based around a quality flake or pellet food. A good balance of prepared and live foods is required for optimal health. Daphnia, brine shrimp, and bloodworms all make excellent choices for live foods. Some green foods like lettuce are good too. Dip a washed lettuce leaf in boiling water to soften it. Take care to remove the uneaten lettuce from the tank within a few hours. 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 are not exceptionally difficult to care for provided their water is 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 Slender Rasbora is a schooling species that spends much of its time in the middle regions of the aquarium. They are very active swimmers, so they tend to do better in larger and longer aquariums where they can school. A school of 6 - 10 need to be kept in a tank of 20 gallons or more. It is fairly hardy and will adapt to most aquarium conditions.

The key to making this fish extra beautiful is making it feel at home. Setting up a habitat that resembles their natural environment is the best way to do this. Their natural habitat provides a lot of direct sunlight, so placing the aquarium where they can get natural sunlight will be a plus. If this isn't possible get a high quality light that will simulate this. They prefer medium hard, slightly acidic water conditions. A good filter creating a reasonable water current is also pleasant for these fish. The tank should be carefully covered as these fish are liable to jump if startled or excited.

Provide a sandy or fine gravel substrate with a few smooth rocks and pebbles. The tank must be densely planted with a good variety of plants to make them feel safe as well bring out their colors. They are extremely active swimmers, so also need open space to swim unobstructed. Have plantings reaching the surface of the aquarium around the sides and back with a few broad leaved plants for shelter. With the right water chemistry for this fish, many aquatic plant species can flourish. Bogwood is also a great addition because it will releasing tannins which help get the water to the swampy and acidic conditions favored by this species. Aquarists who really want the natural feel could add some aquarium sealed dried bamboo to simulate the reeds that grow along the shoreline of their natural habitat.

  • Minimum Tank Size: 20 gal (76 L) - A school will do best in larger and longer aquariums.
  • Suitable for Nano Tank: Yes
  • Substrate Type: Any
  • Lighting Needs: Moderate - normal lighting
  • Temperature: 71.0 to 80.0° F (21.7 to 26.7° C)
  • Breeding Temperature: 80.0° F - Breeding temperatures need to be slightly higher than normal aquarium temperatures.
  • Range ph: 6.0-7.5
  • Hardness Range: 8 - 17 dGH
  • Brackish: No
  • Water Movement: Moderate
  • Water Region: Middle - The Slender Rasbora is a mid-water fish.

Social Behaviors

These fish require a sizeable school of at least 6 to 10 individuals to display healthy coloration and behavior. They will have a pecking order but will never really cause harm to each other. The males will display their best colors as they compete for the attention of females.

These fish are peaceful but quite active. Although they occasionally quarrel they are generally good natured. They should be mixed with fish of similar temperament. Good tankmates include many popular community fish. Cyprinids are especially good as well as some of the larger characins and live bearers. They also do well with bottom dwelling peaceful catfish and loaches, and even some of the dwarf cichlids.

  • Temperament: Peaceful - This fish will occasionally quarrel with tankmates but without damage.
  • Compatible with:
    • Same species - conspecifics: Yes - Needs to be kept in schools of at least 6 - 10 individuals.
    • Peaceful fish (): Safe
    • Semi-Aggressive (): Threat
    • Aggressive (): Threat
    • Large Semi-Aggressive (): Threat
    • Large Aggressive, Predatory (): Threat
    • Slow Swimmers & Eaters (): Safe
    • Shrimps, Crabs, Snails: Safe - not aggressive
    • Plants: Safe

Sex: Sexual differences

The females are slightly plumper, stronger, and deeper bodied, and have a whitish belly. Males are more slender and smaller, with a yellowish or reddish belly.

Breeding / Reproduction

The Slender Rasboras are relatively easy to breed, and it can be successfully accomplished with either pairs or in schools. Like other cyprinids they exhibit no parental care for the young, but they differ slightly in their spawning method. Rather than being open water egg scatterers, their eggs are shed among the leaves of plants. Condition them 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.

A large tank (20+gallons) is required for spawning as part of the courtship is a very intense chase. The water should be medium hard at about 12° dGH. From their normal water conditions, slightly drop the pH (to slightly acidic at about 7.0 pH) and slightly increase the temperatures. Filtration isn't really necessary, but you can add a small air-powered sponge filter or some peat filtration. A pair will spawn on fine leaved plants, so be sure to include Hornwort, Cabomba, Milfoil, or a similar species in the breeding tank. Java moss or Crystalwort (Riccia) work too if they are anchored down.

Courtship consists of displays and chasing by the male, with the female hiding among the plants until she is ready to spawn. Spawning will usually occur in the morning hours. They assume a side-by-side position with the male attempting to curl around the female. Eggs will then be shed among the plant leaves, and the female will find another hiding area for the next spawn.

After the spawn, remove the parents as they will eat the eggs. The fry will hatch in 3 to 4 days. The young are fairly large and become free-swimming in about 3 more days. Provide starter foods like infuser for the first few days. They grow quickly, and will soon be large enough to eat baby brine shrimp. See Fish Food for Fry for information about types of foods for raising the young.

  • Ease of Breeding: Moderate

Fish Diseases

Slender Rasboras are very hardy and disease is not usually a problem in a well maintained aquarium.
Some disease the are common in rasboras are dropsy, fin rot, and Ich if good water quality, nutrition, and maintenance is not provided. With any additions to a 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 add to an established tank prior to introduction, so as not to upset the balance.

These fish are very resilient but knowing the signs of illness, and catching and treating them early makes a huge difference. 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 best way to proactively prevent disease is to give your fish the proper environment and a well balanced diet. The closer to their natural habitat the less stress the fish will have, making them healthier and happy. A stressed fish will is more likely to acquire disease. For information about freshwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.


The Slender Rasbora is difficult to find, but specialized fish stores may carry them and they are sometimes available online, and they are relatively inexpensive.


Author: Barbara Roth, Clarice Brough CFS, Jeremy Roche
Lastest Animal Stories on Slender Rasbora

kris - 2013-03-23
I have 32 of these fish in my community tank and they are my cheapest and most favorite fish I have.  They keep my tank from being boring, they all group together and swim from side to side of my 100 gallon aquairum. They really are a beautiful sight to see... I have a blue light bulb and a white bulb on my tank and wow their colors really pop out! The gold stripe looks fluorescent and they are so happy. Mine never hide they are not shy at all... I have them in with large veil angels, mollies, platies, all types of tetras, clown loaches, cory cats, rainbows, dwarf gouramis, bumblebee catfish, green & pink kissers, chinese algea eaters, plecos, cuckoo squeaker catfish & a red and blue crawfish...I LOVE MY TANK!!!!

Znaika - 2012-06-19
I have a school of 9, bought separately 7+1+1. Interestingly enough, 7 keep together most of the time, whereas two (I suspect the two bought separately) tend to keep alone or with one another, but rarely join the 7. These fishes are very shy compared to barbs and like to hide in upper levels of vegetation at any sign of outside movement.

DebbyB - 2011-08-08
I have 6 in my 30g-Long tank. It's planted with Amazon swords. They coexist with a beautiful blue betta and a snail. I agree that they are easy to care for. I'd like to pick up some more if I can find them. I stumbled upon these about three years ago. None have died at this point. They seem to be very vigorous fish.

  • Charlie Roche - 2011-08-08
    Works for me - great glad
janek51 - 2007-11-15
I got five of these rasboras, as well. They were in a tank at the LFS with a hodgepodge of fish, all priced at $2 a piece. They were washed out and I thought they were red-lined rasboras, so I got them to add to my school. Anyway, I got them home and as they colored up a little, I could see they had a gold line. The black line colored up as well. After trying two other tanks where they didn't seem happy, I finally put them in a 20-gallon with some checkered barbs and harlequin rasboras. Then they settled down and their colors came out in full glory. I think these fish are real beauties. The color combination is great, so I think I really lucked out by mistake.

DebbyB - 2011-08-08
I have 6 in my 30g-Long tank. It's planted with Amazon swords. They coexist with a beautiful blue betta and a snail. I agree that they are easy to care for. I'd like to pick up some more if I can find them. I stumbled upon these about three years ago. None have died at this point. They seem to be very vigorous fish.

  • Charlie Roche - 2011-08-08
    Works for me - great glad