Zebra Danio

Zebrafish, Striped Danio, Zebra Fish

Family: Cyprinidae Danio rerioPhoto © Animal-World: Courtesy David Brough

The Zebra Danio is a popular aquarium fish favored for its charm and grace as well as its hardiness!

The Zebra Danio Danio rerio (previously Brachydanio rerio) is a lively little schooling fish that only reaches about 2 1/4 inches (6 cm) in the aquarium. It's easy to recognize with its attractively striped, black and white "zebra" patterned body. This is one of the first types of tropical fish to ever be kept in the aquarium, and it is still enormously popular. This pretty, inexpensive fish is a great choice for both beginning and advanced aquarists. Other common names it is known by are Zebrafish, Striped Danio, and Zebra Fish.

Dozens of variations of this Danio are selectively bred today, with a variety to suit every taste. Some of the best known include the Longfin Zebra Danio and color morphs like the Golden Zebra Danio, Albino Zebra Danio, Longfin Blue Danio, and Sandy Zebrafish. Other well known varieties are the Leopard Danio and Longfin Leopard Danio, both of which have spots instead of stripes. There is also a variety called the Hybrid Danio, for those who just can’t choose between spots and stripes, which has a combination with both. A recently introduced variety is a Zebrafish (Danio rerio) genome known as the “Glo-fish.” This is a genetically modified little fish available in beautiful fluorescent colors of bright red, green, orange-yellow, blue, and purple.

These hardy and attractive Cyprinids are ideal for beginners. They are prolific breeders and the easiest type of egg layers to breed. A schooling fish, they should be kept in a small group of at least 3 individuals, though 5 or more is best. Because they are so small, a school is suited to a smaller aquarium of at least 20 gallons. They can be housed with most any community fish. Just make sure that the danio will not be eaten and that the other fish aren’t startled by swift movement.

Zebrafish are very durable and can withstand an impressive range of water temperature and conditions. They will generally do just fine without a water heater as they are comfortable at temperatures down to the low 60s (F). But even though they are not finicky about water conditions, it's best to not keep your aquarium at any extreme. Don’t be surprised if the school spends a lot of time in the water flow of the filters or pumps as a swift-moving environment is what they are accustomed to in nature.

Take care that neither specimens of this fish nor fertilized eggs be released into the environment. Zebrafish are tropical and can't survive in areas of extreme weather conditions. They have been used for mosquito control and have invasively populated some environments.

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

Habitat: Distribution / Background

The Zebra Danio Danio rerio (previously Brachydanio rerio) was described by Hamilton in 1822. They are found in Asia from Pakistan to India and as far as Myanmar. They occur in the Kosi River in Uttar Pradesh, northern India, and in smaller numbers in Nepal, Bhutan, and Bangladesh. This species is listed on the IUCN Red List as Least Concern (LC) as they are widespread throughout their range with no major identified threats. Other common names this species is known by include Zebrafish, Striped Danio, and Zebra Fish.

There are dozens of variations of this Danio, with the Albino Zebra Danio being a naturally occuring color morph. Many varieties and color morphs, including the Albino, Longfin, Golden, Sandy, and Leapard Zebra Danios, are bred in captivity today. A more recently introduced variety is a Zebrafish (Danio rerio) genome known as the “Glo-fish,” a genetically modified little fish developed by scientists. They added a natural fluorescent gene to the fish, which will absorb light and then re-emit it, in the hopes of being able to detect contaminates in waterways. Though Glo-fish are perhaps the most controversial little fish in the hobby, at present there are no known adverse effects to the fish or to the environment. They became commercially available in the United States in late 2003 and are available in beautiful fluorescent colors of bright red, green, orange-yellow, blue, and purple.

Zebrafish inhabit the lower reaches of streams, canals, ditches, and ponds. Their habitat varies greatly depending on the time of year. Adults are found in large numbers in seasonal pools and rice paddies during the wet season where they spawn and feed. These are still waters with a substrate that is silty and heavily vegetated. The adults then return to the faster moving waters of rivers and streams for the dry season, where the substrate is normally rocky and shaded. The young will stay in the still waters until maturity, then they too migrate to the rivers. In the wild, these fish are considered micropredators and feed on worms, small aquatic crustaceans, insects, and insect larvae.

• Scientific Name: Danio rerio
• Social Grouping: Groups
• IUCN Red List: LC - Least Concern

Description

The Zebra Danio has a slender, compressed body and a barbel at the end of each lip. These small fish reach lengths of only up to about 2 1/4 inches (7 cm) in the aquarium, though they can get slightly larger in a pond. They are thought to be primarily an annual species in the wild, but in captivity they can have a lifespan of 3 to 4 years. Some have lived up to 5 1/2 years with proper care.

The body of this species has a very pale yellow to white background marked with five steel-blue horizontal stripes that fade into the fins and extend onto the tail fin.

Some varieties and color morphs of this fish include:

• Long finned Zebra Danio
  This is merely the Zebra Danio selectively bred to have extended fins. It has nearly exceeded the traditional variety in popularity.
• Leopard Danio & Longfin Leopard Danio
  Although sometimes separated as different species, the Leopard Danio is actually a captive-bred color morph first developed by a Czech scientist. Instead of stripes, this sides of this fish are adorned with steel blue spots. They will readily school with regular Zebra Danios, and they can even breed together. The longfin variety has been bred to have an extended tail and fins.
• Hybrid Danio
  The Hybrid Danio is a selectively bred color morph for those who just can’t choose between spots and stripes. Its sides are spotted about halfway down the body, at which point the spots condense into stripes. Hybrid danios are fairly new to the hobby. They can breed with either the Leopard or Zebra Danio, but offspring won’t stay true to the parent’s coloration.
• Golden Zebra Danio
  This gold color morph of the Zebra Danio has had the blue stripes bred out. This fish can sometimes be confused with the Pearl Danio Danio albolineatus, which is an entirely different species.
• Albino Zebra Danio
  This color morph is a naturally occurring phenomenon. As the name suggests, this variation has no pigments. Do not confuse it with the Pearl Danio.
• “Glo-fish”
  This little fish is a recently introduced Zebrafish (Danio rerio) genome. It has been genetically modified to sport fluorescent red, green, orange-yellow, blue and purple colorations. They also glow in the dark or under a black light. Their care does not vary from the natural Zebra Danio.

• Size of fish - inches: 2.4 inches (5.99 cm)
• Lifespan: 4 years - They have an average lifespan of about 3 1/2 years, though some have lived up to 5 1/2 years with proper care.

Fish Keeping Difficulty

The Zebra Danio is a great choice for beginning aquarists, and they are great companions in a community aquarium. These fish will eat just about anything that is offered as long as it floats at the surface where they can readily consume it. They tolerate water condition changes without too many issues and can even be kept without a heater.

• Aquarium Hardiness: Very Hardy
• Aquarist Experience Level: Beginner

Foods and Feeding

These fish are omnivorous, feeding mostly on a variety of worms, small crustaceans, and insect larvae in the wild. In the aquarium, they will eat most any prepared or live aquarium food, though it does need to float at the surface.. They enjoy chasing after tubifex worms, either living or freeze-dried. These fish will do best when offered food several times a day, but 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 easy to care for provided their water is kept clean. Aquariums are closed systems, and regardless of size, all need some maintenance. Over time, decomposing organic matter, nitrates, and phosphate build up, and water hardness increases due to evaporation. Replace 25 to 50% of the tank water at least once a month. If the tank is densely stocked, 20 to 25% should be replaced weekly or every other week.

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

Aquarium Setup

The Zebra Danio is a schooling species that will spend most of its time in the top and middle regions of the aquarium, particularly if there is open water or water current. This fish is fairly hardy and will adapt to most aquarium conditions. The waters they inhabit in the wild are acidic, but the stock now available in the hobby is many generations past this. Though a school of danios can be kept in a smaller aquarium, they will do best in about a 20-gallon size. Provide good filtration and keep the tank covered as these fish may jump.

These fish are most effectively displayed in tanks that simulate their natural habitat and bring out their colors. Use a dark, fine gravel or sand substrate, and provide a variety of plants to make them feel safe. Some good selections include Water Wisteria, Hornwort, and Java Moss. As with most Cyprinid fish, they are most at home in well-planted aquariums, but as these fish are extremely active swimmers, they also need some open areas for swimming.

• Minimum Tank Size: 10 gal (38 L)
• Suitable for Nano Tank: Yes
• Substrate Type: Any
• Lighting Needs: Moderate - normal lighting
• Temperature: 64.0 to 75.0° F (17.8 to 23.9° C)
• Range ph: 6.0-8.0
• Hardness Range: 2 - 20 dGH
• Brackish: No
• Water Movement: Weak
• Water Region: All - They will spend most of the time in the top and middle regions of the aquarium, particularly if there is open water or some current.

Social Behaviors

The lively Zebra Danio makes a good community fish. It will get along with its own kind and most other species. They are best kept in a school of 5 or more of their own kind. Groups of this fish can be hierarchal, and a pecking order may emerge in the school, but nothing will come of it. Select tankmates that are similar in temperament. You want tankmates that can keep up with the fast-paced lifestyle of this Danio. Mellower fish that need a less hectic environment can become stressed.

• Temperament: Peaceful - They are good community fish with other fast-moving tankmates.
• Compatible with:
  • Same species - conspecifics: Yes - They are best kept in groups of 5 or more.
  • Peaceful fish (): Safe - Tankmates need to be able to tolerate the lively nature of this species.
  • Semi-Aggressive (): Monitor
  • Aggressive (): Threat
  • Large Semi-Aggressive (): Threat
  • Large Aggressive, Predatory (): Threat
  • Slow Swimmers & Eaters (): Monitor - Large groups of Zebra Danios may make these fish nervous because of their activity level.
  • Shrimps, Crabs, Snails: Safe - not aggressive
  • Plants: Safe

Sex: Sexual differences

The females are generally more colorful while the males are more streamlined and slim.

Breeding / Reproduction

The Zebra Danios are very easy to breed, and it may even occur on accident. Two fish will form a breeding pair, which they often keep for life. If you wish to retain the young, the breeding tank should be empty except for a 2-inch layer of large glass marbles, 1/2 to 1 inch in diameter. Add the female to the tank, and let her settle for about a day before adding the male. When they are both in the tank, adding a few cups of cold water will cause the courtship to begin.

If conditions are favorable, the female will release her eggs in open water, and the male will fertilize. The eggs will then sink to the bottom and fall through the marbles, out of their parents' reach. The fry will emerge from the marbles after about 7 days. At that time or before, parents should either be removed or kept constantly well-fed. See the description of breeding techniques in Breeding Freshwater Fish: Barbs. Also, see Fish Food for Fry for information about types of foods for raising the young.

• Ease of Breeding: Easy

Fish Diseases

Zebra Danios are extremely hardy, so disease is not usually a problem in a well-maintained aquarium. They are primarily susceptible to Ich if good water quality is not provided. Anything you add to your tank can also bring disease. Not only other fish but plants, substrate, and decorations can harbor bacteria. Take great care and make sure to properly clean or quarantine anything that you add to an established tank 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 dealt with 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 more closely their environment resembles their natural habitat, the less stress the fish will have, making them healthier and happier. A stressed fish is more likely to acquire disease. For information about freshwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.

Availability

The Zebra Danio is inexpensive and readily available in stores and online.

References

• Animal-World References: Freshwater Fish and Plants
• Dr. Rudiger Riehl and Hans A. Baensch, Aquarium Atlas Vol. 1, Publisher Hans A. Baensch, 1991
• Joseph S. Nelson, Fishes of the World, Wiley, 2006.
• Glen S. Axelrod, Brian M. Scott, Neal Pronek, Encyclopedia Of Exotic Tropical Fishes For Freshwater Aquariums, TFH Publications, 2005
• David Alderton, Encyclopedia of Aquarium and Pond Fish , DK Publishing, Inc., 2005.
• Dick Mills, Aquarium Fish (101 Essential Tips), DK (Dorian Kinglsey) Adult, 2004.
• Dr. Herbert R. Axelrod, Aquarium Fishes of the World, TFH Publications, 1998
• Danio rerio (Hamilton, 1822) Zebra danio, Fishbase.org
• Danio rerio, The IUCN Red List of Threatened Species

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