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?Danio rerio
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Cypriniformes
Family: Cyprinidae
Genus: Danio
Species: D. rerio
Binomial name
Danio rerio
(Hamilton, 1822)
  • Barilius rerio
  • Brachydanio rerio
  • Cyprinus chapalio
  • Cyprinus rerio
  • Danio foankei
  • Danio lineatus
  • Nuria rerio
  • Perilampus striatus

The zebrafish, Danio rerio, is a tropical freshwater fish belonging to the minnow family (Cyprinidae) of order Cypriniformes.[1] It is a popular aquarium fish, frequently sold under the trade name zebra danio, and is an important vertebrate model organism in scientific research.

Taxonomy[edit | edit source]

The zebrafish are Cyprinidae with a derived member of the genus Danio. It has a sister group relationship with Danio kyathit.[2]

Zebrafish are closely related to the genus Devario, as demonstrated by a phylogenetic tree of close species. Figure 2. Phylogenetic relationships among danios.

Distribution[edit | edit source]

The zebrafish is native to the streams of the southeastern Himalayan region,[2] including the countries India, Pakistan, Bangladesh, Nepal, and Myanmar.[3] It arose in the Ganges region in Eastern India. It commonly inhabits streams, canals, ditches, ponds, and slow-moving to stagnant water bodies, including rice fields.[4]

Zebrafish have been introduced to parts of the United States, presumably by deliberate release or by escape from fish farms.[3] They have also been sighted in Colombia.

Description[edit | edit source]


A young zebrafish (Danio rerio)

The fish is named for the five uniform, pigmented, horizontal blue stripes on the side of the body, all of which extend to the end of the caudal fin. Its shape is fusiform and laterally compressed, with its mouth directed upwards. Males are torpedo-shaped and have gold stripes between the blue stripes; females have a larger, whitish belly and have silver stripes instead of gold. Adult females will exhibit a small genital papilla in front of the anal fin origin. The zebrafish can grow to Template:Convert/cmTemplate:Convert/test/A, although it is uncommon for them to grow past 4 cm in captivity. Life-span in captivity is around 2–3 years, although in ideal conditions, may extend to 5 years.[4]

Reproduction[edit | edit source]

The approximate generation time for the Danio is 3–4 months. A male must be present for ovulation and spawning to occur. Females are able to spawn at intervals of 2–3 days, laying hundreds of eggs in each clutch. Upon release, embryonic development begins; absent sperm, growth stops after the first few cell divisions. Fertilized eggs almost immediately become transparent, a characteristic that makes D. rerio a convenient research model species.[4] Development progresses rapidly. Precursors to all major organs appear within 36 hours of fertilization. Hatching takes place 48–72 hours after fertilization, depending on the embryo's internal conditions and the external temperature, ideally Template:C to F. Swimming and feeding behavior begin about 36 hours later. The sex of juveniles cannot be distinguished except by dissection, and sex determinants are not clearly understood.

Feeding[edit | edit source]

The zebrafish is omnivorous. It primarily eats zooplankton, insects and insect larvae, and phytoplankton. It can eat a variety of other foods, such as worms and small crustaceans if its preferred sources are not readily available.[4] Most Danios accept common food flakes and tubifex worms in the aquarium.

Strains[edit | edit source]

Recently, transgenic zebrafish have become commercially available that express green fluorescent protein, red fluorescent protein, and yellow fluorescent protein. They are tradenamed GloFish. Other subspecies include golden, sandy, longfin and leopard.

The leopard danio, previously known as Danio frankei, is a spotted colour morph of the zebrafish caused by a pigment mutation.[5] Xanthistic forms of both the zebra and leopard pattern, along with long-finned subspecies, have been obtained via selective breeding programs for the aquarium trade.[6]

Wild-type strains[edit | edit source]

The Zebra Fish Information Network[7] provides up-to-date information about current known wild-type (WT) strains of D. rerio. The most commonly found WT strains are: AB, TÜ, IN and WIK.

AB/C32 (AB/C32)
AB/Tuebingen (AB/TU)
C32 (C32)
Cologne (KOLN)
Darjeeling (DAR)
Ekkwill (EKW)

Hong Kong (HK)
India (IND)
Indonesia (INDO)
Nadia (NA)
Singapore (SING)

SJD/C32 (SJD/C32)
Tuebingen (TU)
Tupfel long fin (TL)
Tupfel long fin nacre (TLN)

Hybrids[edit | edit source]

Hybrids between different Danio species may be fertile: for example, between D. rerio and D. nigrofasciatus.[8]

See link for photos of hybrids: Figure 1. Danio pigment pattern diversity and phenotypes of D. rerio hybrids with other danios.

Aquarium care[edit | edit source]

Zebrafish are hardy fish and considered good for beginner aquarists. Their ease of keeping and breeding, beauty, price, playful nature and broad availability all contribute to their popularity. They thrive best in Template:Convert/-Template:Convert/test/A water. They need an aquarium of Template:Convert/USgalTemplate:Convert/test/A or more, and they do well in schools. They also thrive as shoals of six or more, and interact well with other fish types in the aquarium. However, they are susceptible to Oodinium or velvet disease, microsporidia (Pseudoloma neurophilia), and Mycobacterium species. Given the opportunity, adults eat hatchlings, which may be protected by separating the two groups with a net, breeding box or separate tank.

In scientific research[edit | edit source]

Zebrafish chromatophores, shown here mediating background adaptation, are studied by scientists

D. rerio is a common and useful model organism for studies of vertebrate development and gene function.[2] George Streisinger at the University of Oregon established its utility. Success with it in large scale forward genetic screens (commonly referred to as the Tübingen/Boston screens) consolidated its importance. The scholarly journal Development[9] devoted an issue[10] to research using it in celebration of this landmark. It has a dedicated online database of genetic, genomic, and developmental information, the Zebrafish Information Network (ZFIN). D. rerio is one of the few fish species to have reached space. They may supplement higher vertebrate models, such as rats and mice.

File:Zebrafish embryos.png

A zebrafish pigment mutant. The mutant called bleached blond was produced by insertional mutagenesis.[11] The embryos in the picture are four days old. At the top is a wild-type embryo, below is a mutant. The mutant lacks black pigment in its melanocytes because it fails to synthesize melanin properly.

Research with D. rerio has allowed advances in the fields of developmental biology, oncology,[12] toxicology,[13] reproductive studies, teratology, genetics, neurobiology, environmental sciences, stem cell and regenerative medicine,[14] and evolutionary theory.[8]

Attractive characteristics[edit | edit source]

Its greatest advantages for use as a model system include:

  • Fully-sequenced genome
  • Well understood, easily observable and testable developmental behaviors
  • Availability of well-characterized mutants

Other advantages:

  • Rapid embryonic development (progressing from eggs to larvae in under three days, although overall generation time is comparable to that of mice)
  • Large, robust, and transparent embryos that develop outside the mother[15]
  • Nearly constant size during early development facilitates simple staining techniques
  • Drugs may be administered by adding directly to the tank.
  • Unfertilized eggs can be made to divide
  • Two-celled embryo can be fused into a single cell, creating a homozygous embryo
  • Demonstrated similarity to mammalian models and humans in toxicity testing
  • Exhibits a diurnal sleep cycle with similarities to mammalian sleep behavior and physiology[16]

Regeneration[edit | edit source]

Zebrafish have the ability to regenerate fins, skin, the heart[17] and the brain (in larval stages). Heart muscle regeneration does not make use of stem cells; instead, mature heart muscle cells regress to a stem-cell-like state and redifferentiate.[17] In 2011 the British Heart Foundation ran an advertising (including on television and online) campaign publicising their intention to study the applicability of this ability to humans by "spend[ing] £50 million on a programme of groundbreaking research that could help us begin to repair damaged [human] hearts."[18]

Zebrafish have also been found to regenerate photoreceptor cells and retinal neurons following injury. The mechanisms of this regeneration are unknown. Researchers frequently amputate the dorsal and ventral tail fins and analyze their regrowth to test for mutations. This research is leading the scientific community in the understanding of healing/repair mechanisms in vertebrates. It has also been found if the same fin is damaged enough times, the fish will grow a new fin which will have mutated only a small amount. Most scientists believe this is a defence mechanism to try to prevent the fin from being damaged again.[citation needed]

In medical research[edit | edit source]

In cardiovascular research the zebrafish is being used to model blood clotting, blood vessel development, heart failure, and [[congenital heart defect|

Repairing retinal damage[edit | edit source]

In 2007, researchers at University College London grew a type of zebrafish adult stem cell found in the eyes of fish and mammals that develops into neurons in the retina—the part of the eye that sends messages to the brain. These cells could be injected in the eye to treat diseases that damage retinal neurons—nearly every disease of the eye, including macular degeneration, glaucoma, and diabetes-related blindness. Retinal damage is responsible for most cases of sight loss. The researchers studied Müller glial cells in the eyes of humans aged from 18 months to 91 years and were able to develop them into all types of retinal neurons. They were able to grow them easily in the lab. The stem cells successfully migrated into diseased rats' retinas and took on the characteristics of the surrounding neurons. The team is working on the same approach in humans.[19]

See also[edit | edit source]

References[edit | edit source]

  1. Template:FishBase species
  2. 2.0 2.1 2.2 Mayden, Richard L., Tang, Kevin L.; Conway, Kevin W.; Freyhof, Jörg; Chamberlain, Sarah; Haskins, Miranda; Schneider, Leah; Sudkamp, Mitchell; Wood Robert M.; Agnew, Mary; Bufalino, Angelo; Sulaiman, Zohrah; Miya, Masaki; Saitoh, Kenji; He, Shunping (2007). Phylogenetic relationships of Danio within the order Cypriniformes: a framework for comparative and evolutionary studies of a model species. J. Exp. Zool. (Mol. Dev. Evol.) 308B (5): 642–654.
  3. 3.0 3.1 USGS NAS - Nonindigenous Aquatic Species
  4. 4.0 4.1 4.2 4.3 Spence R, Gerlach G, Lawrence C, Smith C (February 2008). The behaviour and ecology of the zebrafish, Danio rerio. Biological Reviews 83 (1): 13–34.
  5. Watanabe M, Iwashita M, Ishii M, et al. (September 2006). Spot pattern of leopard Danio is caused by mutation in the zebrafish connexin41.8 gene. EMBO Rep. 7 (9): 893–7.
  6. Mills, Dick (1993). Eyewitness Hnbk Aquarium Fish, Harper Collins.
  7. ZFIN
  8. 8.0 8.1 Parichy, DM (September 2006). Evolution of danio pigment pattern development. Heredity 97 (3): 200–210.
  9. Development journal
  10. (December 1996). Zebrafish issue. Development 123 (1).
  11. See link for pigmentation mutants of D rerio: Figure 5. Pigment pattern mutants within D. rerio. Mutant names are shown along with gene identities in parentheses when known. For example, the picasso phenotype results from mutations in errb3
  12. Xiang J, et al. (February 2009). Identifying Tumor Cell Growth Inhibitors by Combinatorial Chemistry and Zebrafish Assays. PLoS ONE 4 (2): e4361.
  13. Hill AJ, Teraoka H, Heideman W & Peterson RE (July 2005). Zebrafish as a Model Vertebrate for Investigating Chemical Toxicity. Toxicological Sciences 86 (1): 6–19.
  14. Major RJ, Poss KD (2007). Zebrafish heart regeneration as a model for cardiac tissue repair. Drug Discov Today Dis Models 4 (4): 219–225.
  15. (2006). The Zebrafish Exposed. American Scientist 94 (5): 446–453.
  16. Jones, Rachel (16 October 2007), "Let Sleeping Zebrafish Lie: A New Model for Sleep Studies", PLoS Biology (Public Library of Science) 5 (10): e281, doi:10.1371/journal.pbio.0050281, PMID 20076649, PMC: PMC2020498,, retrieved on 27 March 2011 
  17. 17.0 17.1 includeonly>Wade, Nicholas. "Research Offers Clue Into How Hearts Can Regenerate in Some Species", New York Times, March 24, 2010. Retrieved on March 29, 2010.
  19. Zebra fish may point way to cure for blindness The China Post Friday, August 3, 2007.

Further reading[edit | edit source]

  • Lambert, Derek J (1997). Freshwater Aquarium Fish, 19, Edison, New Jersey: Chartwell Books.
  • Sharpe, Shirlie. Zebra Danio. Your Guide to Freshwater Aquariums. URL accessed on December 15, 2004.
  • Kocher TD, Jeffery WR, Parichy DM, Peichel CL, Streelman JT, Thorgaard GH (2005). Special feature--roundtable discussion. Fish models for studying adaptive evolution and speciation. Zebrafish 2 (3): 147–56.
  • The Zebrafish Information Network (ZFIN)
  • Bradbury J (2004). Small Fish, Big Science. PLoS Biology 2 (5): 568–72.

External links[edit | edit source]

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