- For the venomous Australian coral reef fish which is also known as zebrafish, see red lionfish.
The zebrafish or zebra danio, Danio rerio, is a tropical
fish belonging to the minnow family (Cyprinidae).[1] It is a popular aquarium fish, where it is frequently sold under the trade name zebra danio, and is also an important
model organism.
Taxonomy
The zebrafish is a derived member of the genus Danio.
It has a sister group relationship with Danio
kyathit.[2]
Distribution
The zebrafish is native to the streams of South-eastern Himalayan region.[2] The zebrafish arose in the Ganges region in Eastern India and is also native to Pakistan, Bangladesh, Nepal and
Myanmar. It commonly inhabits streams, canals, ditches, ponds and slow-moving to stagnant water bodies, including rice fields.
Zebrafish have been introduced in Japan and the
United States as well as Australia, where they are kept
in aquariums. [1]. They have also been sighted in Colombia, presumably having escaped from
an aquarium.
Description
The fish is named for its five uniform, pigmented, horizontal blue stripes on the side of the body, all of which extend to the
end of the caudal fin. 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. The zebrafish grows to 3.8 cm, lives
for around 5 years, and produces 300-500 eggs per spawning.
Varieties
Recently, transgenic zebrafish have become commercially available that express green fluorescent protein, red fluorescent protein, and
yellow fluorescent protein. These fish are tradenamed GloFish. Other varieties include leopard and longfin.
The Leopard danio, previously known as Danio frankeri, is a spotted colour morph of the zebrafish Danio rerio caused by a pigment mutation.[3] Xanthistic forms of both the
zebra and leopard pattern, along with long-finned varieties have
been obtained via selective breeding programs for the aquarium trade.[4]
Aquarium Care
Zebrafish are hardy fish and considered good for beginner aquarists. Their ease of keeping
and breeding, beauty, price and broad availability may all contribute to their popularity. They thrive best at temperatures above
22 degrees celsius and below 27 degrees celsius. They also thrive as shoals of 6 or more, although they do interact well with
other fish types in the Aquarium. However, they are susceptible to Oodinium, or
Velvet disease, Microsporidia
(Pseudoloma neurophilia),and mycobacterium species.
Model organism for development and genetics
D. rerio are a common and useful model organism for studies of vertebrate development and gene function.[2] They may supplement or replace higher vertebrate models, such as rats and mice. Pioneering work
of George Streisinger at the University of Oregon established the zebrafish as a
model organism; its importance was consolidated by large scale forward genetic screens
(commonly referred to as the Tübingen/Boston screens). The scholarly journal Development devoted an issue to research using the fish in celebration of this landmark.
[2] An
online database of zebrafish genetic, genomic, and developmental information (ZFIN) has been established. D. rerio is one of the few species of fish to have been
flown into space (see Animals in space).
A Zebrafish Pigment Mutant. The mutant called bleached blond was produced by insertional
mutagenesis. The embryos in the picture are four days old. At the top is a wild-type embryo, below is the
mutant. The mutant lacks black pigment in the melanocytes because it fails to synthesise
melanin
properly.
Zebrafish embryonic development provides advantages over other vertebrate model
organisms. Although the overall generation time of zebrafish is comparable to that of mice,
zebrafish embryos develop rapidly, progressing from eggs to larvae in under three days. The embryos are large, robust, and
transparent and develop externally to the mother, characteristics which all facilitate experimental manipulation and observation.
[5] Their nearly constant size during early development
facilitates simple staining techniques, and drugs may be administered by adding directly to the
tank. Unfertilised eggs can be made to divide, and the two-celled embryo fused into a single cell, creating a fully
homozygous embryo.
A common reverse genetics technique is to reduce
gene expression or modify splicing in zebrafish using Morpholino antisense technology. Morpholino oligonucleotides are stable, synthetic macromolecules that contain the same bases as DNA or RNA; by binding
to complementary RNA sequences, they reduce the expression of specific genes. The
journal Genesis
devoted an issue to research using Morpholino oligos[3], mostly in D. rerio. Morpholino oligonucleotides can be injected
into one cell of a zebrafish embryo after the 32-cell stage, producing an organism in which gene expression is reduced in only
the cells descended from the injected cell. However, cells in the early embryo (<32 cells) are interpermeable to large
molecules[4], [5], allowing diffusion of Morpholinos between cells. A known problem with gene
knockdowns in zebrafish is that, because the genome underwent a duplication after the divergence
of ray-finned fishes and lobe-finned fishes, it is not always easy to silence the activity one of the two gene paralogs reliably due to complementation by the
other paralog.
Despite the complications of the zebrafish genome a number of attempts have also been made to
develop global platforms for analysis of both gene expression by microarrays and
also promoter regulation using ChIP-on-chip.
Zebrafish have the ability to regenerate fins, skin, the heart and the brain
(in larval stages). Zebrafish have also been found to regenerate photoreceptors and
retinal neurons following injury. The mechanisms of this regeneration are unknown, but are
currently being studied. Researchers frequently cut 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.
The results of genetic engineering in these fishes have been used to produce the Glofish, an
aquarium pet with fluorescent pigments. Other varieties include golden, sandy and long fin fish.
In December 2005, a study of the golden strain identified the gene responsible for the unusual pigmentation of this
strain as SLC24A5, a solute carrier that appears to be required for melanin production, and confirmed its function with a Morpholino knockdown.
The orthologous gene was then characterized in humans and a one base pair difference
was found to segregate strongly between fair skinned Europeans and dark skinned Africans. [6] This study featured on the cover of the academic journal
Science and demonstrates the power of zebrafish as a model organism in the relatively
new field of comparative genomics.
In January 2007, Chinese researchers at Fudan University raised genetically modified
fish that can detect estrogen pollution in lakes and rivers, showing environmental officials
what waterways need to be treated for the substance, which is linked to male infertility. Song Houyan and Zhong Tao, two
professors at Fudan's molecular medicine lab, spent three years cloning estrogen-sensitive genes and injecting them into the
fertile eggs of zebrafish. The modified fish turn green if they are placed into water that is polluted by estrogen[7].
On August 1, 2007, British researchers said they had successfully grown in the laboratory a type of adult stem cell found in the eyes of both fish and
mammals that develops into neurons in the retina.
In future, these cells could be injected into the eye as
a treatment for diseases such as macular
degeneration, glaucoma and diabetes-related
blindness, according to Astrid Limb of University College London's (UCL) Institute of
Ophthalmology.
Damage to the retina -- the part of the eye that sends messages
to the brain -- is responsible for most cases of sight loss.
"Our findings have enormous potential," Limb said. "It could help in all diseases where the
neurons are damaged, which is basically nearly every disease of
the eye."
Limb and her colleagues studied so-called Mueller glial cells in the eyes of people aged from 18 months to 91 years and found they were able to develop
them into all types of neurons found in the retina.
They were also able to grow them easily in the lab, they reported in the journal Stem Cells.
The cells have already been tested in rats with diseased retinas,
where they successfully migrated into the retina and took on the characteristics of the
surrounding neurons. Now the team is working on the same approach in humans.[8].
See also
References
- ^ Froese, R. and D. Pauly. Editors.. Danio rerio. FishBase. Retrieved on 2007-04-07.
- ^ a b c
- ^ Watanabe M, Iwashita M, Ishii M, Kurachi Y, Kawakami A, Kondo S, Okada N.
(2006) Spot pattern of leopard Danio is caused by mutation in the zebrafish connexin41.8 gene. EMBO Report.7:
893-897.
- ^ Mills D (1993) Aquarium Fish Harper Collins ISBN 0-7322-5012-9
- ^
Dahm, Ralf (2006), "The Zebrafish Exposed", American Scientist 94 (5): pp.
446-453
Further reading
- Danio rerio (TSN 163699). Integrated Taxonomic
Information System. Accessed on 12 November 2004.
- "Danio rerio".
FishBase. Ed. Ranier Froese and Daniel Pauly. October 2004 version. N.p.: FishBase,
2004.
- Lambert, Derek J (1997). Freshwater Aquarium Fish. Edison, New Jersey:
Chartwell Books, Page 19. ISBN 0-7858-0867-1.
- Sharpe, Shirlie. Zebra Danio. Your Guide to Freshwater Aquariums. Retrieved on December 15, 2004.
- Kocher, Thomas D et al.. Zebrafish, Vol. 2, #3, 2005 Roundtable Discussion- "Fish Models for Studying Adaptive Evolution and
Speciation,".
- The Zebrafish Information Network (ZFIN)
External links
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