The Zebrafish (Danio rerio) is a tropical fish belonging to the minnow family (Cyprinidae). It is a popular aquarium fish, where it is frequently sold under the trade name Zebra danio, and is also an important model organism.
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.
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 1.5 in (3.8 cm), lives for around 5 years, and produces 300-500 eggs per spawning.
Recently, transgenic zebrafish have become commercially available that express green fluorescent protein or red fluorescent protein. Other varieties include leopard and longfin.
The Leopard danio, previously known as Danio frankeri, is a spotted color morph of the zebrafish Danio rerio caused by a pigment mutation. 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.
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. However, they are susceptible to Oodinium, or Velvet disease, Microsporidia (Pseudoloma neurophilia),and mycobacterium species.
Zebrafish as an introduced species
Zebrafish have been introduced and become established in Japan and the United States. They have also been sighted in Colombia, presumably having escaped from an aquarium.
Model organism for development and genetics
D. rerio are a common and useful model organism for studies of vertebrate development and gene function. 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 genetic screens (commonly referred to as the TÃ¼bingen/Boston screens). The scholarly journal Development devoted an issue to research using the fish in celebration of this landmark. D. rerio is one of the few species of fish to have been flown into space.
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, transparent and develop externally to the mother, all of which facilitate experimental manipulation and observation. Their nearly constant size during early development facilitates simple staining techniques, and drugs may be administered by adding directly to the tank. Unfertilized eggs can be made to divide, and the two-celled embryo fused into a single cell, creating a fully homozygous embyo.
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. 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.