Zebrafish
The zebrafish, Danio rerio, is a tropical freshwater fish belonging to the minnow family (Cyprinidae) of order Cypriniformes. It is a popular aquarium fish, frequently sold under the trade name zebra danio, and is an important vertebrate model organism in scientific research. It is particularly notable for its regenerative abilities.
Taxonomy
The zebrafish is a derived member of the genus Danio, of the family Cyprinidae. It has a sister-group relationship with Danio kyathit. Zebrafish are also closely related to the genus Devario, as demonstrated by a phylogenetic tree of close species. The zebrafish was referred to in literature as Brachydanio rerio for many years until its reassignment to the genus Danio.
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| Zebrafish |
image source: http://www.flickr.com/photos/buymelunch/
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| Zebrafish |
image source: http://www.flickr.com/photos/buymelunch/
Distribution
The zebrafish is native to the streams of the southeastern Himalayan region, and is found in parts of India, Pakistan, Bangladesh, Nepal, and Burma. The species arose in the Ganges region in eastern India, and commonly inhabits streams, canals, ditches, ponds, and slow-moving or stagnant water bodies, including rice fields. Zebrafish have been introduced to parts of the United States, presumably by deliberate release or by escape from fish farms.
Description
The zebrafish is named for the five uniform, pigmented, horizontal, blue stripes on the side of the body, which are reminiscent of a zebra's stripes, and which extend to the end of the caudal fin. Its shape is fusiform and laterally compressed, with its mouth directed upwards. The male is torpedo-shaped, with gold stripes between the blue stripes; the female has a larger, whitish belly and 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 6.4 cm (2.5 in) in length, although it seldom grows larger than 4 cm (1.6 in) in captivity. Its lifespan in captivity is around two to three years, although in ideal conditions, this may be extended to five years.
Reproduction
The approximate generation time for Danio rerio is three to four months. A male must be present for ovulation and spawning to occur. Females are able to spawn at intervals of two to three 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. Development progresses rapidly – precursors to all major organs appear within 36 hours of fertilization, and hatching takes place 12–36 hours later, depending on the embryo's internal conditions and the external temperature, which is ideally 28.5 °C (83.3 °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.
To encourage the fish to spawn, some researchers use a fish tank with a sliding bottom insert, which reduces the depth of the pool. The technique is most effective in the early morning, given that ovulation and spawning are enhanced by light. Researchers have been able to collect 10,000 embryos in 10 minutes using this method.Male zebrafish are furthermore known to respond to more pronounced markings on females, i.e., "good stripes", but in a group, males will mate with whichever females they can find. What attracts females is not currently understood. The presence of plants, even plastic plants, also apparently encourages spawning.
To encourage the fish to spawn, some researchers use a fish tank with a sliding bottom insert, which reduces the depth of the pool. The technique is most effective in the early morning, given that ovulation and spawning are enhanced by light. Researchers have been able to collect 10,000 embryos in 10 minutes using this method.Male zebrafish are furthermore known to respond to more pronounced markings on females, i.e., "good stripes", but in a group, males will mate with whichever females they can find. What attracts females is not currently understood. The presence of plants, even plastic plants, also apparently encourages spawning.
Feeding
The zebrafish is omnivorous. It primarily eats zooplankton, insects, insect larvae, and phytoplankton, although it can eat a variety of other foods, such as worms and small crustaceans, if its preferred sources are not readily available. Most zebrafish accept common food flakes and tubifex worms in the aquarium.
Aquarium care
Zebrafish are hardy fish and considered good for beginner aquarists. Their enduring popularity can be attributed to their playful disposition, as well as their rapid breeding, aesthetics, cheap price, and broad availability. They thrive best in water temperatures of 22–28 °C (72–82 °F), and require an aquarium volume of at least 10 US gallons (38 L). They also do well in schools or shoals of six or more, and interact well with other fish species 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.
Strains
In late 2003, transgenic zebrafish that express green, red, and yellow fluorescent proteins became commercially available in the United States. The fluorescent strains are tradenamed GloFish; other cultivated varieties include 'golden', 'sandy', 'longfin' and 'leopard'.
The leopard danio, previously known as Danio frankei, is a spotted colour morph of the zebrafish which arose due to a pigment mutation. 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.
The leopard danio, previously known as Danio frankei, is a spotted colour morph of the zebrafish which arose due to a pigment mutation. 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.