Zebrafish (Danio rerio) is a freshwater fish belonging to the minnow family of the order Cypriniformes. Native to South Asia, zebrafish has been widely introduced into tropical and temperate aquaculture systems around the world. A hardy species, zebrafish is able to tolerate a wide range of environmental conditions and is therefore well-suited for use in scientific research. Zebrafish are frequently used as model organisms in developmental biology, toxicology and disease models due to their rapid life cycle, external fertilization and transparency at key stages of development.
First described by Francis Buchanan-Hamilton in 1822, zebrafish are named for their distinctive striped patterning. Adult zebrafish typically reach a length of 4-6 cm (1.6-2.4 inches), with males being slightly larger than females on average. The body of the zebrafish is compressed laterally, with a small head and large eyes that are positioned laterally on the skull. The mouth is located at the tip of the snout and contains small teeth arranged in rows on both jaws. The dorsal fin extends along almost the entire length of the body, while the anal fin is shorter and located closer to the tail end. The caudal peduncle –the narrow region connecting the tail fin to rest of body–is particularly slender in zebrafish compared to other fish species.
The coloration of zebrafish varies depending on genetic background and environmental conditions; however, adults typically display dark vertical stripes against a light brown or golden background coloration (hence their common name). Juvenile zebrafish lack this stripe pattern and instead have a uniform silver coloration with pale yellow fins; they develop stripes as they mature into adults over a period of 10-14 days following hatching from eggs .
Zebrafish are found in freshwater habitats throughout South Asia including Pakistan, India, Nepal, Bangladesh and Myanmar . Within this region they inhabit rivers, streams , canals , ponds , lakes and wetlands . In recent years there has been an increasing number of reports detailing sightings of wild zebrafish outside their natural range in countries such as Japan , Korea and Singapore . It is thought that these individuals were most likely released accidentally or deliberately into local waterways by aquarium owners . ZebraFish have also been successfully introduced into several other continents including Europe , Australia and North America where they have established populations in certain areas . However it should be noted that releases of non – native species can often cause problems for local ecosystems so care should be taken before doing this .