<P> The zebrafish is a derived member of the genus Danio, of the family Cyprinidae . It has a sister - group relationship with Danio aesculapii . Zebrafish are also closely related to the genus Devario, as demonstrated by a phylogenetic tree of close species . The zebrafish was referred to in scientific literature as Brachydanio rerio for many years until its reassignment to the genus Danio . </P> <P> The zebrafish is native to the streams of the southeastern Himalayan region, and is found in parts of India, Pakistan, Bangladesh, Nepal, and Myanmar . 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 are most commonly found in low flow streams that has sandy substrates . Zebrafish have been introduced to parts of the United States, presumably by deliberate release or by escape from fish farms . </P> <P> 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 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 over five years . </P> <P> The approximate generation time for Danio rerio is three 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 . </P>

What is the size of the largest zebrafish