The zebrafish (Danio rerio) used in the laboratory is derived from wild type zebrafish native to the subtropical waters of South-East Asia. Knowledge about the animal’s natural environment and life style provides information on optimal zebrafish housing conditions.

Zebrafish are freshwater fish that belong to the carp family. Their natural habitat consists of bodies of (1) stagnant or barely-moving water that are relatively clear (visibility > 30 cm) and shallow (depth cm – 100 cm); (2) frequently inundated by monsoon rains and/or irrigation, such as rice fields; (3) with overhanging vegetation and aquatic plants; and (4) a bed of clay loam, mud, rock and/or gravel. Zebrafish will tolerate a very wide range of temperatures (depending on season and location) from 6 to 38 degrees Celsius. The tolerated pH value of the water ranges from slightly acidic (pH 5.9) to slightly basic (pH 8). 

There exist a great many zebrafish lines, e.g. AB, Tübingen (TU), Tupfel Long Fin (TL), leopard and albino (figures 1 to 5). All these lines are genetically, morphologically, physiologically and behaviourally distinct. Research makes use of both adult zebrafish and embryos and larvae.

The figures to the right show examples of a male and a female from two different zebrafish lines. The female has a distended abdomen, filled with eggs. TL fish have long fins and a spotted skin pattern, rather than a striped one. Both changes are the result of spontaneous mutations. The TL line is used frequently because of its high egg production. Figure 5 shows a male and female fish from an albino line (an unpigmented fish), swimming.

The Humane Endpoints team has compiled a 'white paper' with a wealth of information on zebrafish: lifestyle, lab animal husbandry, common diseases and humane endpoints. The present website contains the key elements of this white paper. The white paper can be requested by sending an E-mail to This white paper is only avalable in Dutch.

Furthermore, more information about various zebrafish abnormalities and their severity can be found on the following website.


Figure 1. AB female


Figure 2. AB male


Figure 3. TL female


Figure 4. TL male


Figure 5. Albino male and female, swimming