SCIENTIFIC NAME Danio rerio

Taxonomy PHYLUM: Chordata CLASS: Actinopterygii ORDER: Cypriniformes FAMILY: Cyprinidae

Physical description

Credit: Katie Vicari

The zebrafish is a freshwater fish belonging to the minnow family and named for the distinctive pigmented stripes that span the length of its body and broaden to the end of the caudal fin. Males have alternating golden and blue stripes, while females have silver stripes. The fish has a laterally condensed shape with its mouth pointed upwards, and although individuals can grow up to 6.5 cm in length, their usual length is 4 cm. Zebrafish typically live for 2–4 years but may have a lifespan of up to 6 years.

Reproduction and life cycle

In addition to being a common aquarium fish, the zebrafish is also an important vertebrate model organism in research. As early as the 1930s, the zebrafish was being used as a model for studies of development1, largely due to its short production time of approximately 3–4 months. Mature females can reproduce every 203 d, laying hundreds of eggs at a time. All major organs appear within 36 h of fertilization, and hatching takes place 12–36 h later. Another advantage of the zebrafish is the transparency of embryos and larvae, which permits real-time imaging of pathologies as they develop1.

Research résumé

Zebrafish models of a wide variety of human diseases have been generated using genetic methods. One major area of study is the biological processes associated with pigmentation. Recent studies have focused on using the striped pattern of zebrafish as a model for the investigation of mechanisms of animal pigmentation2. The zebrafish pigment pattern is generated by a combination of different pigment cell types (or chromatophores), including melanophores, xanophores and iridophores3. Molecular genetic studies suggest that the interactions between the different types of pigment cells play a key role in stripe formation4. The migratory pathways of the three cell types are differentially regulated, and disruption of any of these pathways can contribute to variations in pigment pattern and colors3.

Many genes related to the pigmentation of zebrafish and the formation of skin patterns have been identified and characterized through the generation of mutant strains. These strains can diverge widely in appearance, from the spotted leopard and dali to the thickly striped obelix. Golden is a light-colored mutant that has provided new insight into the genetic basis of pigmentation differences in humans1. The golden phenotype in zebrafish, as well as the light-skinned phenotype in humans, is associated with a smaller number, a smaller size and a lower pigment density of melanosomes (melanin-containing organelles). A single polymorphism in SLC24A5, the human version of the gene affected by the golden mutation, contributes to 25–38% of the difference in skin color between Africans and Europeans5.

The pigment cells of vertebrates are also implicated in human pathologies, including melanoma, one of the most common and most deadly cancers that is caused by the transformation of melanocytes (melanin-producing cells). Melanophores in zebrafish and melanocytes in humans depend on many of the same genes and pathways, and melanomas with characteristics equivalent to those of human melanomas can be induced in zebrafish in order to study the disease6.