zebrafish

Zebrafish (Danio rerio) are small freshwater fish native to rivers and floodplains of South Asia, notably the Ganges region. They are widely used as a vertebrate model organism in biology and biomedicine because of their transparent embryos, rapid development, and well-characterized genetics.

Adults reach about 2.5 to 4 cm in length. They reproduce by external fertilization: females lay hundreds of eggs that are fertilized externally and develop outside the mother. Embryogenesis is rapid; embryos are transparent, allowing direct observation of developing organs. Most organs form during the first week after fertilization. Zebrafish reach sexual maturity in about 2 to 3 months, and a single pair can produce thousands of offspring per year under optimal conditions. The genome has been sequenced, and about 70% of human disease genes have a zebrafish counterpart. A range of genetic tools is available, including CRISPR/Cas9, TALENs, morpholinos, and transgenic lines to label or modify tissues.

In research, zebrafish are used for development, organogenesis, genetics, neuroscience, toxicology, cancer biology, and drug screening. They are also used in education. Husbandry involves freshwater aquaria at 26-28°C, with filtration and a regular light cycle; they are social and kept in groups.

While they share many features with humans, there are notable differences; not all human genes have equivalents, and some organ systems differ. Nonetheless, zebrafish offer rapid development, external embryos, and genetic tractability, making them a widely used vertebrate model.