We describe the basic biology of the Danio rerio experimental system. We summarize embryonic development and how it can be used to study early developmental processes. We describe different basic genetic techniques available in this model organism, including mutagenesis, transgenesis and gene editing. We study different systems to control gene expression by either Morpholinos, RNA injection or transgenesis like Gal/UAS. We present different examples of the use of this organism in cancer and systems (memory and behavior) research. JG