Zebrafish is an ideal model organism to study adult neurogenesis. New neurons are born in various parts of zebrafish brain all through its lifespan. Analyzing neuron renewal in adult brain provides a valuable insight into neurodegenerative diseases. Bromodeoxyuridine (BrdU) is a thymidine analog and it incorporates into the DNA only if the cells are at S-phase. BrdU labeling is a reliable method to locate the cells that are actively dividing. Here we describe the steps required for BrdU labeling in adult zebrafish brain starting from BrdU injection to the final analysis in the microscope. We utilize a paraformaldehyde fixation, vibratome slicing, fluorescent labeling of incorporated BrdU and finally confocal imaging.
For a thorough coverage on the topic zebrafish neurogenesis, readers are referred to  from which this protocol is adapted. A protocol on diverse applications of BrdU labeling can be found in protocol series by Jackson and Cook   .