Behavioral criteria and techniques to define sleep in zebrafish

Sleep is an essential physiological state in the animal kingdom including humans. Sleep benefits the brain in varied levels ranging from maintenance of single cells to plasticity of neuronal networks, memory, and learning. While in mammals, birds, and some reptiles, sleep can be defined by electroencephalography and behavior, in other species, including fish, primarily behavioral criteria have been traditionally used to define sleep. The zebrafish is the leading fish model used to study the mechanisms of sleep. Here, we review the behavioral criteria and methods to define sleep in zebrafish adults and larvae. The advantages and limitations of each criterion, and potential additional tools to define sleep are discussed.