In the lecture, first, mammalian sleep-related spontaneous neural events will be discussed. Second, sleep in zebrafish, and zebrafish neuroanatomy, will be briefly reviewed and, third, the presence of spontaneous neural activity in zebrafish is described. It is suggested t hat this activity is the zebrafish homologue of hippocampal sharp waves. Spontaneous neural activity is argued to be instrumental in the formation and maintenance of neural circuits. In mammals, spontaneous activity is observed in the spinal cord, brainstem, diencephalon, and neocortex, but has been most extensively studied in the hippocampus and is prominent during slow-wave sleep. Using whole-brain in vitro recordings the presence of spontaneous activity in the zebrafish telenchephalon is established. Only two areas exhibit spontaneous activity: The entopeduncular nucleus (EN) and (more prominently) the anterodorsal lobe (ADL). Interestingly, the ADL is part of the lateral telencephalic pallium, an area hypothesized to be functionally equivalent to the mammalian hippocampus. The EN, however, has been hypothesized to be equivalent to the mammalian basal ganglia. The spontaneous activity is GABA modulated and sensitive to glutamate and chloride transporter antagonists and is abolished by sodium pump blockers; moreover, the spontaneous activity is a slow (approximately 100 ms) multiband event that is characterized by an embedded fast ripple (approximately 200 Hz). Thus, the spontaneous activity shares neuroanatomical and physiological features with hippocampal sharp waves in rodents. We suggest that this activity is homologous to hippocampal sharp waves and is important for the formation and maintenance of neural circuits in zebrafish; moreover, we argue that applying techniques unique to the fish may open novel routes to understand the function of spontaneous activity.