Fellowship of the fin: Fish empathy and oxytocin.

Zebrafish exhibit fear contagion, a basic form of empathy, and when observing social fellows that have been exposed to predation cues, will themselves exhibit similar distress behaviours. As in mammals, the nonapeptide hormone oxytocin is essential for this empathic response, and homologous areas of the brain are involved, suggesting that the mechanistic basis of empathy may be conserved among vertebrates.