Evolutionarily conserved role of oxytocin in zebrafish social reward encoding

Social rewards may have evolved in social species to reinforce adaptive social interactions. Yet, evidence for social rewards is still scarce, and the underlying mechanisms remain unclear. A key candidate to regulate the value of social stimuli is oxytocin due to its role in social affiliation, which is traced to its origins in ray-finned fish-but whether it encodes rewards is uncertain. Using a single-trial conditioned place preference test, we found that wild-type zebrafish increased preference for a neutral unpreferred cue associated with a same-sex sibling, while oxytocin receptor (oxtr) mutants did not. These findings demonstrate the necessity of oxtr for social rewards, while the short exposure infers its role in encoding rather than consolidation. Our results provide evidence for an evolutionarily conserved role of oxytocin in social reward encoding given the available evidence for similar effects in rodents.