Recognizing and remembering another individual in a social context could be beneficial for individual fitness. Especially in agonistic encounters, remembering an opponent and the previous fight could allow avoiding new conflicts. Considering this, we hypothesized that this type of social interaction forms a long-term recognition memory lasting several days. It has been shown that a second encounter 24 hours later between the same pair of zebrafish males is resolved with lower levels of aggression. Here, we evaluated if this behavioral change could last for longer intervals and a putative mechanism associated with memory storage: the recruitment of NMDA receptors. We found that if a pair of zebrafish males fight and 48 or 72 hours later fight again, they resolved the second encounter with lower levels of aggression. However, if immediately after the first encounter opponents were exposed to MK-801 (NMDA receptor antagonist), they resolve the second one with the same levels of aggression, that is, no reduction in aggressive behaviors was observed. These results suggest the formation of a long-term social memory related to recognizing a particular opponent and/or the outcome and features of a previous fight.