Human society is cooperative and characterized by spontaneous prosociality. Comparative studies on endotherm vertebrates suggest that social interdependence causes the evolution of proactive prosociality. To test the generality of this hypothesis, we modified a prosocial choice task for application to the convict cichlid, Amatitlania nigrofasciata, a monogamous fish with biparental care and a strong pair bond. We show that subject males learned to favor prosocial choices when their mates were the recipients in neighboring tank. When the neighboring tank was empty, males chose at random. Furthermore, in the absence of their mates, males also behaved prosocially towards a stranger female. However, if the subjects’ mate was also visible in a third tank, or if a male was the potential recipient, subjects made antisocial choices. In conclusion, fish may show both spontaneous prosocial and antisocial behaviors, according to their social relationships with conspecifics and the overall social context.