Monogamy

                                           Monogamy is a mating system where partners live and exclusively mate with only each other. These pair bonds can be transitory, just for a single breeding season, extend for several years or even a lifetime. Fish that form strong pair bonds include: American freshwater catfish, some cichlids, and many butterflyfish. The Four-Eyed Butterflyfish (Chaetodon capistratus) is one such fish that mates for life – very rare in the fish world. (fishionary.fisheries.org/monogamy)

Four-eye butterfly fish mate for
life