Ritualized morning interactions, called greeting, were investigated for a natural population of the monogamous pipefish Corythoichthys haematopterus. Every morning, pair members moved to a fixed site in their overlapped home ranges within an hour of sunrise to engage in greetings for a few minutes. After the greetings, they separated and each returned to its original site. On the day of spawning, the behavioural pattern of greetings differed from that on the other days and exchanged displays intermittently until spawning, which occurred 1-3 h after sunrise. In the field experiment where either of pair members was isolated in a cage for a day, the temporarily mate-losing fish (called resident fish) approached an unpaired fish of the opposite sex, which was released at the greeting site next morning, but thereafter few interactions occurred between them. In contrast, when the partner was released after the withdrawal of the unpaired fish, the resident fish immediately approached it and they exchanged greetings. This fact suggests that each individual discriminates its partner from others. The function of daily greetings in this pipefish is discussed from aspects of the reproductive synchronization of a pair and the maintenance of monogamy without mate guarding.
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