A recent study of the monogamous pipefish Corythoichthys haematopterus by Japanese scientists has indicated that the members of a mate pair are capable of discriminating their partners from other conspecifics.
Publishing their results in the latest issue of the Journal of Fish Biology, Atsushi Sogabe and Yasunobu Yanagisawa of Ehime University in Japan studied breeding pairs of Corythoichthys haematopterus, a species of monogamous pipefish inhabiting shallow waters of the Indo-Pacific.
Individuals of this species reside within home ranges, with those of a pair always overlapping with its partner s and several other conspecifics.
Only pair members exchanged greetings (ritualized displays) every day, mostly within an hour of sunrise, and at a site close to the spawning site.
The greetings lasted 1-3 minutes and started significantly sooner on the day of spawning than on other days.
The greeting process consists of "approach" (one fish rapidly approaching the other to assume a parallel position), "parallel swim" (both fishes swimming forward in a close parallel formation), "cross" (one fish crossing abruptly over or under the other), "arch" (one or both fishes arching the body to lift the abdomen upwards) and "up" (one fish lifts off from the substratum and orients itself vertically to the other) phases.
The researchers next experimentally removed one member of the mate pair and introduced an unpaired fish of the opposite sex and found that the resident (mate-losing) fish approached the newcomers, but ignored them hereafter.
When the missing mate was reintroduced, both fish immediately approached each other and initiated greetings.
The greeting process, which is common to monogamous syngnathids of the genera Hippocampus and Corythoichthys, is thought to function in synchronizing the reproductive cycle of the pair and to maintain pair bonding.
By synchronizing the reproductive cycle, the non-brooding interval between the hatching of a brood (the eggs are carried by the male until they hatch and the male cannot mate in the meantime) and remating; this enhances the reproductive efficiency of the pair.
For more information, see the paper: Sogabe, A and Y Yanagisawa (2007) The function of daily greetings in monogamous pipefish Corythoichthys haematopterus. Journal of Fish Biology 71, 585-595.