Vibrational communication during spawning behavior in the himé salmon (landlocked red salmon,Oncorhynchus nerka)

Summary Sexual behaviors of the salmon are composed of a stimulus-reaction chain, which ensures synchronous spawning between the sexes and successful fertilization. To characterize the signals involved in such a stimulusreaction chain, the body vibration and electromyographic activity of the trunk muscles during spawning were simultaneously recorded from freely behaving male and female pairs of himé salmon (landlocked red salmon,Oncorhynchus nerkd) and were analyzed in combination with a videographic analysis of behavior sequences. The results showed that the himé salmon have an elaborate communication system in which characteristic vibrational signals are exchanged. These are produced by body vibration due to trunk muscle activity related to spawning and are transmitted between the sexes with an accurate timing through the stimulus-reaction chain. They act as timing cues to synchronize gamete release and are thought to be shared among a wide variety of fishes. It was hypothesized that the lateral line sense is involved in the detection of these vibrational signals. Furthermore, based on the sequence matrix analysis as well as on information theory, intersexual behavioral sequences during spawning were analyzed statistically. The results showed that statistically significant interactions occur between the sexes and statistically significant amounts of information are transmitted through the interactions, supporting the results from recording experiments mentioned above. Characters of the signalling system and possible origins of the vibrational signals are also discussed.