Pink Salmon Spawning sequence 2-09

When the salmon are in the act of egg and milt release they open their mouths fully and quiver their bodies for the duration which lasts up to ten seconds. My theory on the open mouth gape is it is a way to more fully contract the muscles to aid in expelling the eggs and milt. It is also a signal to the males. When the female first opens her mouth that is when all the males rush in and start to release their milt.