We see fish yawn fairly often, but have to be in the right place at the right time to capture the behavior. In Papua New Guinea, this Lacy Rhinopias, a member of the scorpionfish family, was on the same coral head every day for a week so everyone had a chance to photograph it from every angle. Ned saw it yawn from a distance and knew he wanted that head-on shot, so he went back and sat for quite a while, waiting for the right moment to press the shutter button. This is how it usually happens – we see it from a distance then try to position ourselves for the shot and wait. Sometimes the fish will yawn again right away; sometimes it can take 30 minutes.
While we associate yawning in humans with boredom or sleepiness, I’ve heard a few different theories about why fish do it. One is that they are stretching their mouths to be ready to feed – kind of like flexing their muscles. Another is it is a sign of annoyance or warning, like “Hey you with the big camera – back off!”
While I was looking for information about fish yawning, I came across this cool site about yawning with everything you could ever want to know about the topic. It has a number of articles about yawning in fishes, including one that concludes it increases muscle tone, aiding in preparing the animal for action.
If you want to see yawning fish in action, check out this short video over at our Blenny Watcher YouTube channel: