While out today i noticed alot of the bass i could see occasionally 'yawning' theyd hold their mouths open very wide for a second or two then close them and flare their gills. I dont think bass yawn so what are they doing when they do this? I know its irrelevant to fishing for them but the biologist in me is curious. Any thoughts?

They might be stretching there jaws if they haven't been that aggressive and feeding that much, but that is a very good question.

,Bill

If they were just suspending there all chill id imagine they were just getting water flow through em.

If moving, well, maybe they found the worlds largest plankton

they were breathing i believe. the only time ive seen bass do that were when they were suspended. or possibly it has something to do with the "bladder" or whatever it is that allow fish to sit still and suspend like that, as some species of fish i believe have to swim nonstop.

Yup. They do that a lot. Especially with my baits  .

I think they like to occasional stretch out their jaw and gill muscles.

I've seen it a few times myself while out, but never did any research on it. 

Last time I was out they were snoring zzzzzzzzzzzzzzzzzzzzzzzzzzzzzz

Yawning has been observed by anglers, divers, and fish behavior researchers and almost all the observations I'm aware of surround oxygen intake and activity level. In this way it is a true yawn and bodes well for nearby anglers . 

I think it was Doug Hannon who documented bass doing this prior to becoming more active & feeding.

I had bass in an aquarium and it looked like yawning to me .

Maybe they were watching the Golf Channel.LOL

I see this a lot. Why they do it? I don't know. Every time I see this happen however is when I see a big bass and the same bass sees me. Instead of swimming off, the bass yawns with its mouth really wide showing me what I am missing. Then the fish swims off. 

I see this a lot. Why they do it? I don't know. Every time I see this happen however is when I see a big bass and the same bass sees me. Instead of swimming off, the bass yawns with its mouth really wide showing me what I am missing. Then the fish swims off.

Fwiw every bass that i saw yawning i could not get to bite. One was a large female on a nest and the others were smaller, not on nests. I even saw a few 6-8 inchers doing this. The funny thing is, i didnt even see some of the fish until they yawned. The whites of their mouths and gills gave them away.