Last night i sat by my betta tank and i saw my lit'l vaio 'yawning'...
what was he doing actually? is it something wrong with the water condition that made him yawn like that?
It might be the first signs of parasites in it's gills or throat. Keep a close eye on it. Do some research on disease sites and be ready if it continues.
yawning can be a sign of toxins in the water, trying to clear parasites from the gills or just plain old tired. try checking the parameters of the water for ph,nitrites,nitrates and ammonia. if you have any ornaments that decay could be forming move them around and do a gravel wash if you have any.
Most of my fish yawn from time to time and there's nothing wrong with any of them (except for naughty little Ruya'il who keeps gnawing on his tail,) so I wouldn't be to worried about it. I'd check the water, though, just to make sure