Water temperature? Food change? Condition of fins? Eating? Sorry for all the questions but you know I worry when my little friends get the "willies". No, this is not a good thing even though it can be depression. Depression in a
betta will eventually lead to disease. (simply because they will quit taking care of themselves) Can he see the tank with the ladies and the other fish? If so he may be royally pouting because you are spending time with them, but this doesn't sound like just that although a Betta pout is one heck of a pout. Try the added attention and much love and cooing over him and hike the temperature up to 82 just to be on the safe side and watch for spots or any other sign of other problems. It is obvious that his immune system is not at the best right now so we don't want to start something if there isn't anything there yet.
Please let us know how he is and I will probably be up on "sick baby watch" tonight if you need to post. Not mine, yours. I do that you know. I will check in every few hours.
Rose
