I have two bettas, one of which I bought only a few days ago.
The first of the pair, Mr. T, has recently been treated for velvet. The velvet is now gone, but his fins are not as full as they were before. I am not certain if that is simply because he will not flair them out; but his other behavior is now normal, which leaves me in doubt.
The other betta, Axel, is the newer of the two. I have noticed that, at all times, I can see a little of his gills behind the opercula. Furthermore, he tends to keep his gills slightly expanded. He was this way when I bought him, but I realize that does not negate the possibility of trouble.
I am very new to betta care and have been doing research about these behaviors, but I am not certain whether I am being overly cautious or they really need treatment. If someone could advise me, I would be much obliged.
Well, how is Axel acting? I have one betta who has one gill expanded more than the other, but he has never shown distress, gasping, discoloration, or even sickness including parasites so I stopped worrying
Some bettas as they get older, or go through a tough disease/recovery sometimes do not hold their fins as grand. Or, like us when we are sick, then finally get better, we have to work to get ourselves back up the way we were before we were sick, and sometimes bettas do that too.
Gasping, can be with the mouth, or his gills moving more rapidly. Sometimes they "yawn" with their gills too, which my Skull tends to do (the one with the somewhat opened gill) but it hasn't been too recent. Also when a betta is new, they can have inflamed gills, reddened or sore, flukes (parasites), or ammonia burns that are uncomfortable.
It is a 2.5 gallon tank, with the divider in between. Since I just got back from college, I very recently cleaned everything and refilled the tank completely. It has been less than a week since I did so.
2.5 gall with 2 betta . 2.5 gall kind of too small for 2 betta. And you need to do minimum 1-50 and 1-100% water changes a week. Or even i would do 100% every 3-4 days.
Also i am not sure what Axel have. If he has parasites he will give it to Mr. T.
The symptoms that you describing i don't know what is the problem. But Sena might help you better. Sena wrote that it can be parasites.
Not sure what she meant internal or external.
External parasites : fish will also dart around like crazy, try to rub the body on subjects, Also you will able to see it on the body, i guess if he get worse. It would be white dots or looks like he cover with salt.
Internal parasites his poo will be white , clear stringy,wormy shape.
I can't diagnose but you definitely need to do more water changes and i would separate them. Even if the other tank is one gall. it still batter to separate and see if he don't have anything contagious.
Always when you buy new betta try do not put it with your other betta. Always quarantine and make sure it not sick .
Sorry i hope he don't have anything contagious.
Also i don't know what Sena will recommend take her advice if she think differently but i really think for now as first aid you need to do water changes. Since you wrote that last water change was week ago.
I would really do 50% today if you can . And 50% tomorrow. Then just keep doing 50% and 100% a week.
Like Sena wrote Axel behavior might be due also to ammonia burns and once a week for 2.5 gall with 2 betta is not enough water changes.
Good luck :)
EDIT: When you change water especially 100% make sure new water +-4 * the same as they have..