Sick Betta

are it's gills porcupined out? might be dropsy? could also be constipated if it's only it's belly is bloated.

How long have you had him? Also, can you tell us your parameters: ammonia, nitrite, nitrates, ph, temp, type of test kit, type of dechlorinator.

What have you been feeding him? Can he leave the surface or is it difficult for him to swim down?

If the only area of swelling is his tummy then it could be bloat from constipation or intestinal blockage.

Look at him from above. Does his body seem swollen so that the scales are standing out like a pinecone, or is the swelling only in the abdomenal area?

Also, I can't tell, but is the area I circled his anal fin or if not what is it?

Do you have another small tank you could put him in. He may be really constipated and you can start a treatment to help him.

I'm not a Betta keeper, but I've read many many threads and posts that say they can swallow a lot of air when they gulp dry flakes. If you put him in a little quarantine tank, put a plant that he can rest on near the surface if possible, and fast him for about 4 days.

Then feed him nuked frozen english peas. Take the pea skins off, you want the pea kind of mushy. I take a little tank water and put it in a cup with a handful or less of peas. I nuke for about 45 seconds. Yours may take more or less, you just want to be able to pop the peas out of the skins and have them mushed a bit.

This will help with constipation or blockage.

Pristine water is of utmost importance. Isolating him would really be good. If that is a bit of bowel hanging out of his anal vent then other fish may start picking at it. If it is a loop of bowel it can retract back inside if the blockage or constipation is relieved.

I can see the same thing in the first pic, only it is dark and in shadow. It looks like something hanging out of his anal vent.

Could be constipated, try fasting him. Betta pellets are much better food than flakes. Atisons or Hikari brand.