Illness/Sickness: Axolotl floating, swollen on one side.

[Veleran]

My 3-4 year old Axolotl has been floating for a couple days. I have seen him on the bottom, so he can sink if he wants to, but he has been repeatedly gulping air and floating. I handled him while looking at the bulge and moving him in to a container, and accidentally squeezed him (gently) as he tried to get away, and a heap of air was expelled. He instantly gulped in more.
Normally I would pass this off as him just entertaining himself, but he has a bulge on his left side, and has started floating that side up, nearly turning upside down.
He has not eaten since he started floating, and he has only just pooped a few minutes ago, though it is quite small and thin.
I don't have a test kit on hand so I can't test the water, but I have two other axolotls in the tank with him who are both fine. This is my first axolotl, and one of the toughest axolotls I've seen. I had an incident a couple years ago where our water went toxic, forcing his tank mates to panic and try to escape, eventually dying, but he acted like nothing was wrong at all.

 

[Hayleyy]

Oh wow. I think air often passes through but if he is having difficulty it might be worth fridging him. Where did the air expel from when he was squeezed?
Is there anything in the tank the axolotl could have eaten? Rocks, snails, etc?
Keep updating on his condition in case any other signs pop up and other's might have more suggestions.

 

[Veleran]

I ended up fridging him for a few days. Last night and today he seemed to be able to keep himself upright. I added him back into his tank a couple hours ago and he immediately gulped more air.
If I gently massage him he releases the air out of his mouth. He is having trouble staying under water now with his back end floating. The area around his cloaca is as hard as a rock.

His substrate is sand so there is nothing big enough to get caught. There are a few snails but they are tiny (like 1mm wide).

 

[Hayleyy]

If he was improving while being in the fridge I would put him back in until you're not seeing any floating or swelling. I'm not too sure about the hard cloaca other than something trying to pass through but I'll see if I can find anything.

 

[Veleran]

The swelling wasn't improving in the fridge. I left him in his tank, but in a container so he could reach the ground and keep himself upright. Unfortunately he passed by morning. Thanks for the help.

 

[Hayleyy]

Very sorry to hear that, wishing you all the best