His body has already been released for burial. No autopsy was authorized by his family members. j/k When I noticed him I was in a rush and had just enough time to remove his body before I left for work. I didn't even think of dissection and now he's gone. Sorry.

Thanks for all the suggestions. We did try adding in extra aeration and cutting back on the lighting. And there are plenty of live plants in the tank, so he has greens for his diet. Yes, we do primary feed the fish tropical flakes, but I never see him eat them. There are several fish in the tank ...

I'll test the water again and post the results. The fish is still alive and no one else is sick. He isn't as pale white anymore. But the blisters are all still there. I've been keeping the lights off.

There's been nothing new added to the tank. No new plants or fish. So it would have been something that can naturally grow in the tank without an external contributor. If its cancer or tumors, can this infect the other fish?

That's a good suggestion Jools. But I can rule this out. I have no heater in the tank. Its a 150G and I live in Florida. If anything, the water gets a little too hot, all on its own. (mostly due to the plant lights) So I've been going heaterless for years now.

I haven't touched or popped the blisters so I'm not positive if its air, gas or solid. They look like air. He is in a 150G tank. There are very few fish in it, and a lot of live plants, so the tank mostly takes care of itself. I do maybe 2-3 inches of water change a month. When we saw he was sick ...

Both. He has one really big blister on his side. Then a smaller one on his back, and a third on the opposite side. I took another picture today of the biggest blister. Do you think its a gas bubble?

My upside down catfish is sick. It looks like a blister or something. I’ve attached a picture. Does anyone know what I should do or what ailment this is? Are there any treatments or should I just mercifully put him down?
Please let me know. I haven’t quarantined him either. I don’t want to add extra ...