if your heater was broken that means that electrical current was able to flow into the water. This happened to me once. I went to get a piece of debris out of the tank and got the shock of my life. I was stunned. So i tried again lol, and bam again shocking. I tried in a different spot and no curent. The electricity was following the water flow. Could stress out your fish over time and have all kinds of wierd side effects. I swear by titanium heaters now. Especially when keeping medium to large catfish. Catfish are notorius for eating heaters and breaking them. Sorry for your loss. That is truely sad. If you really want to know why his belly is swollen. Disect him. It will help you learn what to do better in the future when keeping catfish. I don't think those temps that you mentioned are much of an issue. I know it sucks, but trust me now you know what was wrong you have a chance to do things better. We've all been there and done that. Use titanium next time if you are going to have large fish, or put it in your sump if you have a sump filter tank. Good luck, and again it's a very sad loss.
