I have two fancy goldfish, I am not sure exactly what kind.  I've have them for 3 years and they've grown quite a bit and have very round bodies.  Both are prone to swim bladder disease and I supplement their diet with peas and sinking shrimp pellets. Problem is one of the fish has an irreversible swim bladder disease and cannot swim up easily or float as all. The fish (Willy) has been like this since March but has managed to live ok and eat. However, 3 days ago he developed a large mass on his backside, to be honest it looks like he could have swallowed a piece of gravel. I feel really bad and I forgot to mention that he was born with one eye. Hence his name One Eyed Willy. I am not sure what to do for the little guy he's still trying to swim but between the swim bladder issue and this creepy growth he's weighed down even more.  I am a true animal lover but I'm not sure it's worth a vet visit (my husband would kill me) Any thoughts, do fish feel pain?? It's quite disturbing to see him like this. Although he is still swimming around, on the bottom of the tank. Has anyone heard of anything like this?? I've posted a pic, it's not great quality but I think you can see what I'm talking about.

Thanks, Willy is a cool fish too. Before the swim bladder issue (that was caused by floating goldfish pellets that shouldn't be marketed as such) he was great.   I unfortunatly don't think there is much I can do either at this point. Sad to watch and look at. I haven't seen him eat the past 2 days. A one eyed, fish that doesn't float with a pebble in its belly. Yikes. Appreciate the response though. 

This is the reason why I choose not to have gravel in the tanks. Before two of my fish kept getting gravel stuck in their mouths. My husband had to catch the fish and get the gravel out. They were small then so I decided I'm not going to wait till they get big and actually swallow a gravel. So for the meantime it's going to be bare bottom until I'll find the ideal gravel size.

If you feel like it won't get any better and it's best to humanely kill Willy, well you can put him in the freezer for a peaceful death. That is last resort in my opinion and would take mine to a vet first. I would try the epsom salts, but are you sure it is a piece of gravel? It could actually be a growth or a swelling of the organs.

I'm not sure sorry

Thank you all for the advice and suggestions. It is most bizarre, especially since the growth seemed to happen really really fast and came out of nowhere.  I'll have to make some decisions on what's best for Willy.

Thanks again

Ah, I forgot to answer one question: Yes, fish do feel pain, but they are special in the way that they can't feel intense pain. Now, I don't know how to motivate that, but it's a scientifical fact. That's at least a comfort, but just seeing the fish being in such bad shape breaks my heart I've had two incredibly sick fish and it was terrible

Thanks pappy-fish, those look like two humane ways to put our dear goldies to sleep... thanks for posting it!

Thank you for the ideas for humanly euthanizing Willy.  However even though I bought the clove oil and had everthing ready to go I couldn't do it. Clove oil must be the most toxic substance ever. I left it in a plastic cup that was prepared for Willy's demise overnight after the pardon. Clove oil actually melted the plastic wow glad I didn't kill my fish that way.  Willy is a special fish I suppose and he has started eating and swimming more. Guess he now is just a one eyed, non floating tumor fish.

The freezer method shuts off the fish, just like the hibernation thing, so he's practically asleep when he freezes. And as long as you leave him completely alone in the dark freezer (OH NOO!! ) He should die peacefully and painlessly.

But so far... I've thought about euthanizing both Marneus and Claymore, but I just couldn't... the moment after when I decided to check on my babies (they weren't sick at the same time, there was about 6 months between each), they were both dead already