Corydoras Disease or blister?

[Nich200]

I have a Corywho seems to have a blister or ball on the top tip of his front fin. No other fish in my tank have any signs of a disease. Have researched and can not find anything similar. I found it on him after he was swimming frantically around the tank a few days ago constantly gasping for air. The water is 78-80 degrees f and has been running for almost 4 years. Over the last month I lost two fish a silver tip tetra and a neon tetra. I was assuming from old age but now I am questioning this. My water parameters are perfect. THe Cory has calmed down since I have done two 50% water changes over the last two days. His diet consists of shrimp pellets, algae wafers, and left over garlic fish food. The other Cory in the tank seems fine. It doesn't look like ich to me but I can't think of what else it could be besides a tumor of sorts. Any ideas what this is?
Ok here are some other pics. I never realized how hard it was to take a pic of a fish. Okay I am not a Cory guru so you guys have more of an idea of what type of fish it is over me. As to his barbells... He and his friend have never had any. I got the tank from a friend about 6 mo ago and they were part of it, as is.

[MarlonnekeW]

I'm not sure about the medical problem, but to me your cory looks like a Corydoras habrosus instead of a paleatus. He also seems to have a problem with his barbels. It looks like they are completely gone.

[bekateen]

I agree that doesn't look at all like paleatus. And maybe it's just me, but I can't clearly see the bump you're describing. Can you get photos which are better focused? Finally, what other fish died (what species)? If they were also corys and only four years old, that may not be old age. Many fish live for a decade or longer.

Thanks and good luck with its health.

Regards, Eric

[Nich200]

New pics. I hope you can see the dot now. Sometimes it blends in with the rocks.