Weird growth on emerald green corycat

Hello! I have three emerald green cory catfish in my 10 gallon tank. Two of them appear to have a small growth or bubble at the base of their dorsal fin - right where it connects to the body. They both have these growths in exactly the same spot. Cannot find a description of this in any fish disease list on the Internet. Could it be gas bubble disease? Aside from this growth, they seem healthy. No other growths anywhere else on their bodies.

None of my other fish appear to be affected. I have three neons, three glowlights, and these three corycats in my 10 gallon tank. Last I checked (on Friday), all of my water parameters were great - Ph 7.2, Am-Ni-Na all 0.

I do a 25% water change every week, and did one last Friday after I checked my levels.

Any ideas about what's going on and how to treat would be appreciated!

Unfortunately, no. Don't have my camera with me tonight. Maybe I can describe it better?

My emerald green corys are about 2 inches long. The growths are kind of teardrop shaped, and slightly pearly looking. They are perhaps a 1/4 centimeter long. They are fleshy and move around when they swim. They appeared quickly, just over the weekend.

And if this could mean anything: last Thursday, after my water change, I thought that perhaps the corys were 'flashing'. They were careening around the tank and seemed like they were itchy or something. But then it stopped and they don't appear to be doing that anymore.