Whats wrong with my lemon tetra?

[Fae]

To start, this tank has mycobacteria. Not much I can do about it besides more frequent water changes. All it means is fish are healthy, until they're not. And when they're not, they decline rapidly.



This lemon randomly got a very sunken stomach, and I'm not sure what the orange coloured mass would be in its stomach. As you can see, it looks different from the others.

Usually when they decline in health, it's black spots all over caused by internal bleeding. This looks different. Parasites? Something else?
Anyone? Any ideas?

 

[BigManAquatics]

Sunken bellies do usually make me think of parasites.