Hello, I've got a problem with my old synodontis catfish. He's had a swollen belly for a few weeks now. He looks like as if he has eaten something big (looks like a gulper catfish eating a whole fish that you can see on youtube videos). Other than that he is fine, but definitely he is not healthy. I suspect he's got parasites but I have no clue as to what should I do and how to cure him. He is alone in the aquarium, no plants, a few roots and sand as a substrate.