I've had a bluegill as a pet for 5 years?

Is that ok? He's in a 55 gallon tank with a 4 inch red tail catfish(i got him at the store.) I saved the blue gill from one of those places that kills them after u pick it out hes 5 inches long and I've never had a a problem with him! Is it ok to have him? They told me he was born in a fish farm.