Freshwater Stingray

Does anyone here have much experience with these guys.  I'm having some trouble
judging what is enough/or too much food to be feeding a 3-4 inch reticulata. 
He is eating frozen bloodworms early in the morning and 1-2 small earthworms in
the afternoon.  Is this too much, or just enough?  He is quite fat by the way;
pelvic bones not visible at all...