can't really tell much with the picture. Is it an open wound? Anyway it doesn't seem serious as I can't hardly see any red meat so don't think its a wound. Ray seem to be skinny as the side bone sticking out. Try to feed it more often.
It is not open. Just a white dot and nothing more. This ray is skinny. It was once fat but he is not getting enough food right now. It's because of this stupid pike cichlid that eats everything. I'm trying to sell him...what a waste of money those fish were.....$100 down the drain.
most rays will develop white/Grey splotches on their ventral side as they grow out of their ''pink''stage. the pink stage is when they are young and the tissue is thin and still developing.
judging by the picture u provided i would say that is normal ray pigmentation for a maturing ray. however, the only other thing i can think of is, either a bacterial infection or possibly fungus... but i highly doubt that. i only say that because lack of nutrition will weaken the immune system; making the ray vulnerable to disease.
also, i would isolate the ray right away and fatten it up!!!
this is the pink stage and the pigmentation change of maturity: