Black Sharks are primarily algae raspers,their teeth being very small and bristle like,ideal for removing the mucus from fish.These fish often take advantage of any large fish that doesn't have the speed to get out of their way, ie Gars,Polypterus large Cichlids etc, I have highlighted these species because I have had bad experiences in my younger days with these combinations. Black sharks are a lovely looking fish as adults but they are best kept with much smaller fish they cannot catch and rasp on such as medium sized Barbs,large Tetras over 3", Metynnis (Silver dollar sp) etc.
In my opinion a definite no no with Rays, wouldn't even dream of such a combination. I think KNH had already made your mind up for you but it doesn't hurt to hear it again.