Man, I gotta agree with toby. In the wild almost everything has some sort of parasite, etc. Many die from them and many are strong enough to provide for themselves, as well, and survive. That's one instance where nature takes its course. In captivity the rays we own are lucky enough to not have to fend off these parasites because our pets are captive bred and/or treated for them. They have enough stress to deal with being confined to a tank, water changes, the food we feed, etc. It's not worth introducing wild food to our pets IMO.