This is a pretty common practice... As long as u freeze the fish u catch to rid of parasites its more than fine. No different than purchacing fillets that someone else prepared for u in the same fashion. Many ray keepers do it also to cut costs.
Started with a couple of pounds. They take a month or so to settle in and start reproducing. Once they do then there are tons. You can also look for them locally on Craigslist or wherever (might be called composting worms)...