I'm not sure about the red mark but I've heard from this website that it is not a good idea to feed fish with dog food or catfood for health concerns. In my opinion, it is a simple process to go to a local farm supply store, tractor supply co., or southern states or similar store because they all sell fish food. I have noticed smaller fish will eat up all the fish food you can put out. Catfish and bream will run to the food but bass don't seem to like it too good. I guess they like live fish better. Hope this helps.