All species of fish have scales, though sometimes they are too small for us to see. In some cases scales on fish are almost microscopic so they are barely visible to the human eye. The most visible scaling of fish can be found around the head as well as the cheeks and the sides of the body which are triangular in shape and located near the head.
Those who catch their own tuna or other types of fish will want to make sure that they scale it properly in order to avoid ideal taste. Although it is true that the scales on fish are not considered to be edible, the skin underneath is. As long as you thoroughly scale the fish you catch, you should be able to eat the skin and meat with no problems whatsoever.