There are two classical fish cuts. There is a flat fish and a round fish. Having a sharp knife is important, because a work done by a blunt knife does not look good and it might look like a laced curtain at the end of the day. You cut a line parallel across the fish's gills. Then you dig in a little bit and cut across the body of the fish down to the fin. Then you take that piece aside and trim off the stomach area. Thus, you have one piece of fillet! Do the same procedure for both sides of the two fishes to get your fillets. You can expect to get two fillet from a round fish and four or two from a flat fish.