There are small bones along the lateral line, basically tiny y-bones like in a pike or walleye. Start cutting around the ribs and just cut through these "y-bones" then finish filleting meat off ribs. I finish by removing the fillet at the pectoral fin, leaving a strip of belly meat from the pectoral fins down to the anal fin, about a 1/4"-1/2" wide. Some people "butterfly" them and keep that belly meat and leave both fillets attached. The tiny y-bones that are left in the fillet will soften up when you fry them, you shouldn't even notice them on all but the largest of the perch. Might want to check out youtube, there are probably videos on there that will help you out.