Depending on the recipe, the fish may require filleting. Although most fish can be bought ready filleted, it is just as well to know what to do. As fish come in two basic shapes, round and flat, there are also two ways of filleting. Flat fish are probably the easiest fish to cope with as they have a flat bone that is easy to negotiate, and there is also a line, the lateral line, down the fish from head to tail which acts as a cutting guide. This line runs from the centre of the tail up the middle of the fish towards the head; just before the head, it curves off to one side around the pectoral fin and finishes behind the gills. Round fish have a curved rib cage, which makes it more difficult to negotiate, and a line of small bones that have to be freed from the backbone.