Cooking time for fish depends entirely on the size of your fillet. When cooking on the stovetop, a thicker fillet will take between five and six minutes per side, while a thinner one will be closer to two or three. A good rule of thumb in the oven is to cook your fillet for ten minutes for each inch of thickness.u003cbr/u003eu003cbr/u003eOvercooked fish tends to get mushy, while undercooked fish will lack the flakiness that makes it so delicious.