Heat the fat until it is hot enough to cook at once, but not burning, sputtering hot. Lay in the fish, turnheat down to barely a medium flame, and begin to brown the fish. Keep the fish loose from the pan bottom with a thin metal spatula.
Taking 8-10 minutes to a side (turn heat low if it seems to fry too fast), brown the fish slowly until crisp. Do not overcook. When the flesh is opaque the fish is done; one hopes it's all browned by then.