Season the fillets on both sides with salt and pepper. In a sauté pan, preferably nonstick, heat the oil over high heat until it just begins to smoke. (If you are using an aluminum or stainless—steel pan, the oil should be even hotter—it should be distinctly smoking; if using whole butter, sauté over medium heat.) Place the fillets in the pan. Put skin-on fillets skin side down and immediately press down on them with the back of a spatula, moving from fillet to fillet every few seconds, for a total of about 30 seconds.