In a bowl, mix together the paprika, cayenne, thyme, ancho chili, chili powder, garlic powder, cumin, salt and pepper. Spread the blackened spice mix on a plate. Dredge the fillets in the spice mixture and set aside.
Heat a large cast iron fry pan or saute pan over high heat until it is very hot.
Add oil to the pan. When oil begins to slightly smoke, and fillets and cook on each side, about 2 to 3 minutes each. Cook in batches, if necessary.
To serve, top each fillet with 1/2 tablespoon of butter and serve with lemon wedges.
Or, you can serve with eggs, rice or vegetables.