With their thin skin and tiny scales, trout do not need scaling and are often cooked whole. To fillet larger fish, use a sharp, thin knife. With the trout lying on its side, insert the knife behind the gills, and cut in an arc down to just above the backbone. Continue cutting parallel to the backbone toward the tail. Bring the knife up at the tail and remove the fillet.
To bone, use scissors to snip off the pelvic fin (the forward belly fin) and use a sharp knife to cut off the dorsal fin (on the back) and anal fin (the rear belly fin). Remove the head with a sharp knife. Using a sharp knife, open the belly cavity, reach inside, and cut through the tiny ribs on each side of the backbone. Pull backbone free, scraping away flesh with a sharp knife. Then gently lift out ribs with a knife. Run you fingers over the flesh to make sure all bones are gone.
Rinse fish and pat dry with a paper towel. Whole trout may be stuffed with rice and vegetables. Place whole, boned filleted trout in a baking pan. Brush with butter and oil and season with salt and pepper, or cover with a piquant sauce. Bake in a preheated oven at 400°F (200°C) until a knife slice in the thickest part reveals the flesh to be opaque but still moist.
Place whole small fish or fillets on perforated aluminum foil over a greased grill, 4 to 6 inches (10 to 15cm) above prepared coals or fire. Baste with butter, oil, or marinade, and close hood of grill. Cook until opaque and moist on the inside, 6 to 8 minutes for fish less than 1 inch (2.5cm) thick; 10 to 15 minutes for fish larger than 1-inch (2.5cm) thick.
Rinse whole fish, fillets, or boned and butterflied trout, and pat dry with a paper towel. Place fish on a rack above a baking dish. Preheat broiler and adjust oven rack so fish is 3 to 4 inches (7.6 to 10cm) from the element. Brush with butter or oil and season with salt and pepper. Broil, turning once, until fish is opaque but still moist in the center, 3 to 10 minutes, depending on size of the fish.
Rinse trout, and pat dry with a paper towel. Dredge in flour and seasonings if desired. Shake off any excess flour. Heat frying pan until hot, then add butter or oil. Put in fillets and cook, turning once, until fish is opaque but still moist in the center, 2 to 10 minutes, depending upon size of the fish.
Bring poaching liquid, consisting of water, broth, and herbs and spices, to a simmer. Slip trout in, then cover pan and keep liquid at a simmer for about 8 minutes per inch (about 2.5cm) of thickness.
Place trout on a greased perforated rack over 1 to 2 inches (about 2.5 to 5cm) of rapidly boiling water. Cover with a tight-fitting lid and keep water at a constant boil through cooking time, 8 to 10 minutes per inch (about 2.5cm) thickness of fish.