Clean, scale, and rinse the trout under cold water, making sure there are no blood vessels left in the cavity. Make 3-4 diagonal cuts on each side of the fish just a little deeper than the skin. Pat the fish dry and set aside. Mix the flour, salt, pepper, oregano, and cayenne in a shallow bowl. Melt the butter and olive oil over medium heat in a large frying pan. Dredge the fish in the flour mixture until well coated. Fry in the oil and butter, turning once to cook thoroughly. The trout is ready to serve when it flakes easily with a fork.