Dredge the fish in the flour. Meanwhile, heat the oil in a large skillet over medium heat until it shimmers. Add the fish and brown about 3 minutes on each side. Carefully lift the fish out of the skillet and set it aside on a platter; sprinkle with the salt and pepper.
Add the garlic and the fennel to the skillet and sauté slowly until limp. Reduce heat to low and return the fish to the pan and add the wine or water and thyme. Cover and cook 5 minutes or until the fish flakes when tested with a fork or the tip of a knife. Sprinkle with minced fennel fronds.