Heat 1 inch of oil in a large, heavy skillet over medium heat. While oil is heating, rinse catfish fillets, and pat dry with paper towels. Place sesame seeds in a shallow dish. Press fillets into sesame seeds to fully coat on both sides.
Carefully place catfish, 1 fillet at a time, in the hot oil, and cook for 3 to 4 minutes on each side, or until fish flakes easily when tested with a fork. Drain on paper towels. Serve fillets with sauce spooned over them.
Sweet and Sour Sauce:
In a mixing bowl, combine and dissolve the first 5 ingredients, and keep nearby. Heat a small but heavy saucepan over high heat until hot, and then add the oil. When oil is hot, Add the garlic and ginger, and stir for 10 to 12 seconds. Do not brown.
Add the bowl of liquids to the saucepan of garlic and ginger, and heat until bubbling.
Stir in the cornstarch mixture. Stir until sauce thickens. Remove from heat.