Add the first seven ingredients to a jar with a tight-fitting lid and shake them well. Place the catfish in a shallow bowl and pour the marinade over the fish, tossing the fish to coat it thoroughly with the marinade. Cover the bowl and chill the fish for 30 minutes or longer. Reserving the marinade, remove the fish from the bowl. String the pineapple, vegetables, and fish on the skewers, starting and ending with pieces of bell pepper. Brush the skewers on all sides with the remaining marinade. Place the skewers on a hot grill, and cook the kebabs for 4 minutes on each side or until the fish is just cooked through.