1. Wrap tortillas in foil, and bake at 200° for 10 to 15 minutes or until warm.
2. Combine flour and next 3 ingredients in a large, shallow bowl. Let stand 5 minutes.
3. Heat 1 inch oil in a 10-inch heavy pot (2 to 3 inches deep) over moderate heat until a deep-fat thermometer registers 360°.
4. Dip fish into batter to coat, draining excess. Fry fish in batches, turning once, 4 to 5 minutes or until golden. Drain on paper towels.
5. Assemble tacos with warm tortillas, fish, and Chipotle Crema. Garnish, if desired.