* In a bowl whisk beer and salt into flour until smooth. Drain sardines and pat dry. Cut lime into 8 wedges.
* In a 3 quart saucepan heat oil over moderately high heat until a deep-fat thermometer registers 375°F Working in batches of about 8 and holding sardines at head end to avoid breaking, dredge fish in batter to coat completely, dragging lightly against side of bowl to remove excess, and fry, stirring, until golden, 2 to 3 minutes. With a slotted spoon transfer sardines as fried to paper towels to drain.
* Fry lime wedges in oil until they begin to turn golden, about 30 seconds, and transfer to paper towels to drain. Serve sardines with lime.