Soak alewives in cold water for at least 3 hours.
Drain and wipe dry.
Carefully split fish open to keep whole.
Place, skin side down, in well-greased shallow baking dish.
Combine butter and lemon juice.
Spoon half of mixture evenly over fish.
Bake fish in preheated moderate oven (350Â°F.) for 7 minutes.
Spoon remaining butter-lemon mixture evenly over fish and bake for 5 minutes longer.