Cut off the heads, tails and fins of the bloaters and remove the backbones. Put into a greased ovenware dish and dot them with butter. Sprinkle on the lemon juice, salt and pepper. Cover and bake at 350°F, 180°C, gas mark 4 for ten minutes.
Bloaters are a speciality of East Anglia. They are whole fresh herrings which are dry-salted and lightly smoked. They were very popular in Victorian times and were often made into a strongly-flavoured paste.