Heat butter in a saucepan but do not let it brown. Blend in the flour, salt and pepper. Heat until the mixture bubbles. Add the cream slowly, stirring to keep the sauce from lumping. Cook as rapidly as possible until thickened. Remove from flame and let cool. Flake fish. When sauce has cooled, blend in fish and egg yolk.
Shape the mixture into small balls, about ¾ inch in diameter, and dip into the beaten eggs. Roll in fine bread crumbs.
Deep fry, uncovered, only as many of the balls as will float without crowding each other in your frying kettle. Turn often until lightly browned.