Preparation :
Melt the margarine in a pan, add 1/2 glass flour and saute for 2 minutes while stirring. Add a pinch of salt to the milk and add this milk gradually to the pan while stirring very rapidly at the same time so that flour and margarine absorb the milk. Cook until the mixture becomes like a pudding. Scrape off the scales do the fish and gut. Cut off the heads and fins, wash well then drain. Place in cold water to cover and add the scraped and washed carrot, bay leaf, celery leaves, lemon juice, egg whites, salt and black pepper. Place the pan on heat, blanch for 10 minutes, remove from heat and leave to cool. After removing the skins and small bones of the fish, flake the flesh. Sprinkle chopped parsley over flaked fish and mix well together, pour the prepared sauce over. Add 2 egg yolks and place the pan over moderate heat warm for 2 minutes while stirring with a wooden spoon. Brush flat surface with oil and pour the mixture over, spreading it over so that it will be half inch thick, then let it cool, afterwards from the desired shapes with a glass. Break the third egg into a procelain bowl, add a pinch of salt and beat. Flour the fishballs, using the rest of the flour, brush with the egg mixture and then roll in breadcrumbs, and put in a frying pan filled with olive oil. Fry on high temperature until brown. Place the fish balls on a plate, decorate with lemon slices and serve.