Mix the flour and melted butter. Boil the mass, stirring it from time to time. Pour 2 cups of strained fish bouillon boiled with the sprigs of parsley and celery, into the mass. Boil on low heat until thick. Peel the cucumbers and remove the seeds. Cut them into small rectangular pieces. Cut the mushrooms fine. Add the chopped cucumbers, mushrooms, and olives to the thickened liquid. Let the sauce boil for a while and add the tomato paste. Serve the sauce hot with a large boiled fish.