In a medium saucepan, combine soup, cream cheese, and onions. Heat until cheese is melted, stirring. Blend in mayonnaise. Remove from heat.
In another saucepan sprinkle gelatin over water. Over low heat, stir until gelatin is dissolved. Stir into soup mixture. Add crab meat and celery. Pour into 6 cup mold (fish shape).
Refrigerate 6 hours or until firm. Unmold on serving platter over curly lettuce. If using fish mold, use olives for eyes and carrot strips for fins.