Squeeze the juice from grapefruit. Put gelatin sheet into the juice for swelling. As soon as the gelatin will become soft, heat he juice till the gelatin complete dissolving, but do not boil. Cool under the room temperature, pour into the mould and leave in the refrigerator for jelly setting.
Whip 2/3 of the total volume of shrimps, salmon and cream in the kitchen blender until smooth. Add lemon juice, salt and pepper according to the taste. Separately whip egg whites with a pinch of salt.
Carefully combine shrimp-salmon mass, the remaining shrimps and whipped egg whites. Pour the mousse into the fireproof mould, then put this mould into the larger one filled by half with water. Bake in the oven under 180°C for 15 minutes. Cool the ready mousse, cut by portions and combine with pieces of grapefruit jelly.
The mousse can be also cooked in the microwave oven in 6 minutes under 600W.