Hemoglobin (Hb), is the oxygen-transport metalloprotein which contains iron in the centre of its structure. This metalloprotein is found in the red blood cells (erythrocytes). The function of hemoglobin is to transport the oxygen through the blood carries from the lungs to the rest of the tissues. Oxygen is necessary for the aerobic respiration in order to provide energy for the functions of the organism (metabolism).
When you do that the fish will die. That is because it will take too much water in it and die from it, or rather, the fish's cells will take too much water in.
