When the salmon egg is ready to hatch, the baby salmon will break free of the egg's soft shell retaining the yolk as a nutrient-rich sac that hangs below it's body (yolk sacks are the orange pouches underneath them). At this stage, they are called Alevin and are about one inch in length. During the next month, the alevin will remain hidden in the gravel nest and feed from the nutrient-rich yolk sac until it is completely absorbed. The yolk sacks contain protein, sugar, minerals, and vitamins. These yolk sacks are also known as "lunch bags". The "lunch bag" lasts only a month until they have to hunt for themselves! once the "lunch bag" is gone then they start to become a fry. At this stage alevin are swimming though out the redd and surviving off their yolk sack.