The alevins hatch from within the salmon eggs. As the salmon grow and develop space becomes very limited. Wiggling motion within the egg causes the protective layer to rip and the alevin pushes out. Alevin will continue to grow and develop within the gravel. Attached to their stomach is a yolk sac. The yolk sac will provide the nutrients for 24-30 days. During this time period the alevins will continue to grow and develop.