Cycles are changes that occur in patterns, which repeat. Plants and animals change in some way when they are part of a cycle. The life cycle of anadromous salmonids encompass six distinct stages, which demand specific environmental conditions and habitat requirements that allow for the survival of the species. In the early stages of development the eggs incubate in the gravel of the stream bed and eventually hatch into alevins. The alevin feed off of a yolk sac as they mature in the gravel bed of the stream and eventually will become mobile enough to swim up out of the gravel as fry.