They are very tiny, less than 1 in. Bulging yolk sacs provide nourishment until the baby fish can get food for themselves. During this time, they hide in the gravel, more like worms than like little fish. When the yolk sacs are used up and disappear, they wiggle out of the gravel and move into deeper water. The baby salmonids are now called swim-up fry.
Salmonid fry develop parr marks or stripes on their sides.
These marks help to camouflage or hide the young so they will not be eaten. Larger fish and birds such as mergansers, kingfishers and great blue herons are just a few creatures who love to feed on fry. They grow quickly while feeding on tiny plants and animals. Some stay in fresh water only months, while others stay a year or more before they migrate to the ocean. When the fry are ready to leave fresh water and migrate to the ocean, they undergo a special process called smolting, and are called smolts.