You could write all day long on this question. Simply put after hatching and absorbing their yoke sacks and emerging from the gravel the fish are referred to as fry/fingerlings. They reside in the fresh water system (river/lake) until they get the urge to migrate to the marine environment. When they get the call to exit the fresh water for the marine they are referred to as smolts. Smolts undergo both physical and behavior transformations. Different species spend different periods of time in fresh water before smolting. Steelhead can spend 1-4 years but typically smolt as 2 year olds. Coho spend about 1-1/2 years before smolting. Chum and pinks smolt almost immediately after emerging from the gravel. Chinook get real complicated, as there are basically two types. Ocean type chinook are referred as “ninety day wonders” because they smolt in about three months, these are typically your fall run chinook. River type chinook can spend up to 1-1/2 years or more before smolting and are typically your summer or spring chinook. Sockeye is another whole story. Adults are mature fish returning to their system of origin to spawn.
As with anything else with fish nothing is etched in stone and there are variations to all of this depending on races within species and food availability for the fry prior to smolting.