 There are two major reproductive strategies of teleosts ; semelparity and iteroparity . In the former , an individual breeds once after reaching maturity and then dies . This is because the physiological changes that come with reproduction eventually lead to death . Salmon of the genus Oncorhynchus are well known for this feature ; they hatch in fresh water and then migrate to the sea for up to four years before travelling back to their place of birth where they spawn and die . Semelparity is also known to occur in some eels and smelts . The majority of teleost species , however , have iteroparity , where mature individuals can breed multiple times during their lives . 
