Complex sentence: Salmon ("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.
Split into simpler sentences: Salmon ("Oncorhynchus") are well known for this. These species hatch in fresh water and then travel to sea for up to 4 years before travelling back to their place of birth where they spawn and die.