What is Salinity?

• Salinity is the relative salt content of a given solution. This ratio can be of a small sample or of a large sample such as the ocean. Salinity has an effect on all water-based organisms.
  
  

Those Who Can Survive

• There are a handful of fish in North America that are able to survive extreme changes in salinity. Those fish include the American eel, striped bass, Atlantic tomcod, rainbow smelt, brook trout, Atlantic salmon, American shad, blueback herring, alewife, Atlantic sturgeon, shortnose sturgeon and the sea lamprey.
  
  

Born In Fresh Water

• These fish hatch from eggs that are laid in fresh water. They begin their lives in these rivers; however, they then move on to the salt water of the ocean for their adult lives. They live out their lives in the saltwater until it becomes time for them to reproduce.
  
  

The Return to Fresh Water

• When they are ready to lay their eggs, these fish will return to the rivers where they were born. They are able to travel upstream long distances. It is a dangerous journey, but it is the final step in completing their life cycle.
  
  

How Do They Do It?

• Unlike most fish, these diadromous fish are able to regulate salinity levels in their bodies. They are able to expel excess salt and water so that they are able to survive. The ability to control this process allows them to also be called osmoregulators.