What is the unique about salmon move to spawn?

Almost all Salmon swim back to the place they were born themselves to spawn. This requires them to undertake extremely long journey, right up to the stream source where they were born.

For reaching there the salmon have to swim upstream ( against the flow of stream), which is quite exhausting for them. Additionally when the salmon swim back for spawning they are hunted enthusiastically by many carnivores like Bears etc. This results in death of many salmon during the journey.

When the salmon leave ocean ( where they habit after becoming adults) to go back to freshwater streams to spawn the fish undergoes physical transformation to adapt itself from the saltwater to fresh water conditions.

All Pacific Ocean salmon die after spawning. Whereas the Atlantic Ocean salmon might return back to ocean after spawning to continue its lifecycle.