Problem:

To spawn, salmon return to the river in which they were born. Is it because the individuals remember the specific river, or because populations are genetically conditioned to follow specific environmental cues that guide them to the specific river?

In other words, if a salmon is artificially taken to lay eggs in a different, ("wrong") river, will its progeny return, when grown, to the river where they were born, or that where their mother was born?

If salmon that was grown in a fish-farm is taken to the sea, does it return to a river? How does it choose which? Please justify your answer.