Question

a salmon moves from a saltwater ocean to a freshwater river. What takes place in the salmon's cells as it moves?

Answer 1

When the fish is put into fresh water, suddenly the concentration around them is very low and the water potential is extremely high. Water will now move from the relatively high water potential in the water to the relatively low water potential in the cells, the cells start to burst and the fish dies. 

Answer 2

The cells fill with water because of the movement of water by osmosis.

is the Apex answer