Asalmon follows a scent trail upstream to find its way back to the stream where it hatched. what type of sensory receptor cell would it use?

chemoreceptor

Explanation:

salmon have a very strong sense of smell due to presence of chemoreceptors  through out their body.Due to presence of chemo-receptors, Salmon have capability to taste what they touch and can  smell the presence of any chemical. Salmon can go downstream to find food and to protect themselves from the attach of brown bear. Salmon can sense the bear presence due to chemical given off by bear skin. Once they are far, their sensory cells (chemoreceptors) help them to find the right way upstream back to home and rely on the scent to find the right stream and place where they started life from.  

from the original order (top to bottom) the new order will go

1 (founder)

4 (hawk)

2 (mutate)

3 (next generation)