Scents might attract and they might repel, somethings smell tasty, somethings are are just plain foul smelling. The only way I gave to describe a trout's sence of smell is to say it can follow scent trails, which puts it up there in sensitivity. I would say it is as close to that of a catfish with out needing wiskers.
Fish have a good sence of smell and no nose, a good sence of hearing and no ears, and good vision. They could not manage the last one without eyes.