Download and read  "The Practical Angler Or the Art of Trout Fishing More Particularly Applied to" by W C Stewart

...what anglers wish to know is how to capture them, and we shall therefore consider trout in a purely angling point of view. With regard to the much-vexed question of whether trout hear or not, naturalists say that they have ears, but we think that these organs are rather intended by nature to convey any agitation in the water, to which they are keenly alive, than external noise. This much seems evident, that no noise out of the water can be heard by a trout in it. Guns have been fired not many yards from trout, but they exhibited no symptoms of alarm, which they would certainly have done had they heard ; and, though some English works upon angling caution the angler against speaking loud at the water- side for fear of alarming the fish, this much is certain, that neither by speaking, nor any other noise the SENSES OF TROUT. 15 angler can make, is there the least danger of alarming them. They have frequently been caught below a railway bridge at the very time a train was passing...