The food of trout in our mountain streams is mainly insects. It is, in part, land insects that fall on the water and are taken as they float upon its surface, but in a much larger part it is insects that grow up in the water and are taken in their immature stages. These are the constant and dependable food-supply. They have been little studied hitherto. This bulletin is a report of a preliminary examination of some Utah streams, made for the purpose of discovering what forms of life are present in the streams and in what relative abundance. Some are beneficial and some injurious to trout, being competitors with them for food.
Needham, James G. and Christenson, Reed O., "Bulletin No. 201 - Economic Insects in Some Streams of Northern Utah" (1927). UAES Bulletins. Paper 167.