A seasonal analysis of the diet and feeding dynamics of brown trout, Salmo trutta L., in a small nursery stream

Abstract

. The diet of brown trout, Salmo trutta L., in the Owendoher Stream, a tributary of the River Dodder, was examined at monthly intervals from June 1981 to May 1982. The diets of the three main age groups, 0+, 1 + and 2+/3+ fish, have been separately described and compared. Ephemeropteran nymphs, larval and adult chironomids as well as a variety of other adult insects were the most frequently consumed foods. While 0+ trout largely concentrated on aquatic organisms, adult insects, in particular those of terrestrial origin, became progressively more important in the diet with increasing age of the fish. Daily ration calculations indicated that food intake was highest during the summer and early autumn months when it was well in excess of maintenance requirements. This corresponded to a period of good growth. For the remainder of the year food intake was not much higher than maintenance requirements. In fact, 1+ and older (2+/3+) fish probably experienced an energy deficit on occasions during the winter which was reflected in their poor condition and weight loss. The relationship between growth and production in the system are further discussed.