Feeding ecology of various age-classes of brown trout in River Nera, Central Italy

We studied the composition of the stomach contents of brown trout (Salmo trutta trutta) of different ages in the river Nera, Central Italy. Each age class of fish consumed significantly different prey taxa. Plecopteran nymphs tended to increase in percentage as the individuals became older, while ephemeropteran nymphs were always present in high percentage. Trichopteran larvae were the most abundant prey in trout younger than 2+, while their percentage decreased considerably in older fish. The remaining aquatic prey (except dipteran larvae) were scarce and, finally, terrestrial prey were consumed more by older individuals. Vanderploeg & Scavia's index shows a high preference for species of Trichoptera by trout younger than 3+, plecopteran species by those older than three years, and a general negative preference for species of Ephemeroptera by all age classes.