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FEEDING ECOLOGY OF VARIOUS AGE-CLASSES OF BROWN TROUT IN RIVER NERA, CENTRAL ITALY

2008; Volume: 138; Issue: 2 Linguagem: Inglês

2295-0451

R. Fochetti, Roberto Argano,

Aquatic Invertebrate Ecology and Behavior

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 per- centage as the individuals became older, while ephemeropteran nymphs were always present in high percentage. Trichopteran lar- vae were the most abundant prey in trout younger than 2+, while their percentage decreased considerably in older fish. The remain- ing 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. FOCHETTI et al. (2003) studied the stomach contents of brown trout from the Nera River (Central Italy), confirm- ing the presence of selectivity in its feeding behaviour. In fact, the electivity index showed a negative selection for some species of Ephemeroptera and Diptera and positive selection for species of Trichoptera. Moreover, it was also found that ephemeropteran species dominated spring and summer diets, while trichopteran species prevailed in winter. Since the diet of fish often changes with body size (ELLIOTT, 1967; WERNER & GILLIAM, 1984), and in sal- monids older fish shift their preferences towards larger prey (KEELEY & GRANT, 1997), the aim of the present study was to analyse the possible changes in diet between the different age classes of individuals of brown trout in a river of Central Italy. Moreover, we wanted to verify the relationship between the availability of potential mac- robenthic prey and their actual presence in the diet, and to compare the electivity values shown by brown trout of different ages.