Ontogeny and dietary specialization in brown trout (Salmo trutta L.) from Loch Ness, Scotland, examined using stable isotopes of carbon and nitrogen

The trophic ecology of many fish species in cold temperate lakes is often c haracterized by a generalist or opportunist strategy. In this study, the di ets of polytrophic brown trout in Loch Ness, Scotland, have been examined u sing stable isotopes of carbon and nitrogen to complement gut content analy ses and aging by otolith annuli counts. Using the stable isotope ratios, it was possible to trace trout ontogeny from parr development in a natal rive r to piscivory in the pelagic. Potential dilution of maternal isotope signa tures from eggs to parr was also demonstrated. Despite the low productivity of the loch, intraspecific variability in isotope ratios suggested dietary specialization, rather than opportunism, in some individuals.