Feeding habits of Salmo cettii (Rafinesque, 1810) in Central Italy: studying a residual population of an endangered species using non-invasive methods

The aim of this study was to gather information about the feeding habits of Salmo cettii (Rafinesque, 1810), in order to improve managing policies for this endangered species. The study area was located in Monumento Naturale Oasi di Ninfa (Central Italy, Latium, UTM 33T 41.582341, 12.955213), and is composed by a lake, formed by several springs, from which the Ninfa stream gushes out and flows across the Natural Monument. The waterbed is completed by an intricate network of small channels, streams and pools creating a peculiar micro-hydrographic system. A total of 119 fishes were collected by electrofishing sessions. Gastric lavage was performed instead of stomach removal, considering status and low numbers of this species. The trophic strategy of S. cettii was analyzed through the modified Costello (1990) graphical method (Amundsen et al. 1996).S.cettii resulted to be specialized on Echinogammarus sp., the other preys to be considered as accessory. The Shannon and Evenness indexes describing the niche width for each age class, showed the highest values for 1+ and 2+ age classes, the most represented. Ichthyophagy is a trend meanly appearing at older age classes. ANOVA model based on mean sizes of ichthyophagous and non-ichthyophagous trouts showed a significant difference (p=0.02593), the first group with 31.39 cm mean size, the second with 21.93 cm mean size.The marked stenophagy and the weak ichthyophagy trend of S. cettii are stressed out, suggesting scarce ability in performing a strong top-down control on the stream community