Prima segnalazione del cavedano europeo Squalius cephalus (Linnaeus, 1758) nel bacino del fiume Tevere

For the first time in the Tiber River basin (Italy) the presence of the chub Squalius cephalus was recorded. A total of 116 specimens were collected during two fish samplings carried out in 2011 e 2017 in a tributary of the Tiber river, namely Rio Grande d’Amelia. The introduction of the alien species is probably due to unauthorized stocking by local anglers. The aim of the present paper was to provide information on age and growth for this species outside its natural range. A total of 116 specimens were collected and 6 age classes (0+ - 5+ ) were identified. The equation for the total length-weight relationship was: W=0.006TL3.16. The equation of the theoretical growth curve in length was: TL=37.03(1−exp−0.239(t+0.425)). Because of its abundance at the sampling site and the presence of different age classes, including the young-of-the-year, we assumed that the species was quickly established with self-sustaining populations. Our results suggested to monitor the further expansion of the species through the hydrographic network, in order to prevent the risk of hybridization and competition with the native congeneric species, as Squalius squalus and Squalius lucumonis.