Invasive Carassius spp. in the Tiber River basin (Umbria, Central Italy): population status and possible interactions with native fish species
The purpose of the research was to analyse the distribution, abundance and growth of Carassius spp., a taxon which includes non-native species introduced into the water bodies of the Umbrian portion of the Tiber River basin during the late 1980s. Additionally, the study estimated the relative weight for Barbus tyberinus, Squalius lucumonis and Sarmarutilus rubilio to investigate the presence of competitive interactions between Carassius spp. and these native species that characterize the middle and lowland reaches of the Umbrian watercourses. Currently, Carassius spp. is widely distributed in both the stagnant and the slow-running waters of the entire basin. The presence of these species was recorded in 34.81% of the total sampling sites; the results showed that the presence of Carassius spp. was associated with the presence of other non-native species and with poor water quality. In total, 4520 specimens of Carassius spp. were collected and the age composition ranged from 0+ to 9+. The equation for the length-weight relationship (TL-W) was determined as W = 0.010TL3.180. For the Etruscan chub Squalius lucumonis, an endemic species of central Italy, the mean value of the relative weight was significantly higher when Carassius spp. was absent. The results of the research suggest the need to establish effective management conservation strategies for this endemic species.