Feeding ecology of Padogobius nigricans (Canestrini, 1867) and P. bonelli (Bonaparte, 1846) in Aggia River (Umbria, Italy) and their diet overlap

The Arno goby Padogobius nigricans is an endemic species to Central Italy. The populations of this species are in sharp decline due to habitat modifications and potentially competition with Padanian goby Padogobius bonelli, an endemic species to Northern Italy, introduced in some watercourses of Central Italy. The purposes of this paper were to analyze dietary composition of the two species, determine the degree of overlap in their diets and investigate the feeding ecology of P. nigricans in terms of absence and presence of the alien species. Specimens were collected from the Aggia River, a tributary of Tiber River. Gut contents were analyzed and prey items were identified to the lowest recognizable taxa and counted. All the obtained results showed that P. nigricans and P. bonelli in the Aggia River share a similar diet. Both species fed extensively on Chironomids and no statistically significant ontogenetic changes in feeding habits were found. A high degree of diet overlap was observed. Diet of P. nigricans and P. bonelli also included fish and where the species live in syntopy, individuals belonging to Padogobius genus were found in stomach, suggesting that mutual predation may occur.