Reproductive parameters in native and non-native areas of Padogobius bonelli and comparison with P-nigricans (Actynopterigii, Gobiidae)

The introduced goby Padogobius bonelli has established abundant populations in the River Tiber basin (Central Italy) and its expansion coincided with the decrease of the endemic P. nigricans. P. bonelli exhibits a more aggressive behaviour than P. nigricans, but other biological attributes may advance its colonization success. To test this hypothesis, some reproductive parameters (gonado-somatic index, age at maturity, egg size, absolute and relative fecundity) of a long-time established non-native population of P. bonelli were analysed and compared to a population from the native area as well as to those of P. nigricans inhabiting the same river. As a result, no differences between non-native and native populations of P. bonelli were observed. On the contrary, non-native P. bonelli showed higher values of gonado-somatic index for both sexes, a more protracted spawning season and produced a greater number of eggs than P. nigricans. These results indicated a greater reproductive output of P. bonelli that can enhance its invasion process and favour the expansion outside of its native range, causing further decline of P. nigricans populations.