Cryptic alternative male mating strategies in invasive alien round goby (Neogobius melanostomus) of the upper Danube River

Male alternative mating strategies are a widespread life history choice, yet they have hardly been assessed in the context of fish invasions. As established proxies for alternative life-history strategies, body length and sexual maturity of Ponto–Caspian round goby (Neogobius melanostomus) from the recently invaded upper Danube River were contrasted and differential trophic niche occupation was assessed. Only about 4% of analyzed gobies qualified as potential sneakers which may be explained by the recent and ongoing invasion process. This study provides evidence for the occurrence of sneaking behavior of invasive round goby in the upper Danube River.