Non-native western tubenose gobies

The tubenose goby, Proterorhinus semilunaris, has expanded its range throughout Europe. Comprehensive studies to identify its impact on native riverine ecosystems, however, are relatively scarce. Here, we evaluate dietary preferences of P. semilunaris on a non-native river to reveal any such impacts. Fish were sampled monthly over 2011–2012 from three sites along the River Dyje (Czech Republic; Danube basin) with differing population levels and food availability. Both the amount of food consumed and dietary composition varied seasonally, with site having a strong effect. Food consumed differed between males and females, but not dietary composition; while diet differed between age classes, but not food consumed. In general, Trichoptera, Chironomidae and zooplankton dominated the diet at all sites, with Trichoptera taken more often earlier in the year and zooplankton later. Mussels were always avoided, despite high abundance, while less preferred prey were occasionally taken in high numbers in response to increased availability or energy demand (e.g. spawning). Fish eggs and fry (all P. semilunaris) were only taken in high numbers at one site, being related to high population level and fry drift from a reservoir. Male feeding declined over the breeding season, presumably due to nest guarding, while female feeding declined over winter, possibly resulting in high mortality. Proterorhinus semilunaris is a feeding opportunist, which may facilitate colonisation in habitats with poor prey availability. No predation pressure on native species was observed through consumption of eggs or fry, though small/young indigenous fish may be affected through diet competition.