Since its discovery in the year 2000 in the Austrian waterbodies, the Round goby (Neogobius melanostomus) has become the most abundant bottom dwelling fish species in the Danube River. Thus, it is now a crucial key stone species in the riverine food web. In order to gain information on the diet of N.melanostomus in Austria, especially in terms of the impact of hydropower plants, specimens were collected by longlines (n=167) and electrofishing (n=52) in the impounded sections from March 2014 to October 2014. Additionally, in July 2014, 61 individuals were caught by electrofishing in the Donau-Auen National Park, which is still a free flowing section. Diet analyses were carried out by dissections. Prey items were identified at least on order level, where possible up to species level, and quantified by a visual estimation (gridded petri dish). Means for the assessment of spatial, seasonal and ontogenetic variation in dietary habits were the Costello (1990) method, qualitative profiling and quantitative cluster analyses. Moreover, an additional goal was to express the resource polymorphism. Benthic insect larvae (Diptera, Trichoptera) and invertebrates (Mollusca, Crustacea) were the dominant prey elements in N.melanostomus diet. Piscivory was not observed in any individual at any time. Further, 25 different feeding profiles were described. Moreover, the investigated population was subdivided according to its predominant prey item in four dietary groups (Mollusca-type, Crustacea-type, Diptera-type and Mixed-type). We documented distinct spatial, seasonal and ontogenetic differences in their diet. The diet of those specimens affected by the impoundment differed remarkably from those of in the National Park.