The worldwide trend of continually increasing records of non-native species has resulted in an increasing number of potentially invasive species that have a dramatic impact on native biota. In the case of a predator introduction, its impact is mainly displayed via the consumption rate of native species. The non-native fish – round goby (Neogobius melanostomus) poses a serious threat to native macrozoobenthos, which represents a main diet component in invaded or seasonally colonized regions. Therefore, a quantification of the consumption rate of invasive, emergent, or potentially invasive predators is a keystone step to their effective management and prevention of continuous spreading. The functional response (FR) evaluating predator-prey interaction based on predator foraging efficiency has become an effective tool in ecological modelling to determine a predator foraging efficiency. Moreover, this method allows to experimentally determine the foraging efficiency of the invasive species under various biotic factors, as in the present Ph.D. thesis, or to compare the impact of non-native species with its native analog. In the present thesis, various prey types in density gradients were offered to the round goby to determine the FR and impact potential (IP) of this species. Based on the results, the foraging efficiency, foraging capacity in multiple prey systems as well as under stress caused by presence of apex predator or regarding population size structure in the round goby were quantified.The round goby showed a type II FR in all experiments, including different prey types, such as isopods, or chironomid larvae or early stages of crayfish. Neither the body size of the round goby as a predator nor the tail-flip antipredator strategy of the crayfish as a prey changed the type of FR. The round goby showed equal handling time and significantly lower attack rate to isopods than crayfish when both prey types were offered separately. The combination of both prey types led to prolonging the round goby handling time and increased or decreased attack rate depending on the ratio of both preys. Despite that, no prey selectivity was detected in the round goby except for the highest prey density (100 individuals.box-1), where crayfish were preferred. The round goby can seriously threaten native endangered crayfish species in smaller tributaries where it continually or seasonally spreads, regarding its equal foraging towards tested prey and lower reproduction rate of crayfishes.Our results also confirmed that the predator (round goby) body size represents an important parameter influencing its foraging efficiency towards isopods. Small individuals showed significantly lower attack rates and longer handling times than large ones. However, the lower per capita foraging efficiency of the small individuals is compensated by their numerical dominance in population structure. Therefore, the small-sized cohort of the round goby reached the highest overall impact potential (IP) compared to medium or large-sized cohorts with lower proportional abundance in the investigated population. Nevertheless, overlooking the body size structure of the round goby population in calculating the species IP led to only a minor overestimation of the IP in the investigated population. However, the body size cohort used to estimate the round goby IP should always be cautiously chosen reflecting body size structure of particular investigated population to prevent misestimation.Although the round goby is a voracious predator of macrozoobenthos, our results showed that chemical cues signalizing predation risk by the apex predator (European eels) remarkablyinfluenced both attack rate and handling time of the round goby as a mesopredator. The chemical cues of the European eel combined with conspecific alarm cues significantly decreased the attack rate of the round goby. On the contrary, the handling time was significantly prolonged if the round goby was exposed to chemical cues of European eel fed by heterospecific prey. These findings suggest that optimized management of apex predator populations might lead to a decrease in the impact of the round goby at the invaded areas driven by its lowered consumption rate.The round goby’s non-selective foraging and effective consumption of a wide prey spectrum make this fish a serious threat to native freshwater biota. Even small round goby individuals having lower consumption rate may reach a high total impact potential upon invaded ecosystem regarding their abundance population. Despite that, it seems that native apex predators through their non-consumptive effect can noticeably decrease the overall round goby’s negative impact. However, that relies on rehabilitating the native apex predator population, which depends on restoring freshwater ecosystems currently facing highanthropogenic pressures. This work was carried out with the support of the South Bohemian Research Center of Aquaculture and Biodiversity of Hydrocenoses (CENAKVA, ID 90238) in accordance with the objectives of the european consortium DANUBIUS-RI.