Global biodiversity and ecosystems are highly impacted by anthropogenic activities, such as climate change and introduction of non-indigenous species (NIS). As numerous species from the Ponto-Caspian region have established in the North and Baltic Seas, as well as in the Laurentian Great Lakes, there have been large number of studies examining environmental tolerance of these species to determine their future spread potential. However, many of those studies were conducted only on adult stages, while neglecting possibility that early life history stages might not be equally resilient. To determine if juveniles would demonstrate the same environmental tolerance as their parents, we examined salinity tolerance of adults and juveniles of one Northern European (Gammarus salinus), one Ponto-Caspian (Pontogammarus maeoticus) and one North American species (Gammarus tigrinus). Additionally, we compared our study to that of Paiva et al. (2018). Our study determined that both adults and juveniles of all three species tolerated wide ranges of salinity, with juveniles of G. salinus tolerating slightly narrower salinity range, while those of P. maeoticus and G. tigrinus 12 g/Kg narrower salinity range than their parents. Even though, at the end of the experiments mortalities of adults among species were not so different irrespectively of the treatment, our study determined better performance of juveniles of G. salinus in higher salinities and those of P. maeoticus in lower salinities. Therefore, based on juvenile salinity tolerance, our study in a way supported findings of Paiva et al. (2018), where Northern European species perform better in higher, while Ponto-Caspian in lower salinities. As early life-history stages are often less tolerant to environmental variabilities than adults, as well as water chemistry and parasitism differ among habitats, it is of great importance to take into account all of these factors when predicting future resilience of ecosystems and biodiversity change.