When the salinity was gradually changed, the respiration was retained in all groups in the interval from 0 to 17 parts per thousand (temperature 18-20C). However, in salinities above 10 parts per thousand, the organisms gradually die (the cause of their death is the disturbance of the osmoregulatory processes). The method of physiological adaptations that was applied made it possible, on the one hand, to determine the optimal and lethal salinity metabolism zones for each ecological group of organisms living in confined natural salinity conditions, and, on the other hand, made it possible to determine their 'potential resistance.' The potential metabolism resistance for all Dreissena that were studied turned out to be the same. This indicates the close affinity of various groups of Dreissena. Hence, the potential resistance is a characteristic feature of the species or even the genus.