Salinity alterations in freshwater ecosystems greatly affect the survival and life history of zooplankton and, therefore, have an effect on higher trophic levels. Salinity is an essential and critical factor in determining the presence, dominance, and succession of organisms. After being collected in the field, Scapholeberis mucronata and Simocephalus vetulus were brought to the laboratory in water. Under laboratory conditions (24 +/- 1 degrees C; 16:8 h photoperiod), we evaluated the effect of different salt concentrations on the neonates. The LC50 values were determined at different halotolerance levels for S. mucronata (0.375 g L-1) and S. vetulus (0.250 g L-1). Results of experiments demonstrated that S. vetulus was more sensitive than S. mucronata, which has hyponeustonic behavior. Morphometrics of the body in salinity stress were measured for S. mucronata. In the measurements of body length, body width, and spine lengths, there were significant differences determined by post hoc analysis between the control, 0.250, and 0.375 g L-1 dose groups and the 0.500 and 0.625 g L-1 dose groups. However, no clear relation between ovum size and salinity concentration was found. This study demonstrated how an increase in salinity significantly affects survival and life history properties, which can cause changes in the zooplankton community structure.