The planktonic ciliated protozoa of 2 Ponds of increasing salinity were investigated in the saline of Sfax, Tunisia. The samples are taken from the two basins (A5 and M2) of salinities 42 p.s.u and 216 p.s.u. At the level of these two basins, we have followed the structure and composition of the ciliary populations concerning the physic-chemical parameters of the environment, particularly the importance of salinity and the fixative's choice on the ciliated protozoa. In the Sfax saltworks, the water's salinity gradually increases from the A5 basin (S = 42p.s.u) to the M2 basin (S = 216 p.s.u). This increasing gradient in salinity has an influence on the evolution and structure of biological stands. Salinity was considered the fundamental ecological parameter for the distribution of planktonic populations in the Sfax saltworks. With regard to water temperature, water density, and MES, the latter increase with the increasing gradient of salinity. Accurate determination of the abundance of ciliates is crucial for estimating the carbon balance. However, the effect of fixatives on the abundance and biomass of ciliates was examined in cultures, lakes, and marine ciliates.