The study was to investigate changes in infestation levels of Ergasilus lie on economically important fish species, thick lip grey mullet (Chelon labrossus) from Beymelek Lagoon Lake located on the western Mediterranean coast (Antalya, Türkiye). In context, the infestation levels of E. lizae in relation to fish sexes, fish sizes and season were evaluated statistically. The research was conducted seasonally between May 2008 to April 2009, and the gills belonging to 103 fish samples were examined. The overall infection prevalence and mean values were 60.2% and 15.95, respectively. A total of 998 parasites were counted during the study period. The prevalence and mean intensity of E. lizae for thicklip grey mullet male and sexually unidentified fish samples (92%, 16.78; 55%, 21) were higher than that for females (48.3%, 13.61) respectively. E. lizae accumulated on host male and unidentified individuals than that female. The number of parasites found in a single host male and unidentified individual were counted as almost twice the number of parasites found in females. Prevalence and mean intensity were determined the highest in size class I with 69.6% and 26.3, and almost the same values in size groups II and III. E. lizae on host fish was observed in every season. The highest prevalence and mean intensity of E. lizae was recorded in spring with 100%, 24.88. About 60% of the total number of parasites counted were recorded in the spring. The lowest prevalence of E. lizae was recorded in summer at 12% and the lowest mean intensity of E. lizae was in the summer and the winter respectively with 9, 8.67 respectively. The infestation level of E. lizae was statistically significant with host sex and season, but there was no effect on fish size groups.