Age frequency, growth, and mortality of Aphanius fasciatus were studied using 1084 specimens collected from three locations in the Messolongi and Etolikon lagoons. The three sampling stations, Rebakia, Astrovitsa, and Alykes, differed in terms of physicochemical parameters of the water, composition of the bottom, depth of the water, and presence of predators. The caudal fin was longer in males than females. Specimens from the station with a high salinity regime (Alykes) had longer caudal fins than those from the other stations. The region with rich vegetation of shallow waters (Rebakia station) had the highest number of age classes. The Rebakia specimens were also heavier than those of the other stations. At Alykes, females were heavier than males for fish of the same length. Females, and specimens from Rebakia had longer observed and back-calculated total lengths at each age class, than males and specimens from Astrovitsa (area with deep waters and fish predators present) and Alykes, respectively. The values of total mortality were higher for males than females. At Rebakia the mortality rate of both sexes was lower than at Astrovitsa and Alykes.