Almost half of the sampled fish population located in Saronikos gulf harboured the infection with S. chrysophrii at a low mean parasitic intensity (< 1.5 adults) (Table 4). Prevalence and mean intensity showed an increasing pattern while the experiment was progressing. Prevalence reached a 100% level during the whole medication period while the mean intensity was insignificantly higher in control fish, 30 days after the initiation of treatment. At the final sampling however, mean intensity was significantly reduced in fish administered caprylic acid. S. chrysophrii eggs were observed only during the second month of the trial in 21 and 25% of sampled treated and control fish, respectively. Another monogenean, the diplectanid Furneshetinia echeneis was also diagnosed in both groups at low intensity (Table 4). Growth remained unaffected by caprylic acid treatment. Cumulative mortalities within sampling period were below 1 and 1.7% in treated and control fish, respectively.