In this study, dactylogyrid parasites on the gills of four cyprinid fishes (Blicca bjoerkna, Rutilus rutilus, Scardinius etythrophthalmus, Vimba vimba) in Lake Manyas, Turkey, were examined oil the basis of samples taken from on-site surveys carried out between January-1997 and November-1998. The intensity of Dactylogyrus infection was investigated depending on the parasite species, the years and seasons, and host fish size. Four Doctylogyrus species were identified on the gills of host fishes: D. sphyrna on B. bjoerkna, D. crucifer on R. rutilus, D. difformis on S. erythropthalmus, D. cornu on V. vimba. The prevalence and mean intensity of Dactylogyrus infection for each parasite species was determined as follows: D. crucifer (41.5%, 10.65 +/- 5.79 specimens/fish), D. cornu (14.2%, 30.24 +/- 11.30), D. difformis (28.1%, 31.71 +/- 30.95), D. sphyrna (28.7%, 16.76 +/- 16.88). While maximum intensity was recorded for D. difformis, the lowest was for D. crucifer. However, it was not a statistically meaningful difference for all the parasite species. As regards the prevalence of the parasite species depending oil the years, it was observed higher in 1998 than in 1997. Regarding the seasonal changes in the intensity and prevalence level, a very sharp decrease in the intensity levels of the parasite species was determined for the three fish parasites, except D. crucifer, between the late autumn and winter.