For this study 368 roach (Rutilus rutilus) were examined and 37 parasites and 93 Ligula intestinalis were found in the abdominal cavity of the host (prevalence 10.1%, mean intensity 2.51 specimens/fish). Based on season, the highest number of infected fish occurred during summer (33.3%, 4 parasite/fish), and during the other season the mean intensity of infection was relatively low (prevalence 3.3%, 1 specimens/fish). On the other hand, the parasite species was determined especially on small

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... medium host fish sizes (2.17-100%). Basic criteria for the assessment of the parasite species of host fish were the general parameters related to parasite populations, which are prevalence, mean intensity, seasonal variation, and relationship between host size and infection.