The Outlying Mean Index (OMI) method was used to test a microhabitat partition of P. anguillae and P. bini communities parasitising European eel (Anguilla anguilla L.) in four seasons. No differences in occurrence of parasites were found in different seasons or on different gill arches. The OMI analysis showed that hemibranch separation and gill segments were the main factor explaining variation in parasite niche occupation for the first factorial axis which was generally more significant than the second factorial axis. The OMI and Tolerance indices were compared for both species in the seasons studied, and the main differences between species indices were recorded. Pseudodactylogyrus anguillae and P. bini communities were partitioned in the seasons with higher epidemiological parameters of the infection. In seasons with low epidemiological parameters of the infection or in seasons where parasite species show preference for gill arches, the characters of gill division (lower level of gill division than gill arches) were not important for partition of the Pseudodactylogyrus communities. The Outlying Mean Index (OMI) method was used to test a microhabitat partition of P. anguillae and P. bini communities parasitising European eel (Anguillae anguilla L.) in four seasons. No differences in occurrence of parasites were found in different seasons or on different gill arches. The OMI analysis showed that hemibranch separation and gill segments were the main factor explaining variation in parasite niche occupation for the first factorial axis which was generally more significant than the second factorial axis. The OMI and Tolerance indices were compared for both species in the seasons studied, and the main differences between species indices were recorded. Pseudodactylogyrus anguillae and P. bini communities were partitioned in the seasons with higher epidemiological parameters of the infection. In seasons with low epidemiological parameters of the infection or in seasons where parasite species show preference for gill arches, the characters of gill division (lower level of gill division than gill arches) were not important for partition of the Pseudodactylogyrus communities.