Spatial distribution of Dactylogyrus (Monogenan) on the gills of the host fish

The spatial distribution of six Monogenean species, Dactylogyrus extensus, Dactylogyrus auriculatus, Dactylogyrus difformis, Dactylogyrus difformoides, Dactylogyrus amphibothrium and Dactylogyrus hemiamphibothrium on the host fish gill was investigated. There were no preference found in the distribution of Dactylogyrus species over the gill arches between left and right sides of the hosts. There were, however, preferences for the specific gill arches or for particular faces of the hemibranches. The first gill arch (I) was preferred by D. amphibothrium, gill arch II by D. auriculatus, gill arch III by D. auriculatus, D. difformis and D. difformoides, and gill arch IV by D. difformis and D. difformoides. D. extensus, D. auriculatus exhibited a preference for the inner side of the gill. Furthermore, D. extensus showed preference for the distalmedian and distal- ventral parts of the gill, D. auriculatus preferred proximal-ventral, and proximal median segments and D. difformis and D. difformoides preferred distal-dorsal segments of the host fish. These specific preferences might be effected by the interaction of several factors such as differences in the water current over different parts of the gill surface, parasite density, as well as ecological and morphological differences between monogenean species