What makes a fish a suitable host for Monogenea in the Mediterranean?

Monogenean richness of marine fish is highly variable among host families and species. On the basis of 160 fish species selected because their parasite fauna was considered as ‘adequately’ investigated, an attempt was made to find associations between parasite richness and various characters of the hosts. No clear correlation was found with maximal size, although the smallest species (less than 10cm) seem to never harbour monogeneans. Correlations were found with nectonic, migrating and gregarious behaviours. However, taxonomy of fish appears to be extremely important as a determinant of monogenean richness. In the absence of a satisfactory phylogeny of hosts, no attempt was made to control the analysis for phylogeny. However, removing some families characterized by a high parasite richness (sparids, sciaenids, mugilids) shows that the association with gregariousness holds, whereas the others tend to disappear.