Differences in the occurrence of monogeneans on lamellae of fish gill arches were observed in this study. These differences were attributed to variations in water current on the gill surfaces or to greater area of certain arches. Two computer simulation programs based on gill area and water current were written to generate parasite melapopulations with clumped patterns. The results obtained were compared with true distributions of selected freshwater monogenean taxa. The combination of both theoretical models (gill area and water current) had greater explanatory power than either of the models alone.
During surveys of parasites of the whitemouth croaker Micropogonias furnieri (Desmarest) and the mullet Mugil platanus Günther from Samborombón Bay, Argentina, Trichodina puytoraci, T. lepsii, T. jadranica, T. murmanica, Diparitella simplex and Trichodina scalensis sp. n. were morphologically studied. Taxonomic and morphometric data for these trichodinids based on dry silver nitrate-impregnated specimens are presented. This study is the first formal report of these trichodinids from the southwest Atlantic Ocean, and the description of a new species from M. platanus.