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The distribution and coexistence of gill ectoparasites of 121 specimens of Cephalopholis argus Bloch et Schneider, caught between October 1994 and October 1995, were investigated. Adults of the monogenean Benedenia sp. and copepod Hatschekia sp., the larval caligid copepod Caligus sp. (copepodite and chalimus stages), and praniza larvae of the isopod Gnathia sp. were found. All species were aggregated within the host population. Infracommunities were poor, with only 40.5% of fish infected by two parasite species. Only two individual fish harboured all the parasite species observed at the component community level. Prevalences were less than 50% and mean intensities were low (less than 6 parasites/host). No dominant parasite species were observed in the host population. The spatial distribution of each parasite species was studied on different partitions of the gill arches. Adult parasite stages that are mobile showed much overlap in their distribution, whereas temporarily attached larvae of Caligidae were more site specific. Copepodite and chalimus larvae showed niche restriction that is probably due to gregarious behaviour. Positive associations between caligid larvae reflected intraspecific interaction for site and/or resources. Each of the Caligus sp. larval stages prefers specific sites, as do the adults, which occur exclusively in the buccal cavity of the host. Infracommunities were too poor and too few to induce processes of interspecific competition.

A study on the spatial distribution of two congeneric monogenean species Pseudodactylogyrus anguillae Yin et Sproston, 1948 and P. bini Kikuchi, 1929 on the gills of large size European eel Anguilla anguilla (L.) were conducted. Results were analysed with regard to: single-species infection, mixed infection and general occurrence of the parasites in the eel population. Statistical analysis revealed that the distribution of these species on the gill apparatus is fairly similar and the zones in which they occur more numerously coincide to a great extent. However, a number of differences were found. Both the possibility of simultaneous occurrence on the host and similar distribution of the above species on the eel's gills indicate the reciprocal tolerance of these parasites.

In piglets suffering from natural coccidiosis, post-mortem examination showed that pathological changes induced by Isospora suis were evident from day 7 to day 14 of life, and particularly, by days 9 and 10. Macroscopically, the changes were manifest as enteritis varying from catarrhal to pseudomembraneous form. Microscopically, they consisted of more or less extensive atrophy of villi whose apical parts were necrotic, of metaplasia and erosion of epithelium. With the exception of duodenum and the adjoining sector of jejunum, the alterations were manifest along the entire small gut though intensity of lesions and incidence of endogenous stages of Isospora suis varied from sector to sector of the intestine. Predilected was a portion limited approximately by 50 and 140 cm cranially from ostium ileocecale, viz. the caudal sector of central jejunum and the cranial sector of the caudal jejunum. Within this area, lesions were more severe and frequent than in sectors situated cranially and caudally of it. The predilection persisted even in case of concurrent adenovirosis. The lesions contained meronts and gamonts at the same time though gamonts predominated. Advanced merogony and gametogony resulted in distinct displacement of cell nuclei and in cell walls bulging into the inner diameter of the gut. We assume that endogenous stages of Isospora penetrate the submucosis via the narrow opening at the orifice of lymph follicle; such was the case with gamonts and oocysts detected in activated lymph tissue of Peyer's patches.