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The material represented by 75 specimens of minnow of the age 2-2(+) was collected according to the standard technique in the Chovju River (tributary of the Vychegda River, a region of the settlement Nizniy Chov, district of Syktyvkar town) during the period June-September 2000. The quantitative estimation of the structure of the component parasite communities was performed by calculating errors of the equation of regression for each species group separately, with subsequent summarizing of means of errors by all parasite groups comprising the community (Dorovskikh, 2001 6; 2002 B). In order to have a possibility to get data complementing each other, the calculation of variety indexes and other indexes have been made for metazoan parasites only and for the whole community, including the protozoan parasites. In both cases, i.e. considering only metazoan parasites and the whole composition of parasite species, three states of the component parasite community have been recognised: the formed community (June), the community in destroying (July and August), the community in the process of formation (September). In the course of working on the total species composition we recorded the beginning of community destroying on 30th of June, and the beginning of community formation in August. Considering only the metazoan parasites, the community is defined (after: Pugachev, 1999) as the mature (balanced) one in June, while in July, August and September, it was unmature (off-balance) by its characteristics. Regarding the protozoan parasites, the community in June, August and September was characterized as the mature one based on indices of parasite biomass, and as unripe one based on the number of parasite individuals; however in July, both groups of indices allowed to refer it to the unripe state. However, these unripe states are essentially different. In July, it is the result of dieing out the parasites of the past generation; in August and September, it is the result of the appearances of new generations. Therefore we recognise three states of parasite community named above. Considering the whole species composition of parasites we noted the greater difference of index values based on the parasite specimen numbers and their conventional biomass, that was in the case of the metazoan parasites only. It is particularly noticeable in the middle of the June, in the period of the formed community. This fact, together with high errors of the equations of regression and the presence of the high number of Apiosoma, points to the disturbance in the structure of component parasite community in the minnow from the Chovju River. This is easily explicable, because the Chovju River is the polluted reservoir, and pollution comes from agricultural fields, Verhny-Chov settlement, pigsties and cow-sheds. The pollution is a seasonal factor here. The most powerful pollution was noted at May-June, and then it decreased along the beginning of rains in the end of August; in September it increased again. It is important to point out that the monitoring of the metazoan parasites only allows to reveal the general dynamics of the community during the period of observation, but does not allow to catch the beginning of its destroying and developing and to notice possible disturbances in the community structure caused by pollution of reservoirs, particularly, if this pollution is a seasonal factor as in the Chovju River. Three named states of the component community of the fish parasites take place in other periods of year than this observed in the intestional parasite communities of fish helminths of the temperate climate zone. The developing of parasite communities of the intestinal helminths of the Anguilla anguilla in England (Kennedy, 1997) and of Leuciscus idus from the Rybinsk reservoir (Zhohov, 2003) starts in the beginning of summer. In May, their species diversity is minimal and in August is maximal. In conditions of the middle stream of the Vychegda River, the species diversity of parasite community associated with the minnow is maximal in June and minimal in August, when it only begins developing.