[The structure of fish helminth populations]

Typification and some qualitative characteristics of populations of the fish helminths are given which allow to explain some peculiarities of their numbers, genetical interrelations, action of immunological factor. Simplification of the structure of helminth populations provokes large fluctuations of the helminths number. Differences in the structure of helminth populations are to be considered as one of mechanisms of development of stability of parasitic system.