The probability of occurrence of parasitic diseases of salmonid fishes in modern fish-breeding enterprises of the Leningrad region and Karelia is very significant. Wild fish, in particular whitefish, are a reservoir of invasion, intermediate and final hosts for a number of parasites that are dangerous for rainbow trout. The purpose of this work is to study the characteristics of parasitic diseases of salmonids in fishery reservoirs of the Leningrad Region and Karelia. The studies of the parasite fauna of vendace were carried out in the period from 2019 to 2020. The examination of fish for the presence of parasites and their determination was carried out according to the generally accepted standard method. Of the helminthiases found in rainbow trout during artificial cultivation in the farms of the Leningrad Region and Karelia, monogeneans and cestodes present the greatest problem, and to a lesser extent, trematodes. In the fishery reservoirs of these regions, where cage aquaculture is actively developing, whitefish live, among which the European vendace or ripus (Coregonus albula) attracts special attention. In the study of the parasite fauna of vendace, 11 species of parasites from different systematic groups were noted. At the same time, gull tapeworm Diphyllobothrium dendriticum is of veterinary and medical importance. The parasites found in vendace can potentially be dangerous for cultivated salmonids, with special attention to the monogenetic fluke Discocotyle sagittata and the cestode D. dendriticum. These representatives of the ripus parasite fauna are also dangerous for rainbow trout. The control of the epizootic state makes it possible to detect infection and carry out a set of necessary therapeutic and preventive measures. Further study of the parasite fauna of wild whitefish in the lakes of the North-West of Russia is also important for the aquaculture of the region.

According to presently used biotechnics of salmon farm reproduction, producers are withdrawn (fishing out) from spawning (fish spawning grounds), and the survival rate of one-year-old farmed juveniles in nature (in the form of “spawning return”) is half of the standard. To exclude these most important biotech imperfections, a new biotechnological approach based on the identification and use of species potencies of reproduction, survival and growth in an adequate species-specific complex of optimal habitat conditions are developing. The purpose of our full-system research is to develop effective biotechnics for the artificial reproduction of salmon fish populations in the North-West. To refine the previously developed basic full-system method of reproduction of salmon and sturgeon fish populations to the possibility of its industrial use is the main task of the work. The new “Method for production offspring of sturgeon and Atlantic salmon in seawater” includes the maintenance of brood-stock and the production of offspring of migratory fish in a wide range of salinity of the brood pond. To do this, at the onset of spawning temperatures, producers are sorted according to the degree of readiness for spawning and physiological (hormonal) stimulation of the mature producers gonads maturation are carried out with a natural hormonal preparation — an isolated anterior pituitary lobe, in established species temperature-dependent doses. And immature producers are subjected to environmental (ecological) stimulation of maturation by a periodic influx of fresh water and, upon reaching readiness for spawning, they are stimulated by preparate of the isolated anterior pituitary lobe. The method provides the efficiency increase of natural and artificial reproduction of migratory fish by expanding the possibilities of obtaining offspring from producers in the marine habitat.