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.
Currently, the relevance of echinococcosis is due to their wide prevalence in Russia. Cases of the disease are registered in more than 30 of the 88 administrative territories of the country. In establishing the final diagnosis of echinococcosis, the main importance is given to instrumental (ultrasound, CT, MRI) and serological methods (determination of specific antibodies based on ELISA). However, imaging methods in some cases do not allow to differentiate echinococcal cysts from other volumetric formations, and serological tests can give false negative results. Hydatidoses are characterized by a long course, and are often diagnosed late when complications develop. The surgical method is considered a radical method of treatment. Confirmation of the diagnosis is the results of pathomorphological examination of the surgical material. Of the 47 examined samples of operational material performed by cito! Protoscolexes of E. granulosus were found in 31 patients (65.7%). In two cases (4.3%), only single hooks of larvae of this parasite were found in the studied samples. In three patients (6.4%), the echinococcal nature of cysts was confirmed by delayed pathomorphological studies of the surgical material with the production of histological sections. In eleven patients (23.4%), the parasitic nature of the volume formations was excluded.
Studies of the parasite fauna of rainbow trout have revealed a number of pathogens of parasitic diseases at enterprises that use open water bodies as sources of water supply. Of the parasitic protozoa, the most dangerous is Ichthyophthirius multifiliis. This is due to the presence of a free-living stage in this ciliate, as well as to the possibility of localization under the fish scales. Of the helminthiases that occur in rainbow trout during artificial cultivation on the farms of the North-West region of Russia, the most problematic are monogenes and cestodes, which cause gyrodactylosis and trienophorosis. The plerocercoids of the cestode Triaenophorus crassus, in particular, are localized in the musculature of fish and, with a high degree of invasion, trout loses its commercial value. In the presence of a focus of parasitic diseases in natural reservoirs, wild fish are a reservoir of invasion, aquatic invertebrates (planktonic crustaceans, molluscs) are the most important element of the parasite-host system, and fish-eating birds, being the final host, contribute to the spread of invasions. In cage farms, due to the peculiarities of the cultivation technology, the fight against parasitic protozoa is extremely difficult and requires significant labor costs. In basin farms, on the contrary, the design of fish-breeding tanks and the water supply system allows for the most efficient implementation of therapeutic and prophylactic measures. Nevertheless, outbreaks of parasitic diseases can be observed in violation of the cultivation technology (overcompaction of the planting, violation of the feeding regime, etc.). Control of the epizootic state makes it possible to identify infection and carry out a set of necessary therapeutic and preventive measures.
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