Peculiarities of the course of bacterial diseases of rainbow trut in industrial farms of North-West Russia

Abstract

Currently, in the Leningrad Region and the Republic of Karelia, trout farming is carried out mainly in cage farms, and in recent years, small closed water supply units (RAS) are gaining popularity and are actively used. In the first years of operation, outbreaks of serious infectious diseases occurring in the form of bacterial hemorrhagic septicemia, as well as toxicosis, were observed in such installations. In cage farms, a joint course of bacterial and parasitic diseases is possible. In the course of the work, 11 cage farms in the Leningrad Region and the Republic of Karelia were surveyed, as well as 4 RAS in the Gatchinsky and Luga Districts of the Leningrad Region. The manifestation of aeromonas bacterial and infection and trienophorosis in the cage farm was associated with the growing conditions — high water temperatures, lack of feeding, and the presence of a formed focus of invasion in the water source. In the spring-summer and summer-autumn periods in cage farms, the manifestation of myxobacteriosis caused by Flavobacterium psychrichila is possible. In summer, the danger is a bacterial infection proceeding as a bacterial hemorrhagic septicemia (pathogens — Yersenia ruckeri and Flexibacter columnaris). In autumn, outbreaks of pseudomonosis are possible in cage farms. The causative agent is Pseudomonas fluorescens. However, it is also possible to find Pseudomonas putida, which is more characteristic of cyprinids. In the RAS, the death of fish was caused by mixed infections. The causative agents are Yersenia ruckeri and Carnobacterium piscicola; bacteria of the genera Flavobacterium and Aeromonas. Such a complex of aeromonads with flavobacteria is characterized by increased aggressiveness and can cause a serious septic infection. Timely measures taken, including the normalization of housing and feeding conditions, as well as therapeutic and prophylactic measures, made it possible to suppress the development of infections, toxicosis and improve the condition of fish on these farms.