Comprehensive condition assessment of the black-backed sea shad (<i>Alosa kessleri</i>, Grimm, 1887) in the Lower Volga

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The purpose of the research is to assess the condition of the black-backed sea shad (Alosa kessleri, Grimm, 1887) in the Lower Volga according to parasitological, microbiological, toxicological, and biochemical parameters, and to determine the correlation between the above during the spawning. Materials and methods. The research object was the black-backed sea shad caught with a river shore seine. Sampling for comprehensive studies was performed from 15 black-backed sea shads during the spawning migration in 2017. The fish were studied by the method of partial parasitological dissection (the protozoa class was not studied). The fish were collected and dissected, and cameral treatment was performed per Bykhovskaya-Pavlovskaya method. Microbiological studies were conducted by common methods. Species identification of identified helminths and microorganisms was performed according to standard identification guides. Toxicological studies included the determination of lead, cadmium, mercury, and petroleum hydrocarbons in the muscle tissue of the studied shad specimens by atomic absorption. In fish muscles, we studied the number of total lipids by the Zollner method, and water-soluble protein by the spectrometric Warburg-Christian method. The Fulton's condition factor was used for fatness determination. The obtained results were processed statistically. Results and discussion. The results of the comprehensive studies of commercial species of the black-backed sea shad (Alosa kessleri, Grimm, 1887) showed that the parasite fauna of fish was distinguished by a poor species composition as contracted with a qualitative microbiota biodiversity. Infection of the black-backed sea shad proceeded at the asymptomatic carrier level, which indicated a balanced relationship between parasites and the host. The levels of accumulated toxicants in shads were close to the characteristic values for fish in the Volga-Caspian basin. On average, the stock of energy resources in the studied fish had a positive trend in relation to the previous research period. The study results of the black-backed sea shad during the spawning showed the correlation of parasitological, microbiological, toxicological, and biochemical parameters that comprehensively affect the general physiological state of the studied fish.