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Abstract

The golden grey mullet Chelon auratus (Risso, 1810) is a valuable commercial species, ranking first among the Black Sea indigenous mullet fish in commercial and recreational fishing (Boltachev & Karpova, 2012). The high importance of C. auratus in the regional fishery for demersal fish requires the development of a system for assessing of the health status of this species. Carrying out this kind of researches are based on an integrated approach and includes the use of biochemical and pathomorphological methods, that allow you to study the changes that occur in the fish organism before the appearance of visible changes, disruption of the processes of growth and reproduction, reduction of their commercial size and population. The aim of the investigation was studying of pathomorphological changes in complex with some biochemical indicators of golden grey mullet tissue to assess its state of health. A visual examination and pathological autopsy of fishes were carried out. For histological analysis, samples of gills, liver, kidneys, gastrointestinal tract, spleen and pancreas were fixed in a Davidson solution and processed using standard methods. The state of the fish organism based on histological studies was carried out using a modified semi-quantitative analysis of alterations according to the Bernet et al. protocol (1999) and assessing the prevalence of damage to organs according severity gradation scale. The factors of significance of the identified lesions, the values of organ alteration indices and the general pathology index of golden grey mullet were determined. During biochemical studies, the level of oxidized proteins (OP), lipid peroxidation (LPO) and urea, the activity of aminotransferases and alkaline phosphatase (ALP) in the liver, and the concentration of albumin and glucose in the blood serum were determined. The four reaction pattern (circulatory disorders, regressive and progressive changes, inflammatory processes) and parasites were found in the organs of golden grey mullet. The parasitic agents, which identified in juvenile mullet were represented by several species belonging to different systematic groups (protozoa, monogenes, trematodes, nematodes). The most severe histopathological changes were caused by a parasitic protozoan presumably Ichthyophonus sp. In a semi-quantitative assessment of the identified alterations of fish, they were conditionally divided into two groups: conditionally healthy and infected individuals, between which a comparative analysis of pathomorphological data and some biochemical parameters was carried out. Significant differences were found in the values of organ alteration indices between two groups of C. auratus in the kidneys, liver, gastrointestinal tract and pancreas. The values of the general index of fish pathology also significantly differed. During biochemical studies, a significant increase in the urea content in the liver of fish from the second group was determined, which may indicate a damage of the excretory function of the kidneys and gills and is confirmed histologically. Significant differences in the level of LPO and OP, as well as the activity of aminotransferases in the liver of conditionally healthy and infected groups of mullets were not detected. The results of the work confirm the great information content of the studied indicators for assessing the state of health of the golden grey mullet.

Authors

T. Gavruseva

senior researcher, PhD

https://orcid.org/0000-0002-9102-0861

https://www.elibrary.ru/author_profile.asp?id=292944

T. Sigacheva

senior researcher, PhD

https://www.elibrary.ru/author_items.asp?authorid=814387

I. Chesnokova

senior researcher, PhD

https://orcid.org/0000-0002-7883-0755

https://www.elibrary.ru/author_profile.asp?id=772853