Hematological parameters and parasite fauna of the gudgeon Gobio gobio (Linnaeus, 1758) in a fish-breeding pond

Abstract

The gudgeon (Gobio gobio (Linnaeus, 1758)) is a very interesting object for genetic, ichtyopathological and parasitological studies. This typical bottom species is sensitive to water pollution. Analysis of hematological parameters of the gudgeon can be used as an objective indicator of the ecological state and the degree of anthropogenic impact on the ecosystem of the reservoir. G. gobio is characterized by a wide range of nutrition and is itself included in the diet of predatory fish and fish-eating birds, thus playing a significant role in circulation of various parasites. In fish-breeding ponds, the gudgeon is often the object of unwanted fish because it can be a source of diseases of valuable fish species. The aim of this research was to study hematological parameters and parasite fauna of the gudgeon in a fish-breeding pond, in which it is a "weed" species. The ichthyological material was caught in July 2018 in Granny pond (53°81.24..N, 49°93.74..E). Table 1 shows hydrochemical parameters of the pond, allowing it to be attributed to relatively clean water bodies. The research complies with the ethical principles of the European Convention for the protection of vertebrate animals used for experimental or other scientific purposes (Strasbourg, 18 March 1986). The fish were kept in separate rooms in aerated aquariums with optimal planting density, which minimized stress and anxiety levels. Animals received sufficient food. The study used a minimum number of fish, which were killed in a humane way. We conducted hematological studies of 21 individuals of G. gobio. Blood smears were fixed with ethanol and stained according to Romanovsky-Giemsa. We identified blood cells by Groff, Zinkl (1999). With each drug, differential count of white blood cells among 1000 erythrocytes in 5-10 fields of view was conducted. In order to assess the physiological state of fish and their immune status, we analyzed the ratio of blood elements, studied the leukocyte formula, determined the level of erythropoiesis, and recorded possible pathologies of erythrocytes. Research of macroparasites in 26 individuals of the gudgeon was carried out according to Bykhovskaya-Pavlovskaya (1985). For quantitative characteristics of infection of the animals, we used the following indicators: Prevalence, intensity of infection and mean abundance. The leukocyte composition of the blood of the gudgeon was characterized by a wide variety (See Tables 2 and 3). The most numerous group of cells were lymphocytes. The average percentage of individual groups of leukocytes was within the physiological norm. The exception was eosinophils, the occurrence of which in the leukogram (up to 21.82% in ind.) indicated the development of eosinophilia. The proportion of immature red blood cells in most of the studied smears did not exceed 10% (See Table 4). 66.67% of gudgeon individuals had pathologically altered red blood cells in the bloodstream; 8 different types of disorders were observed (See Table 5). The most common pathology was poikilocytosis, registered in 61.90% of fish; 2.77% of the analyzed erythrocytes were characterized by the presence of this aberration. The frequency of occurrence of cells with other types of disorders among the total number of the studied ones did not exceed the value of their appearance in spontaneous mutagenesis (1%). The parasite fauna of fish in terms of fish ponds significantly depleted (See Table 6). 2 species of parasites (the cestode Neogryporhynchus cheilancristrotus, pl. (Wedl, 1855) and the nematode Contracaecum microcephalum, larva III (Rudolphi, 1819)) infect the host by alimentary means. These species were first observed in the parasite fauna of the gudgeon of the Volga river basin. All studied individuals of the gudgeon were infected with parasitic crustaceans Ergasilus sieboldi Nordmann, 1832, which is an extremely pathogenic parasite. A high degree of fish invasion by crustaceans (up to 57 specimens per individual) can be a factor causing deviations in hematological parameters of the gudgeon.