Mercury distribution in tissues of black sea gobiids from the coastal zone of Sevastopol

Introduction. Marine aquatic organisms, especially with nutritional value, accumulate pollutants from the environment and therefore must be constantly monitored for toxic elements content. Mercury, even in inorganic form and in sub-lethal amounts, is a risk factor for aquatic biota. The aim of the work is to measure mercury concentrations in the tissues of the Black Sea gobies; identification of species accumulating mercury to a greater or lesser extent, as well as intraspecific features of mercury accumulation. Material and methods. Muscles, liver and gills of Black Sea goby fish (round goby Neogobius melanostomus, niger-goby Gobius niger, knout goby Mesogobius batrachocephalus, caught in 2019–2020) were used as material for the study of mercury concentration. The population parameters of the fish caught in the bays of the Sevastopol were analyzed, and then the organs were prepared for the study of the mercury content in them using the atomic absorption method. Food objects were also examined using a binocular microscope. Results and discussion. Mercury was detected in all analyzed samples, but the concentrations observed in fish tissues are below the legal level of sanitary and hygienic standards for marine fish (0.5 mg/kg). The average concentrations of mercury in the liver of different species of gobies exceeded the concentration of mercury in the gills, with the exception of the round goby. On average, the knout goby accumulates more mercury than the round goby and the black goby. In M. batrachocephalus, unlike other species of Gobiidae, a correlation was found between age and mercury concentration in fish organs: high correlation in muscles (0.7 < r = 0.75), significant r — in gills and liver. The connection between the standard length of species analyzed and the concentration of mercury is characterized as: middle — in the gills, high — in the liver. The revealed differences in the cumulative capacity of the objects studied are associated with different nutritional preferences. Almost all the intestines of the toad (knout) goby at the time of capture were empty, which indicates a faster digestion of food objects, as well as the coincidence of the time of capture with a long starvation associated with spawning and protection of eggs laying. Consequently, in this species, the main “load” falls on the gills, which indicates the route of toxicant entry into the body mainly through respiration, and not through food chains. In round goby, the toxicant studied, on the contrary, enters through food objects — bivalve mollusks. The black goby has the widest food spectrum; values of mercury content, comparable with other species of Gobiidae, are associated with the natural accumulation of the toxicant (with age), partial ingress of mercury through food chains. Conclusion. Mercury concentrations in different tissues of gobies did not exceed the legal standard for marine fish. The average values of mercury concentration in the liver of different gobies exceeded those in the gills, with the exception of N. melanostomus. On average, the toad goby accumulates more mercury than other species of Gobiidae. A relationship was found between the standard length of the goby and the concentration of mercury: in the gills — moderate, in the liver — significant. The studied fish species can be considered as suitable indicators of mercury pollution in the Sevastopol bays. Limitations. When studying the level of mercury accumulation in the tissues of the Black Sea gobies from the coastal zone of the Sevastopol, 137 samples, and at ichthyological analyze — 190 round goby, 50 knout goby, 20 niger goby were done, which is a sufficient sample volume to describe the degree of toxicity of different fish tissues, as well as the mechanisms of mercury accumulation.