This article considers the main results of experimental research work aimed at determination of the catchability coefficients of a fingerling survey dragnet for the juveniles of common carp and herbivorous fish species (silver carp, grass carp), conducted in the rearing ponds of the Aquaculture Research Center “Vzmorye” (“Seacoast”) in 2019–2020 with the purpose of improving the appraising method for fish assessment. The factors influencing and determining the catchability coefficient of the survey fishing gear are discussed. The methods for conducting the appraisal surveys of fish juveniles are presented. According the methodology developed by the authors for conducting experimental research work and for determination of the calculated catchability coefficient for a survey dragnet, the source data were collected and processed; based on those data, the catchability coefficients for a survey dragnet, size 15×2 m, targeting the common carp juveniles weighted 10 g and 40–85 g, have been evaluated. The possibility of using a fingerling survey dragnet for the juveniles of herbivorous fish species (silver carp of the average weight 10 g, and grass carp of the average weight 15–25 g) has been considered, and its catchability coefficients have been identified. The possibility of using a longer dragnet, of the size 302 m, in the appraising surveys of herbivorous fish species (silver carp) has been evaluated experimentally. The results showing the unfitness of the 15×2 m dragnet for the appraisal surveys of the juveniles of herbivorous fish species (silver carp, grass carp) in the rearing ponds of the Azov Sea and Don River Region upon a headwater level 0.6–1.2 m have been obtained.

This work presents the data characterizing qualitative and quantitative parameters of the roach juveniles, reared in 2020 in the spawning and rearing farms (hatcheries) of the Krasnodar Territory; the hatcheries belong both to the liman (East-Akhtarsk and Chernoerkovsk Hatcheries) and floodplain (Beysug and Yeysk Hatcheries) types. In the East-Akharst Hatchery, all migrating juveniles reached their standard weight and were characterized by good physiological status. In the Chernoerkovsk Hatchery, the weight of around 70 % of the released juveniles was lower than the normative values (300 g); their physiological status was acceptable. Density of the roach juveniles distribution in this hatchery exceeded 40,000 ind./ha, which led to high food competition. In the water bodies of the Beysug Hatchery, the average body weight and physiological status of the released roach juveniles were compliant with the normative values. In the Yeysk Hatchery, due to poor hydrological regime during the reproductive season, the efficiency of roach reproduction was extremely low.

Following the increasing anthropogenic load on the Black Sea ecosystem, monitoring surveys of phytoplankton as the foundation of the trophic pyramid become more and more essential. The data on composition and functional characteristics of the phytoplankton in the Kerch coastal waters (Black Sea), collected in the course of the expeditionary trip of the Research Vessel “Professor Vodyanitskiy” in July, 2019, are presented. The samples were collected and processed using standard methods of hydrobiological research. Estimation of the biomass was conducted using the enumerative volumetric method based on the personally collected measurement data. Mathematical processing was performed with the original software “Phytoplankton”, developed in the Laboratory of the Systems Analysis of Aquatic Biological Resources and Databases. The changes in phytoplankton composition within the hydrological layers are shown; the quantitative parameters of the development of phytoplankton communities are analyzed. Thespecies composition and the combination of the most abundant species were compliant with those of the summer season. The highest species diversity and quantitative values of the plankton were recorded in the surface and thermocline levels. Coccolithophore Emiliania huxleyi comprised the majority of its abundance, and the dinoflagellates were the most sizable in terms of biomass. The cold mixed layer was inhabited by low-species algocoenoses with low abundance and biomass.

Integration of new fishing or harvesting targets in the food production is always associated with the examination of the raw material and the products derived from it in terms of the safety for human consumption. A targeted harvesting of jellyfish in the Azov and Black Seas, according to the Fishing Regulations, is to be conducted within 15 June – 30 September timeframe that is characterized by the average daily air temperature around 25 °С. The results of investigation of microbiological characteristics indicate the possibility for preserving the quality of barrel jellyfish Rhizostoma pulmo during its cold storage. Microbiological safety of the raw jellyfish bells is determined for mesophilic aerobic and facultative anaerobic microorganisms, bacteria of the coliform group, and pathogenic microorganisms, including salmonella (Listeria monocytogenes). Recommended shelf life of chilled jellyfish (bells) is established at the duration of 4 days at the temperature in a refregirating chamber 4±2 °С, which should involve one of the possible cooling methods: with ice, by water immersion, or by aimbient air; recommended shelf life of frozen jellyfish at the storage temperature no higher than minus 18 °С is established at the duration of 5 months. It is shown that content of toxic elements (lead, cadmium, mercury, arcenic) in jellyfish does not exceed the specified allowable level.

The Veselovsky Reservoir is surrounded by agricultural land, where the use of pesticides is an integral part of the production cycle. By transferring with the air masses or seeping through the soil, pesticides can enter the water of the water bodies of fisheries importance, be deposited in bottom sediments, and negatively affect the vital activity of hydrobionts. The aim of the study was to detect the content of 20 active ingredients of the pesticides of modern classes most widely used in agriculture in the region, the half-life of which can exceed six months. It was found that the concentrations of pesticide active ingredients in the living environment of hydrobionts in the Veselovsky Reservoir are by more than an order of magnitude lower than the established maximum allowable concentrations (MAC), which indicates the relative safety of the environment for hydrobionts.

The monitoring results for the oil pollution of the Azov Sea water in the summer and autumn seasons of 2018–2020 are presented. The identified concentrations of petroleum products are given based on the total content of the main petroleum components: hydrocarbons, resins, and asphaltenes. The concentrations of petroleum products in the water ranged from <0.02 to 0.85 mg/dm3 in the summer season, and from <0.02 to 0.11 mg/dm3 in the autumn season. In some years, the weighted average values of the content of petroleum products in water exceeded the maximum allowable level: by 2.4 times in the summer season, and by 1.2 times in autumn. Based on the averaged data for the investigated period, the most severe water pollution was recorded in the central area of the Taganrog Bay and the sea itself. The highest influx of petroleum products occurs to the eastern parts of the Taganrog Bay and the sea in the autumn season, and to the southern part of the sea in summer. Along with the petroleum products identified in water, the highest content of petroleum hydrocarbons in the organs and tissues of the investigated fish was recorded in the roach, captured in the Taganrog Bay in the summer and autumn seasons of 2018. In other examined pelagic fish species of the Azov Sea (anchovy, Black Sea sprat, zander), content of petroleum products ranged at the level of determination limit.

This paper presents a review of academic sources concerning the issue of age estimation in crayfish. It describes several popular methods for estimation of the age composition of a crayfish population: age and length composition of a population, the relationship between age and lipofuscin content in nervous tissues, and counting of “growth bands”. It has been established that the most promising method for crayfish age estimation is the one based on the identification of “growth bands”. Analysis of the other methods has also shown their viability; however, for consistent age determination in crayfish, they need further elaboration.

This paper presents the analysis of the field data collected in 2012–2020 and the academic sources concerning the population status of common bream (Abramis brama) in the Veselovsky Reservoir (Rostov Region) under current biotic and abiotic conditions. In the recent period (2012–2020), 6-yearlings prevail in the age composition of the bream population; older age groups are recorded in small number. The age composition varies depending on the productivity of a generation. Absolute fecundity of the females, on average, is 96.8 thousand eggs. Fishing stocks of this species are relatively stable despite inter-annual fluctuations of its abundance and biomass, which indicates that, at present, the bream population in the Veselovsky Reservoir is in a satisfactory condition; its fishing stocks in the coming years are predicted to be at the level of 162–165 t.

Roach and zander are valuable semi-anadromous fish species, targeted by fishing operations in the Azov Sea, which necessitates evaluation of their current status. This article analyzes the data collected during the trawl surveys in the Azov Sea, the assessment of the juveniles of exploitable fish species in the Lower Don, the investigation of the reproduction in the water bodies of the Azov limans and spawning and rearing farms (hatcheries), and the monitoring of fishing catches in 2018–2020. In these three years, the feeding area of roach and zander decreased from 2,618 to 1,400 and from 1,230 to 822 km2, respectively. Roach catch decreased from 730.243 to 282.110 t. For the time, the exploitation of zander was suspended after the temporary fishing ban introduced in 2017. Age composition of the roach fishing stock consisted of four age groups; among them, three-yearlings (30.5 % by abundance, 23.6 % by weight) and four-yearlings (54.2 % by abundance, 51.4 % by weight) prevailed. Average age decreased from 3.1 to 2.8 years. Age composition of the zander fishing stock in the Don River was characterized by three age groups. In terms of abundance, three-yearlings prevailed (69.5 %), four-yearlings comprised 25.7 % of the total abundance, and five-yearlings comprised 1.5 % of it. In the Kuban River population of zander consisted of seven age groups. The most abundant were yearlings (54.4 %). Two-yearlings comprised 8.9 % of the total abundance, the share of three-yearlings was 25.0 %, and the eldest age groups of 4–7 years comprised 10.7 %. Quantities of the juveniles released in 2018–2020 from the water bodies used for natural and artificial reproduction came to be insufficient for proper recruitment to roach and zander stocks. Water bodies belonging with the hatcheries are the main sources for roach recruitment, and the Azov limans of the Krasnodar Territory serve the same purpose for zander.

A brief description of the biology, fishery and stock units of big-scale sand smelt, flathead grey mullet, and picarel is given for the Russian fisheries in the coastal areas of the Black and Azov Seas. The data on the annual catches in 2000–2020, age, length and weight compositions of the catch in 2018–2020, and the present status of the stocks of these species in 2020 are presented. The estimates for the abundance, biomass and fishing mortality of the three investigated stock units based on the Jones’ length cohort analysis are presented. It is shown that the present stock of big-scale sand smelt, as compared with that for the two previous years, has decreased, the stock of flathead grey mullet has increased, and the stock of picarel has remained stable. If ranked by their status over the last 3 years and the degree of their thermophility, the stock of flathead grey mullet, the most thermophilic species, was increasing, the stock of picarel, which holds the middle position, remained at the same level, and the stock of big-scale sand smelt, the least thermophilic species, was decreasing.