The paper describes the first finding of the European hake Merluccius merluccius (Linnaeus, 1758) in the northern part of the Black Sea, off the coast of Crimea, in December 2022 with a sea surface temperature of 13°C. The individual was found in the catch of a bottom trap installed at a depth of 24 m. The specimen with a total body length of 30.6 cm and a weight of 213.5 g was a sexually mature 3 years old male. According to the results of back-calculations obtained during the analysis of the otolith section, the individual growth of the caught fish occurred as follows: the total length was 17.7, 25.5, and 30.6 cm by the end of the first, second, and third years of life, respectively. No food items have been found in the gastrointestinal tract of the caught specimen. The geographical variability of the hake life cycle is considered. The species reaches its maximum size and age at high latitudes and at low water temperatures. Presumably, the maximum size and age of the hake in the Black Sea may be slightly higher than in the Mediterranean Sea, but lower than in the Northeast Atlantic. The prospects for further resettlement and increase in the number of the hake in the Black Sea are analyzed. Apparently, low salinity and competition with the native ichthyofauna may prevent successful naturalization of the species. However, the continuation of the trend of increasing salinity of the Black Sea under warming conditions will increase the possibilities of the hake naturalization.

The article presents the species diversity, abundance, and distribution features of ichthyoplankton and fodder zooplankton in the northern Black Sea in summer 2021. The intensification of cyclonic activity over the Black Sea in June–July slowed the formation of summer-type thermal stratification in the studied water area. At the beginning of July, only 13 species of eggs and fish larvae were observed in ichthyoplankton of the Crimean Peninsula, and their average abundance was 29 and 2 ind./m2, respectively. At the beginning of August, summer-type vertical thermal stratification off the coast of the Caucasus had already formed. The number of ichthyoplankton species increased to 20. Activation of atmospheric processes in June–July intensified the intraseasonal wind “pumping” of the upper layer of the sea. The Black Sea Rim Current transformed into a pronounced jet over the continental slope, oriented alongshore, partially extending to the shelf. This did not affect the spawning activity of mass fish species. The average abundance of eggs in the shelf and deep-water zone was about 160 ind./m2, and the average abundance of larvae on the shelf was almost five times higher, 452 ind./m2.

The European barracuda Sphyraena sphyraena (Linnaeus, 1758) is occasionally recorded in the Black Sea, however its findings in the 21st century have become more frequent. This paper presents the results of biological analysis of a mature female barracuda with a total length of 35.4 cm and weight of 196.4 g, aged 4+ years, caught off the coast of Crimea (Sevastopol) in 2022. Oocytes in the ovaries (weight of 1.999 g) are at the resorption stage. Fragments of the spine of an unidentified fish have been found in the digestive tract of the specimen. Based on literary data, biological characteristics of barracuda individuals previously recorded in the Black Sea are presented. The prospects for the development of the Black Sea waters by this species are assessed; if the climate change trend towards warming persists, the possibility of successful naturalization of the barracuda will increase.

Tonlesapia tsukawakii Motomura et Mukai, 2006 is an endemic freshwater representative of the family Callionymidae (Teleostei: Perciformes: Callionymidei) living in the Mekong River. According to the materials of studies conducted in 2018–2022, the occurrence of the species in catches in the Mekong Delta averaged 20.7

The species diversity and spatial distribution of ichthyoplankton in the coastal and open waters of the northern part of the Black Sea and the southwestern part of the Sea of Azov in June 2020 are presented. The species diversity and abundance of ichthyoplankton changed in accordance with the regional conditions of warming of the upper layer of the sea during the formation of a vertical thermal structure of the summer type. The most favorable conditions for the survival of ichthyoplankton were observed in the open and coastal waters of the Western Sector of research in the initial phase of the summer hydrological season.

The species diversity and spatial distribution of ichthyoplankton in the shelf and deep-sea waters of the northern half of the Black Sea near the Crimean Peninsula and the shores of the Caucasus under the conditions of prolongation of the summer hydrological season 2020 for September–October are presented. The high temperatures of the upper layer of the sea, peculiar of the summer spawning season, caused a continuation of productive spawning of warm-water fish. Eggs and larvae of 19 species from 12 families were identified in the ichthyoplankton. The maximum number of eggs was 302 ind./m2, and larvae — 58 ind./m2. Eggs and larvae of the mass commercial species Engraulis encrasicolus (L., 1758) dominated, whose share in the total population was 92.9 and 84.2% respectively. The highest abundance of ichthyoplankton corresponded to areas with minimal dynamic activity and maximum warming within the limits of coastal-shelf quasi-stationary anticyclonic vortices characteristic of the summer hydrological season.

Климатические изменения в гидрологическом режиме Чёрного моря, отмечаемые с 1990-х гг., отразились на состоянии эпипелагических комплексов морских организмов, прежде всего на сезонной изменчивости их биологических циклов. Это оказало существенное влияние на фенологию нереста природных популяций рыб, видовое разнообразие и пространственное распределение ихтиопланктона, а также на устоявшиеся трофические взаимоотношения в планктонном сообществе. В конечном итоге характер взаимодействия между различными звеньями трофической цепи в эпипелагических комплексах, их сезонная и межгодовая изменчивость влияют на эффективность нереста рыб, прежде всего массовых промысловых видов, и в значительной степени определяют успех пополнения их будущих поколений. С целью изучения видового состава, численности и пространственного распределения ихтиопланктона в октябре 2016 г. (89-й рейс НИС «Профессор Водяницкий», 30 сентября — 19 октября) были проведены исследования в шельфовых и открытых водах Чёрного моря у Крымского полуострова, проанализированы не только икра и личинки рыб, но и биомасса мезо- и макропланктона. Пробы ихтио- и макропланктона отбирали сетью Богорова — Расса (площадь входного отверстия — 0,5 м²; ячея — 300 мкм) методом тотальных вертикальных ловов от дна до поверхности моря в области шельфа и от нижней границы кислородной зоны до поверхности моря в глубоководной части. Ихтиопланктон фиксировали 4%-ным раствором формалина и анализировали позже под микроскопом, определяя таксономический состав организмов и по возможности — наличие и состав пищи в кишечниках личинок рыб. Проанализированы данные о видовом составе и пространственном распределении ихтио-, мезо- и макропланктона, а также о питании личинок рыб Чёрного моря у Крымского полуострова в октябре 2016 г. Период съёмки соответствовал начальной фазе осеннего гидрологического сезона. Ихтиопланктон был представлен икрой и личинками 9 видов тепловодных и 6 видов умеренноводных рыб. Средняя численность икры рыб составляла 2,92, а личинок — 3,56 экз.·м−2. Низкая доля (30 %) мёртвой икры тепловодной хамсы Engraulis encrasicolus, а также наличие её разноразмерных личинок в море свидетельствовали о продолжении результативного нереста. Биомасса зоопланктона возрастала в направлении от шельфа к глубоководным районам. Мелкоразмерные фракции планктонных организмов преобладали на шельфе, обеспечивая здесь лучшие кормовые условия для выживания личинок рыб. Несмотря на значительную биомассу желетелых-планктофагов в октябре 2016 г., их влияние на ихтиопланктонные комплексы Чёрного моря, по-видимому, оставалось несущественным.

During a number of years juveniles and larvae of Atherina boyeri Risso, 1810 and Knipowitschia caucasica (Berg, 1916) were caught in the hypersaline waters of Sivash at salinity up to 70-75%. Once the larvae of Atherina hepsetus Linnaeus, 1758 at a salinity of 54% and A. boyeri at a salinity of 90% were caught. New data on the expansion of the salinity range of the survival of A. boyeri are presented.

The shi drum Umbrina cirrosa is a rare poorly studied fish species in the Black Sea. The largest individual for this water area was recorded off the coast of the Crimea; a male, whose total length was 784 mm, standard length 706 mm, body weight 5515.2 g, age 4 years; gonads of the maturity stage III had a weight of 33.11 g. Mollusks Solen marginatus and Abra segmentum , polychaete of the family Scalibregmatidae, and the jaguar round crab Xantho poressa were found in the diet composition. The paper presents a morphological description of otoliths (sagittae). The information about the known cases of the shi drum capture in the Black and Azov seas is considered. It is revealed that the maximum size of individuals of the species in the Black Sea is higher than in the Mediterranean Sea; possible causes of geographical variability of the sizes are analyzed. It is shown that this species is one of the fastest growing fish in the Black Sea.

The data on species composition and abundance of ichthyoplankton in the open waters of the shelf and in the deep waters of the Black Sea in June 2018 are presented. Totally 17 species of fish eggs and larvae of ten families were identified. The mean number of eggs varied from 5.8 spec./m2 in the western sector of study area to 20.9 spec./m2 in the eastern sector; the number of larvae ranged from 1.7 to 9.7 spec./m2, respectively. In June 2018, a high spawning efficiency of Engraulis encrasicolus was observed: the ratio of the number of larvae to the number of eggs in the sea was an order of magnitude higher than in the 1970s, averaging 23.7%. A decrease in the minimum size of larvae of mass species of warm-water fish was noted, which is probably associated with a reduction in the periods of embryonic and postembryonic development with an increase in sea water temperature >27°C. The heterogeneity of the spatial distribution of the abundance of ichthyoplankton and phytoplankton biomass was expressed in their increase from shelf to deep-water sites in accordance with water temperature contrasts and the nature of circulation on the western and eastern peripheries of regional quasi-stationary anticyclonic gyres and, conversely, in their decrease outside the zone of influence of these hydrodynamic structures.

The species structure, abundance, size composition, and trophic characteristics of fish larvae are presented for the northern part of the Black Sea within the Russian EEZ in July–August 2019. Larvae of 21 fish species belonging to 14 families are found in ichthyoplankton. The average larvae abundance varies from 17 ind./m2 in the deep-sea areas to 38 ind./m2 on the shelf. The dominant commercial species is the European anchovy Engraulis encrasicolus, which accounts for 77.4% of total larvae abundance. The maximum larvae abundance is noted off the coast of the Caucasus (148 ind./m2), high values (116 ind./m2) are recorded in the northwestern part. The larvae abundance follows the areas of high abundance of forage zooplankton (3305 ind./m3 off the Caucasian coast and 13,913 ind./m3 in the northwestern part of the sea). The high abundance, wide size range of fish larvae, and the abundance of food organisms in the intestines testified to a good food supply as the most important factor for their development and survival.

— The paper presents characteristics of the species composition, spatial distribution, and trophic interactions of ichthyoplankton and zooplankton in the spring–summer period 2017 dependent on intensity of the warming-up of the upper sea layer against the background of transition in a system of the surface currents from the winter-to summer-type of the circulation. In April–May, successful spawning of temperate-water fish species was prolonged due to low values of the sea surface temperature (8–9°С) on the shelf of Crimean Peninsula between Kerch Strait and the cape Sarych. The maximum abundance of Sprattus sprattus eggs was 162.8 egg/m 2 and larvae –116 ind/m 2 . Warm-water species occurred only in the western sector from Herakleian Peninsula to the Cape Tarkhankut, where the water temperature was at its maximum and peaked at 14–15°С. In June–July the delayed summer hydrological season hampered the warming-up of the upper quasi-homogenous layer, which thickness varied from 1–5 to 10–15 m. Notwithstanding the large number of species in the ichthyoplankton, maximum abundance did not exceed 50 egg/m 2 and 14 ind/m 2 for larvae. The proportion of larvae of temperate-water fish species averaged 32% and reached 40% in deep water areas. Juvenile stages of copepods of the cold-water complex were dominant in the larval fish diet both in the spring and summer seasons.

This paper is focused on the ichthyoplankton species composition and spatial distribution in the Black sea shelf zone and the deepwater regions off Crimean Peninsula and coast of the Caucasus during the spring hydrological season. Recent changes in the hydrological regime of the Black sea induced by the climate warming have led to an extension of the active and productive spawning of the dominant temperate-water species Sprattus sprattus until the end of the spring hydrological season. An intensive spawning of sprat was detected in March, April and May 2016, 2017 and 2019, which was confirmed by a predominance of younger age group larvae. The maximum number of eggs reached 224 ind./m2 , and the larvae - 116 ind./m2. The wide size range of larvae as well as the low proportion of larvae with empty guts evidenced a favorable fodder base for their survival. The reduction in the age and sizeweight composition of sprat stock in the Black sea observed since 2016 as a result of an increase in its commercial fishing on the shelf of the Crimean Peninsula, did not affect sprat’ spawning activity.

The study examines changes in the abundance (density) and distribution of European Sprattus sprattus (Linnaeus, 1758) eggs and larvae, as well as the phenology of its spawning depending on hydrologic factors and abundance of gelatinous macroplankton in the Black Sea in November 2016–2017. An increase in temperature of the sea surface layer observed since the beginning of the century and the enhanced heat content of the cold intermediate layer contributed to the preservation of warm-water mesozooplankton at the end of the fall hydrologic season, which provided favorable trophic conditions for all planktophages. The biomass of scyphomedusa Aurelia aurita was the third largest in the gelatinous macroplankton in 2016 and the largest in 2017 for the long-term annual research in fall months. Gelatinous macroplankton, however, did not have a significant impact on the survival of sprat in the early stages of its development. The average number of sprat eggs and larvae in November 2016 (184 and 11 ind/m2, respectively) and November 2017 (268 and 21 ind/m2, respectively) exceeded their maximum values recorded in the 1950s. The larvae did not differ in length composition in the beginning of the spawning season in 2016 and 2017.

В прибрежной акватории Юго-Западного Крыма летом 2013 г. изучены видовой состав и количественные показатели мезо-, макро- и ихтиопланктона, а также питание личинок рыб. В ихтиопланктоне обнаружены икра и личинки 33 видов рыб из 24 семейств, что вдвое превысило показатели 1990-х гг. В мае 2013 г. в прибрежной акватории Севастополя наблюдался результативный нерест хамсы, которому способствовали благоприятная температура воды в море (+21 °C) и хорошие кормовые условия. Наибольшее количество летненерестующих видов зарегистрировано в июне при температуре поверхностной воды +22,7 °C. Численность икры рыб в 2013 г. увеличилась по сравнению с таковой в 2000 г. в 3,4 раза, личинок ― в 2,3 раза, что связано с их большей выживаемостью при улучшившихся условиях питания в результате относительно высокой численности зоопланктона с преобладанием мелкоразмерной фракции и доминированием в ней ювенильных стадий копепод. Другими факторами, улучшившими состояние кормовой базы личинок, были низкая численность гребневика Mnemiopsis leidyi A. Agassiz, 1865 и его слабое воздействие

Nauplial stages of copepods are known to be the main food items for fish larvae. Their identification in fish larvae guts is usually a difficult task and a time-consuming procedure. Original approach to identification of larvae and juvenile fish common food items – nauplial stages of the Black Sea copepods of family Calanidae – is proposed. This work is a continuation of the initiated studies on the developing a method for determining the juvenile copepod stages from fish larvae guts. On the example of nauplial stage III of Calanus euxinus Hulsemann, 1991, specific features that can be used in identifying nauplial stages of three species of the Black Sea copepods from fish larvae guts are shown.