Vol 63, No 3 (2023)

A new species of bathypelagic whalefishes of the genus Cetomimus is described; its two specimens were caught over the central tropical part of the Mid-Atlantic Ridge at the layers of 1500–0 and 2680–0 m. The species is characterized by the presence of 31/2 gill arches (with a small slit behind the third gill arch) and cavernous tissue developed only around the anus and above the bases of the first to sixth rays of the anal fin; large pores in the lateral line canal, which are approximately as wide as this canal; the absence of large, valve-shaped triangular outgrowths along the margin of septa between pores in the posterior part of the lateral line; 42–48 vertebrae; and 20, 17–18, and 18 rays in the pectoral, dorsal, and anal fins, respectively; 17–18 pores in the lateral line canal between the upper margin of the gill cover and the end of the caudal peduncle, as well as by some other diagnostic features. The first molecular genetic data for the described species (mtDNA COX-1 sequences, or DNA barcodes) and analysis of interspecific divergence in the genus Cetomimus are given

Analysis of the structure of the morphological diversity of the Altai osmans of the genus Oreoleuciscus in the Urt River (water system of the Tes River) indicates that this is a polymorphic population, consisting of three forms, clearly differentiated by a set of characters. The ratio of differences between these forms and forms previously identified in the Zavkhan (water system of the Great Lakes Hollow) and Tuin (water system of the Lake Valley) rivers suggests that the characters considered in the study are adaptively plastic, and the revealed structure of the morphological diversity of the genus is mostly determined by local patterns of environmental conditions.

The results of visual assessments of the flying fish (Exocoetidae), marine mammals, birds, and sea turtles, carried out mainly in the northern part of the Central Atlantic Ocean both during the ship was under way and at stations, are presented. Schematic maps of the quantitative distribution of the detected animals and of the specific biomass of the flying fish are provided. In terms of abundance and biomass of the flying fish, the studied region of the Atlantic south of 30° N is one of the most productive in the World Ocean, no signs of decreasing productivity have been found when compared with data obtained earlier. Tremendous abundance of gulfweed (Sargassum) in the study area is expected to have a positive effect on the abundance of birds and four-winged flying fish (subfamily Cypselurinae); at the same time, it apparently had a negative impact on the abundance of two–winged flying fish (genus Exocoetus). As a result, four-winged flying fish began to significantly predominate in the study area replacing the two-winged flying fish that dominated by abundance for almost a century. The relationships between the abundance of the flying fish and birds and some environmental parameters have been studied. An attempt has been made to assess the influence of various environmental factors on the quantitative distribution of the flying fish and birds using mathematical models.

The main objectives of this study were to estimate the age and growth of reared Atlantic bluefin tuna and to reveal possible differences in growth between reared and wild specimens. A total of 806 specimens, ranging from 102 to 284 cm in length, were sampled from a Greek tuna farm in the Mediterranean Sea. The first spine of the first dorsal fin was used to estimate the age. Estimated ages ranged from 3 to 20 years, and the reproducibility of the ageing method was high. The proportion of the mean number of missing annuli per age due to vascularization ranged from 27.8 to 40.0%, with an average loss of 33.5%. No significant differences in the number of missing annuli were observed between 6–month and 18–month reared specimens of the same age group. The von Bertalanffy growth model was fitted a) to mean FL-at-age data and b) to mean RW-at-age data, and the growth equations found were: Lt = 296.6[1 – e(−0.114) (t + 1.026)] and Wt = 591.6[1 – e(−0.100)(t + 1.755)]3. Our results showed that the rearing process accelerates the growth of the Atlantic bluefin tuna and this was also evident in the calcified structure. In comparison with previous studies of growth in wild bluefin tuna from the Mediterranean Sea, mean weights at age of the reared fish were higher than those from wild fish in all age groups and lengths at age of the reared bluefin tuna were higher in younger fish, up to 6 years old.

Analysis of long-term fishing and biological data has made it possible to determine the proportion of respawning individuals (the “remainder”) in populations of Atlantic salmon Salmo salar inhabiting large rivers of the Kola Peninsula. The contribution of respawning individuals to the dynamics of the Atlantic salmon population was assessed using the mathematical simulation model. It is shown that the model population becomes more resistant to fishing with increase in the “remainder” proportion; however, the influence of such individuals on the population dynamics is noticeable only when their relative number is more than 5% in the spawning population. The results of different model experiments are interpreted. The role of respawning salmons may be determined not so much by their quantitative contribution to the reproduction process as by the maintenance of the genetic diversity of the population within the reproductive strategy characteristic of the Atlantic salmon

The diet composition and reproductive properties of European conger, Conger conger (Linnaeus, 1758) were investigated from the Aegean Sea of Türkiye to compare our data with those from other regions of the Mediterranean Sea and throughout all four seasons. A total of 100 individuals were examined. Totally 19 prey taxa belonging to three large taxon (cephalopods, crustaceans, and fishes) were identified in the stomachs of European conger. According to the relative significance index the crustaceans were dominant food in diet of individuals smaller than 50 cm, while fish prevailed in diet of fish with length between 75 and 100 cm. Histological analysis of 80 gonads showed that all individuals were immature (20%) and maturuing females (80%). Maturing females were with oocytes in the previtellogenic (16% of all fishes) and early vitellogenic phases (64%). The oocyte diameters were 80–476 μm at previtellogenic (diameter range 80–240 μm) and 245–476 μm at early vitellogenic individuals. Immature females had the gonads with the oocyte diameter < 30 μm

Based on the data on the abundance of 53 generations of pink salmon Oncorhynchus gorbuscha of Iturup Island (spawners on spawning grounds, downstream migrating juveniles and the return of mature fish), a model describing the dependence of the abundance of mature pink salmon offspring on the initial abundance of generations and the effect of external factors was constructed using nonlinear regression analysis. The model explains about 80% of the replenishment variability, and it depends more on the effect of external factors in the freshwater period of life. The variability of replenishment is most closely related to factors related to the hydrological regime of rivers. The dependence of replenishment on the abundance of juveniles migrating downstream from spawning grounds, described by the dome-shaped curve, indicates the limiting effect of density factors on the formation of the abundance of pink salmon during the marine period of life. At the same time, a statistically significant effect of the abundance of juveniles released from fish hatcheries on the dynamics of the replenishment was not found.

European sea bass Dicentrarchus labrax (Moronidae), which has a high commercial value, is mainly produced in the Mediterranean region. Prolactin (PRL) is a member of the helix bundle protein family that is secreted in the anterior pituitary gland and has a significant role in osmoregulation and growth in teleost fish. In this study, we investigated the genetic variation of the partial sequence of 3rd, 4th introns, and 4th exon regions of the PRL gene in Dicentrarchus labrax and its association with growth traits that were reared in cage conditions. Two SNPs (g.484 A > C, g.529 T > C) and one 15 bp indel (insertion/deletion) have been found in the 3rd intron region of the PRL gene of Dicentrarchus labrax. A significant association has been identified between the total body weight and the genotypes for PRL g.529 T > C locus (р < 0.05). The heterozygote genotype of the PRL g.529 T > C locus has a significantly higher total body weight than the other genotypes in the population (p < 0.05). Association analysis indicated that this SNP in the PRL gene is correlated with growth traits and could be used for genomic selection programs in Dicentrarchus labrax breeding.

Lipid and fatty acid modifications induced by the effects of various salinity patterns on the juvenile pink salmon Oncorhynchus gorbuscha (the Olkhovka River and the White Sea) within the experiment have been revealed. Concentrations of steroids, saturated fatty acids, and signaling molecules such as phospholipids (phosphatidylserine and phosphatidylinositol) and arachidonic acid under the hyperosmotic stress-related effects (keeping the fish for 1 h in the seawater after the time of transfer from the freswater) tend to increase. Decreases in phosphatidylcholine and n-6 saturated, monounsaturated, and polyunsaturated fatty acids are recorded in the juvenile pink salmon fish kept for 24 h in the seawater after the time of transfer them from the freswater, while the levels of phosphatidylethanolamine and n-3 polyunsaturated fatty acids (especially eicosapentaenoic and docosahexaenoic acids), on the contrary, tend to rise significantly. Lipid composition modifications in the juvenile pink salmon fish kept under the hypoosmotic stress conditions (24 h in freshwater after 24 h in seawater) induce stabilization of functioning the cell membrane structure, since the levels of bioeffectors including phosphatidylserine, phosphatidylinositol, and arachidonic, eicosapentaenoic, and docosahexaenoic acids tend to decrease. A reduced amount of lipids (triacylglycerols) stored as an energy reserve is shown for all the experimental fish groups. The outcomes indicate the high levels of adaptive potential of the juvenile pink salmon fish kept under the effects of abrupt salinity change in the water environments and their readiness for downstream migration not long before leaving the nests.

A new record of the Short–snouted scorpionfish, Scorpaenopsis obtusa Randall et Eschmeyer, 2002 is reported from India’s southeast coast. Three specimens were collected (67.6–75.1 mm SL) as trawl-fishery bycatch at Tuticorin fishing harbour, India on 21 April 2022. Morphometric and meristic characters were measured and compared with published data. The record of this species from India expands the known distribution of S. obtusa, previously reported from Myanmar eastward. The above species is a new addition to the list of marine fishes of Indian coastal waters.