Rhizocephalan barnacle Parasacculina pilosella Van Kampen & Boschma, 1925, being a common parasite of the spider crab Pugettia aff. ferox Ohtsuchi & Kawamura, 2019, was founded for the first time on the crab Scyra bidentata (A. Milne-Edwards, 1873) (Brachyura: Epialtidae) in Peter the Great Bay (Russian waters of the Sea of Japan). Taxonomical identification of the parasite was made using morphological and molecular methods.
Appendicularians play an important role in marine food webs, but the alimentary canal of hermaphroditic oikopleurids, which prevalent among urochordates, is little studied ultrastructurally. Serial microtomy revealed that the alimentary canal of Oikopleura gracilis consists of a wide pharynx and a U-shaped gut with typical for oikopleurids anatomy: oesophagus, a bilobed stomach, the vertical, short mid- and voluminous distal or rectal intestines, ending the anal papilla. The mid-intestine leaves under the right gastric lobe. TEM analysis diagnosed the following features in the alimentary canal of Oikopleura gracilis. First, the pharynx is lined with a single layer of highly flattened non-ciliated epithelium. Above the anterior part of the endostyle the pharyngeal epithelium forms a thickening – ciliated ring. It is formed by cells of two types: prismatic, ciliated microvillar cells arranged in several parallel rows, and two rows of narrow parietal cells covering the first cell type. Ciliated ring serves as a kind of first valve, prevents food reflux. Second, in the pharynx of one of the specimens three flagellate protozoans with ultrastructurally similarities of free-living kinetoplastids were found. Third, an additional row of gastric band cells was revealed in the upper part of the right gastric lobe compared to that of the gastric floor. Giant electron-lucent vesicles with homogenous content associated with rough endoplasmic reticulum found in the cytoplasm of the gastric band cell, indicating probable storage the protein digestive secrets in these cells. Large multivesicular bodies diagnosed in gastric band cells ultrastructurally corresponded to autophagosomes. Forth, a new cellular type was found, the osmiophilic enterocytes, scattered throughout the digestive epithelium, that shared ultrastructural signs with apoptotic cells. Fifth, TEM data revealed the peritrophic membrane structure and proposed its formation. The absence of its own microflora in the peritrophic membrane, i.e., the absence of an immunity barrier, may be connected with the short ontogeny of appendicularians. The ultrastructural features revealed in the alimentary canal of O. gracilis expand our knowledge of the functioning of the appendicularians and serve as the basis for further research.
A total of 122 coho salmon specimens were examined. The fish were caught in the coastal zone and in the rivers of Iturup Island (southern Kuril Islands) during their spawning migration in August–October 2021. Almost all females and males close to maturity in that year had spent 1 year at sea and were at ages of 1.1+ (66.7%) and 2.1+ (30.0%). Fish that had spent 2 years at sea were found singly: one specimen at an age of 1.2+ and three specimens at an age of 2.2+ (2.5%). Taking into account the age at maturity and the body weight (an average of 2.63 kg for females and 2.44 kg for males), an assumption can be made that the examined fish bred in short streams. The high value of the gonadosomatic index (up to 20–22% for some females) did not indicate that all the fish caught in the coastal waters would have run to other spawning grounds. At least a portion of them should have spawned in the water courses of Iturup Island, as was evidenced by the captures of a few coho salmon immediately in the rivers. Along with the fish running to the spawning grounds, two actively feeding coho females at an age of 0.0+ (0.55 kg) and 1.0+ (1.11 kg) were also caught with stake nets.
The relationship of Amur pink salmon catches in 1980–2018 with those landed 2 years before the current year’s fishing season is assessed. This relationship can be well approximated by a linear regression equation; the deviations from it are explained almost completely by variations in precipitation and air temperatures in the autumn and winter of the spawning year. It has been shown that the overestimated forecast of pink salmon catch for 2018 is due to the lowest amount of precipitation for the 40-year period with the lowest air temperature in 2016. The causes for the strength variations between the pink salmon year-classes of even- and odd-numbered years are discussed.
The current status of the stocks, the dynamics of commercial fisheries, and the distribution of the saffron cod Eleginus gracilis in the fishery areas of the Far East are analyzed. In the Far Eastern basin, saffron cod makes the greatest contribution to the total catch of aquatic biological resources in the Karaginsky subzone (8.1%) and off western Kamchatka (3.6%). The total saffron cod catch from the Far Eastern seas in 2003–2022 ranged within 16 700–50 600 tons, with an average of 33 900 t. According to the data of bottom trawl surveys conducted in 2016–2023, the largest saffron cod aggregations are traditionally observed in the shelf waters off western Kamchatka, in the southwestern and northwestern Bering Sea, where the catch per unit effort reaches 4500 kg per trawling hour. Off western Kamchatka, the biomass of this species was estimated at 197 400 t; in the Karaginsky subzone, 100 400 t; in the West Bering Sea zone, 32 800 t; in the East Sakhalin and Petropavlovsk-Commander subzones, the values were similar, 17 100 and 17 200 t, respectively; and in the North Okhotsk Sea area, 8700 t. Almost all the exploited stocks in recent years have been above their average long-term annual level or fluctuated within its range. In general, the status of the saffron cod stocks in the fishery subzones at the present time can be considered satisfactory.
The significant decline in the abundance of the Greenland halibut Reinhardtius hippoglossoides matsuurae in the Northwest Pacific was one of the impetuses to scrutinize the age determination methods for this species based on different age-recording structures. The present study was carried out in accordance with recommendations of the Northwest Atlantic Fisheries Organization (NAFO) and the International Council for the Exploration of the Sea (ICES). An analysis of age determination data for the Greenland halibut has shown underestimation of age estimated using scales or whole otoliths compared to the technique using otolith sections through the peri-sulcular tuberosity. A resource exploitation strategy based on incorrect age determination can either be the major cause of negative trends in the status of the Greenland halibut stock or have a combined effect with natural factors.
The information currently available in the literature as regards gametogenesis in the pink salmon Oncorhynchus gorbuscha Walbaum is summarized. The periods of indifferent development and sex differentiation, the features of testis and ovary development, and the formation of fecundity are considered. The patterns of sex reversal, which is unique for salmonids, and also the evolutionarily acquired specific features of oogenesis for providing the short life cycle are analyzed.
Data on juvenile pink salmon from the continental coast of the Sea of Okhotsk for the 1960th–2010th are summarized. Timing and dynamics of downstream migration, qualitative characteristics, and feeding habits are considered. Brief information on the early marine life period is provided. Mass downstream migration of pink salmon fry begins when river water warms up to 2.5–4.0°C. Pink salmon fry migrate from rivers to the coastal marine waters diurnally. During downstream migration, their body length and weight usually do not vary significantly, but the proportion of fish that have switched to external feeding increases. On a long-term scale, the relative abundance of externally feeding juveniles in rivers is higher in the years of weak spring floods.
Some parameters of abundance dynamics for the Pacific salmon species breeding in Russian waters are clarified and their possible catch on a medium-term scale estimated. The average annual catch for the 1907–2022 period was approximately 250 000 t. A complete cycle from the minimum values on the curves of one low-abundance period to the respective parameters of another period took approximately 72 years; from the relative maxima of one high-abundance period to another took 75 years. The duration of the high-abundance period was almost 35 years; the low-abundance period was almost 40 years. Taking various uncertainties into account, the periods of high and low abundance were approximately equivalent and remained within a relatively stable range from 35 to 40 years. Most of the high-catch seasons occurred in the odd-numbered years. Dominants usually changed during the periods of increase in Pacific salmon abundance. The average annual catches are expected to be higher than 250 000 t in the second half of the 2020s and the first half of the 2030s. Catch sizes are unlikely to be lower than 200 000 t even in the least productive years. In the final part of the high-abundance period, the raw material base of the Russian salmon fishery does not provide conditions for profitable operations at most of the fishing sites allotted for commercial harvesting.
The spatial distribution of the Pacific herring Clupea pallasii in the Sea of Okhotsk waters at the northeastern coast of Sakhalin Island is described on the basis of data of the surveys using bottom and midwater trawls and a Danish seine conducted in June–October 1989 and 1997–2020. Herring are distributed widely, with the main aggregations forming in the area with depths of less than 100 m between Lunsky Bay and Piltun Bay, where herring of the North-East Sakhalin population feed. Herring in deeper waters presumably belong to the Okhotsk population.
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