Long-term changes of abundance and population structure for sockeye salmon in Lake Dalneye (southeastern Kamchatka)

Effects of interannual fluctuations of sockeye salmon escapement to the spawning grounds on dynamics of sexual, age and length-weight structure of the population are demonstrated on generalized data of long-term observations in Lake Dalneye in 1939–2020. Mature sockeye specimens were caught in the Dalnaya River during their anadromous migration to the lake and analyzed by the authors, personally; archive and earlier published data were used, as well. The escapement was evaluated by visual assessment of the sockeye migrants entered to Lake Dalneye and confirmed by counting of mature individuals on the littoral spawning grounds in the lake. Number of dwarf sockeye salmon was estimated using the earlier found correlation between their stock and forage zooplankton biomass (Kurenkov, 1991; Pogodaev, Kurenkov, 2012). The zooplankton biomass was assessed on samples of zooplankton collected monthly at a stationary station in the central part of the lake (once a month during the ice period and up to three times per month during the ice-free period) from the layer 0–50/55 m by vertical towing of Juday plankton net (mouth diameter 18 cm). The numbers of anadromous sockeye males and females had ratio 1 : 1 in years with the maximum spawning stock, but < 1 : 1 when their returns to the lake decreased. Besides, the males were smaller in such years and the dwarfs (matured without migration to the sea) and jacks (matured with short marine period) were able to escape commercial fishing gears. Age of the spawners had a tendency to increase with decreasing of spawning runs and, conversely, more abundant runs were formed by younger spawners. Long-term pressure from fishery and selection of larger individuals caused the body length and weight decreasing for mature sockeye salmon, shortening of their period of marine feeding, and increasing of the smallsized males portion in the population.

Factors determining spawning run dynamics and current state of sockeye salmon Oncorhynchus nerka resources in the Kamchatka River

Hydrological regime and morphodynamics of the outlet part of the Kamchatka River, dynamics of mixing zone, patterns of juvenile Pacific salmon distribution and migration in the coastal waters of Kamchatsky Gulf in the zone of operating trap nets were analyzed on the results of complex field works prowided in summer period in 2018–2019; fishing and specifics of sockeye salmon spawning run in the river was described. In the course of analyzing the entire complex of available long-term data, an assessment of the likely impact of some key factors on the dynamics of anadromous migration of sockeye salmon in the Kamchatka River was made; biological statistics of spawners and current state of reproduction of this stock was demonstrated. It is found, that natural environmental factors, neither abiotic nor biotic (including fish health as population internal factor), could not cause disturbance of sockeye salmon spawning run dynamics in the Kamchatka River in recent years. Smoller body size and physiological imperfection of the spawners before the anadromous migration due to effects of high number of pink salmon in recent years are suggested to be the most likely cause of spawning run delay in late sockeye salmon morph. Regime of commercial use of the stock and general increasing pressure on the spawning stock by coastal fisheries are demonstrated to be the strongest outer factors to affect modern state of the resources and sockeye salmon population structure in the Kamchatka River, causing permanent escapement deficiency on spawning grounds in the river basin (first of all in the late morph), and also infact lead to disballance between different subpopulation groups in the composition of the stock. Recommendations in order to provide recovery and sustainable level of the Kamchatka River sockeye salmon stock are given in the perspective of more efficient commercial use of the stock next several years; highlights for further researches are outlined.

Differences in growth and condition of juvenile Oncorhynchus mykiss related to sex and a migration-associated genomic region.

The expression of anadromy in partially migratory salmonid populations is influenced by sex-specific interactions among an individual’s genotype, condition, and environment, but genotype-phenotype relationships prior to the expression of migratory type are poorly understood. We examined whether juvenile growth and condition differed with respect to sex and a migration-associated genomic region (Omy05) in a coastal California population of steelhead/rainbow trout (Oncorhynchus mykiss). Sex and Omy05 genotype had additive effects on annual growth from age 0+ to age 1+ (approximately 6–18 months old), with higher growth in males and individuals with copies of the rearranged/resident haplotype. Condition at age 1+ increased with the number of copies of the rearranged/resident haplotype, with similar support for additive or interactive effects with sex; additive effects suggested that genotype differences occurred in both sexes and also that condition was slightly higher in males, while interactive effects suggested that the genotype differences occurred only in males. Our results indicate that phenotypic differences related to sex and Omy05 genotype occur well in advance of anadromous migration or freshwater maturation in this southern O. mykiss population.

TO THE METHODOLOGY FOR SEPARATION OF MIGRATING POPULATION COMPLEXES OF THE OKHOTSK SEA PINK SALMON IN THE PACIFIC WATERS AT KURIL ISLANDS USING THE GONAD-SOMATIC INDEX

New method is proposed for operational differentiation of pink salmon runs with different time of spawning and different state of gonads measured quantitatively with a gonad-somatic index. Results of this new method and traditional methods of differentiating are compared. The conception of spatial niches in the Pacific waters adjacent to Kuril Islands for certain temporal groupings of the Okhotsk Sea pink salmon is critically revised on the base of these new results. The runs cannot be separated using any fixed value of the gonad-somatic index. The zones of different groupings could be spatially overlapped. The method is tested on the data of trawl survey conducted aboard RV Professor Kaganovsky in May-July 2018, during anadromous migration of pink salmon, and shows a high compliance with the regional groupings ratio determined on the data of pink salmon catch in the Okhotsk Sea and their escapement to rivers. Tendency of the late-maturing forms of pink salmon to migrate through the southern Kuril waters is confirmed, whereas the portion of early-maturing pink has increased toward the Ocean.

Review of data on the role of cortisol at the final stages of spawning migration and the reproductive cycle in sturgeons (Acipenseridae)

This review presents data on the role of cortisol (F) at the final stages of the reproductive cycle in migratory sturgeons (Acipenseridae) of the Volga-Caspian region: Russian sturgeon (Acipenser gueldenstaedtii Brandt et Ratzeburg, 1833), stellate sturgeon (Acipenser stellatus Pallas, 1771) and beluga (Huso huso (Linnaeus, 1758) obtained using a special variant of enzyme-linked immunosorbent assay (ELISA), which allowed us to compare the indicators of different years. The dynamics of F level in blood serum (BS) and the state of the interrenal gland (IG) in sturgeons were studied during feeding in the sea and at the beginning of the anadromous migration, as well as at the reproduction in the conditions of hatcheries. Higher levels of F in BS and high functional activity of IG are characteristic of sturgeon migrants when entering the river compared with data for fish during feeding in the sea. Reservation of sturgeon breeders at the hatchery led to decrease of the F serum level; and hormonal stimulation of maturation caused an increase in this indicator. Data on the F content in oocytes and abdominal (coelomic) fluid during maturation of female sturgeon are also presented. The F “profiles” were evaluated in sturgeon breeders under stress impacts that are unavoidable at the conditions of hatchery enterprises, as well as under experimentally simulated stress impacts. Peculiarities of the interaction of the hypothalamic-pituitary-gonadal and hypothalamic-pituitary-interrenal axes in sturgeons during reservation at hatcheries and during hormonal stimulation of fish maturation are discussed. Particular attention is paid to the compilation of data contained in the works performed in the late 90s – early 2000s under the guidance of Dr. Sc., prof. I.A. Barannikova (1926–2017), to whose memory the review is dedicated.

Decoupling of otolith and somatic growth during anadromous migration in a northern salmonid

We assessed the fish length – otolith length relationship (FL–OL) in Dolly Varden (Salvelinus malma malma) to verify proportional growth. A decoupling was detected during first ocean migration where fish growth was occurring at a greater rate than otolith growth. Because of this decoupling, the application of traditional back-calculation models overestimated the size-at-age in premigratory char. We developed modified back-calculation equations from existing traditional models to account for this decoupling based on discontinuous piecewise regressions. The new biological intercept breakpoint method (BI–BP) provided the most accurate representation of fish size-at-age throughout all life history stages when compared with known size-at-capture values in fish. The decoupling indicates that factors other than somatic growth are important for otolith accretion. Physiological changes during smoltification likely alter calcium uptake and thereby affect calcium deposition rates on otoliths during this short but biologically critical time period of life history. It is probable that species exhibiting similar complex ontogenetic shifts in life history will likely exhibit decoupling to some extent in the FL–OL relationship.

The phylogenetic origin and evolution of acellular bone in teleost fishes: insights into osteocyte function in bone metabolism

Vertebrate bone is composed of three main cell types: osteoblasts, osteoclasts and osteocytes, the latter being by far the most numerous. Osteocytes are thought to play a fundamental role in bone physiology and homeostasis, however they are entirely absent in most extant species of teleosts, a group that comprises the vast majority of bony ‘fishes’, and approximately half of vertebrates. Understanding how this acellular (anosteocytic) bone appeared and was maintained in such an important vertebrate group has important implications for our understanding of the function and evolution of osteocytes. Nevertheless, although it is clear that cellular bone is ancestral for teleosts, it has not been clear in which specific subgroup the osteocytes were lost. This review aims at clarifying the phylogenetic distribution of cellular and acellular bone in teleosts, to identify its precise origin, reversals to cellularity, and their implications. We surveyed the bone type for more than 600 fossil and extant ray-finned fish species and optimised the results on recent large-scale molecular phylogenetic trees, estimating ancestral states. We find that acellular bone is a probable synapomorphy of Euteleostei, a group uniting approximately two-thirds of teleost species. We also confirm homoplasy in these traits: acellular bone occurs in some non-euteleosts (although rarely), and cellular bone was reacquired several times independently within euteleosts, in salmons and relatives, tunas and the opah (Lampris sp.). The occurrence of peculiar ecological (e.g. anadromous migration) and physiological (e.g. red-muscle endothermy) strategies in these lineages might explain the reacquisition of osteocytes. Our review supports that the main contribution of osteocytes in teleost bone is to mineral homeostasis (via osteocytic osteolysis) and not to strain detection or bone remodelling, helping to clarify their role in bone physiology.

The phylogenetic origin and evolution of acellular bone in teleost fishes: insights into osteocyte function in bone metabolism

Vertebrate bone is composed of three main cell types: osteoblasts, osteoclasts and osteocytes, the latter being by far the most numerous. Osteocytes are thought to play a fundamental role in bone physiology and homeostasis, however they are entirely absent in most extant species of teleosts, a group that comprises the vast majority of bony ‘fishes’, and approximately half of vertebrates. Understanding how this acellular (anosteocytic) bone appeared and was maintained in such an important vertebrate group has important implications for our understanding of the function and evolution of osteocytes. Nevertheless, although it is clear that cellular bone is ancestral for teleosts, it has not been clear in which specific subgroup the osteocytes were lost. This review aims at clarifying the phylogenetic distribution of cellular and acellular bone in teleosts, to identify its precise origin, reversals to cellularity, and their implications. We surveyed the bone type for more than 600 fossil and extant ray-finned fish species and optimised the results on recent large-scale molecular phylogenetic trees, estimating ancestral states. We find that acellular bone is a probable synapomorphy of Euteleostei, a group uniting approximately two-thirds of teleost species. We also confirm homoplasy in these traits: acellular bone occurs in some non-euteleosts (although rarely), and cellular bone was reacquired several times independently within euteleosts, in salmons and relatives, tunas and the opah (Lampris sp.). The occurrence of peculiar ecological (e.g. anadromous migration) and physiological (e.g. red-muscle endothermy) strategies in these lineages might explain the reacquisition of osteocytes. Our review supports that the main contribution of osteocytes in teleost bone is to mineral homeostasis (via osteocytic osteolysis) and not to strain detection or bone remodelling, helping to clarify their role in bone physiology.

Effects of laboratory salmon louse infection on Arctic char osmoregulation, growth and survival

High salmon lice (Lepeophtheirus salmonis) infestation levels resulting from intensive salmonid sea-cage aquaculture can threaten populations of wild salmonid hosts. This includes anadromous Arctic char (Salvelinus alpinus), which rely on short migrations into more productive seawater environments to build energy stores for maturation, spawning and over-wintering in freshwater. Elevated salmon lice burdens may limit the benefits of migration by constraining osmoregulation, growth, survival and reproduction. To test for these effects, we simulated anadromous migration in tanks by transferring individually tagged Arctic char smolts (n = 352, averaging 133 g) to seawater where they were infected with salmon lice or left as uninfected controls for 1 month, and then transferring them back to freshwater for 2 months. After the seawater phase, infected post-smolts had a mean of 0.33 (range of 0.09–0.91) mobile lice g−1 fish weight. At this point, specific growth rates (SGRs) dropped in infected compared to control fish (0.1% vs. 1.6% day−1). Higher plasma Na+ and osmolality in infected fish also indicate osmoregulatory impairment. Throughout the study, mortality was 18.2% and 1.7% in infected and control groups, but sexual maturation was low and comparable between groups. Infection intensity correlated positively with mortality rate and plasma Cl−, and correlated negatively with SGR and condition factor (CF). CF dropped (ΔCF < 0) at intensities of >0.09 lice g−1 fish weight, and intensities of >0.3 causing zero or negative SGRs and increased mortality were particularly concerning. If infection intensities reach these levels in the wild, char could be impacted by growth restrictions and increased mortality rates, which potentially cause shorter migration durations, lowered reproductive success and possibly also selection against anadromy. This study provides vital information for conservation practitioners wanting to understand the physiologically derived burden salmon lice can have on Arctic char populations, and can be used to define thresholds in the monitoring and conservation of Arctic char populations affected by aquaculture-driven salmon lice infestations.

The phylogenetic origin and evolution of acellular bone in teleost fishes: insights into osteocyte function in bone metabolism

Vertebrate bone is composed of three main cell types, the most prominent of which are the osteocytes. These cells are thought to play a fundamental role in bone physiology, however they are entirely absent in most extant species of teleosts, a group that comprises the vast majority of bony ‘fishes’, and approximately half of vertebrates. Understanding how this acellular (anosteocytic) bone appeared and was maintained in such an important vertebrate group has important implications for our understanding of the function and evolution of osteocytes. Nevertheless, although it is clear that cellular bone is ancestral for teleosts, it has not been clear in which specific subgroup the osteocytes were lost. This review aims at clarifying the phylogenetic distribution of cellular and acellular bone in teleosts, to identify its precise origin, reversals to cellularity, and their implications. We surveyed the bone type for more than 600 ray-finned fish species, fossil and extant and optimised the results on recent large-scale molecular phylogenetic trees, estimating ancestral states. We find that acellular bone is a probable synapomorphy of Euteleostei, a group uniting approximately two-thirds of teleost species. We also confirm homoplasy in these traits: acellular bone occurs in some non-euteleosts (though rarely), and cellular bone was reacquired several times independently within euteleosts, in salmons and relatives, tunas and the opah. The occurrence of peculiar ecological (e.g., anadromous migration) and physiological (e.g., red-muscle endothermy) strategies in these lineages might explain the reacquisition of osteocytes. Our review supports that the main contribution of osteocytes in teleost bone is to mineral homeostasis (via osteocytic osteolysis) and not to strain detection or bone remodelling, helping to clarify their role in bone physiology.