Abnormalities in the ovaries of sockeye salmon spawners in the Kamchatka River in 2019

Based on histological analysis of the ovaries of sockeye salmon spawners in the Kamchatka River, numerous abnormalities leading to resorption are shown in the structure of vitellogenic oocytes. Fertility of mature female sockeye salmon decreases due to the resorption of the vitellogenic oocytes. Presence of ovaries with abnormal oocytes implies oocyte resorption in fish being a phenomenon associated with mechanism of natural regulation of final fertility. Such mechanism is required in view of changing fish body length and weight in the sockeye salmon of the Kamchatka River. Numerous abnormalities in the ovaries indicate of a decreasing reproductive capacity of spawners and commercial quality of the eggs.

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.

Trace element content in tissues of sockeye salmon from several waterbodies of the Kamchatka Peninsula

The results of the study of macro- (Ca, Mg) and micro- (Mn, Zn, Cu, Fe) elements content in the pectoral fin tissue of adult sockeye salmon Oncorhynchus nerka from the rivers Bolshaya and Kamchatka as well as from Azabachye Lake (Kamchatka Peninsula) are presented. The significant differences in the contents in samples from the three waterbodies were found. It was ascertained that the largest ash proportion (and the mass fraction of trace elements) in dry matter contained in the tissues of sockeye salmon from Kamchatka River, the smallest in the sample of Azabachye Lake. The Ca content was 98 % of the ash mass in all samples; Mg accounted for slightly less than 2 %. The proportion of the remaining elements varied within 0.1 %, and exactly in this range the differences in the microelement composition between the samples were revealed. In sockeye salmon tissues from the Kamchatka River, the content of heavy metals as well as Ca and Mg was higher than in other samples, and their percentage ratio considerably differed from the others. Obviously, the water bodies studied sufficiently distinguish in hydrochemical indices, and that is the cause of differences in bioaccumulation intensities of trace elements in fish tissues at the freshwater life stage.

Natural toxic impact and thyroid signaling interplay orchestrates riverine adaptive divergence of Dolly Varden.

Background Adaptive radiation in fishes has been actively investigated over the last decades. Along with numerous well-studied cases of lotic radiation, some examples of riverine sympatric divergence have been recently discovered. In contrast to the lakes, the riverine conditions do not provide evident stability in the ecological gradients. Consequently, external factors triggering the radiation, as well as developmental mechanisms underpinning it, remain unclear. Herein, we present the comprehensive study of external and internal drivers of the riverine adaptive divergence of the salmonid fish Salvelinus malma. In the Kamchatka River, this species splits in the reproductively isolated morphs that drastically differ in ecology and morphology: the benthivorous Dolly Varden (DV) and the piscivorous Stone charr (SC). To understand why and how these morphs originated, we performed a series of field and experimental work, including common-garden rearing, comparative ontogenetic, physiological and endocrinological analyses, hormonal "engineering" of phenotypes.Results We revealed that the type of spawning ground acts as the main external factor driving the radiation of S. malma . In contrast to DV spawning in the leaf krummholz zone, SC reproduces in the zone of coniferous forest, which litter has a toxic impact on developing fishes. SC enhances resistance to the toxicants via metabolism acceleration provided by the elevated thyroid hormone content. These physiological changes lead to the multiple heterochronies resulting in a specific morphology and SC's expansion into a piscivorous niche.Conclusions S. malma represents a notable example of how the thyroid axis contributes to the generation of diverse phenotypic outcomes underlying the riverine sympatric divergence. Our findings, along with the paleoecology data concerning spruce forest distribution during the Pleistocene, provide an opportunity to reconstruct a scenario of S. malma divergence. Taken together, obtained results with the data of the role of thyroid hormones in the ontogeny and diversification of fishes contribute a resource to consider the thyroid axis as a prime director orchestrating the phenotypic plasticity promoting evolutionary diversification under the changing environmental conditions.

FORMING OF FALSE ANNUAL RINGS ON SCALES OF JUVENILE COHO SALMON ONCORHYNCHUS KISUTCH IN THE UPPER REACHES, FLOODPLAIN OLD WATER BODIES AND LAKES IN THE MIDDLE AND LOWER REACHES OF THE KAMCHATKA RIVER

Structure of scales is investigated for coho salmon juveniles from several sites of their feeding in the Kamchatka River basin, from Pushchino (685 km from the river mouth) to Lake Nerpichye (at the mouth). The underyearlings begin their migrations over the river basin to individual plots soon after their emerging from nests, only part of them feed and winter at the spawning grounds (between Pushchino — Milkovo). A number of coho juveniles stay for feeding and wintering in the tributaries of the Kamchatka River, some of them migrate during spring–summer floods (mid May–June) to the old water bodies in its upper and middle reaches (near Milkovo, Dolinovka, Taezhny, Dedova Yurta, Lake Kulpik) and to the floodplain and lagoon–estuary lakes (Lake Kurazhechnoye, Lake Kursin, and others), having or yet having no scales. Aboriginal coho salmon never spawn in these floodplain water bodies, but the juveniles are observed there all the year round. After wintering, seasonal growth and forming a zone of closely-spaced sclerites of scale (ZCS) — annual ring start in early May or middle May (till early June for some individuals), both for coho yearlings and older juveniles. An additional ZCS (1st type) can be formed earlier on the coho scale in some lakes because of the feeding change. Besides, another additional ZSC (2nd type) can be formed on the scale of coho yearlings (1+) in the old water bodies at Dolinovka, Taezhny, Dedova Yurta, in the lakes Kulpik, Kurazhechnoye, Kursin, and Azabachye and in the Azabachya Channel (at the Dyakonovsky Brook) in late July — August because of seasonal changes in the feeding.