The light spectrum is a key factor in aquaculture, but its effects on molecular stress responses during early fish development are unclear. This study examined how light of different wavelengths (spectra) affects embryos of Baikal whitefish Coregonus baicalensis and its hybrid with Yenisei hump-snout whitefish C. fluviatilis. Eggs were incubated from 35 days post-fertilization under white light (1.8 and 20 µmol m-2 s-1), darkness, red (peak at 631 nm), green (peak at 507 nm) and blue (peak at 459 nm) light. We analyzed relative telomere length, telomerase activity, blood profiles, and expression of stress-related genes (HSP-90, MtCK) at key developmental stages. Notably, a significant increase in telomere length was observed throughout early development (from embryo to larva to fry), independent of the light spectrum. Red light and darkness acted as potent stressors, indicating proteotoxic stress and energy imbalance. In Baikal whitefish, this was accompanied by notable telomere shortening at the earliest stage and elongation at later stages under certain conditions, potentially mediated by increased telomerase activity, a response that may be metabolically costly. Conversely, green light was the most neutral. The effect of blue light differed between Baikal whitefish and its hybrid, with the hybrid proving more sensitive. Furthermore, high-intensity white light (20 µmol m-2 s-1) also induced negative effects in the hybrid, such as increased telomere length, suggesting that excessive irradiance itself can be a stressor, independent of spectral composition. We conclude that darkness or a predominance of red light is suboptimal for incubating these whitefish, while green light provides a more favorable environment, offering a basis for optimizing aquaculture light conditions.

An important factor influencing environmental DNA (eDNA) behavior in ecosystems is the particle size distribution (PSD) of eDNA-associated particles and their decay dynamics. However, despite progress in this area, many questions remain open. In particular, the behavior of the particle-free eDNA fraction (pfeDNA) has been less studied, as its isolation typically relies on DNA precipitation from small water volumes. In this study, we investigated the decay, distribution, and diversity of eDNA from the Baikal omul Coregonus migratorius (Georgi, 1775) across DNA fragment sizes and particle size fractions, with a particular focus on pfeDNA. To overcome standard volume limitations, we adapted a diethylaminoethyl (DEAE)-based ion-exchange protocol that enabled the processing of large water volumes and substantially increased pfeDNA yield. Decay-rate analysis revealed temporal instability of the exponential decay constant and showed that particle-bound and particle-free fractions exhibit similar decay kinetics. Field samples from Lake Baikal revealed pronounced seasonal differences. In March, pfeDNA was present across all stations and exhibited high sequence heterogeneity. May samples showed distinct depth-specific PSD patterns, with larger particle fractions predominating at greater depths, while pfeDNA was largely absent. Our findings indicate that PSD analysis combined with large-volume pfeDNA extraction may expand the analytical capabilities of eDNA research and support more effective biodiversity monitoring across diverse aquatic environments.

Understanding the molecular mechanisms that enable vertebrate adaptation to deep-water environments remains a central goal in evolutionary biology. This study used comparative transcriptomics of skeletal muscle tissue to investigate these mechanisms in four endemic sculpin fish species (Cottoidei) from Lake Baikal, which inhabit different depth niches ranging from pelagic to benthic-abyssal zones up to 1642 m. Pelagic species showed increased activity in genes involved in sarcomere structure, calcium handling, and motor proteins, indicating adaptations for sustained locomotion. In contrast, deep-benthic specialists showed enrichment in pathways for glycolytic metabolism, proteasome function, and ubiquitination, reflecting adaptations for energy efficiency and protein homeostasis in a high-pressure environment. We conclude that the colonization of the Baikal abyssal zone by sculpins relies on a suite of shared molecular mechanisms, with distinct ecological pressures driving specific transcriptional changes in motility, metabolic strategy, and cellular integrity. This study provides a systems-level model for deep-water adaptation in vertebrates.

At the SR-XRF stations (X-ray fluorescence analysis using synchrotron radiation) of the VEPP-3 and VEPP-4M storage rings of the Budker Institute of Nuclear Physics (BINP), Siberian Branch, Russian Academy of Sciences, a test quantitative analysis of chemical elements in the soft tissues of fish is carried out and one-coordinate scanning of fish scales is performed. In the studied samples, the concentrations of 20 chemical elements are determined and differences are identified depending on the type of tissue analyzed, the growth conditions (natural/aquaculture), gender, and taxonomic affiliation of the analyzed individuals. The analysis of biological tissue with minimal sample preparation and the ability to study large samples is an undeniable advantage of the SR-XRF method and can be an effective tool for the environmental monitoring and control of growing process of aquaculture fish products.

Acclimation through the hormesis effect increases the plasticity of organisms, which has been shown for many ectothermic animals, including fish. We investigated the effect of temperature acclimation in Baikal whitefish Coregonus baicalensis (Dybowski, 1874). Telomere length, telomerase activity, and the expression of genes, whose products are involved in the regulation of telomere length and defense against reactive oxygen species, were selected to assess the state of the larvae. Acclimation and acute temperature stress (+12 °C) had no effect on telomere length, but altered telomerase activity (acclimation decreased it; stress increased it) and the levels of genes expression. Under stress, the expression of superoxide dismutase genes was increased in acclimated larvae and that of glutathione peroxidases in non-acclimated larvae, which may indicate lower reactive oxygen species formation and slower antioxidant responses in acclimated fish. The expression of some telomere-related genes was reduced under temperature stress, but the expression of the tzap and smg genes, whose products improve the control of telomere length by preventing them from lengthening or shortening, was increased in acclimated individuals. The data obtained indicate a positive effect of acclimation on the state of the Baikal whitefish larvae by remodulation of their telomerase activity and the transcriptional profile.

For the first time, new data have been presented on the spleen transcriptome of the Baikal cisco Coregonus migratorius Georgi, 1775 (Salmoniformes: Coregonidae), infected with parasites of different systematic groups. Transcriptomic libraries were sequenced on an Illumina NextSeq550 sequencer using the NextSeq® 550 High Output Kit v2. The de-novo transcriptome was assembled. Conserved domains and their associated Gene Ontology annotations were predicted with Blast2Go. The annotation results of the obtained transcripts found that transcripts were distributed in the spleen into the following categories: molecular functions, biological processes, and cellular components. Among the molecular functions, transcripts of enzyme binding (25.8%), transferase activity (24.7%), hydrolase activity (24.4%), catalytic activity affecting proteins (22.2%), and DNA binding (21%) predominated. Biological processes were dominated by transcripts of cellular processes (46.7%), metabolic processes (38.6%), biological regulation (38.2%), and regulation components of biological processes (36.6%). The category of cellular GO components identified terms, namely cytoplasmic vesicles (25.9%), cytoplasmic membranes (23.1%), nucleoplasm (22.1%), cytoskeletal part (18.6%), cytosol and cellular compounds (17%) in a greater extent.

In this work, we describe the transcriptional profiles of preadapted and non-adapted one-month-old juvenile Baikal whitefish after heat shock exposure. Preadapted fish were exposed to a repeated thermal rise of 6 °C above the control temperature every three days throughout their embryonic development. One month after hatching, preadapted and non-adapted larvae were either kept at control temperatures (12 °C) or exposed to an acute thermal stress (TS) of 12 °C above the control temperature. In response to this acute stress, an increase in HSP gene expression (HSP-30, HSP-40, HSP-47, HSP-70, and HSP-90) and TRIM16 was detected, independent of preadaptation. The expression levels of genes responsible for the response to oxygen levels, growth factors and the immune response, HBA, HBB, Myosin VI, Myosin VII, MHC, Plumieribetin, TnI, CYP450, and LDB3 were higher in individuals that had previously undergone adaptation. Genes responsible for the regulation of metabolism, MtCK, aFGF, ARF, CRYGB, and D-DT, however, increased their activity in non-adapted individuals. This information on transcriptional profiles will contribute to further understanding of the mechanisms of adaptation of whitefish to their environment.

Questions of the evolution and taxonomic status of the humpback whitefish Coregonus pidschian and its relationships with the complex C. lavaretus sensu lato (s.n.) are as of yet unresolved problems in the study of Coregonus fauna. With the exception of the Amur basin, the only representatives of the genus Coregonus in native Mongolian fauna are humpback whitefishes (Kottelat, 2006; Dulmaa, 2015). The taxonomic status and origin of the previously described forms found in Mongolia require clarification. The study analyzes their relationships with other representatives of the Coregonus genus using phylogenetic reconstruction based on the mtDNA cytochrome b gene. It is discovered that there are two divergent mtDNA lines of humpback whitefishes coexisting in lakes of the Darkhad Depression. A potential history of their migration to Lake Dood Tsagaan through the upper reaches of the Yenisei River is proposed. The hypothesis of the Darkhad Depression being a refugium that gave birth to a quick-growing form of the Issatchenko whitefish ( C. fluviatilis Isaczenko, 1925, Yenisei basin), separate from the C. lavaretus complex, is disproven. It is shown that a form conspecific with the Issatchenko whitefish definitely occurs on the territory of Mongolia, but only in the Selenga River basin, from where its range extends throughout the Angara–Yenisei basin to the Nizhnyaya Tunguska.

New data were presented for the first time on the intestinal transcriptome of the intestines (posterior section) of the Baikal omul Coregonus migratorius Georgi, 1775 (Salmoniformes: Coregonidae) belonging to the deep water bottom morphological group (Lake Baikal) infected with parasites of various systematic groups: cestodes Dibothriocephalus dendriticus, Proteocephalus longicollis, Eubothrium crassum, and nematode Contracaecum osculatum baicalensis. Sequencing of the transcriptomics libraries was performed on an Illumina NextSeq550 sequencer using the NextSeq® 550 High Output Kit v2. Based on the obtained data, de-novo transcriptome assembly was performed. Conserved domains and their associated Gene Ontology annotations were predicted using Blast2Go. As a result, it was found that in the posterior section of the intestine enriched with lymphoid tissue (GALT), expression of functional proteins was observed that were primarily associated with enzymatic activity, with the development of specialized tissues, with cellular, metabolic and secretory processes. It should be noted that a significant proportion of gene ontology terms is associated with the functioning of the immune system, and with the cellular response to stress, which, under conditions of sensitization by the metabolic end products of helminths and their traumatic and antigenic effects, is quite understandable. The identified transcriptome may provide new information for understanding the functions of lymphoid organs in salmonids with parasitosis.

One of the little-studied ways that climate warming or temperature increases in aquaculture could affect aquatic animals is through accelerated aging. This study is dedicated to understanding the principles of molecular and cellular aging in the target tissues of juvenile whitefishes (Yenisei hump-snout whitefish and its hybrid) under the influence of acute heat stress (up to 26 °C), and the effects of thermal preconditioning as pre-adaptation. Non-adapted stressed hump-snout whitefish showed a higher induction threshold for functionally active mitochondria in the blood and a decrease in telomerase activity in the liver after heat shock exposure as a long-term compensatory response to prevent telomere shortening. However, we observed heat-induced telomere shortening in non-adapted hybrids, which can be explained by a decrease in mitochondrial membrane stability and a gradual increase in energy demand, leading to a decrease in protective telomerase activity. The pre-adapted groups of hump-snout whitefish and hybrids showed a long-term or delayed response of telomerase activity to heat shock, which served as a therapeutic mechanism against telomere shortening. We concluded that the telomerase and telomere responses to thermal stress demonstrate plasticity of tolerance limits and greater stability in hump-snout whitefish compared with hybrids.

The species composition, abundance, biomass, and productivity of zooplankton have been studied in different biotopes of Lake Dood Tsagaan in July 2022. Concerning to the qualitative composition, the lake community is characterized as cladoceran–copepod and almost equally represented by cladoceran and copepod crustaceans. Based on biomass data, dominant species have been identified in the nearshore and deepwater zones of the lake. The copepods Mixodiaptomus incrassatus (Sars), Arctodiaptomus paulseni (Sars), Arctodiaptomus anudarini Borutzky, Mesocyclops leuckarti (Claus), and Cyclops scutifer (Sars) were dominant in biomass in all biotopes of the lake. The mean zooplankton abundance in the lake was 86 300 ± 24 300 ind./m 3 and biomass was 1463.7 ± 415 mg/m 3 . The qualitative and quantitative indicators of zooplankton have not significantly changed over the last 60 years. With respect to the quantitative characteristics of zooplankton, the trophic status of the lake can be considered as a-mesotrophic, with a medium food supply for planktophagous fishes.

Tapeworms of the genus Dibothriocephalus are widely distributed throughout the world, some of which are agents of human diphyllobothriasis, one of the most important fish-borne zoonoses caused by a cestode parasite. Genomic and transcriptomic data can be used to develop future diagnostic tools and epidemiological studies. The present work focuses on a comparative analysis of the transcriptomes of adult and plerocercoid D. dendriticus and the identification of their differentially expressed genes (DEGs). Transcriptome assembly and analysis yielded and annotated 35,129 unigenes, noting that 16,568 (47%) unigenes were not annotated in known databases, which may indicate a unique set of expressed transcripts for D. dendriticus. A total of 8022 differentially expressed transcripts were identified, including 3225 upregulated and 4797 downregulated differentially expressed transcripts from the plerocercoid and adult animals. The analysis of DEGs has shown that among the most differentially expressed genes, there are important genes characteristic of each stage. Thus, several genes are characteristic of D. dendriticus plerocercoids, including fatty acid-binding protein and ferritin. Among the most highly expressed DEGs of the adult stage of D. dendriticus is the Kunitz-type serine protease inhibitor, in two putative isoforms. The analyses of GO and KEGG metabolic pathways revealed that a large number of the DEGs of D. dendriticus are associated with the biosynthesis of various substances such as arginine and folate, as well as with various metabolic pathways such as galactose metabolism, selenocompound metabolism, and phosphonate and phosphinate metabolism. This will contribute to further research aimed at identifying targets for new generation drugs and the development of specific vaccines.

The results of a study on the qualitative and quantitative composition of modern planktonic Crustaceans (Cladocera, Diaptomidae, and Cyclopidae) of Lake Dood Tsagaan (northwestern Mongolia) are presented. A comparative analysis of the species composition of crustaceans according to new data and data obtained in the last century (1962–1963) has revealed an increase in the list of crustaceans by five Cladocera species and three Copepoda species, two of which belong to the order Cyclopoida and one to the order Calanoida. Ultrastructural studies of the main morphological parts of the copepod crustaceans Mixodiaptomus incrassatus (Sars, 1903), Acanthodiaptomus paulseni (Sars, 1903), and Cyclops glacialis Flossner, 2001 have been carried out for the first time using a scanning electron microscope (SEM). A detailed study of morphometric and morphological characters, including the use of a SEM, shows that C. glacialis from Lake Dood Tsagaan is identical to the species described in Turgen Kharkhiraa Uvs aimag and Nogoon nuur lakes in the northwest of Mongolia. Nowadays, the biomass of M. incrassatus, an important food object for the whitefish and other fish species, reaches 1100 mg/m3.

The timing of the start and end of the spawning migration of the Baikal omul is specific for each of its populations, is closely related to the temperature regime in their areals and fluctuates from year to year in accordance with the variability of climatic conditions in the basin of the lake. Since the thermal and water regime of Lake Baikal is changing under the influence of global warming, the omul populations are adapting to shifts in the rhythms of the functioning of the lake's ecosystem. The purpose of this work is to analyze changes in the current ecological and morphological composition of spawning stocks of omul on the example of the posolskaya population in connection with the recorded changes in the timing of its migration for spawning in the 2000s. To analyze the nature of the variability in the timing and dynamics of spawning migration in 2009–2019, we used data from calendar records of the catch by a fixed river seine of mature individuals entering spawning rivers – tributaries of Posolsky Sor Bay. For ecological and morphological analysis, we used data on the morphometry of the omul that entered the Bolshaya Rechka River (one of the main tributaries of the Posolsky Sor. Bay) in different periods of the spawning season of 2020. The results of measurements of spawning migrants in 2020 indicate that, against the background of a general delay in the timing of migration, the dynamics of the morpho-ecological composition of spawning shoals is identical to that in the 1960s and 1980s and is typical for the population under the study. At the same time, data on the morphometry of fish that entered the river in different periods of the spawning season of 2020 indicates a change in the ecological and morphological structure of the population, namely, the quantitative ratio of spawning migrants from various subpopulations changes towards the predominance of "pelagic predators" – inhabitants of the deep-sea areas of Lake Baikal.

Macrohectopus branickii is species endemic to Lake Baikal. The number of amphipod species in Lake Baikal is over 350, but M. branickii is the only species with an exclusively pelagic lifestyle. This work we are study of the population structure M. branickii based on the molecular genetic data. In our study, we used the COI marker - fragment of the cytochrome oxidase subunit 1 of mitochondrial DNA (mtDNA). Based on these sequences, we constructed a haplotype tree using the Network software as well as a phylogenetic tree using the BEAST software packages and molecular clock calibrations. The network showed the presence of separate haplotype groups in the population structure. The dates in the nodes of the phylogenetic tree of M. branickii were near with those of other Baikal endemic amphipod Gmelinoides fasciatus Stebbing, 1899. This may indicate a commonality of events that influenced their population structure in the past, such as the influence of past geological and climatic changes.

Using five microsatellite loci, Bwf1, Bom22b, Cocl23, Cam1, and Cam5, the polymorphism of nine populations of the all three Lake Baikal coregonid species (the omul, lacustrine whitefish and lacustrine-riverine whitefish), were studied. The total sample consisted of 244 individuals. The omul and lacustrine whitefish populations cluster into two separate groups with small pairwise genetic distances. The distance between the groups is also small, suggesting that the omul/lacustrine whitefish pair divergedin the recent geological past. The omul population from Lake Kulinda (basin of the Kichera River, the northern tributary of Lake Baikal) is located at a great distance from these groups, which testifies to its isolation from the omul/lacustrine whitefish species pair. The intermediate position of the omul population spawning in another northern tributary of Lake Baikal, the Upper Angara River, between the other omul populations and the Kulinda omul, indicates the presence of a gene flow from Lake Kulinda to the northern tributaries of Lake Baikal. The revealed genetic polymorphism pattern points to recent sympatric divergence of the omul, lacustrine whitefish, and their populations and supports the geographical isolation of one of the populations of the omul in Lake Kulinda, which is of glacial-tectonic origin. The population of the Upper Angara lacustrine-riverine whitefish, representing the third species of Lake Baikal coregonid fishes, is also at a considerable distance from all the other populations, despite the partial overlape in spawning time and grounds with the Upper Angara omul. This finding do not contradict the hypothesis on long allopatric divergence of the ancestor of the Baikal lacustrine-riverine whitefish outside the lake.

This work simulates the consequences of HIREC using stone sculpins as model organisms. Sex-dependent effects of long-term noise exposure at mean sound pressure levels of 160–179 dB re 1 μPa (SPLpk–pk) were measured. We applied a multilevel approach to testing the stress response: a comparative analysis of the macula sacculi and an assessment of hematological and molecular stress responses. Noise exposure resulted in hair cell loss, changes in some cytometric parameters in blood, and an increase in the number of functionally active mitochondria in the red blood cells of males and its decrease in females, demonstrating a mitochondrial allostatic load and depletion of functional reserve. Finally, a statistically significant decrease in the telomerase activity of the auditory epithelium and a shortening of telomere length in the brain as molecular markers of stress were observed after noise exposure only in females. No significant decrease in telomerase activity and shortening of telomere length in nerve target tissues were observed in stressed males. However, we recorded an increase in the telomerase activity in male gonads. This sex-dependent difference in load may be associated with accelerated cellular aging in females and lower stress-related long-term risk in males. In this article, we discuss possible reasons for these noise-induced stress effects.

Telomeres are the end regions of eukaryotic chromosomes. In addition to maintaining the integrity of the genome, they are involved in aging, regeneration, stress, and disease. We study the telomere biology in Baikal and Siberian planarians, mollusks, and fish. Using these hydrobionts as an example, we study how changes in body size, life expectancy, reproductive strategy, and habitat have reflected in telomeres during evolution, how telomere length changes during ontogeny, and whether stress factors affect its dynamics. We observe both the common features in the telomere biology of such different hydrobionts and their species-specific features. The obtained data indicatea possible influence of physiological and environmental features on the functioning of telomeres.

Microbial polymorphism in water, on the skin, and internal organs of juvenile trout, reared in Recirculation Aquaculture System (RAS) of a trout farm, was analyzed by 16S rDNA amplicon Meta Sequencing (Illumina sequencing technology). The microbiome pattern of water from different locations indicated the perfect work of RAS. Flavobacterium was identified as the only pathogen in the ulcers and internal organs of the diseased fish larvae. We proposed that pathogenic Flavobacterium sp. entered a trout farm through contaminated eggs. Metagenomic analysis of the microbial community is a sensitive and informative indicator of the epidemiological situation in RAS. In terms of amplicon metasequencing, modern NGS technologies become a powerful instrument for microbial monitoring in fish aquaculture.