Omul Research Articles

Ultrastructure of the mesonephros of whitefishes from the Lake Baikal basin.

The article presents a study of the mesonephros ultrastructure of Baikal omul Coregonus migratorius, Baikal whitefish Coregonus baicalensis, and a cross between Baikal whitefish and humpback whitefish (C. baicalensis × Coregonus pidschian). The mesonephros ultrastructure was studied using electron microscopy methods. The results of the study show that the number of mature granulocytes is a systematic feature and does not depend on the ecology of fish. The quantitative characteristics of blood cells and the ultrastructural features of leukocytes in the mesonephros are associated with the functioning of the nonspecific defence system in fish. Morphological diversity of epithelial cells in nephron tubules is the ancestral characteristic of the modern omul population, associated with geological and climatic events in the history of Lake Baikal. The development of haematopoietic tissue in the mesonephros, the ultrafine structure of ion-transporting interstitial cells, as well as some ultrastructural features found in the nephron, reflect the adaptive capabilities of the species to live in the ultra-deep Lake Baikal.

Assessment the state of the omul stock <I>Coregonus migratorius</I> in the waters of Northen Baikal according to hydroacoustic investigations

Recently in Lake Baikal there was observed decrease in population of the most abundant species among commercial fish – Baikal omul (Coregonus migratorius). That is why restrictive measures have been imposed on its catches. A hydroacoustic method based on hydroacoustic surveys was used to assess the evolution of the Omul population during the period of restrictive measures in one of the most productive fishery areas – the Northen Baikal. This work represented the results of three-year hydroacoustic research (2021, 2022 and 2023) in the first decade of June. Taking into account the confidence intervals for estimating the number and biomass of Omul, the stock in Northen Baikal is quite stable. The omul spatial distribution on the investigated areas is also stable.

Unexpected Discovery of an Ectoparasitic Invasion First Detected in the Baikal Coregonid Fish Population

The omul, Coregonus migratorius (Georgi, 1775), an endemic fish of Lake Baikal, is the main commercial species of essential economic importance for the extensive region of Eastern Siberia. Despite the continuous 250-year study of Baikal omul and intensive commercial fishing, neither fishers nor biologists have ever mentioned or found external annelid parasites in numerous omul catches. Targeted parasitological studies have also never detected these ectoparasites on the body of this fish. In this study, we present the first reliable information on the existence of specific annelid parasites infecting the pelagic population of Baikal omul and report a 4% infestation of spawners in the Selenga River, the largest tributary of Lake Baikal. We also obtained the main morphometric parameters of the infected fishes, the morphology of the unknown parasite and its feeding strategy. DNA-based analysis was applied to ascertain the taxonomy of the leeches and revealed no closely related taxa existing in international genetic databases (e.g., GenBank) to date. A maximum genetic identity of 89–91% was detected with European Caspiobdella fadejewi. The genetic distances in 9–11% of the substitutions from the closest relatives were very high for a reliable molecular identification of a taxon. The Selenga omul leech may represent a potentially new species and genus.

Изучение микробиологических показателей ферментированного байкальского омуля, изготовленного с применением молочнокислых бактерий

The work is devoted to the study of the effect of the fermentation process on the microflora composition of fermented product from the Baikal omul (Coregonus migratorius (Georgi, 1775)), produced with the use of bacterial concentrate of lactic acid bacteria Latilactobacillus sakei ((Katagiri et al. 1934) Zheng et al. 2020). It has been established that, according to microbiological indicators, fermented Baikal omul meets the requirements of regulatory documentation. The microflora of the control (without the use of bacterial preparations) and experimental (with the use of a bacterial concentrate of lactic acid bacteria) batches had significant differences.

Unique and ancestral features in trunk kidney microanatomy and ultrastructure of omul Coregonus migratorius.

This study presents novel data on the microanatomy and ultrastructure of the omul Coregonus migratorius trunk kidney. Adult individuals of C. migratorius were sampled in the Barguzin Bay of Lake Baikal. Active leuko- and erythropoiesis were found in the interstitium of the mesonephros. For the first time, cells with radially arranged vesicles have been described in the renal interstitium of C. migratorius. The quantitative characteristics of blood cells and ultrastructural parameters of leukocytes reflected the functioning of the non-specific defence system in the organism. The share of the renal interstitium, morphological diversity of the epithelial cells of the nephron tubules, the ultrastructural features of the renal corpuscles and nephron tubules and the number of mitochondria in leukocytes and ion-transporting cells were typical for representatives of the whitefish Coregonus lavaretus complex and thus considered ancestral features of the present-day C. migratorius population reflecting its adaptive potential to living in an ultra-deep Lake Baikal.

Length‐weight relationships of Baikal omul <i>Coregonus migratorius</i> during the feeding season in the Selenga area, Russia

Aim . To refine the LWR coefficients for the Baikal omul Coregonus migratorius (Georgi, 1775). Material and Methods . The data set (number of fish, standard length ( SL ), weight ( W ), sex and morpho‐ecological group (MEG) for the study of the LWR coefficients were taken from the Baikal Omul database. The analysis includes data from 3,091 specimens of Baikal omul, collected in May to June 2003, 2006 and 2007 and in September 2004 in the area adjacent to the delta of the Selenga River. The construction of regression models of LWR was carried out for all data without taking into account gender and MEG. In addition, regression models of LWR data were obtained, grouped by gender and belonging to a certain MEG. Results . Dependencies with close values of the coefficients of the power function are obtained. There were no significant differences between fish of different sexes and MEG, the coefficients differing at the level of statistical error. It is shown that the LWR in fish during feeding periods of different years is quite stable. Conclusion . We offer the equation W=10,9(SL dm ) 3.02 that has acceptable coefficients for C. migratorius resource estimations during feeding period without carrying out controlled fishing.

Assessment of PCBs in Surface Waters at Ultratrace Levels: Traditional Approaches and Biomonitoring (Lake Baikal, Russia)

This article presents the results of the assessment of PCB concentrations in surface waters at ultratrace level of concentrations. The assessment of PCB concentrations is based on data from monitoring PCBs in Baikal water within the conventional approach as well as from biomonitoring of PCBs using Baikal omul, Coregonus migratorius, Georgi, 1775 (C. migratorius), as a bioindicator. The time cycle of the monitoring covered the period from 2014 to 2021. The concentrations of PCBs in the water were estimated from the concentrations of seven indicator congeners: 28, 52, 101, 118, 138, 153, and 180, and from congeners of dioxin-like (dl) PCBs in the tissues of C. migratorius. The average value and the statistically significant range of the detected total concentrations (Ʃ7PCBs) in Baikal water were 0.30 and 0.26–0.34 ng/L, respectively. In the tissues of C. migratorius, the average value and the range of Ʃ7PCB concentrations were 5.6 and 4.9–6.3 ng/g (ww), respectively, and for dl-PCBs, 1.5 and 1.3–1.7 ng/g (ww), respectively. The total toxicity equivalent of the detected dl-PCBs was in the WHO-TEQ (2005) range from 0.03 to 0.06 pg/g (ww). The concentrations of Ʃ7PCBs in Baikal water and dl-PCBs in the tissues of C. migratorius corresponded to the concentration levels in the European alpine lakes and the tissues of S. trutta fish inhabiting these lakes.

Comparative morphological characteristics of spawning populations of Baikal omul (Coregonus migratorius, G.) in the Posolsky Sor, Selenga and Barguzin rivers

The morphological structure, size-age variability and dynamics of age-related fertility of producers of Baikal omul of pelagic, near-bottom and coastal morpho-ecological groups during the depressive state of the population were studied. There is an improvement in the indicators of the growth rate of fish, maturation and an increase in absolute individual fertility against the background of the dilution of the population and the release of the feeding area. A comparative characteristic of some morphological features of fish among morphological-ecological groups is given. The number of gill rakers on the first gill arch significantly distinguishes different morpho-ecological groups and ranges from 36 to 43 pieces for the near-bottom, from 40 to 46 pieces for the coastal and from 44 to 53 pieces for the pelagic morpho-ecological groups. It is noted that the spawning populations of the coastal and pelagic groups are mainly represented by young individuals. With age, the proportion of females increases in all groups. The largest indices of the pectoral, abdominal and anal fins, responsible for movement in the vertical plane, rotation and stop, are noted in the near-bottom group.

Influence of abiotic factors on incubation of Baikal omul eggs in the Selenga River (Lake Baikal Basin)

Abiotic factors affecting the choice of spawning sites for the Baikal omul (Coregonus migratorius) in the Selenga River over 27 years were studied. A total of 3,450 samples were collected using the Dulkeit scraper in Decembers of 1987-2014, at 24 trans-sections in the Selenga River channel over a total length of 410 km. At each sampling site we recorded omul egg density, substrate particle size, water depth, water flow velocity, and ice thickness. Omul eggs were found mainly on hard substrates (sand, gravel, pebbles, and pebble-cobbles combinations). Omul has been found to avoid spawning at depths less than 1.5 m and greater than 6.0 m. Water velocity and ice thickness did not strongly influence the choice of site. Omul eggs were found at flow rates of 0.05-0.7 m/s with a maximum at 0.1 m/s.

Spawning Behaviour of Whitefishes (Coregonidae)

We observed, photographed, and recorded (video and audio) spawning of five whitefish species — Coregonus migratorius (Baikal basin), C. peled, C. tugun, C. pidschian, C. muksun (the Ob basin) — in the spawning devices. All species spawned in autumn in the dark and the spawning period lasted 10–30 days. Individual fish spawned several times during the night and the spawning behaviour consisted of three, cyclically repeated phases: courtship, mating and recovery. Spawning occurred in male–female (with males to be initiators) or male–male combination, and took place either in the water column or near the water surface. A mating act consisted of a rhythmic parallel movement of the fish swimming side by side with the synchronous release of the gametes. Three types of mating acts were observed: vertical (from bottom to top), horizontal and combined including both vertical and horizontal movements. The male in the spawning pair moved forward towards the female by the length of its head; it rhythmically struck the back of the female's abdomen by bending the caudal peduncle. Depending on the species and size of the fish, the mating act lasted for 0.3–3 s within 0.3–2 m. The frequency of rhythmic body collisions was on average 17 Hz for C. migratorius and C. pidschian, while for C. tugun and C. peled it was 25–27 Hz. An egg batch released during the mating act amounted to about 90 eggs for C. tugun and 290–370 for C. peled, which corresponded to 1%–6% of the total fecundity of a female. A female participated in 20–100 mating acts during 1–3 nights. Eggs cannibalism was also observed. During spawning, eggs were widely dispersed across the spawning area, which may be regarded as an adaptation aimed at increasing survival rate during embryogenesis.

Vertical distribution, seasonal differentiation and trajectory of movement of zooplankton and pelagic fish of Lake Baikal

In Lake Baikal, the majority (87%) of fish biomass is generated in the pelagic zone. Two species of Comephorus, three species of Cottocomephorus and Coregonus migratorius inhabit in the pelagic zone of the lake. Currently, only C. migratorius is considered a resource species, the harvest of which accounts for about 50% of the total fish harvest. Food items for pelagic fish are copepods Epischura baikalensis and pelagic amphipods Macrohectopus branickii. The seasonal distribution and formation of zooplankton concentrations determine the food migrations of fish. The patterns of the seasonal distribution of zooplankton and pelagic fish were described by M.M.Kozhov (1954, 1964). Comparative analysis of the abundance of zooplankton in South Baikal over time, showed that during the period of maximum development of E. baikalensis in the months of July, August, and October, zooplankton concentration in the decade 1997 to 2007 was twice more than in 1951 (Kozhov 1954; Kiprushina 2010). The distribution of E. baikalensis is directly dependent on the water temperature. Yet there is an inverse relationship in the surface layer 0–25 meters. During warming up of the surface water layers, which had been observed in 2002 year E. baikalensis left the upper zone and migrated deeper, to a layer of 50–100 meters. In other months of the year, no changes in the average values of the E. baikalensis abundance were revealed. At present, when the ecosystem of Lake Baikal is changing, there is a need to restart such complex studies, and to use the results obtained by M.M. Kozhov for comparative analysis.

Limits for <i>Coregonus migratorius</i> (Georgi, 1775) catches and likely ecological effects

Aim. This study aims to discuss the validity of introducing restrictions on the catch of Coregonus migratorius (Georgi, 1775) with a forecast of the likely environmental consequences of doing so.Discussion. We show the results of the analysis of the assessment of the state of C. migratorius stocks and the reasons for their decline. We indicate that the biostatistical and hydroacoustical methods for estimating fish numbers, which are traditionally used to substantiate allowable catches, have some disadvantages and limitations. We consider unrecorded catches and unfavourable natural and climatic environmental factors to be reasons for the decline in C. migratorius stocks. We discuss ecological and anthropogenic factors of changes in stocks of this commercially important species for the region. We show the anticipated ecological effects of currently established limits.Conclusion. The results of changes in the modelling of the number and age composition of fish with different protection strategies indicate that maintaining a low level of replenishment stock the limits would not increase commercial stocks of C. migratorius. Restrictions imposed on the commercial and amateur fishing would significantly increase environmental risks through increase of poaching (including during the spawning period) as well as as a consequence of amateur fishing of other commercially valuable fish species.

A Study of Protein Fractional Composition during Incubation of Diphyllobothrium dendriticum (Cestoda) Plerocercoids in a Medium Containing Blood Serum of the Host, the Baikal Omul Coregonus migratorius (Coregonidae)

The change in the composition of the protein fraction of Diphyllobothrium dendriticum (Cestoda) plerocercoids during incubation in a medium containing blood serum of their host—the Baikal omul Coregonus migratorius (Coregonidae)—was investigated. The change in the composition of the protein fraction of the incubation medium also was studied. On the one hand, the appearance of new high-molecular fractions with a molecular weight (MW) of 193 kDa after 3, 12, and 24 h of incubation and 88 kDa after 24 h was detected, which was associated at plerocercoids with the appearance of a new 189 kDa fraction after 12 h and the disappearance of the 80 kDa fraction. On the other hand, a decrease or the disappearance of two low-molecular fractions 57 and 42 kDa in the incubation medium after 3, 12, and 24 h of incubation were observed.

Prospects of Fish-Husbandry Utilization of Maloye More Fishing Area: Economic Assessment and Substantiation

The article was written on the basis of the results of the research conducted by the staff scientists of Limnological Institute of Siberian Branch of the Russian Academy of Sciences and Baikal State University. The aim was to define ecological and economic viability of planting of prospective autochthonous aquatic species including Baikal omul Coregonus migratorius in Maloye More fishing area. The process of fish planting is considered in the light of the need for satisfying the demand for omul both among the local population and tourists visiting Maloye More. The authors give a brief analysis of the demand for fish among the above mentioned categories. On the basis of calculations, a conclusion is drawn that it is impossible to satisfy the need for omul among the population of Maloye More and tourists visiting the area, whose number is growing fast, solely by means of natural propagation. Thus, the authors made an economic assessment of viability of measures aimed at stocking Maloye More fishing area with fish. These measures include acquisition of juvenile omul and its transportation from fish-breeding farms in Irkutsk Region and the Republic of Buryatia and also construction of a fish-breeding farm in Maloye More fishing area.

Estimation of the Coefficients of the Equation of Acoustic Target Strength Based on the Morphology of Coregonus migratorius (Georgi, 1775) Swim Bladder

Aim. The aim of the study was to estimate the coefficients of the equation TSmax=f(SL) considering the characteristics of an acoustic scattering model based on the morphological characteristics of the swim bladder of the Coregonus migratorius (Georgi, 1775). Material and Methods. Ninety‐nine living specimens of C. migratorius served as the study material. For each specimen, the target strength in the cage was measured using an Kongsberg Simrad EY500 echo sounder and the morphology of the swim bladder was studied. Measurements, analysis of images and data were conducted using Image Pro 6.0. Excel and SciLab software resources. Results. We determined the main morphological characteristics of the swim bladder in C. migratorius as well as the correspondence of its dimensions and proportions in relation to the length of the fish’s body. The coefficients of the equation TS=20log(SL)‐60, calculated on the results of the acoustic scattering model of a prolate spheroid, agree well with the coefficients calculated from maximum values obtained in the cage experiment. During the conversion of the coefficients relating to the allometric changes in the length of the swim bladder relative to fish length, the equation TS=23.2log(SL)‐64.4 was obtained. A comparative analysis of the available equations of the target strength for C. migratorius with those obtained in the study was undertaken. Conclusion. The equation obtained on the model of the swim bladder as a prolate spheroid adequately describes the dependence of the maximum values of the target strength on the body length of the C. migratorius and confirms the previously obtained dependence by maximum values of TS in the cage experimental conditions and can serve as a basis for further theoretical studies.

Complete mitochondrial genomes of Baikal endemic coregonids: omul and lacustrine whitefish (Salmonidae: Coregonus sp.)

Coregonid fishes are among the most successful groups in the subarctic, boreal, and subalpine fresh waters of the northern hemisphere. Limnetic–benthic sympatric species-pairs from two different evolutionary lineages, the North American lake whitefish (Coregonus clupeaformis species complex), and the European whitefish (Coregonus lavaretus species complex), are becoming the subject of close attention to explore the role of natural selection during the ecological speciation. Baikal endemic coregonids, limnetic omul (Coregonus migratorius), and benthic lacustrine whitefish (Coregonus baicalensis) are the only representatives of another unique lineage that has not left the lake since the divergence from the two above. Due to Pleistocene oscillations sympatric limnetic–benthic divergence has been replicated here many times within the same water body over a long geological period in contrast to both Europe and America where sympatric species-pairs are the results of post-glacial secondary-contacts between glacial isolates during the Late Pleistocene on the territory of each continent. Mitochondrial genomes encode genes that are essential for respiration and metabolism. Data on complete mitogenomes of Baikal endemic coregonids provided here will complement ongoing investigations on energy metabolism as the main biological function involved in the divergence between limnetic and benthic whitefish.

Fatty acid composition of salted and fermented products from Baikal omul (Coregonus autumnalis migratorius).

The fatty acid (FA) composition of raw, salted, and fermented fish products prepared from two populations of Baikal omul (Coregonus autumnalis migratorius) was determined. Total lipid content in the raw, salted, and fermented fish products was 3.85, 4.04, and 3.76%, respectively. Overall, the most abundant fatty acids were 14:0 (myristic acid), 16:0 (palmitic acid), 16:1n-7 (palmitoleic acid), 18:1n-9 (oleic acid), 20:5n-3 (eicosapentaenoic acid), and 22:6n-3 (docosahexaenoic acid, DHA). Polyunsaturated FAs were the main fatty acid group. Among unsaturated FA, n-3 forms dominated. The highest amounts of n-3 FAs were found in raw fish, followed by fermented and salted fish. Salting significantly increased the content of some FAs (15:0, 16:2n-4, 18:3n-3, 20:3n-3) compared with raw fish and decreased the DHA content. The FA composition of fermented fish did not differ from that of raw fish. The n-3:n-6 ratio did not differ between raw, salted, and fermented fish from population A, while the ratio was higher in raw fish from population B. Overall, thiobarbituric acid reactive substances, and thereby oxidation, were significantly lower in raw fish than in salted and fermented fish. Salting, but not fermentation, affected the FA composition of fish.

Modelling future hydroclimatic effects on the <i>Coregonus migratorius</i> spawning migration in the Selenga River and Lake Baikal

Abstract. Regional climate change affects the flow conditions in river basins which can impact the health of aquatic ecosystems. Potential impacts of future climate scenarios on Coregonus migratorius spawning migration in the Selenga River were assessed. A regional process-based hydrological model was used to reproduce the historical trends in the annual flow and assess its future changes under several climate change scenarios. Annual flow projections were used to identify preferential river reaches for spawning activity of the Arctic cisco (Coregonus migratorius), based on the significant negative correlation of spawning activity with the Selenga River streamflow. The applied methodology shows that the projected decline in runoff of 10 % to 25 % in XXI century may result in shifting of the spawning locations further upstream of the Ulan-Ude city, a local “pollution hotspot”.

The results of the first hydroacoustic studies of the winter distribution of Coregonus migratorius in Lake Baikal

We have obtained the first data on the distribution and behaviour of C. migratorius using thehydroacoustic recording of fish in the monostatic mode from the ice cover of Lake Baikal. The results of the studies have shown the nature of the winter distribution of C. migratorius, which also persists in the early spring. We assume that C. migratorius simultaneously executes three behavioural strategies. Observations of the C. migratorius behaviour in winter using the hydroacoustic method can be useful for the future studies of the characteristics of different behavioural and nutritional models as well as the age and size structure of populations inhabiting various zones of the lake. This approach, as a basis of the quantitative method of automatic recording of individual behavioural acts and changes in the fish aggregation, together with the use of hydrophysical equipment can show the response of fish to the changes in certain environmental parameters.

The effects of sound pollution as a stress factor for the Baikal coregonid fish

We have studied morphological features of the hearing epithelium affected and unaffected by increased long-term sound (at 160 dB re 1 μPa) on the example of the Baikal omul (Coregonidae, Coregonus migratorius). The sensory epithelium was analyzed using the 3D confocal laser scanning techniques. We observed local epithelium damages in the rostral, central and caudal regions of the saccule, e.g. sticking stereocilia, vacuolization and round shape gaps. This article discusses the reasons for the local effects of sound on different regions of the sensory epithelium. We assume that using of morphological screening of sensory acoustic system in the artifcial rearing of the Baikal coregonid fshes under the conditions of intense noise could contribute to indicating the most stress-resistant forms, which are promising for high-tech industrial aquaculture, and developing more gentle approaches to its creation.