Coregonid Species Research Articles

The Contact Zone of Phylogenetic Lineages of Freshwater Fish in Arctic Eurasia: Genetic Polymorphism of Coregonid Populations

The reconstruction of regional fauna history is very important in the context of recent climate change and anthropogenic transformation. We analyzed the mitochondrial nd1 gene polymorphism in populations of whitefish Coregonus lavaretus and certain widespread Eurasian ciscoes species: vendace Coregonus albula and least cisco Coregonus sardinella, inhabiting waterbodies from the Anadyr River in the east (the Pacific Ocean basin) to Loch Lomond in the west (the Atlantic Ocean basin). Distinct phylogenetic lineages and secondary contact zones have been found in these species. Most of these are species-specific with the exception of the zone from the Pechora River basin to at least the western part of the Taymyr Peninsula, in which whitefish, vendace, and least cisco share with each other and with various cold-water hydrobionts. We associate differences in the geographical position and propagation of the secondary contact regions with the species-specific morpho-ecological features, in particular, with the ability for long-term migrations. Based on the data obtained, we also discuss certain limitations of the phylogeography and phylogeny of the considered coregonid species and the correctness of the taxonomic status of certain populations or their groups.

Spatio-temporal variability of eDNA signal and its implication for fish monitoring in lakes.

Environmental DNA (eDNA) metabarcoding is revolutionizing the monitoring of aquatic biodiversity. The use of eDNA has the potential to enable non-invasive, cost-effective, time-efficient and high-sensitivity monitoring of fish assemblages. Although the capacity of eDNA metabarcoding to describe fish assemblages is recognised, research efforts are still needed to better assess the spatial and temporal variability of the eDNA signal and to ultimately design an optimal sampling strategy for eDNA monitoring. In this context, we sampled three different lakes (a dam reservoir, a shallow eutrophic lake and a deep oligotrophic lake) every 6 weeks for 1 year. We performed four types of sampling for each lake (integrative sampling of sub-surface water along transects on the left shore, the right shore and above the deepest zone, and point sampling in deeper layers near the lake bottom) to explore the spatial variability of the eDNA signal at the lake scale over a period of 1 year. A metabarcoding approach was applied to analyse the 92 eDNA samples in order to obtain fish species inventories which were compared with traditional fish monitoring methods (standardized gillnet samplings). Several species known to be present in these lakes were only detected by eDNA, confirming the higher sensitivity of this technique in comparison with gillnetting. The eDNA signal varied spatially, with shoreline samples being richer in species than the other samples. Furthermore, deep-water samplings appeared to be non-relevant for regularly mixed lakes, where the eDNA signal was homogeneously distributed. These results also demonstrate a clear temporal variability of the eDNA signal that seems to be related to species phenology, with most of the species detected in spring during the spawning period on shores, but also a peak of detection in winter for salmonid and coregonid species during their reproduction period. These results contribute to our understanding of the spatio-temporal distribution of eDNA in lakes and allow us to provide methodological recommendations regarding where and when to sample eDNA for fish monitoring in lakes.

Genome assembly, structural variants, and genetic differentiation between lake whitefish young species pairs (Coregonus sp.) with long and short reads.

Nascent pairs of ecologically differentiated species offer an opportunity to get a better glimpse at the genetic architecture of speciation. Of particular interest is our recent ability to consider a wider range of genomic variants, not only single-nucleotide polymorphisms (SNPs), thanks to long-read sequencing technology. We can now identify structural variants (SVs) such as insertions, deletions and other rearrangements, allowing further insights into the genetic architecture of speciation and how different types of variants are involved in species differentiation. Here, we investigated genomic patterns of differentiation between sympatric species pairs (Dwarf and Normal) belonging to the lake whitefish (Coregonus clupeaformis) species complex. We assembled the first reference genomes for both C. clupeaformis sp. Normal and C. clupeaformis sp. Dwarf, annotated the transposable elements and analysed the genomes in the light of related coregonid species. Next, we used a combination of long- and short-read sequencing to characterize SVs and genotype them at the population scale using genome-graph approaches, showing that SVs cover five times more of the genome than SNPs. We then integrated both SNPs and SVs to investigate the genetic architecture of species differentiation in two different lakes and highlighted an excess of shared outliers of differentiation. In particular, a large fraction of SVs differentiating the two species correspond to insertions or deletions of transposable elements (TEs), suggesting that TE accumulation may represent a key component of genetic divergence between the Dwarf and Normal species. Together, our results suggest that SVs may play an important role in speciation and that, by combining second- and third-generation sequencing, we now have the ability to integrate SVs into speciation genomics.

Vendace (Coregonus albula) in Lake Inari — What Has Changed in 50 years?

Lake Inari is a subarctic, oligotrophic, regulated lake in northern Finland, connected via the Paatsjoki (Pasvik) River to the Arctic Ocean. A new coregonid species, the vendace (Coregonus albula), was introduced into the watershed in the 1960s and gradually established a population in the lake becoming part of its ecosystem. The annual vendace catch in 1989 reached 300 tonnes, while during the following 25 years the vendace catches declined stabilizing at a very low level. Vendace introduction radically changed the fishing practices within a short time, and its population became firmly established in the lake. It benefited both fisheries and predatory fishes, especially salmonids. The vendace year-class strength varied greatly between 1983 and 2019. According to winter seine CPUE data, the strongest year-classes were up to 100 times greater than the weakest ones. Winter seine CPUE of one-year-old fish correlated positively with catches in the coming years. The growth data for the period 2015–2021 revealed a decrease in the youngest vendace age-groups.

РОЗМІРНО-ВАГОВІ ПОКАЗНИКИ МОЛОДІ РІЗНИХ ВИДІВ СИГОВИХ (COREGONINAE) РИБ, ВИРОЩЕНИХ В УМОВАХ ЗАМКНЕНОГО ВОДОПОСТАЧАННЯ

Purpose. Determining the growth dynamics of whitefish juveniles in conditions of recirculated aquaculture systems to current needs of industrial aquaculture of Ukraine. Methodology. The work was performed in accordance with generally accepted guidelines used for coregonid rearing in industrial aquaculture. The study was conducted in a specialized farm for whitefish breeding - "Lavaretus" LLC. Findings. Weight and linear growth during the period of cultivation in controlled conditions of whitefish young-of-the-year were characterized by dynamics, which were generally close to that typical for coregonids. The study included four coregonid species with different feeding types. Planktivorous (peled), bentivorous (whitefish), polyphagous species that is able to feed on various food organisms (muksun) and peled/broad whitefish hybrid. Feeding regime: during the transition to the mixed feeding was carried out 48 times a day (14 hours with an interval of 15 and 30 minutes) manually; further, according to an increase in fish weight was reduced to 4 times a day using automatic feeders. The average weight and length of young-of-the-year grown in a recirculating aquaculture system was: - peled – 5.6 ± 0.4, muksun – 10.1 ± 0.6.9, Baltic whitefish – 8.6 ± 1.2 g, peled/broad whitefish hybrid – 7.9 ± 0.2 g. The coefficient of variability of weights were: peled – 40.4%, muksun – 32.2%, Baltic whitefish – 21.1%, peled/broad whitefish hybrid – 41.9%. Originality. New data on piscicultural-biological parameters and dynamics of growth of juveniles of various coregonids or cultivation in conditions of a recirculating aquaculture system were obtained. Practical value. The development of whitefish farming technology in RAS conditions, which, in contrast to salmon cultivation, is only at the initial stage of implementation, so obtained data will be the basis for the development of whitefish culture in Ukraine. Key words: recirculating aquaculture system, young-of-the-year, coregonids, length-weight parameters, rearing.

Genetic Assessment of Inconnu (Stenodus leucichthys) in Great Slave Lake, Northwest Territories, Canada

Inconnu (Stenodus leucichthys) is a large freshwater migratory coregonid species that is commercially fished in some parts of its range. In Great Slave Lake, NT, Inconnu are one species that is caught in a mixed species gillnet fishery that is subject to restrictive management because four of the seven known stocks are declining or have been extirpated. The seven known Inconnu stocks have been identified based on the river systems that support or once supported a spawning population. To help identify key geographic areas for harvest control and other management approaches, we estimated the genetic diversity and population genetic structure of Inconnu in this area with 17 microsatellite loci. Temporal and spatial genetic structure was examined in four river systems, lower and upper Mackenzie River, Buffalo River, Slave River and Marian River/Lake and within Great Slave Lake. Analyses suggested that genetic diversity was greater in lower/upper Mackenzie River populations compared to populations in Great Slave Lake. Genetic structure was temporally stable at all locations except one, and spatial structure was found with significant isolation by distance detected among locations. Bayesian clustering analysis suggested five genetic groups of Inconnu, one in the lower and upper Mackenzie River and four within Great Slave Lake. The substructuring within Great Slave Lake included a genetic group representing fish collected in the lake itself. In addition, three genetic groups corresponded to river systems (Buffalo River, Marian River/Lake, Slave River), indicating that each river has genetically distinct Inconnu populations. These results suggest that the sustainability of Inconnu in and around Great Slave Lake depends upon maintaining stocks associated with river systems, especially those that are geographically disparate.

Overfishing of a small planktivorous freshwater fish, vendace (Coregonus albula), in the boreal lake Pyhäjärvi (SW Finland), and the recovery of the population

Vendace (Coregonus albula) is a small and rapidly reproducing planktivorous coregonid species that is known to endure very high fishing pressure. Catch levels of 10–25 kg ha−1 a−1 have been sustained for extended periods in several Finnish lakes without signs of fishery-related deterioration of recruitment or decline of spawning stocks. However, data from the lake Säkylän Pyhäjärvi (SW-Finland) in the 1990s indicate an episode of recruitment overfishing of the vendace population. The combination of unfavourable spring weather and unusually high abundance of piscivorous fish led to poor vendace recruitment in two successive years (1990, 1991). In spite of the reduced stock, fishing effort remained high, which resulted in excessively high premature mortality, a depressed spawning stock, and markedly reduced catches. Fishing mortality remained high until the mid-1990s. Then, because of the impaired profitability of the fishery, part of the winter seine crews ceased fishing altogether. The ensuing reduced fishing pressure immediately brought about lowered mortality of vendace, and the spawning stock gradually recovered during the late 1990s. In the 2000s the year-class size stabilized to an average level about half of that in the 1980s. Concurrently, the importance of winter seine fishing diminished due to weakening ice conditions in the warming climate, resulting in a reduced overall fishing pressure on the vendace stock. This study shows that even small, rapidly reproducing freshwater planktivores can be overfished. In the case of Pyhäjärvi, the fishery was self-regulating through economic forcing. A recovery from overfishing was possible because the biological features of vendace make it a highly resilient species.

Small Lakes Ecosystems under the Impact of Non-Ferrous Metallurgy (Russia, Murmansk Region)

This paper presents integrated research on ecosystems of small lakes experiencing the direct impact of a copper-nickel ore processing plant, the “Kolskaya GMK” (MS KGMK), near the town of Monchegorsk Kola Peninsula, Russia. An integrated research method with the analysis of both abiotic and biotic components of aquatic ecosystems was used. It was found that the water ecosystems developed under the conditions of extreme pollution depleted the species composition of the hydrobionts and the number indices. Much of the pollution resulted in a transformation in the phytoplankton community structure: the share of mixotrophic algae and Cyanobacteria increased. Anthropogenic eutrophication resulted in a decrease in toxic impact. Despite high anthropogenic load, Salmonid and Coregonid species were found in a number of water bodies. The size and weight indices and the heavy metal accumulation intensity had a distinct gradient nature. The macrozoobenthos in the water bodies studied was characterized by depleted taxonomic composition and extremely low numbers. The basis of the zoobenthos was formed by chironomids Psectrocladius, Procladius, Cricotopus, and Orthocladius, spread widely in water bodies polluted with heavy metals.

The Long-Term Dynamics of Parasite Infection in Coregonids with Different Food Specializations

The long-term dynamics of the parasitic infection of two coregonid species with different food specializations, peled Coregonus peled (Gmelin, 1789) and Siberian whitefish Coregonus lavaretus pidschian (Gmelin, 1788), during spawning migration in the Synya River (a Polar Urals tributary of the Lower Ob) has been studied. The differences in the parasite species composition and infection of the two fish species are determined their food spectra features, as well as by their use of different biotopes in feeding water bodies and the interannual dynamics of the fish age composition. A trend towards a decrease in the rate of peled infection by myxosporidium and cestode with a simultaneous decrease in its abundance due to intensive catches has been revealed. The stability of the composition of the coregonid parasite fauna in the Ob lower reaches indicates stable relationships between parasites and hosts and a relatively stable state of the ecosystem of the Lower Ob.

The role of European smelt Osmerus eperlanus in fish fauna structure of the Imandra Lake Basin (Murmansk Province)

The current trends of the fish community transformation processes in the Imandra Lake Basin (Murmansk Province) under processes of climate and hydrological regime changes, intensification of water eutrophication and pollution were studied. The continuing anthropogenic pollution load on the lake together with the uncontrolled fishery and the lack of favorable conditions for fish reproduction led to a decrease of quantity and share of long-cycle stenobiont fall-spawning salmonid and coregonid species in fish fauna structure. At the same time the amount of eurybiont spring-spawning low commercial value species, such as a European smelt Osmerus eperlanus (Linnaeus) was seriously increased. It was found that the smelt population growth is accompanied by an increase in its size and weight parameters. The highest size values of this species now are comparable to smelt of the Onega and Ladoga lakes. It was also mentioned that smelt demonstrates quite an intense self-dispersion within the Imandra Lake Basin. Smelt expands rapidly within the subordinate lake and river system of Bolshaya Imandra Lake. One of the most interesting phenomena now is a process of fish self-dispersion along the Bolshaya Belaya River. It was found that the smelt shows a very active expansion of habitat, despite of the intense impact of apatite-nepheline production and strong eutrophication of water. It is shown that European smelt have good opportunity to naturalize and form an isolated self-reproducing population in a typical mountain reservoir – Bolshoi Voodyavr Lake, influenced by intensive mining industry. The observed expansive strategy of low commercial value species could be consider as invasion of alien species, reducing resistance and resource potential of the freshwater ecosystems of the North.

Coregonus peled (Gmelin) transplanted into Ulaagchny Khar lake (western mongolia) showed no evidence of hybridization with other introduced Coregonus species

Coregonus peled (Gmelin) (Teleostei: Salmoniformes: Coregonidae), which is considered an important object of coldwater aquaculture, had been successfully introduced into an enclosed Western Mongolian lake Ulaagchny Khar in the early 1980s. At the same time larvae of two other Coregonus species—Baikal omul C. migratorius (Georgi) and least cisco C. sardinella Valenciennes—had also been released into the lake. Baikal omul was then reported as a naturalized species. This might have caused interspecific hybridization and gene introgression. Identification of coregonids by morphology can be problematic, so to determine which species was dominant in the lake (we presumed it was peled) and if its gene pool was affected by other introduced Coregonus species we sampled 40 individuals and analyzed them by sequencing a fragment of mtDNA cyt b and by allozyme electrophoresis. The analysis showed that all the fish belonged to C. peled with no evidence of admixture from other coregonid species. Taking into account mass release of both species in 1980s, it is evident that naturalization of peled in the lake was much more successful than that of Baikal omul.

On-Feeding and Juvenile Production of Coregonid Species with Formulated Dry Feeds: Effects on Fish Viability and Digestive Enzymes

The present study describes a successful method for on-feeding and fingerling production of C. atterensis and C. marena using solely formulated dry feeds. Also the development and differentiation of the digestive system in relation to different feed types was investigated. The tested commercially available starter feeds were not suitable for on-feeding of larvae of the two species. Only self-formulated starter feeds containing zooplankton or Artemia in defined quantities and organic acids as preservatives resulted in survival rates and growth rates similar to the live zooplankton control. For successful fingerling production resulting in survival rates and growth rates similar to a live feed control not only a suitable starter feed was necessary, but also specific feeding regimes where starter feed was replaced with intermediate feed and then with commercial feed in defined chronological sequences. Trypsin, chymotrypsin, lipase, phospholipase A, and acid and alkaline phosphatase occurred in the digestive tract of larvae of C. atterensis and C. marena. At the onset of exogenous feeding the digestive system of C. atterensis was less developed than the digestive system of C. marena. In both species the activities of the investigated digestive enzymes depended strongly on the administered feed types. Inadequate feeds significantly decreased activities of the assayed digestive enzymes.

Absence of intrinsic post-zygotic incompatibilities in artificial crosses between sympatric coregonid species from upper Lake Constance.

A full factorial crossing experiment with five females and five males of each of two coregonid species from upper Lake Constance was used to test for intrinsic post-zygotic incompatibilities during early ontogeny. Up until shortly before hatching, there was no difference in embryo mortality between homo and heterologous crosses. A maternal effect on mortality was found in both species, but paternal effects and female-male interactions were absent. Thus, genetic incompatibility during early ontogeny does not appear to prevent introgressive hybridization, suggesting that genetic divergence between these species is maintained primarily by pre-zygotic barriers. The recent genetic homogenizations of coregonid species flocks in European alpine lakes may have been caused by a flattening of adaptive landscapes through eutrophication, but intensive stocking with larvae obtained in hatcheries from artificially fertilized eggs is also likely to be a contributing factor. To safeguard diversity among sympatric coregonids, it is important to re-establish ecological conditions conducive to species divergence and to revise traditional management strategies.

Differences in Brain Transcriptomes of Closely Related Baikal Coregonid Species

The aim of this work was to get deeper insight into genetic factors involved in the adaptive divergence of closely related species, specifically two representatives of Baikal coregonids—Baikal whitefish (Coregonus baicalensis Dybowski) and Baikal omul (Coregonus migratorius Georgi)—that diverged from a common ancestor as recently as 10–20 thousand years ago. Using the Serial Analysis of Gene Expression method, we obtained libraries of short representative cDNA sequences (tags) from the brains of Baikal whitefish and omul. A comparative analysis of the libraries revealed quantitative differences among ~4% tags of the fishes under study. Based on the similarity of these tags with cDNA of known organisms, we identified candidate genes taking part in adaptive divergence. The most important candidate genes related to the adaptation of Baikal whitefish and Baikal omul, identified in this work, belong to the genes of cell metabolism, nervous and immune systems, protein synthesis, and regulatory genes as well as to DTSsa4 Tc1-like transposons which are widespread among fishes.

Morphofunctional transformations in fishes of the middle and lower Ob’ basin under increasing anthropogenic influence

The results of a long-term (1981–2009) study on the gametogenesis and sexual cycles are given, and the state of gills and liver is characterized in Coregonidae, Cyprinidae, and Percidae fishes in waterbodies of the Ob’-Irtysh Basin considered intact and in those affected by anthropogenic influence to various degrees. The resistance to pollution of the branchial epithelium, liver, and gonads in fishes is shown to decrease in the following sequence: cyprinids → percids → coregonids → juvenile coregonids. Specific features of the composition and quantitative dynamics of primary sexual cells during the embryonic and early postembryonic periods are described in different coregonid species. The influence of weak pulsed electromagnetic fields on coregonid embryos and larvae has been analyzed with the purpose of developing methods for increasing the ecological plasticity under extreme natural and technogenic conditions.

Documentation of Annual Spawning Migrations of Anadromous Coregonid Fishes in a Large River using Maturity Indices, Length and Age Analyses, and CPUE

Coregonid fi shes contribute to major food fi sheries throughout the Yukon River drainage in northwest North America. Research and management activities related to these coregonid fi shes, however, have been minimal because of the commercial and international focus on Pacifi c salmon Oncorhynchus spp. populations that share the drainage. We studied fi ve coregonid species at a fi sh- wheel sampling site 1,200 km from the Bering Sea. They were inconnu Stenodus leucichthys, broad whitefi sh Coregonus nasus, humpback whitefi sh C. clupeaformis, least cisco C. sardinella, and Bering cisco C. laurettae. Otolith chemistry studies have shown that anadromy is a common or prevailing life history strategy for all fi ve species at our fi sh-wheel sampling site. Radio telemetry studies revealed major spawning habitats for four species in the Yukon Flats, an extensive braided region of the river 1,600 to 1,700 km upstream from the Bering Sea. The objectives of this study were to document the demographic qualities of migrating coregonids at the fi sh-wheel sampling site and to defi ne seasonal periods of relative abundance based on daily catch rates. Maturity indices indicated that nearly all fi sh were mature and preparing to spawn. Minimum lengths and ages of maturity ranged from low values of 23 cm and 2 years for least cisco, to high values of 58 cm and 7 years for inconnu. A video system on the sampling fi sh wheel provided seven years of species-specifi c catch rate data that we used to identify the timing of seasonal spawning migrations for all species except least cisco.

Energetic costs and benefits of cyclic habitat switching: a bioenergetics model analysis of diel vertical migration in coregonids

Recent studies on diel vertical migration (DVM) of two coregonid species ( Coregonus spp.) in Lake Stechlin (Germany) have suggested that the nocturnal distribution of fish is linked with metabolic benefits. We used a spatially explicit bioenergetics-based foraging model to test whether energetic constraints contribute to explain DVM of both species. The newly parameterized model was compared with independent data from Lake Stechlin that covered a 9 month period. Predicted growth rates matched observed growth rates of each fish species reasonably well. The simulation of different migration scenarios showed that even slight changes in night-time depths modified growth rates, primarily owing to temperature-dependent respiration. Fish that performed DVM grew faster than nonmigratory fish that occupied deep hypolimnetic water over a diel cycle. However, the most energy-efficient strategy simulated had fish remaining within the metalimnion. Here, energetic benefits (foraging) clearly outweighed higher energetic costs (respiration) in the warmer waters. Although DVM can be energetically beneficial, it is not the most efficient strategy performed by coregonids in Lake Stechlin. We suggest that multiple factors, rather than bioenergetics efficiency alone, are the evolutionary basis for DVM of many freshwater fish species.

Freshwater Mollusks Survive Fish Gut Passage

Freshwater mollusks figure prominently in the diets of humpback whitefish (Coregonus pidschian) and broad whitefish (C. nasus), two benthic-feeding coregonid species. A recent examination of pea clams (Sphaeriidae), valve snails (Valvatidae), and pond snails (Lymnaeidae) from the lower digestive tracts of these fish found that many of the mollusks were alive. Survival completely through gut passage would indicate a dispersal mechanism for freshwater mollusks that has not been previously recognized. A field investigation was conducted with wild-caught humpback and broad whitefish to test the hypothesis that clams and snails are capable of surviving complete gut passage. Wild fish were captured alive and held in collection totes to obtain feces samples. Pea clams and valve snails were abundant in fish feces, and pond snails were present but not abundant. An average of 483 pea clams and 833 valve snails per fish were observed to have survived complete gut passage, while only a single surviving pond snail was found. These findings suggest that fish may play an important role in the dispersal of freshwater mollusks within freshwater systems.

Discrimination of the Endangered Atlantic Whitefish from Lake Whitefish and Round Whitefish by Use of External Characters

AbstractThe scope of phenetic variation exhibited by populations of lake whitefish Coregonus clupeaformis in the Canadian Maritime Provinces is not known, which complicates the task of accurately identifying specimens of the endangered Atlantic whitefish C. huntsmani. We developed criteria for accurate (≥95% correct classification) species discrimination using morphological data acquired from archival and recent coregonid collections from the Maritime Provinces. We used discriminant function analyses to assess (1) the usefulness of Atlantic whitefish external typological characters in accurately identifying species, (2) the temporal stability of reportedly diagnostic characters, and (3) which morphological characters could be used to accurately identify these coregonids to species. Not all external typological characters were robust in the discrimination of recent Atlantic whitefish and lake whitefish collections. Several previously identified diagnostic characters exhibited significant temporal variation but remained robust in species discrimination. Species‐specific differences for the number of lateral line scales, mouth position, and proportional pectoral fin length could be used concomitantly for accurate (≥95% correct classification) identification of coregonid species in the Canadian Maritime Provinces. Atlantic whitefish possessed a significantly (P < 0.001) greater number of lateral line scales (range = 90–102; mean ± SD = 93.79 ± 2.70) than lake whitefish (range = 66–91; mean = 77.18 ± 4.21), a significantly (P < 0.01) shorter pectoral fin than lake whitefish (11% and 16% of fork length, respectively), and a significantly (P < 0.001) more terminal mouth than lake whitefish (ratio of upper jaw to lower jaw: mean ± SD = 0.98 ± 0.07 and 0.82 ± 0.06, respectively). These characters can also be used to distinguish between Atlantic whitefish and round whitefish Prosopium cylindraceum collected in the Maritime Provinces.

Localization of 5S rRNA loci in three coregonid species (Salmonidae).

In the present study the chromosome distribution of the 5S rDNA loci and its relation to the major rDNA genes were investigated in three Coregonid species (Salmonidae): Coregonus lavaretus, Coregonus peled and Coregonus albula, a family which has experienced large karyotype rearrangements along its evolution starting from a tetraploid ancestor. 5S PRINS/CMA3 sequential staining together with previous data enabled us to locate 5S rRNA genes and nucleolar organizer regions (NORs) in the three species analyzed. PRINS revealed the 5S rDNA cluster at the distal part of the long arm of a similar submetacentric chromosome pair in the three species. Our data indicate that 5S rDNA clusters have probably conserved chromosomal location in the genus Coregonus, whereas 45S rDNA (NOR) sites are clearly differentiated, from a single locus in C. peled, to multiple loci in C. lavaretus and highly polymorphic multichromosomal location in C. albula.