Coregonus Lavaretus Research Articles

Phylogeography of Common Whitefish (Coregonus lavaretus L.) of Northwestern Russia

This paper elucidates the features of colonization by whitefish (Coregonus lavaretus L.) of waterbodies of the European part of Russia in relation to Pleistocene glaciation. Based on the data on the frequencies and phylogenetic relationships of mitochondrial DNA haplotypes, a significant role of migrants from the western periglacial refugia is shown. The first large refugium was located at the North Atlantic; the second was at the South-Eastern Baltic. Until the last glaciation, with the maximum at about 20000 years ago, migrations from Siberia took place as well. However, at present the descendants of these migrants in the waterbodies of Northwestern Russia are not the dominants. The size of the refugium where the population lived prior to expansion may be an important condition for the successful spreading of common whitefish.

Specific Features of Morphology, Ecology, and Mitochondrial DNA Polymorphism of the Whitefish (Coregonus lavaretus L.) from the Keret’ River as a New Object for Artificial Propagation

The results of a study of the specific features of morphological and genetic polymorphism of the population of the anadromous White Sea common whitefish (Coregonus lavaretus L.) from the Keret’ River are presented. As assessed by its morphological features, the whitefish population of the Keret’ is homogenous. A comparison of the Keret’ whitefish with whitefish populations of both Europe and Siberia revealed clear differences. These differences relate first and foremost to the fish locomotion and orientation in space: body depth, length and positions of fins, and interorbital width. The characteristics of skull features (craniological analysis) of the White Sea whitefish are presented for the first time. The results of an analysis of the polymorphism of the ND1 fragment of the mitochondrial DNA confirmed an earlier suggestion about the mixed origin of the Keret’ River whitefish: the descendants of three different phylogenetic lineages were revealed in the population.

Comparative Analysis of Content of Omega-3 Polyunsaturated Fatty Acids in Food and Muscle Tissue of Fish from Aquaculture and Natural Habitats

Two fish species reared in aquaculture (pink salmon Oncorhynchus gorbuscha and whitefish Coregonus lavaretus) and ten fish species from natural habitats (whitefish C. lavaretus, tugun Coregonus tugun, broad whitefish Coregonus nasus, least cisco Coregonus sardinella, vendace Coregonus albula, boganid charr Salvelinus boganidae, charr Salvelinus alpinus complex, northern pike Esox lucius, sharp-snouted lenok Brachymystax lenok, and taimen Hucho taimen) have been studied. The content of two long-chain polyunsaturated omega-3 fatty acids (PUFAs), eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA), in the muscle tissue of the fish and in their food (intestine contents) are compared. In the aquacultures of whitefish and pink salmon, the total content of EPA and DHA is significantly higher in feed than in the muscle tissue of the fish, which indicates losses of PUFA in the two-link food chain of the aquaculture during their transfer to the upper trophic level. EPA and DHA losses in aquaculture, which are confirmed by numerous literature data, mean an inefficient usage of the available sources of PUFAs and the aggravation of the global deficit of these biochemicals in the human diet. A study of natural fish populations reveals the accumulation of EPA and DHA in their biomass compared to food in many cases, although opposite phenomena are also observed. An assumption on the presence of an optimal, physiologically adequate species-specific level of PUFA in the fish muscle tissue has been made based on our data and literature data. If the level of PUFAs in the muscles is lower than optimal, their accumulation (bioaccumulation) from food and/or de novo synthesis are observed. When the optimal level is exceeded, the content of EPA and DHA in biomass approaches maximum species-specific values; however, part of these PUFAs entering from food is not digested or is catabolized. According to the obtained data, the species of the order Salmoniformes have an optimal level of 2 to 6 mg/g of wet weight. It has been found that in aquaculture approaching to maximum values of EPA + DHA content was accompanied by their losses (scattering) in the food chains, while in natural ecosystems the maximum values of PUFA content in the fish biomass are achieved by their accumulation from the lower trophic level. Boganid charr S. boganidae had the highest content of EPA + DHA in the muscle tissue among all known fish species (32.78 mg/g of wet weight).

Fish assemblages in deep Italian subalpine lakes: history and present status with an emphasis on non-native species

We provide a comprehensive overview of the status of fish assemblages in eight Italian subalpine lakes using multiple data sources: historical records, standardised sampling and fishery catch statistics. Thirty-four fish species were recorded, twenty of which are native, seven introduced historically and another seven introduced recently. The number of fish species in individual lakes has increased by between 25 and 65% from 1855 to the present, with the increase being higher in the larger lakes. Non-native species contributed between 4.0 and 71.5% to standardised catches by numbers and between 4.8 and 65.1% by biomass. Roach Rutilus rutilus and pumpkinseed Lepomis gibbosus dominated electrofishing and benthic catches by number, while open-water catches were dominated by the coregonids European whitefish Coregonus lavaretus and gangfish Coregonus macrophthalmus. In terms of biomass, electrofishing catches were dominated by crucian carp Carassius carassius, largemouth bass Micropterus salmoides and wels catfish Silurus glanis, benthic catches were dominated by roach, European whitefish and crucian carp, and open-water catches by coregonids. Commercial fisheries are important ecosystem services provided by subalpine lakes, with their harvests now dominated by non-native species. To deliver effective biodiversity conservation and ecosystem services provision, the prioritisation of targets and interventions of management of non-native species is needed.

Foraging habits of invasive three-spined sticklebacks (Gasterosteus aculeatus) – impacts on fisheries yield in Upper Lake Constance

A massive increase in the pelagic population of non-endemic three-spined sticklebacks, Gasterosteus aculeatus L. in Lake Constance has coincided with drastic declines in fishery yields. This study assesses the possible direct and indirect impact of the mass occurrence on native fish species in the lake. Laboratory foraging experiments showed that larvae of roach Rutilus rutilus L., perch Perca fluviatilis L. and whitefish Coregonus lavaretus L. are accessible to sticklebacks as food. However, distinct species effects were apparent, with whitefish showing no effective predator avoidance strategy and therefore experiencing drastically increased mortality risk compared to the other predator adapted prey species. Furthermore, in absence of larval prey, sticklebacks were shown to feed predominantly on Daphnia in the field, indicating a strong interspecific food competition with whitefish.The results suggest that sticklebacks, acting as both an invasive species and a predator in the pelagic zone where prior no predator or neozoon existed, create a unique challenge to the unadapted autochthonous fish, and thus threaten the ecological resilience of the lake. Impacts on recruitment, e.g. through larval predation and interspecific competition for zooplankton could explain recent drastic declines in fishing yields.

Diversifying selection drives parallel evolution of gill raker number and body size along the speciation continuum of European whitefish.

Adaptive radiation is the evolution of ecological and phenotypical diversity. It arises via ecological opportunity that promotes the exploration of underutilized or novel niches mediating specialization and reproductive isolation. The assumed precondition for rapid local adaptation is diversifying natural selection, but random genetic drift could also be a major driver of this process. We used 27 populations of European whitefish (Coregonus lavaretus) from nine lakes distributed in three neighboring subarctic watercourses in northern Fennoscandia as a model to test the importance of random drift versus diversifying natural selection for parallel evolution of adaptive phenotypic traits. We contrasted variation for two key adaptive phenotypic traits correlated with resource utilization of polymorphic fish; the number of gill rakers and the total length of fish, with the posterior distribution of neutral genetic differentiation from 13 microsatellite loci, to test whether the observed phenotypic divergence could be achieved by random genetic drift alone. Our results show that both traits have been under diversifying selection and that the evolution of these morphs has been driven by isolation through habitat adaptations. We conclude that diversifying selection acting on gill raker number and body size has played a significant role in the ongoing adaptive radiation of European whitefish morphs in this region.

De novo transcriptome assembly, annotation and comparison of four ecological and evolutionary model salmonid fish species

BackgroundSalmonid fishes exhibit high levels of phenotypic and ecological variation and are thus ideal model systems for studying evolutionary processes of adaptive divergence and speciation. Furthermore, salmonids are of major interest in fisheries, aquaculture, and conservation research. Improving understanding of the genetic mechanisms underlying traits in these species would significantly progress research in these fields. Here we generate high quality de novo transcriptomes for four salmonid species: Atlantic salmon (Salmo salar), brown trout (Salmo trutta), Arctic charr (Salvelinus alpinus), and European whitefish (Coregonus lavaretus). All species except Atlantic salmon have no reference genome publicly available and few if any genomic studies to date.ResultsWe used paired-end RNA-seq on Illumina to generate high coverage sequencing of multiple individuals, yielding between 180 and 210 M reads per species. After initial assembly, strict filtering was used to remove duplicated, redundant, and low confidence transcripts. The final assemblies consisted of 36,505 protein-coding transcripts for Atlantic salmon, 35,736 for brown trout, 33,126 for Arctic charr, and 33,697 for European whitefish and are made publicly available. Assembly completeness was assessed using three approaches, all of which supported high quality of the assemblies: 1) ~78% of Actinopterygian single-copy orthologs were successfully captured in our assemblies, 2) orthogroup inference identified high overlap in the protein sequences present across all four species (40% shared across all four and 84% shared by at least two), and 3) comparison with the published Atlantic salmon genome suggests that our assemblies represent well covered (~98%) protein-coding transcriptomes. Thorough comparison of the generated assemblies found that 84-90% of transcripts in each assembly were orthologous with at least one of the other three species. We also identified 34-37% of transcripts in each assembly as paralogs. We further compare completeness and annotation statistics of our new assemblies to available related species.ConclusionNew, high-confidence protein-coding transcriptomes were generated for four ecologically and economically important species of salmonids. This offers a high quality pipeline for such complex genomes, represents a valuable contribution to the existing genomic resources for these species and provides robust tools for future investigation of gene expression and sequence evolution in these and other salmonid species.

Sperm pre-fertilization thermal environment shapes offspring phenotype and performance.

The sperm pre-fertilization environment has recently been suggested to mediate remarkable transgenerational consequences for offspring phenotype (transgenerational plasticity, TGB), but the adaptive significance of the process has remained unclear. Here, we studied the transgenerational effects of sperm pre-fertilization thermal environment in a cold-adapted salmonid, the European whitefish (Coregonus lavaretus). We used a full-factorial breeding design where the eggs of five females were fertilized with the milt of 10 males that had been pre-incubated at two different temperatures (3.5°C and 6.5°C) for 15 h prior to fertilization. Thermal manipulation did not affect sperm motility, cell size, fertilization success or embryo mortality. However, offspring that were fertilized with 6.5°C-exposed milt were smaller and had poorer swimming performance than their full-siblings that had been fertilized with the 3.5°C-exposed milt. Furthermore, the effect of milt treatment on embryo mortality varied among different females (treatment×female interaction) and male-female combinations (treatment×female×male interaction). Together, these results indicate that sperm pre-fertilization thermal environment shapes offspring phenotype and post-hatching performance and modifies both the magnitude of female (dam) effects and the compatibility of the gametes. Generally, our results suggest that short-term changes in sperm thermal conditions may have negative impact for offspring fitness. Thus, sperm thermal environment may have an important role in determining the adaptation potential of organisms to climate change. Detailed mechanism(s) behind our findings require further attention.

The Features of Morphology, Ecology and Mitochondrial DNA Polymorphism of the Whitefish (Coregonus lavaretus L.) from the Keret’ River as a New Object of the Artificial Reproduction

The Features of Morphology, Ecology and Mitochondrial DNA Polymorphism of the Whitefish (Coregonus lavaretus L.) from the Keret’ River as a New Object of the Artificial Reproduction

Пищевые взаимоотношения обыкновенного сига (COREGONUS LAVARETUS) и речного окуня (PERCA FLUVIATILIS) в малом лесном озере

Пищевые взаимоотношения обыкновенного сига (COREGONUS LAVARETUS) и речного окуня (PERCA FLUVIATILIS) в малом лесном озере

Effect of different levels of 3, 5, 3’-triiodo-L-thyronine Administration in a dry diet on rearing of Whitefish (Coregonus lavaretus L., Coregoninae) Larvae

Effect of different levels of 3, 5, 3’-triiodo-L-thyronine Administration in a dry diet on rearing of Whitefish (Coregonus lavaretus L., Coregoninae) Larvae

Dependence of pH values in the digestive tract of freshwater fishes on some abiotic and biotic factors

The values of pH in the digestive tracts of 20 freshwater fish species inhabiting various Russian Federation waterbodies were studied. Only in six species (Coregonus lavaretus, Coregonus migratorius, Catostomus catostomus, Carassius gibelio, Rutilus rutilus, Leuciscus leuciscus) out of 20 species, the differences in pH values between different regions of the intestine were significant. Feeding habits, feeding frequency, and gut fullness in fish affected pH values. Temperature was one of the most important factors affecting pH values. During cold seasons (spring and fall; average water temperature: 8–10 and 5–6○C, respectively), the pH values in fish guts were higher than that in the summer seasons(water temperature 22–25°C) for C. gibelio, Perca fluviatilis, Cyprinus carpio, L. leuciscus, and R. rutilus from the Chany Lake. Similar results (lower pH values in intestine at higher water temperatures) were also obtained for C. gibelio in warmer years in comparison to colder years in the same waterbody and in L. leuciscus and P. fluviatilis in the different waterbodies with different water temperatures. It is hypothesized that dependence of pH in fish gut on temperature may serve as a regulatory mechanism for maintaining the activities of hydrolytic enzymes at the required level for their successful functioning.

Estimating species colonization dates using DNA in lake sediment

Abstract Detection of DNA in lake sediments holds promise as a tool to study processes like extinction, colonization, adaptation and evolutionary divergence. However, low concentrations make sediment DNA difficult to detect, leading to high false negative rates. Additionally, contamination could potentially lead to high false positive rates. Careful laboratory procedures can reduce false positive and negative rates, but should not be assumed to completely eliminate them. Therefore, methods are needed that identify potential false positive and negative results, and use this information to judge the plausibility of different interpretations of DNA data from natural archives. We developed a Bayesian algorithm to infer the colonization history of a species using records of DNA from lake‐sediment cores, explicitly labelling some observations as false positive or false negative. We illustrate the method by analysing DNA of whitefish (Coregonus lavaretus L.) from sediment cores covering the past 10,000 years from two central Swedish lakes. We provide the algorithm as an R‐script, and the data from this study as example input files. In one lake, Stora Lögdasjön, where connectivity with the proto‐Baltic Sea and the degree of whitefish ecotype differentiation suggested colonization immediately after deglaciation, DNA was indeed successfully recovered and amplified throughout the post‐glacial sediment. For this lake, we found no loss of detection probability over time, but a high false negative rate. In the other lake, Hotagen, where connectivity and ecotype differentiation suggested colonization long after deglaciation, DNA was amplified only in the upper part of the sediment, and colonization was estimated at 2,200 bp based on the assumption that successful amplicons represent whitefish presence. Here the earliest amplification represents a false positive with a posterior probability of 41%, which increases the uncertainty in the estimated time of colonization. Complementing careful laboratory procedures aimed at preventing contamination, our method estimates contamination rates from the data. By combining these results with estimates of false negative rates, our models facilitate unbiased interpretation of data from natural DNA archives.

Thermal experience during embryogenesis contributes to the induction of dwarfism in whitefish Coregonus lavaretus

Ecotype pairs provide well-suited model systems for study of intraspecific phenotypical diversification of animals. However, little is still known about the processes that account for the development of different forms and sizes within a species, particularly in teleosts. Here, embryos of a normal-growing ‘large’ form and a dwarf form of whitefish Coregonus lavaretus were incubated at two temperatures that are usually experienced at their own spawning sites (2°C for the normal and 6°C for the dwarf form). All fish were subjected to similar thermal treatment after hatching. The present data demonstrate for the first time that different thermal experience in embryonic life has lasting effects on body and muscle growth of this ecotype pair and contributes to the development of the dwarf form. Thus, juvenile fish of the regular form are much smaller and have less muscle mass when pre-hatching thermal conditions were similar to those typical for the spawning sites of the dwarf form (6°C) than when subjected to conditions of their own spawning sites (2°C). Surprisingly, fish of the dwarf form exhibit a similar pattern of response to thermal history (2°-fish much larger than 6°-fish), indicating that in their case, normal spawning site temperature (6°C) is indeed likely to act as a growth limiting factor. Results also demonstrate that the hypertrophic and hyperplastic muscle growth modes are similarly affected by thermal history. Immunolabelling experiments for Pax7, H3P and Mef2 provide evidence that the cellular mechanisms behind the increased growth rates after cold incubation in both ecotypes are increased proliferation and reduced differentiation rates of muscle precursor cells. This is of major significance to aspects of ecological and developmental biology and from the evolutionary perspective.

Total mercury concentrations in liver and muscle of European whitefish (Coregonus lavaretus (L.)) in a subarctic lake - Assessing the factors driving year-round variation

Subarctic lakes are characterised by extreme seasonal variation in light and temperature which influences growth, maturation, condition and resource use of fishes. However, our understanding of how seasonal changes affect mercury concentrations of fishes is limited. We conducted a year-round study (3 ice-covered months, 3 open-water months) with open-water inter-annual aspect (3 years: samples from August/September), focusing on total mercury (THg) concentrations and ecological characteristics of a common freshwater fish, European whitefish (Coregonus lavaretus (L.)) from a subarctic lake. We measured THg concentrations from tissues with fast (liver, n = 164) and moderate (muscle, n = 225) turnover rates, providing information on THg dynamics over different temporal scales. In both tissues, lipid-corrected THg concentrations were highest in winter (liver: 1.70 ± 0.88 μg/g, muscle: 0.24 ± 0.05 μg/g) and lowest in summer (liver: 0.87 ± 0.72 μg/g, muscle: 0.19 ± 0.04 μg/g). THg concentrations increased in winter following the summer-autumn dietary shift to pelagic zooplankton and starvation after spawning. Whitefish THg concentrations decreased towards summer, and were associated with consumption of benthic macroinvertebrates and subsequent growth dilution. Mercury bioaccumulated in both tissues with age, both showing the strongest regression slopes in winter and lowest in summer. THg concentrations in liver and muscle tissue were correlated throughout the year, however the correlation was lowest in summer, indicating high metabolism during somatic growing season in summer and growth dilution. Multiple linear regression models explained 50% and 55% of the THg variation in liver and muscle both models dominated by seasonally-variable factors i.e. sexual maturity, δ13C, and condition factor. Seasonally varying bioaccumulation slopes and the higher level of intra-annual variation (21%) in whitefish THg concentration in muscle than the inter-annual accumulation (8%) highlight the importance of including seasonal factors in future THg studies.

The reasons of genetic heterogeneity of Siberian whitefish Coregonus lavaretus pidschian in the Anabar river

Background. A population genetic study of Siberian whitefish or pidschian Coregonus lavaretus pidschian Gmelin of the Anabar River (North-West Yakutia) has been done to study genetic structure of the species within a river system and for revealing its phylogeographic relations.
 Materials and Methods. Five samples of pidschian from different parts of the river were analyzed for 30 isozyme loci.
 Results and Discussion. The results has demonstrated a significant genetic heterogeneity of the species sampled from lower and middle reaches of the river (0.001 DN 0.056). The most likely reason for genetic differentiation of the species within the river system is a colonization of the watershed by independent phylogenetic lineages of whitefish. At present the phylogenetic lineages in Anabar River are presented by sympatric ecological forms of the species eastern-siberian whitefish and glacial-plains whitefish which maintain their reproductive isolation. The relationships of ecological forms of whitefish dwelling the Anabar River with other populations of the species in Siberia, and possible ways of penetration of discrete phylogenetic lineages of pidschian in the basin of studied river are discussed.
 Conclusions. A genetic heterogeneity of whitefish from Anabar River should be taken into account while creating adequate intraspecific taxonomy and considered in conducting fisheries and environmental measures.

Synchronous decline of three morphologically distinct whitefish (Coregonus lavaretus) stocks in Lake Oulujärvi with concurrent changes in the fish community

Identification of ecologically mediated mechanisms that drive population dynamical changes in fish communities and polymorphic fish stocks such as those of whitefish, Coregonus lavaretus, requires data that are seldom available in freshwater systems. We assessed the stock of each morphologically distinguishable whitefish form (native lesser sparsely-rakered whitefish, native blue whitefish and stocked northern densely-rakered whitefish) in the Lake Oulujärvi during 1973–2014, and related temporal variations in population dynamics to environmental data and catch per unit of effort (CPUE) data on other species having fisheries significance. The results demonstrated a synchronous major decline in the abundance of the native whitefish forms and a decline in the length-at-age of all forms. During the study period, summer time water temperature increased and surface water phosphorous concentration decreased. Recruitment in all whitefish forms showed Ricker-type dependence on spawning stock biomass but little residual correlation with the environmental parameters. Cross-correlation analyses suggested that the re-establishment of pikeperch Sander lucioperca population affected negatively both the recruitment and biomass of whitefish but the exact effect mechanisms require further assessment. Our results exemplify that ecosystem-based fisheries management in inland waters must take into account both natural and human-induced environmental changes as well as stockings, and that knowledge-based inland fisheries management is inherently data-intensive.

Selection strategies for controlling muscle lipid content recorded with a non-destructive method in European whitefish, Coregonus lavaretus

Genetic selection to control lipid deposition in fish offers a valuable means to improve production efficiency and product quality. However, destructive measuring of lipid traits is a fish welfare and logistical issue due to the need for sacrificing fish, which also prevents selection on breeding candidates. We, firstly, validated the reliability of a non-invasive device with recording error, Distell Fish Fatmeter, for European whitefish (Coregonus lavaretus) by assessing the number of repeated records needed per individual, and by determining a predictive equation, which transforms Distell readings to muscle lipid% values. Secondly, using a split-family design, we estimated genetic (co)variances for the predicted muscle lipid% recorded in production environment (PE) in autumn, and in breeding nucleus (NUC) in autumn and again in the following spring. Thirdly, accuracy of selection on muscle lipid% in PE was evaluated by simulating alternative measurement strategies where: muscle lipid% was recorded either from sibs in PE (autumn) or from the breeding candidates in NUC (autumn or spring), or in both environments. Four repeated records per individual was sufficient for obtaining an accurate mean observation for an individual, though the repeatability of measurements varied somewhat between year classes (r=0.7–0.9). Heritability for muscle lipid% was high and of the same magnitude in PE (h2±SE=0.55±0.07) and NUC (0.48±0.09 in autumn, 0.49±0.11 in spring). Genetic correlation between the environments was higher when the muscle lipid% was recorded in autumn (rG±SE=0.78±0.12), compared to when recorded for NUC in spring (0.72±0.12). The rG of muscle lipid% between autumn and spring measurements within NUC was 0.99±0.01, indicating no genotype re-ranking in time over the winter. Selection accuracy was improved 14–16% by shifting from PEautumn to the strategies involving both environments and allowing exploitation of within-family genetic variation. Instead, compared to PEautumn, the strategies NUCautumn and NUCspring reduced accuracy by 7% and 17%, respectively, highlighting the importance of sib measurements in PE. There was substantial between-environment heterogeneity in both genetic and residual variation. However, the changes in accuracies were small when this heterogeneity was removed in additional calculations. In conclusion, Distell meter is a suitable tool for selecting muscle lipid% in a large number of whitefish.

Fish Oil Finishing Diet Maintains Optimal n-3 Long-Chain Fatty Acid Content in European Whitefish (Coregonus lavaretus).

This study examined the effect of substituting vegetable oil for fish oil in feed, with subsequent re-introduction of fish oil-rich feed (finishing feeding) in late stages of growth, on the fatty acids of cultivated European whitefish (Coregonus lavaretus). Restorative finishing feeding with fish oil-rich feed for 15 and 25weeks was sufficient to change the total content of nutritionally valuable long-chain n-3 fatty acids, eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3), to correspond to that of fish fed the fish oil-rich feed throughout their lifespan. Under natural conditions, 15 and 25weeks correspond to weight gains of 75% and 100% (i.e. doubling), respectively. Also, the fatty acid profile of the fish was restored after finishing periods of 15 and 25weeks. Limiting the use of fish oil by lowering the overall fat content of the feed (no vegetable oil added) resulted in a decrease in the long-chain n-3 fatty acids. Based on the results, after receiving a vegetable oil-rich diet, restorative fish oil-rich feeding in the last stages of growth in European whitefish is nutritionally justified in order to balance nutritional gain for consumers with sustainable use of finite marine oils. The results encourage commercial efforts to further utilize and optimize finishing feeding practices.

Ecological speciation in a generalist consumer expands the trophic niche of a dominant predator

Ecological speciation – whereby an ancestral founder species diversifies to fill vacant niches – is a phenomenon characteristic of newly formed ecosystems. Despite such ubiquity, ecosystem-level effects of such divergence remain poorly understood. Here, we compared the trophic niche of European whitefish (Coregonus lavaretus) and their predators in a series of contrasting subarctic lakes where this species had either diversified into four ecomorphologically distinct morphs or instead formed monomorphic populations. We found that the trophic niche of whitefish was almost three times larger in the polymorphic than in the monomorphic lakes, due to an increase in intraspecific specialisation. This trophic niche expansion was mirrored in brown trout (Salmo trutta), a major predator of whitefish. This represents amongst the first evidence for ecological speciation directly altering the trophic niche of a predator. We suggest such mechanisms may be a common and important – though presently overlooked – factor regulating trophic interactions in diverse ecosystems globally.