Mykiss Populations Research Articles

Phenotypic differences between non-native populations of rainbow trout Oncorhynchus mykiss in the Argentinean Patagonia

Phenotypic differences between non-native populations of rainbow trout Oncorhynchus mykiss in the Argentinean Patagonia

Genetic divergence and one-way gene flow influence contemporary evolution and ecology of a partially migratory fish.

Recent work has revealed the importance of contemporary evolution in shaping ecological outcomes. In particular, rapid evolutionary divergence between populations has been shown to impact the ecology of populations, communities, and ecosystems. While studies have focused largely on the role of adaptive divergence in generating ecologically important variation among populations, much less is known about the role of gene flow in shaping ecological outcomes. After divergence, populations may continue to interact through gene flow, which may influence evolutionary and ecological processes. Here, we investigate the role of gene flow in shaping the contemporary evolution and ecology of recently diverged populations of anadromous steelhead and resident rainbow trout (Oncorhynchus mykiss). Results show that resident rainbow trout introduced above waterfalls have diverged evolutionarily from downstream anadromous steelhead, which were the source of introductions. However, the movement of fish from above to below the waterfalls has facilitated gene flow, which has reshaped genetic and phenotypic variation in the anadromous source population. In particular, gene flow has led to an increased frequency of residency, which in turn has altered population density, size structure, and sex ratio. This result establishes gene flow as a contemporary evolutionary process that can have important ecological outcomes. From a management perspective, anadromous steelhead are generally regarded as a higher conservation priority than resident rainbow trout, even when found within the same watershed. Our results show that anadromous and resident O. mykiss populations may be connected via gene flow, with important ecological consequences. Such eco-evolutionary processes should be considered when managing recently diverged populations connected by gene flow.

Empirical and model‐based evaluation of a step‐pool stream restoration project: Consequences for a highly valued fish population

AbstractObjectiveWe sought to measure a step‐pool restoration project's effects on a steelhead Oncorhynchus mykiss population and explore the capability of process‐based modeling to enhance understanding of the results.MethodsWe used before‐after–control‐impact monitoring in combination with a process‐based, individual‐based, spatially explicit fish population model to evaluate a stream restoration project that reconfigured the channel and primarily added step pools to a reach of a second‐order stream in northwestern California.ResultFive years of monitoring both before (2012–2016) and after (2018–2022) restoration indicated that restoration caused substantial increases in the abundance and biomass of steelhead. Individual growth rates and retention of fish in the study reach did not exhibit consistent patterns, even in the first 2 years after restoration, when fish abundance and biomass exhibited extreme increases of about fivefold. Model simulations predicted about a twofold increase in the abundance and biomass of steelhead in the restoration reach, which corresponded with the empirical results 4–5 years after restoration. The model also predicted a similar increase in the production of steelhead out‐migrants, a response we did not attempt to measure in the field.ConclusionStep‐pool restoration benefitted steelhead. The model's correspondence with empirical observations indicates its potential applicability to more complex resource management questions in the study area, such as how restoration will combine with changes in climate to affect the sustainability of salmonid populations.

Ancestry and genetic structure of resident and anadromous rainbow trout (Oncorhynchus mykiss) in Argentina.

Since the first introduction from North America more than a century ago, rainbow trout (Oncorhynchus mykiss) have rapidly established self-sustaining populations in major river basins of Patagonia. Many generations later, only the freshwater resident life history is expressed in the Chubut and Negro rivers of northern Argentinian Patagonia, whereas both the resident and anadromous life histories are found in the Santa Cruz River of southern Argentina. Despite previous studies that have tried to identify the sources of these introduced populations, uncertainty still exists. Here we combined data from many single-nucleotide polymorphisms and microsatellite loci in O. mykiss populations from Argentina and North America to evaluate putative source populations, gene flow between Argentinian river basins, and genetic diversity differences between Argentinian and North American populations. We found that populations from northern and southern Patagonia are highly differentiated and have limited gene flow between them. Phylogeographic analysis also confirmed that they have separate origins, with the northern populations most closely related to the domesticated rainbow trout strains that are raised worldwide and the Santa Cruz River populations most closely related to North American populations from California and Oregon that have an anadromous component. In addition, fish with different life histories in the Santa Cruz River were found to constitute a single interbreeding population. No evidence was found of reduced genetic variation in introduced rainbow trout, suggesting multiple contributing sources. In spite of these advances in understanding, significant questions remain regarding the origins and evolution of the introduced O. mykiss in Patagonia.

Using riverscape genetics to investigate the genetic response of two species and their life-history forms to dam removal

Barriers such as hydroelectric dams inhibit migratory pathways essential to many aquatic species, resulting in significant losses of species, their unique life-history forms, and genetic diversity. Understanding the impacts of dam removal to species recovery at these different biological levels is crucial to fully understand the restoration response. We used the removal of two large dams on the Elwha River as an opportunity to characterize how restored connectivity impacts the reestablishment of two fish species, Chinook salmon (Oncorhynchus tshawytscha) and Steelhead/rainbow trout (Oncorhynchus mykiss), and their unique ocean migration return-timing life-history forms. In this study, we employed riverscape genetics to understand how restoration and the environment influence the distribution of neutral and return-timing genetic variation underlying the migratory life-history forms and species at- and between- sampling sites. We genotyped fish sampled over time and space in the Elwha River using Genotyping-in-Thousands by sequencing (GTseq) loci for both species at neutral and putatively adaptive loci in and near the major effect genic region GREB1L/ROCK1 putatively associated with migration timing. We observed little evidence of genetic structure for either species, but a statistically significant increase in early return-timing alleles in upriver O. mykiss population post-dam removal. For O. tshawytscha, at-site genetic variation was shaped by river distance and a combination of environmental habitat differences, while between-site genetic variation was mainly shaped by river distance. For all O. mykiss, at- and between-site genetic variation is primarily explained by river distance. Genetic variation in juvenile and adult Steelhead, respectively, were influenced by at- and between-site environmental and habitat differences. Our study illustrates the power of using genetics to understand the implications of both demography and environment in facilitating the recovery of species and their diverse life-history forms following barrier removal.

Thermal tolerance and vulnerability to warming differ between populations of wild Oncorhynchus mykiss near the species’ southern range limit

Fish habitat temperatures are increasing due to human impacts including climate change. For broadly distributed species, thermal tolerance can vary at the population level, making it challenging to predict which populations are most vulnerable to warming. Populations inhabiting warm range boundaries may be more resilient to these changes due to adaptation or acclimatization to warmer temperatures, or they may be more vulnerable as temperatures may already approach their physiological limits. We tested functional and critical thermal tolerance of two populations of wild Oncorhynchus mykiss near the species’ southern range limit and, as predicted, found population-specific responses to temperature. Specifically, the population inhabiting the warmer stream, Piru Creek, had higher critical thermal maxima and higher functional thermal tolerance compared to the population from the cooler stream, Arroyo Seco. Arroyo Seco O. mykiss are more likely to experience a limitation of aerobic scope with warming. Piru Creek O. mykiss, however, had higher resting metabolic rates and prolonged exercise recovery, meaning that they could be more vulnerable to warming if prey or dissolved oxygen become limited. Temperature varies widely between streams near the O. mykiss southern range limit and populations will likely have unique responses to warming based on their thermal tolerances and metabolic requirements.

Unveiling the rise of non-native fishes in eastern alpine mountain rivers: Population trends and implications.

Insufficient knowledge about the occurrence and spread of non-native fish in mountain regions has impeded effective management strategies worldwide. To address this gap, this study analysed over 1300 electrofishing surveys across 650 sites, encompassing a vast 7400 km2 area in the Eastern Alps. The primary objectives were to quantify the occurrence of non-native species and predict their spread in different river types. Furthermore, the study estimated population sizes and biomass trends for over 150 sites that were surveyed multiple times between 2000 and 2020. Out of the 42 fish species in the study region, 11 were identified as non-native. Notably, two invasive species of Union concern, Lepomis gibbosus and Pseudorasbora parva, increased their population sizes by 8% and 9% per year, over the past decades, supposedly supported by increasing water temperatures. Among the non-native species relevant for recreational fishing, Oncorhynchus mykiss populations showed a significant increase of approximately 7% per year, Salmo trutta populations remained stable, and Salvelinus fontinalis populations experienced a notable decline of approximately 7.4% per year. These varying population trends may be attributed to disparities in stocking intensities, with S. fontinalis receiving minimal stocking compared to the other species. This study revealed that non-native and invasive fish species are a relevant part of fish communities in mountain rivers. Non-salmonid non-natives thrive in warm rivers at lower elevations, whereas salmonid non-natives consolidate in steeper habitats. Because rising temperatures in mountain rivers will accelerate the spread and growth of these species, this first quantification of the current extent will improve fish management strategies in mountainous areas.

High mercury concentrations in steelhead/rainbow trout, sculpin, and terrestrial invertebrates in a stream-riparian food web in coastal California.

Stream and riparian food webs are connected by cross-habitat exchanges of invertebrate prey that can transfer contaminants including mercury. Marine fog has been identified as a source of methylmercury (MeHg) to some terrestrial food webs in coastal California, suggesting that terrestrial invertebrates might have elevated MeHg relative to stream invertebrates and might lead to higher mercury exposure in fish that consume terrestrial subsidies. As an initial step to examine this possibility, we analyzed mercury concentrations in terrestrial and aquatic invertebrates and two fish species, steelhead/rainbow trout (Oncorhynchus mykiss) and coastrange sculpin (Cottus aleuticus), in a small watershed. Mean MeHg and total mercury (THg) concentrations in terrestrial invertebrates were three to four times higher than in aquatic invertebrates of the same trophic level. MeHg was >1000 ng/g dw in some individual centipede and scorpion samples, and also relatively high (100-300 ng/g dw) in some terrestrial detritivores, including non-native isopods. Mean THg in age 0 trout was 400 ng/g dw compared to 1200-1300 ng/g dw in age 1+ trout and sculpin, and the largest trout sampled had THg >3500 ng/g dw. However, the similar mercury concentrations between age 1+ trout and sculpin, despite different diet types, indicated that Hg concentrations in fish were not related simply to differences in consumption of terrestrial invertebrates. The high mercury concentrations we found in terrestrial invertebrates and fish suggest that further research on the sources and bioaccumulation of mercury is warranted in this region where O. mykiss populations are threatened.

Onchorynchus mykiss alter nutrient dynamics in high-altitude headwater streams in Boyacá, Colombia through displacement of the native fish community

A primary global threat to aquatic ecosystem conservation and biodiversity is the introduction of fish species, both deliberate and unintentional. Much of the research conducted on large predatory fish introductions has focused primarily on top-down controls that regulate the abundance and composition of native species assemblages, yet exotic species that alter ecosystem structure and function may pose an even greater threat. The objective of this study was to examine whether an introduced piscivorous fish alters nitrogen cycles in high elevation freshwater streams in the tropics by displacing the native species community through predation. To test this, we measured biomass and ammonium (NH4+-N) remineralization rates for introduced Onchorynchus mykiss and the two native species found in the area; Trichomycterus bogotensis and Grundulus bogotensis in six study sites along an elevation gradient in the Pómeca River Basin in Boyacá, Colombia. Nonnative O. mykiss populations remineralized ammonium at a rate that was 20 times higher than native G. bogotensis and 47 times higher than T. bogotensis. Our results indicate that high biomass of an introduced predatory fish species can have important implications in nutrient dynamics in freshwater streams through reduction in native species biomass when combined with differential nutrient remineralization rates.

Uncertainty, anxiety, and optimism: Diverse perspectives of rainbow and steelhead trout fisheries governance in British Columbia

Inland fisheries are complex social-ecological systems that can generate important nutritional, economic, cultural, and recreational benefits. Effective management of these systems for multiple user-groups requires an understanding of the complex natural and human dimensions interactions within them. We examine the perceptions of stakeholders, Indigenous rightsholders, and regulatory/governance groups on the current and future status of Oncorhynchus mykiss (including their resident form – rainbow trout – and their anadromous form – steelhead) populations and fisheries in British Columbia (BC), Canada from 65 qualitative interviews and 1029 quantitative survey responses. Participants generally did not believe resident rainbow trout were threatened at the provincial level but were definitive in assessing anadromous steelhead trout as threatened. Habitat alterations, water temperature extremes, and climate change, were key threats identified for all forms of O. mykiss while bycatch in commercial fisheries and predation pressure from pinnipeds were specifically identified threats for steelhead trout. Anglers did not perceive recreational fishing pressure as a key threat in contrast to regulatory and governance groups. Fisheries managers were praised for stocking programs and managing small lakes fisheries but criticized for not doing enough to protect fish populations, for an unwillingness to challenge or confront commercial and Indigenous interests which infringe on conservation, and for a lack of aquatic monitoring. Three factors identified by participants contribute to fishery mismanagement, inaction, and decision paralysis: (1) insufficient resources (funding, staff, time), (2) confusion in jurisdictional authority between provincial and federal governments, and (3) organizational structure of natural resource management agencies which are not autonomous from competing commercial and industrial objectives and directions. Despite conservation being purported as the highest priority of fisheries managers, economic, social, and political drivers are perceived as increasingly influencing conservation decisions and actions. These findings can inform fisheries management and conservation decisions, policies and practices to ensure that they are more salient, robust, legitimate, and effective.

Nutrient Restoration of a Large, Impounded, Ultra‐Oligotrophic Western River to Recover Declining Native Fishes

Declines in many fish populations in large, western rivers have been primarily attributed to the anthropogenic reduction of nutrient inputs and subsequent impacts to the food web. The largest known river fertilization program was implemented starting in 2005 on the Kootenai River in northern Idaho to restore resident fisheries. Annual electrofishing surveys were conducted at multiple sites in Idaho and Montana before and during nutrient addition to evaluate assemblage and population-level responses. Although few responses in fish assemblage structure were observed, the addition of liquid ammonium polyphosphate fertilizer (3 μg/L) to the Kootenai River increased fish abundance and biomass over the 20-km stretch of river downstream of the treatment site. Increases were most notable in Largescale Suckers Catostomus macrocheilus, Mountain Whitefish Prosopium williamsoni, and Rainbow Trout Oncorhynchus mykiss populations, although increases in catch and biomass were detected for nearly all fish species. The Kootenai River is approximately 30 times larger in discharge than other rivers that have been experimentally fertilized and provides compelling evidence that the mitigation of nutrient declines in rivers of similar size can result in positive influences on the fish populations where primary and secondary production are limiting growth, survival, and recruitment. However, results from our study also highlight the importance of completing evaluations across varying levels of biological organization (e.g., assemblage and population) and over biologically relevant timeframes.

Genomics facilitates evaluation and monitoring of McCloud River Redband Trout (Oncorhynchus mykiss stonei)

The McCloud River Redband Trout (MRRT; Oncorhynchus mykiss stonei) is a unique subspecies of rainbow trout that inhabits the isolated Upper McCloud River of Northern California. A major threat to MRRT is introgressive hybridization with non-native rainbow trout from historical stocking and contemporary unauthorized introductions. To help address this concern, we collected RAD-sequencing data on 308 total individuals from MRRT and other California O. mykiss populations and examined population structure using Principal Component and admixture analyses. Our results are consistent with previous studies; we found that populations of MRRT in Sheepheaven, Swamp, Edson, and Moosehead creeks are nonintrogressed. Additionally, we saw no evidence of introgression in Dry Creek, and suggest further investigation to determine if it can be considered a core MRRT conservation population. Sheepheaven Creek was previously thought to be the sole historical lineage of MRRT, but our analysis identified three: Sheepheaven, Edson, and Dry creeks, all of which should be preserved. Finally, we discovered diagnostic and polymorphic SNP markers for monitoring introgression and genetic diversity in MRRT. Collectively, our results provide a valuable resource for the conservation and management of MRRT.

Global Phylogeography of Salmonid Ectoparasites of the Genus Gyrodactylus, with an Emphasis on the Origin of the Circumpolar Gyrodactylus salmonis (Platyhelminthes: Monogenea)

The wageneri species group of Gyrodactylus contains the following molecularly confirmed salmonid parasites in Asia: Gyrodactylus taimeni Ergens, 1971, Gyrodactylus magnus Konovalov, 1967, Gyrodactylus brachymystacis Ergens, 1978, and Gyrodactylus derjavini Mikhailov, 1975; in Europe it contains the following: Gyrodactylus derjavinoides Malmberg, Collins, Cunningham, and Jalali, 2007, Gyrodactylus truttae Gläser, 1974, Gyrodactylus teuchis Lautraite, Blanc, Thiery, Daniel, and Vigneulle, 1999, Gyrodactylus lavareti Malmberg, 1956, Gyrodactylus salvelini Kuusela, Ziętara, and Lumme, 2008 (presented herein as a junior synonym of Gyrodactylus salmonis Yin and Sproston, 1948), and Gyrodactylus salaris Malmberg, 1957, with the lone confirmed North American exception being G. salmonis. The mitochondrial DNA (cox1, 1545 bp) of this group shows a star-like phylogenetic expansion that began 2.05 ± 0.4 million years ago (mya), estimated from the mean distance of the cox1 gene (dMCL = 0.267) using a tentative, potentially high-end, divergence rate of 0.13/Myr. European G. salaris on Thymallus thymallus and Asian G. magnus on Thymallus arcticus have been separated for 1.95 Myr (dMCL = 0.253). The nuclear ITS rDNA region (1,245 bp) of G. salmonis was nearly uniform among North American populations of Oncorhynchus mykiss, Oncorhynchus clarkii, Oncorhynchus nerka, Salvelinus fontinalis, and Salmo salar (and non-native Salmo trutta) as well as on Salvelinus alpinus (under the synonym G. salvelini) from Lake Inari, Finland. Gyrodactylus salmonis is distal in a monophyletic subclade labeled by an apomorphic 56 bp insertion in the ITS1, shared by the European parasites G. lavareti (host: Coregonus lavaretus), Gyrodactylus pomeraniae Kuusela, Ziętara, and Lumme, 2008 (host: Rutilus rutilus), and Gyrodactylus bliccensis Gläser, 1974 (host: Alburnus alburnus). This subphylogeny suggests that a particular host switch from cyprinids to salmonids may have occurred less than 1.8 mya in the Old World [dMCL = 0.234 G. pomeraniae vs (G. salmonis, G. lavareti)] and possibly again among coregonine hosts and Salvelinus 1.2 mya (dMCL = 0.156). Although hypothetical, a transition from coregonines to charr (notably the widely distributed and adaptable Salvelinus alpinus) potentially could have occurred in a proglacial refugium leading to circumpolar distribution of G. salmonis and a secondary transition to other North American hosts. The maximum cox1 genetic distance within G. salmonis on all hosts was dMCL = 0.032, at the same level as in multihosted European G. salaris (dMCL = 0.032), suggesting circa 250,000 yr of population expansion with these parasites since a temporal, coinciding bottleneck.

Taxonomic Status of Four Rare Alien Fish Species of the Kapchagay Reservoir (Balkhash Basin, Central Asia)

—Based on the morphological features, four rare alien species in the Kapchagai reservoir were identified: Coregonus peled, Parasalmo mykiss, Megalobrama mantschuricus, and Oreochromis niloticus. The latter two species were recorded for the ichthyofauna of Kazakhstan for the first time. Self-reproducing P. mykiss populations have been known in the Balkhash Basin since the late 1990s, whereas the introduction of C. peled into the Ili basin in 1968−1969 and 1971 did not lead to the naturalization of the species. The reasons for the great diversity of invasive fish species in the Kapchagai reservoir are overviewed.

Straying and Life History of Adult Steelhead in a Small California Coastal Stream Revealed by Otolith Natural Tags and Genetic Stock Identification

AbstractStraying has been difficult to study directly in natural steelhead Oncorhynchus mykiss populations. We analyzed an opportunistic sample of seven adult steelhead from a small basin on the Big Sur coast of California to determine their life history traits, including whether they were strays. Otolith natural tags (87Sr/86Sr) and genetic stock identification indicated that all seven adults were strays from at least six different sources. Three adults strayed from nearby streams (<72 km) on the Big Sur coast, while three strayed from distant sources, including the Klamath River (680 km to the north); the source of one stray could not be identified. Six strays were progeny of steelhead mothers, but one was the offspring of a nonanadromous mother. Six were female and one was male, and all that could be genotyped were homozygous (n = 4) or heterozygous (n = 2) for the anadromy‐associated haplotype in a migration‐associated genomic region. While the opportunistic nature and small size of the sample prevents us from inferring the rate of straying into the basin, our study nonetheless demonstrates that steelhead may stray across greater distances than generally has been appreciated and that nonanadromous females can produce anadromous offspring that stray, thus providing connectivity among basins.

Phenological mismatch, carryover effects, and marine survival in a wild steelhead trout Oncorhynchus mykiss population

Climate-driven changes in the oceans, such as shifts in prey timing and abundance, could influence variability in population productivity of marine fishes. For example, according to the match/mismatch hypothesis, the temporal matching of the young salmon outmigration from freshwater to the ocean relative to the timing of availability of their prey could influence their marine survival. Indeed, understanding patterns and processes of marine survival is particularly pressing in many salmon and steelhead trout populations due to recent declines. To determine whether phenological mismatches between juvenile salmonids and their prey could contribute to low ocean survival, we analyzed the migration timing and ocean survival of 22,116 tagged juvenile steelhead trout Oncorhynchus mykiss over 12 years from the Wind River, Washington State, USA. We used a Bayesian multilevel modelling approach with variable selection to assess how survival was associated with body size, river exit date, the biological spring transition date (the day when northern zooplankton first appeared in the coastal region near the Columbia River estuary), and the degree of mismatch (the effect of the interaction between individual outmigration timing and biological spring transition date). The variables with the highest probability of contributing to individual survival were fish size (100%), river exit date (99%), the interaction between year and river exit date (91%), and the biological spring transition date (64%). Fish that were larger than average at outmigration had higher ocean survival, providing further evidence that freshwater growing conditions have carryover effects on marine survival. Years with greater annual phenological mismatches such as those years with late biological spring transition dates (i.e., occurring after June 1st), or warm sea surface temperatures, had sufficiently low marine survival to compromise recovery goals. Substantial intra-annual variation in outmigration timing buffered the population from inter-annual variation in optimal outmigration timing. Collectively these findings indicate that freshwater growing conditions, migration timing, and the timing of high-quality food availability in the nearshore coastal environment work in concert to influence individual survival and annual smolt-to-adult returns.

The Impacts of Dam Construction and Removal on the Genetics of Recovering Steelhead (Oncorhynchus mykiss) Populations across the Elwha River Watershed

Dam construction and longitudinal river habitat fragmentation disrupt important life histories and movement of aquatic species. This is especially true for Oncorhynchus mykiss that exhibits both migratory (steelhead) and non-migratory (resident rainbow) forms. While the negative effects of dams on salmonids have been extensively documented, few studies have had the opportunity to compare population genetic diversity and structure prior to and following dam removal. Here we examine the impacts of the removal of two dams on the Elwha River on the population genetics of O. mykiss. Genetic data were produced from >1200 samples collected prior to dam removal from both life history forms, and post-dam removal from steelhead. We identified three genetic clusters prior to dam removal primarily explained by isolation due to dams and natural barriers. Following dam removal, genetic structure decreased and admixture increased. Despite large O. mykiss population declines after dam construction, we did not detect shifts in population genetic diversity or allele frequencies of loci putatively involved in migratory phenotypic variation. Steelhead descendants from formerly below and above dammed populations recolonized the river rapidly after dam removal, suggesting that dam construction did not significantly reduce genetic diversity underlying O. mykiss life history strategies. These results have significant evolutionary implications for the conservation of migratory adaptive potential in O. mykiss populations above current anthropogenic barriers.

Differences in growth and condition of juvenile Oncorhynchus mykiss related to sex and a migration-associated genomic region

The expression of anadromy in partially migratory salmonid populations is influenced by sex-specific interactions among an individual’s genotype, condition, and environment, but genotype–phenotype relationships prior to the expression of migratory type are poorly understood. We examined whether juvenile growth and condition differed with respect to sex and a migration-associated genomic region (Omy05) in a coastal California population of steelhead and rainbow trout (Oncorhynchus mykiss). Sex and Omy05 genotype had additive effects on annual growth from age 0+ to age 1+ (∼6–18 months old), with higher growth in males and individuals with copies of the rearranged–resident haplotype. Condition at age 1+ increased with the number of copies of the rearranged–resident haplotype, with similar support for additive or interactive effects with sex; additive effects suggested that genotype differences occurred in both sexes and also that condition was slightly higher in males, while interactive effects suggested that the genotype differences occurred only in males. Our results indicate that phenotypic differences related to sex and Omy05 genotype occur well in advance of anadromous migration or freshwater maturation in this southern O. mykiss population.

Regularities of Formation of Diversity of Life Strategy and Genetic Variability of The Kamchatka Rainbow Trout Parasalmo mykiss in a Local Population

The diversity of life strategy, population structure, size, age and sex composition, growth and variability of 11 microsatellite loci in mykiss (rainbow trout) Parasalmo mykiss of the Utkholok River (Northwestern Kamchatka) were studied. The mykiss population represents a system of groupings with different types of life strategy: anadromous fish prevail in the population, while river and semi-anadromous (estuarine and riverine-estuarine) fish are less common. Each of the groupings has specific size, age and sex composition, the ratio of the first time-maturing and re-maturing fish. At that, the individuals with different types of life strategy reproduce together on the same spawning grounds and there is no isolation between them. Analysis of the variability of microsatellite loci revealed no significant differences for any locus between the observed genotypic distributions and the theoretical Hardy – Weinberg distributions. The genetic differentiation of mykiss in the Utkholok River relates to the differences between fish with a river-estuarine life strategy and the others in three loci (Ots3, One108, and One112). The results of clustering show the maximum value of the probability of belonging to the same cluster of all mykiss individuals with different life strategies. Significant differences at the some loci are not evidencing their reproductive isolation. It has been found that mykiss population of Utkholok River is an integrated dynamic system of groupings with different types of life strategies, which are formed in each generation because of the cumulative impact of environmental factors and heredity.

Do genomics and sex predict migration in a partially migratory salmonid fish,Oncorhynchus mykiss?

Partial migration is a common phenomenon wherein populations include migratory and resident individuals. Whether an individual migrates or not has important ecological and management implications, particularly within protected populations. Within partially migratory populations of Oncorhynchus mykiss, migration is highly correlated with a specific genomic region, but it is unclear how well this region predicts migration at the individual level. Here, we relate sex and life history genotype, determined using >400 single nucleotide polymorphisms (SNPs) on the migratory-linked genomic region, to life history expression of marked juvenile O. mykiss from two tributaries to the South Fork Eel River, northern California. Most resident fish were resident genotypes (57% resident, 37% heterozygous, 6% migratory genotype) and male (78%). Most migratory fish were female (62%), but were a mixture of genotypes (30% resident, 45% heterozygous, 25% migratory genotype). Sex was more strongly correlated with life history expression than genotype, but the best-supported model included both. Resident genotypes regularly migrated, highlighting the importance of conserving the full suite of life history and genetic diversity in partially migratory populations.