Strains Of Trout Research Articles

Identification of genes involved in cold-shock response in rainbow trout (Oncorhynchus mykiss).

A rapid decline in temperature poses a major challenge for poikilothermic fish, as their entire metabolism depends on ambient temperature. The gene expression of rainbow trout Oncorhynchus mykiss having undergone such a cold shock (0◦C) was compared to a control (5◦C) in a microarray and quantitative real-time PCR based study. The tissues of gill, kidney and liver were examined. The most differently expressed genes were found in liver, many of them contributing to the network 'cellular compromise, cellular growth and proliferation'.However, the number of genes found to be regulated at 0◦Cwas surprisingly low. Instead of classical genes involved in temperature shock, the three genes encoding fibroblast growth factor 1 (fgf1), growth arrest and DNA-damageinducible, alpha (gadd45a) and sclerostin domain-containing protein 1 (sostdc1) were upregulated in the liver upon cold shock in two different rainbow trout strains, suggesting that these genes may be considered as general biomarkers for cold shock in rainbow trout.

Integrative functional analyses using rainbow trout selected for tolerance to plant diets reveal nutrigenomic signatures for soy utilization without the concurrence of enteritis.

Finding suitable alternative protein sources for diets of carnivorous fish species remains a major concern for sustainable aquaculture. Through genetic selection, we created a strain of rainbow trout that outperforms parental lines in utilizing an all-plant protein diet and does not develop enteritis in the distal intestine, as is typical with salmonids on long-term plant protein-based feeds. By incorporating this strain into functional analyses, we set out to determine which genes are critical to plant protein utilization in the absence of gut inflammation. After a 12-week feeding trial with our selected strain and a control trout strain fed either a fishmeal-based diet or an all-plant protein diet, high-throughput RNA sequencing was completed on both liver and muscle tissues. Differential gene expression analyses, weighted correlation network analyses and further functional characterization were performed. A strain-by-diet design revealed differential expression ranging from a few dozen to over one thousand genes among the various comparisons and tissues. Major gene ontology groups identified between comparisons included those encompassing central, intermediary and foreign molecule metabolism, associated biosynthetic pathways as well as immunity. A systems approach indicated that genes involved in purine metabolism were highly perturbed. Systems analysis among the tissues tested further suggests the interplay between selection for growth, dietary utilization and protein tolerance may also have implications for nonspecific immunity. By combining data from differential gene expression and co-expression networks using selected trout, along with ontology and pathway analyses, a set of 63 candidate genes for plant diet tolerance was found. Risk loci in human inflammatory bowel diseases were also found in our datasets, indicating rainbow trout selected for plant-diet tolerance may have added utility as a potential biomedical model.

Microarray-predicted marker genes and molecular pathways indicating crowding stress in rainbow trout (Oncorhynchus mykiss)

Stocking density is considered as a key factor determining the productivity of fish aquaculture systems. The transcriptomic response to crowding stress is, however, still poorly investigated. We aimed to identify potential biomarker genes via microarray analyses to gain insight into molecular pathways modulated by density-induced stress in farmed rainbow trout Oncorhynchus mykiss. Transcriptome profiling in the liver, kidney, and gills was complemented by analysis of classical plasma parameters and behavioural observations. Individuals of two trout strains were exposed for nine days to definite stocking densities, ~10kg/m3 (low density); ~30kg/m3 (moderate); ~60kg/m3 (elevated); and ~120kg/m3 (high). Only the PYGMA gene, encoding the key enzyme of glycogenolysis, was upregulated in gills and kidney, while about 90 genes were differentially regulated in the liver of trout exposed to high density compared with the moderate-density group. Pathway enrichment analyses predicted the upregulation of HIF1A signalling in liver, contributing to glucose homeostasis during stress conditions. This is consistent with the increased plasma glucose levels detected in crowding-stressed trout. The mTOR and PI3K/AKT signalling pathways were impaired in liver at higher stocking densities indicating stress at the cellular level. Contrary to our expectations, protein ubiquitination and cholesterol biosynthesis pathways were found to be underexpressed. Cholesterol is a precursor of the stress hormone cortisol, whose plasma concentrations were indeed within the normal physiological range in all treatment groups. In addition, we did not observe any aggressive interactions, which are known to be triggered through cortisol release. Taken together, we identified a relatively modest number of rainbow trout-specific crowding markers suggesting that farmed rainbow trout have gained enhanced stress-tolerant phenotypes through decades of selective breeding. Statement of relevanceThe comprehensive recording of animal-based biomarkers is becoming increasingly important for the further development of the aquaculture industry with importance for fish well-being and consumer opinion. Previous studies on crowding stress in rainbow trout have used single or multi-gene approaches to assess the relevance of putative biomarkers, but transcriptomic approaches to define crowding stress-induced pathways in salmonids are overdue. The present study compares the transcriptomic profiles of rainbow trout exposed to different stocking densities and correlates these data sets with classical plasma parameters and behavioural observations.

Evidence of a remnant self-sustaining strain of lake trout in the Lake Michigan basin

Abstract Managers have long embraced the need to maintain diversity as a requisite condition for population and community sustainability. In the case of Great Lakes lake trout, diversity has been severely compromised. The identification of new gamete sources may be beneficial to lake trout reintroduction efforts, particularly in situations where native stocks have been completely extirpated such as in Lake Michigan. Lake trout from Elk Lake, Michigan, are genetically distinct from domestic hatchery strains and historical forms of lake trout from Lake Michigan. Importantly, Elk Lake fish were genetically distinct from Marquette strain lake trout which were previously stocked into Elk Lake. Elk Lake fish were most similar to Lake Michigan basin-derived Lewis Lake (LLW) and Green Lake (GLW) hatchery strains and to historical Lake Michigan populations from the Charlevoix, Michigan area. While all individuals exhibited characteristics of lean form lake trout, the body shape of lake trout from Elk Lake, stocked lean fish from Lake Michigan and Lake Superior wild lean strains from near Isle Royale differed. Elk Lake fish were more fusiform, elongate, and streamlined with a narrower caudal peduncle compared to hatchery lean strains and wild lean forms from the Isle Royale region of Lake Superior. The lake trout population in Elk Lake is a remnant of a now extirpated native Lake Michigan population that was established either by natural colonization or stocking from historical Lake Michigan populations. Elk Lake lake trout is as genetically diverse as other strains used in Great Lakes reintroduction efforts and likely represent a viable gamete source representing genetic diversity lost from Lake Michigan.

Marker assisted selection for spawning date and co-variation among economically important fitness traits in a commercial strain of rainbow trout (Oncorhynchus mykiss)

The effects of marker assisted selection for spawning date in males on embryonic developmental rate, growth related traits and precocious male maturation and phenotypic and genetic associations among traits were investigated in a commercial strain of rainbow trout (Oncorhynchus mykiss). The relationship between spawning date category of the sire (early or late) and developmental rate as measured by hatching time was inconsistent among families. However, two half-sib families produced by males with an allelic complement associated with late spawning date had higher rates of precocious male maturation and faster developmental rates than two families produced by males with earlier spawning date alleles. QTL analysis suggests that some of the co-variation between spawning date and developmental rate has a genetic basis as two QTL for developmental rate as measured by hatching time co-localized to the same markers known to be associated with spawning date in this strain. We observed no association between the spawning date category of the sire and progeny length at 61days post-fertilization (alevin stage), body weight at 381days (juveniles), body weight at 614days and specific growth rate, which suggests that selection for early or late spawning date alleles will have little effect on growth traits. Within families, faster developmental rates conferred a size advantage at 61days post-fertilization but not at 381 and 614days. Moreover, no correlation between developmental rate and the propensity of early male maturation was detected within families. Males that matured at 2years were significantly heavier at both 381 and 614days and had higher specific growth rates than immature males and females. Likewise, body weight at 614days and family were significant predictors for the propensity for early sexual maturation in males. This indicates that selection for greater body size will likely result in higher rates of unwanted precocious male maturation. Together, these results suggest that co-variation among economically important fitness traits may present potential trade-offs impacting selection goals. RelevanceAddresses feasibility of using molecular approaches in selective breeding programs.

Assessment of genetic differentiation and genetic assignment of commercial rainbow trout strains using a SNP panel

Rainbow trout (Oncorhynchus mykiss) is the most widely cultured cold freshwater fish in the world. Troutlodge, Inc., one of the largest commercial rainbow trout egg producers in the world, has eight breeding populations of rainbow trout. Assessment of population genetic differentiation is critical for selective breeding, and genetic assignment is often required to address production issues arising on fish farms. Previously, we developed a SNP (single nucleotide polymorphism) panel for parentage assignment in rainbow trout. The objectives of this study were: (1) to characterize the genetic differentiation of the eight Troutlodge breeding populations; and (2) to evaluate the accuracy of genetic assignment to identify Troutlodge fish using the same SNP panel previously developed for parentage assignment. A total of 1732 breeders of the eight Troutlodge breeding populations were genotyped with the SNP panel. The global FST over all SNPs was 0.13 and the pairwise FST between any two breeding populations ranged from 0.056 to 0.195. Both phylogenetic tree and structure analyses revealed that the odd year and even year populations for the same strain were closely related to each other. Also, the eight populations were clustered into two groups. Based on the results of self-assignment, 97.1% of the Troutlodge breeders were correctly assigned to the population of origin. To further evaluate the accuracy of genetic assignment, we also genotyped 280 egg production fish from three Troutlodge populations of known origin, 49 fish from a Canadian farm, 70 fish from a farm in Idaho and 188 fish from four known non-Troutlodge strains. Among the 280 production fish, 98.2% fish were correctly assigned to the Troutlodge strain of origin. Consistent with the purchasing records, the fish from the two farms were also correctly assigned to two Troutlodge strains. Based on the SNP genotypes, 185 out of 188 fish (98.4%) from the four non-Troutlodge strains could be excluded as Troutlodge fish. In conclusion, our previously developed SNP panel for parentage assignment is also useful to characterize genetic differentiation and has sufficient power for genetic assignment of commercial rainbow trout strains used in this study. Statement of relevanceIdentification of fish strains using a SNP panel.

Physiological basis of metabolic trade-offs between growth and performance among different strains of rainbow trout

Adaptive trade-offs define the trait combinations that differentiate taxa and allow coexistence along environmental gradients. To understand the physiological trade-offs associated with growth, we examined relationships among metabolic rate, digestive capacity, tissue energy content, and growth in juveniles of three strains of rainbow trout (Oncorhynchus mykiss) that differ in growth. Fish were reared under satiation, 1% of body mass per day, and complete food deprivation treatments to assess differences in performance and adaptive trade-offs along a gradient of resource availability. The fast-growing hatchery strain had higher standard metabolic rate (SMR), lower aerobic scope, and potentially lower maximum metabolic rates, suggesting that high growth trades off against a reduced capacity to do metabolic work. Trout with high growth rates also generally had larger gastrointestinal tracts, maximum food consumption, and growth efficiency. Results demonstrate (i) higher SMR of fast growers appears to be related to a greater investment in high-maintenance digestive tissue that supports rapid growth; (ii) growth appears to trade off against active metabolism; and (iii) selection on growth involves a suite of integrated physiological and anatomical traits that are affected by both genotype and environment (ration).

The effect of a single prerelease exposure to conspecific alarm cue on poststocking survival in three strains of rainbow trout (Oncorhynchus mykiss)

Significant resources go toward rearing and stocking fish globally, yet poststocking survival is often low, largely due to high predation rates on hatchery-reared fish. Antipredator behavior has been enhanced in many species through exposure to chemical cues that simulate predation events, but the implementation of such protocols may be logistically challenging. It has been suggested that a single exposure of hatchery fish to chemical cues while en route to stocking locations may be sufficient to enhance antipredator behavior and improve survival. We tested whether a one-time exposure to conspecific alarm cues while en route to a stocking site increased poststocking survival of three strains of rainbow trout (Oncorhynchus mykiss (Walbaum, 1792)). We found no difference in mortality rates between strains or between treatment fish (exposed to alarm cues) and control fish (not exposed to alarm cues), suggesting that this quick and easy protocol was insufficient and that more complex techniques should be explored to increase poststocking survival.

Critical Dissolved Oxygen Tolerances of Whirling Disease‐Resistant Rainbow Trout

AbstractA low concentration of dissolved oxygen (DO) is commonly the limiting factor in fish culture systems. Hypoxia tolerance in Rainbow Trout Oncorhynchus mykiss can be affected by both history of domestication and growth rate. As such, selecting strains for specific characteristics such as growth rate or disease resistance could potentially affect DO tolerance, making culture difficult. Here we used two experiments to examine the differences in tolerance to lower DO concentrations among four Rainbow Trout strains and crosses selected for resistance to whirling disease Myxobolus cerebralis. The first experiment examined differences in critical DO concentrations of fry (≥73 mm total length [TL]) when exposed to rapid decreases in DO at 30, 60, 90, and 120 d postswim‐up. In addition, since formalin is a common chemical used in aquaculture to treat for external parasites, the effect of exposure to formalin on tolerance to low DO was evaluated. The second experiment evaluated critical DO concentrations among four strains and crosses exposed to a prolonged decrease in DO at age 7 months (averaging 178 mm TL). Formalin exposure had an effect on low‐DO tolerance, with DO concentrations that resulted in a loss of equilibrium decreasing with an increase in formalin concentration. In addition, low‐DO tolerances were diminished with an increase in fish size, with larger fish losing equilibrium at higher DO concentrations. Differences in DO concentrations resulting in loss of equilibrium and mortality were evident among the strains and crosses in the second experiment. This experiment demonstrated that DO concentrations must be below 2.0 mg/L before loss of equilibrium is observed. However, if fish are soon returned to well‐oxygenated water, losses can be minimized. Additionally, other hatchery practices that compromise hypoxia tolerance may increase mortality more quickly following low‐DO exposure, and care should be taken to correct low‐DO issues shortly after loss of equilibrium is observed.

Genetic diversity and population structure of domestic brown trout (Salmo trutta) in France

Animals in captivity are subject to similar evolutionary forces that act on natural populations, which can facilitate the generation of population genetic structure. Understanding the extent of genetic differentiation among captive populations provides insights into industry practices and the domestication process. We investigated the genetic structure of domestic brown trout (Salmo trutta) in France by surveying fish collected from 20 fish farms. Using microsatellite markers, we calculated basic measures of genetic diversity and differentiation among these various farms. We also evaluated population structure using tree-based approaches, model-based clustering methods, and ordination techniques. Differences in genetic diversity reflected founding histories and source stocks among the fish farms. Fish farms that raise trout originating from Mediterranean watersheds had lower levels of genetic diversity and much higher divergence than populations of Atlantic origin. Stocks believed to originate from the common Atlantic-based trout strain demonstrated low-levels of population structure. We observed fish of mixed ancestry in some fish farms and the presence of multiple genetic stocks within the same facility. Our findings reveal patterns of genetic structure that reflect differences in founding practices and movement of individuals and strains between fish farms. Such findings have consequences for fisheries managers stocking natural ecosystems with captive-reared fish, biologists attempting to understand the interactions between wild and domestic brown trout, and fish farmers involved in stocking or restoration activities. Statement of relevanceGenetics resolve the history and practices of aquaculture.

Genetic variability and differentiation of rainbow trout strains in Iran

To determine the genetic structure and differences of rainbow trout, variations in 9 microsatellite loci in four stocks of rainbow trout from Mazandran, Iran were examined. Three samples were introduced from Norwegian, French stocks, and one was from Iranian stocks rearing in North of Iran. Most but not all loci were polymorphic in all stocks. There was substantial genetic differentiation among populations, with an average FST value of 0.065. The four stocks averaged 5.2–7.4 alleles per locus, with average heterozygosities of around 0.625 to 0.762. A large variation in observed hetrozygocity, averaged over all samples was observed among loci and ranged from 0.015 in OTSG474 to 0.850 in OTSG249. Nine of 20 tests for Hardy – Weinberg expectations gave significant deviations. The cause(s) of these deviations are unknown. The Norway strain was significant deviations from HWE in all 5 polymorphic loci. The degree of differentiation among strain or Nei Genetic Distance compared pairwise accorded well with their likely genetic connectivity. Two of the strains, Iranian and Norway had the highest Nei Genetic Distance (0.213) and were different in all loci except for OTSG3. The level of genetic variation in the domesticated rainbow trout strains that are farmed in European countries (French, Norway) and Iran did not differ significantly neither within nor between the countries, but the highest pronounced difference was comparable with that of the Norway and Iran strains.

Cognitive appraisal of aversive stimulus differs between individuals with contrasting stress coping styles; evidences from selected rainbow trout (Oncorhynchus mykiss) strains

In animals, personality variations in response to stress and energy demands have been established. Cognitive processing of negative stimuli correlates with stress response patterns. Still, the relative contribution of cognitive appraisal or physiological demands to the behavioural output needs to be clarified. In this study we utilized reactive (high-responsive, HR) and proactive (low-responsive, LR) rainbow trout strains to investigate how contrasting reactions to hypoxia are related to individual variation in metabolism and/or cognition. The HR-LR strains did not differ in standard metabolic rate or hypoxia tolerance. HR trout displayed more pronounced avoidance to a signal cue after being conditioned with hypoxia, suggesting that they experienced this stimulus more aversive than LR trout. Together with differences in forebrain c-fos activation patterns in dorsomedial pallium, these results suggest cognitive differences between the strains. These results demonstrate that differences in personality/stress coping style can be related to contrasts in cognition, which are independent of metabolic differences.

Growth Parameters Evaluation and Identification of Growth Hormone Receptor Gene Polymorphisms in Various Strains of Rainbow Trout Oncorhynchus mykiss

In the present study, polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) and restriction fragment length polymorphism (RFLP) methods were compared to analyze the polymorphism of growth hormone receptor (GHR) gene in French, Iranian and Danish strains of Oncorhynchus mykiss. A monomorphic SSCP pattern of AA genotype in the French and Iranian strains and a dimorphic AA and AB genotype in the Danish strain were observed in 3' non-coding regions of GHR gene. In the Danish strain, the AB genotype polymorphism of the GHR gene with its very low frequency (5%) has no effect on the production trait. While, RFLP-Dde1 showed no polymorphism with genetic variation in the location of GHR. Moreover, comparing the condition factors (K) of three different rainbow trout strains showed a significant correlation between the French (1.312 ± 0.13), Iranian (1.245 ± 0.17) and Danish strains (0.763 ± 0.1), respectively (p<0.05). In particular, the French strain obtained a higher K compared to the two others. The length-weight relationship is shown by the following equations W= 0.013 × L2.921, W= 0.012 ×L3.023 and W= 0.007 × L3.176 for French, Iranian and Danish strains, respectively. With the mean (b= 2.921), the studied French strain exhibited a negative allometric growth b<3 while the Iranian (b=3.023) and the Danish (b=3.176) showed positive allometric growths. Regardless of the underlying mechanism(s) responsible for the different relationships, the results of this study suggested that the AA and AB genotypes polymorphism of the GHR gene are not associated with condition factor and environmental variables can influence condition factor and length-weight relationship of rainbow trout strains in this study.

You Can’t Unscramble an Egg: Population Genetic Structure of &lt;i&gt;Oncorhynchus mykiss&lt;/i&gt; in the California Central Valley Inferred from Combined Microsatellite and Single Nucleotide Polymorphism Data

Author(s): Pearse, Devon E.; Garza, John Carlos | Abstract: Steelhead/rainbow trout (Oncorhynchus mykiss) are found in all of the major tributaries of the Sacramento and San Joaquin rivers, which flow through California’s Central Valley and enter the ocean through San Francisco Bay and the Golden Gate. This river system is heavily affected by water development, agriculture, and invasive species, and salmon and trout hatchery propagation has been occurring for over 100 years. We collected genotype data for 18 highly variable microsatellite loci and 95 single nucleotide polymorphisms (SNPs) from more than 1,900 fish from Central Valley drainages to analyze genetic diversity, population structure, differentiation between populations above and below dams, and the relationship of Central Valley O. mykiss populations to coastal California steelhead. In addition, we evaluate introgression by both hatchery rainbow trout strains, which have primarily native Central Valley ancestry, and imported coastal steelhead stocks. In contrast to patterns typical of coastal steelhead, Central Valley O. mykiss above and below dams within the same tributary were not found to be each others’ closest relatives, and we found no relationship between genetic and geographic distance among below-barrier populations. While introgression by hatchery rainbow trout strains does not appear to be widespread among above-barrier populations, steelhead in the American River and some neighboring tributaries have been introgressed by coastal steelhead. Together, these results demonstrate that the ancestral population genetic structure that existed among Central Valley tributaries has been significantly altered in contemporary populations. Future conservation, restoration, and mitigation efforts should take this into account when working to meet recovery planning goals.

Flavobacterium psychrophilum Infections in Salmonid Broodstock and Hatchery-Propagated Stocks of the Great Lakes Basin.

Bacterial coldwater disease (BCWD), caused by Flavobacterium psychrophilum, threatens wild and propagated salmonids worldwide and leads to substantial economic losses. In addition to being horizontally transmitted, F. psychrophilum can be passed from infected parents to their progeny, furthering the negative impacts of this pathogen. In Michigan, both feral and captive salmonid broodstocks are the gamete sources used in fishery propagation efforts. A 5-year study was initiated to follow the prevalence of systemic F. psychrophilum infections in feral broodstocks of four species (steelhead Oncorhynchus mykiss [potadromous Rainbow Trout]; Coho Salmon O. kisutch; Chinook Salmon O. tshawytscha; and Atlantic Salmon Salmo salar) residing in three Great Lakes watersheds. Additionally, captive broodstocks of four species (Rainbow Trout, Brown Trout Salmo trutta, Lake Trout Salvelinus namaycush, and Brook Trout Salvelinus fontinalis) maintained at two facilities were assessed for the presence of F. psychrophilum. The resultant offspring from each broodstock population were sampled for F. psychrophilum infections multiple times throughout hatchery residency. Using selective flavobacterial culture and PCR confirmation, F. psychrophilum was detected in all broodstocks except the captive Lake Trout and Brook Trout. Logistic regression analysis demonstrated that among the infected feral broodstocks, Chinook Salmon from the Lake Michigan watershed had the highest prevalence of systemic F. psychrophilum infection (mean = 63.2%). Among the captive broodstocks, the Gilchrist Creek strain of Brown Trout had the highest infection prevalence (mean = 5%). Collectively, the captive broodstocks were found to have significantly lower infection prevalence than the feral broodstocks. Despite the high prevalence of systemic F. psychrophilum infections in many broodstock populations, the bacterium was rarely detected in their progeny during hatchery rearing. However, heavy losses associated with clinical BCWD outbreaks did occur. Collectively, our results reinforce that BCWD continues to threaten Great Lakes basin salmonids.

Food availability in spring affects smolting in brown trout (Salmo trutta)

Prior to out-migration, salmonid fish typically undergo physiological and morphological changes — a process known as smolting. This study indicates that smolting in brown trout (Salmo trutta) is affected by feeding conditions in spring immediately prior to out-migration. This conclusion was reached after experimentally testing the effect of seasonal variation in food availability on smolt status in the spring. A migratory strain of trout was administered either high or low food rations in the autumn, winter, or spring prior to release in the spring. While fish growth or condition could be affected in any season, it was spring rationing that reduced growth and growth-related variables and that caused increased smolting. Our result supports the idea that smoltification and the decision to migrate is affected by spring food availability regardless of conditions in the previous autumn or winter.

Different gene expression profiles between normal and thermally selected strains of rainbow trout, Oncorhynchus mykiss, as revealed by comprehensive transcriptome analysis

A high-temperature selected (HT) strain of rainbow trout was established from the Donaldson (DS) strain by traditional selective breeding in Japan. The aim of this study is to investigate genes related to upper temperature tolerance in this strain utilizing next generation sequencer (NGS), and to establish comprehensive and comparable datasets in brain, liver, muscle, heart and gill tissues between the HT and DS strains. After assembling, clustering and filtering, 242,530 contigs were obtained. Among them, 7624 transcripts had at least 10 counts in expression analysis in all tissues and used as references. BLASTX homology search showed that 7329 transcripts matched with known genes. Compared to the DS strain, the HT strain expressed 90, 775, 349, 188 and 194 genes 2 folds or more in brain, liver, muscle, heart, and gill, respectively in the case of fish before heat-exposure treatment. Meanwhile, the HT strain expressed 292, 363, 433, 322 and 211 genes 2 folds or more in brain, liver, muscle, heart, and gill, respectively in case of fish after heat-exposure treatment. Many of heat shock protein family genes and transcription factor AP-1 related genes were highly expressed in all tissues of the HT strain compared with the DS strain. These results suggest that these genes play key roles in upper temperature tolerance. These comprehensive and comparable datasets will offer broad visions for upper temperature tolerance in fish species.

Rainbow trout in seasonal environments: phenotypic trade-offs across a gradient in winter duration.

Survival through periods of resource scarcity depends on the balance between metabolic demands and energy storage. The opposing effects of predation and starvation mortality are predicted to result in trade-offs between traits that optimize fitness during periods of resource plenty (e.g., during the growing season) and those that optimize fitness during periods of resource scarcity (e.g., during the winter). We conducted a common environment experiment with two genetically distinct strains of rainbow trout to investigate trade-offs due to (1) the balance of growth and predation risk related to foraging rate during the growing season and (2) the allocation of energy to body size prior to the winter. Fry (age 0) from both strains were stocked into replicate natural lakes at low and high elevation that differed in winter duration (i.e., ice cover) by 59 days. Overwinter survival was lowest in the high-elevation lakes for both strains. Activity rate and growth rate were highest at high elevation, but growing season survival did not differ between strains or between environments. Hence, we did not observe a trade-off between growth and predation risk related to foraging rate. Growth rate also differed significantly between the strains across both environments, which suggests that growth rate is involved in local adaptation. There was not, however, a difference between strains or between environments in energy storage. Hence, we did not observe a trade-off between growth and storage. Our findings suggest that intrinsic metabolic rate, which affects a trade-off between growth rate and overwinter survival, may influence local adaptation in organisms that experience particularly harsh winter conditions (e.g., extended periods trapped beneath the ice in high-elevation lakes) in some parts of their range.

Risks to stocks of native trout of the genus Salmo (Actinopterygii: Salmoniformes: Salmonidae) of Serbia and management for their recovery

Background. Insufficiently controlled stocking compromises the high diversity of wild trout stocks of Serbia. Native brown trout, Salmo cf. trutta Linnaeus, 1758, and Macedonian trout, Salmo macedonicus (Karaman, 1924), reveal remarkable diversity assessed using the mtDNA molecular markers, with the eight exclusive and several more widely spread haplotypes found in them. Four alien trout species and strains and one strain of Macedonian trout were introduced into the home areas of the native wild trout stocks in Serbia. In addition to them, wild trout stocks were also affected by farmed rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), and brook trout Salvelinus fontinalis (Mitchill, 1815), that regularly escape to streams, and from Ohrid trout, Salmo letnica (Karaman, 1924), and Arctic charr, Salvelinus alpinus (Linnaeus, 1758), stocked into streams and reservoirs. Risk of invasiveness that wild trout stocks are exposed to and their restoration were driving forces for this study. Materials and methods. Trout specimens from the Jerma River sampled in 2013 were additionally analysed for their mtDNA haplotype. The invasiveness potential of eleven alien trout species and strains introduced by stocking into wild brown- and Macedonian trout stocks in Serbia were assessed with the Fish Invasiveness Screening Kit (FISK). Results. Five of introduced trout species and strains were classified as having a high risk (sensu lato) and two of them as having a high risk (sensu stricto) of being (or becoming) invasive. Conclusion. Progressively rising and insufficiently controlled fishing and management with stocking of non-indigenous trout in wild brown trout stocks are the main current threats to the original diversity. Alien brown trout strains cross breed with native brown trout and incorporate into their stocks. Currently, feral rainbow-, brook-, and Ohrid trout reveal great invasive potential by naturalization in waters heavily stocked with them. The fisheries measures aiming to control and/or to eradicate alien strains of brown trout involve the restriction of stocking, landing of trout suspected as of alien strain or species, as well as the stringent control of stocking material used for the restorative stocking. They are mandatory, regarding the conservational dependence of wild brown trout stocks.

Risks to stocks of native trout of the genus Salmo (Actinopterygii: Salmoniformes: Salmonidae) of Serbia and management for their recovery

Background. Insufficiently controlled stocking compromises the high diversity of wild trout stocks of Serbia. Native brown trout, Salmo cf. trutta Linnaeus, 1758, and Macedonian trout, Salmo macedonicus (Karaman, 1924), reveal remarkable diversity assessed using the mtDNA molecular markers, with the eight exclusive and several more widely spread haplotypes found in them. Four alien trout species and strains and one strain of Macedonian trout were introduced into the home areas of the native wild trout stocks in Serbia. In addition to them, wild trout stocks were also affected by farmed rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), and brook trout Salvelinus fontinalis (Mitchill, 1815), that regularly escape to streams, and from Ohrid trout, Salmo letnica (Karaman, 1924), and Arctic charr, Salvelinus alpinus (Linnaeus, 1758), stocked into streams and reservoirs. Risk of invasiveness that wild trout stocks are exposed to and their restoration were driving forces for this study. Materials and methods. Trout specimens from the Jerma River sampled in 2013 were additionally analysed for their mtDNA haplotype. The invasiveness potential of eleven alien trout species and strains introduced by stocking into wild brown- and Macedonian trout stocks in Serbia were assessed with the Fish Invasiveness Screening Kit (FISK). Results. Five of introduced trout species and strains were classified as having a high risk (sensu lato) and two of them as having a high risk (sensu stricto) of being (or becoming) invasive. Conclusion. Progressively rising and insufficiently controlled fishing and management with stocking of non-indigenous trout in wild brown trout stocks are the main current threats to the original diversity. Alien brown trout strains cross breed with native brown trout and incorporate into their stocks. Currently, feral rainbow-, brook-, and Ohrid trout reveal great invasive potential by naturalization in waters heavily stocked with them. The fisheries measures aiming to control and/or to eradicate alien strains of brown trout involve the restriction of stocking, landing of trout suspected as of alien strain or species, as well as the stringent control of stocking material used for the restorative stocking. They are mandatory, regarding the conservational dependence of wild brown trout stocks.