Brook Trout Research Articles

USE OF SYMMETRIC DIMETHYLARGININE TO DETECT RENAL LESIONS IN FISH: A PRELIMINARY STUDY IN BROOK TROUT (SALVELINUS FONTINALIS).

Symmetric dimethylarginine (SDMA) is an early marker for renal lesions in mammals. The objectives of this study were 1) to establish a reference interval of SDMA in healthy brook trout, Salvelinus fontinalis (Mitchill, 1814), and 2) to assess its sensibility as a marker of renal pathology. Plasma SDMA was quantified by liquid chromatography-mass spectrometry in 25 adult brook trout, including 20 fish displaying no renal histologic lesions, and five fish displaying chronic nonactive microscopic granulomas. The fish size (P = 0.30) and weight (P = 0.12) were not statistically different among groups, nor were SDMA values (P = 0.22). However, brook trout without microscopic renal lesions tended to have lower SDMA values (no lesions: mean = 24.9 µg/dL; lesions: mean = 31.4 µg/dL). The reference interval (90% confidence interval [90% CI]) for SDMA concentration in brook trout ranged between 10.0 µg/dL (90% CI: 5.4-14.7) and 39.8 µg/dL (90% CI: 34.8-43.9). These values were higher than those previously reported in other vertebrate species. Further research is needed to evaluate the use of SDMA as a marker of renal function in fishes.

Parallel evolution of morphological traits and body shape in littoral and pelagic brook charr, Salvelinus fontinalis, along a gradient of interspecific competition.

The parallel evolution of similar ecotypes in response to comparable environmental conditions is believed to reveal the importance of divergent selection in phenotypic diversifying processes. Systems characterized by the presence of multiple replicate populations expressing resource polymorphism thus provide an ideal opportunity to address the occurrence and factors affecting the parallel evolution of ecotypes. Previous studies have shown that brook charr (Salvelinus fontinalis) exhibit resource polymorphism in some Canadian Shield lakes, where a littoral ecotype feeds mainly on zoobenthos and a pelagic ecotype feeds mostly on zooplankton. Using morphological traits and geometric morphometric analyses on 18 native brook charr populations, we explicitly tested (i) whether brook charr ecotypes show parallel evolution across populations (i.e. the same morphological traits discriminate ecotypes among lakes) and (ii) whether interspecific competition decreases the amplitude of morphological differentiation between ecotypes, if any, because brook charr experience some level of competitive exclusion from the littoral habitat in the presence of creek chub or white sucker. We observed a low level of parallel evolution, where the littoral ecotype was overall stouter with longer fins and smaller eyes than the pelagic ecotype. Interspecific competition had no clear impacts on the amplitude of morphological differentiation. We also observed that inter-lake morphological differences are greater than between ecotypes within lakes, suggesting an important effect of local environmental factors on population morphology. Early-stage of diversification as well as phenotypic plasticity and morphological integration could explain why resource polymorphism is still subtle in brook charr populations.

Phenotypic Variation in Brook Trout Salvelinus fontinalis (Mitchill) at Broad Spatial Scales Makes Morphology an Insufficient Basis for Taxonomic Reclassification of the Species

It was recently proposed that there are three new species of Salvelinus with microendemic distributions in the Great Smoky Mountains National Park, Tennessee, USA. The three species of Salvelinus were hypothesized to be distinct from their congener Brook Trout S. fontinalis based on three meristic traits—pored lateral-line scales, vertebral counts, and number of basihyal teeth. After analyses that included specimens sampled from a larger portion of the geographic range of S. fontinalis, we conclude that the three populations of Salvelinus recently described as new species are not morphometrically distinct from Brook Trout and consider all three to be synonyms of S. fontinalis. Moreover, the low number of specimens originally examined conflates morphological differences among populations with sexual dimorphism and/or phenotypic plasticity, both of which are documented extensively in Brook Trout but were not controlled for in the species descriptions. While there is currently insufficient phenotypic or genotypic evidence to support the hypothesis of three new species that are distinct from S. fontinalis, we acknowledge the need to understand the unique selection pressures that shape evolutionary trajectories in small, isolated populations of Brook Trout and to conserve evolutionarily significant sources of genotypic and phenotypic diversity. To that end, we provide comments on research opportunities to support Brook Trout conservation, including the importance of collaborative, range-wide phylogenetic studies to identify the most appropriate scales of management efforts.

Mathematical modeling and analysis of the heat shock protein response during thermal stress in fish and HeLa cells

The climate change has the potential to dramatically affect species’ thermal physiology and may change the ecology and evolution of species’ lineages. In this work, we investigated the transition of dynamics in the heat shock response when the thermal stress approaches the upper thermal limits of species to understand how the climate change may affect the heat shock responses in ectotherms and endotherms. The heat shock protein 70, HSP70, prevents protein denaturation or misfolding under thermal stresses. When thermal stress increases, the number of misfolded proteins increases, which leads to high levels of HSP70 protein. However, when temperatures approach limits of thermal tolerance (i.e., the critical thermal maximum, CTmax, for ectotherms and the superior critical temperature, SCT, for endotherms), levels of HSP70 protein synthesis start to decrease. Thus, we hypothesized that the temperature at the first reduction of HSP abundance indicates the thermal limits of the species. In this work, we provide a mathematical model to investigate the behavior of the heat shock responses related to HSP70 protein. This model captures the dynamics of HSP70 protein and Hsp70 mRNA, in HeLa cells (i.e., representative for endotherms) and multiple species of fishes (i.e., representative for ectotherms) with different acclimation histories. Based on our hypothesis of the relationship between the HSP70 protein level and CTmax/SCT, our model provides three methods to predict the CTmax of fishes with varying acclimation temperature and the SCT of HeLa cells. The CTmax increases as the acclimation temperature increases in fishes, however the CTmax plateaus when the acclimation temperature is higher than 20°C in brook trout, a representative cool water salmonid. Our model also captures the situation that the heat shock reaction in fish is more sensitive to the heat shock temperature than HeLa cells, when the heat shock temperature is lower than the upper thermal tolerance. However, both fish and HeLa cells are sensitive to the heat shock temperature when the temperature reaches the thermal tolerance limits. Additionally, our sensitive analysis result indicates that the status of some components in the heat shock reaction changes when the temperature reaches the thermal tolerance resulting in failure in protein refolding in fish and speeding up the refolding process in HeLa cells. Mathematical analysis is also applied on a simplified mathematical model to investigate the detailed dynamics of the model, such as the steady states of the substrate, Hsp70 mRNA, and HSP70 protein, at different thermal stresses. The comparison between the original model and simplified model shows that the inhibition on HSP70 protein transcription by thermal stresses leads to the reduction in HSP70 protein at extreme temperatures.

A test of a generalized, optimal habitat selection model for drift‐feeding fishes: brook charr

AbstractOptimality theory is useful for modeling habitat use in animals, although many models have not been rigorously tested. We evaluated the ability of the Grossman et al. net‐energy‐intake (NEI) optimal foraging model for drift‐feeding stream fishes, to predict the holding velocity (microhabitat) of native brook charr (BC; Salvelinus fontinalis) inhabiting a southern Appalachian stream. This model postulates that fish choose holding velocities that maximize their NEI, and is broadly applicable to stream fishes, many of which are drift‐feeders. We used laboratory prey capture success versus water velocity data to quantify the relationship between prey capture success, water velocity, and holding velocity of BC (N = 21, mean standard length = 147 mm ± 14 sd). Parameterization of the Grossman et al. model yielded an optimal holding velocity prediction of 18.5 cm·s−1. Based on fitting criteria from previous work, the model prediction was successful because it fell within the 95% confidence interval (13.5–20.5 cm·s−1) of mean holding velocities (17.0 cm·s−1, N = 26) of BC in Lynn Camp Prong, Tennessee. Consequently, NEI maximization likely is a causal factor affecting BC habitat choice. Our result argues strongly for the general usefulness of this model.

Molecular and physiological responses predict acclimation limits in juvenile brook trout (Salvelinus fontinalis).

Understanding the resilience of ectotherms to high temperatures is essential because of the influence of climate change on aquatic ecosystems. The ability of species to acclimate to high temperatures may determine whether populations can persist in their native ranges. We examined physiological and molecular responses of juvenile brook trout (Salvelinus fontinalis) to six acclimation temperatures (5, 10, 15, 20, 23 and 25°C) that span the thermal distribution of the species to predict acclimation limits. Brook trout exhibited an upregulation of stress-related mRNA transcripts (heat shock protein 90-beta, heat shock cognate 71 kDa protein, glutathione peroxidase 1) and downregulation of transcription factors and osmoregulation-related transcripts (nuclear protein 1, Na+/K+/2Cl- co-transporter-1-a) at temperatures ≥20°C. We then examined the effects of acclimation temperature on metabolic rate (MR) and physiological parameters in fish exposed to an acute exhaustive exercise and air exposure stress. Fish acclimated to temperatures ≥20°C exhibited elevated plasma cortisol and glucose, and muscle lactate after exposure to the acute stress. Fish exhibited longer MR recovery times at 15 and 20°C compared with the 5 and 10°C groups; however, cortisol levels remained elevated at temperatures ≥20°C after 24 h. Oxygen consumption in fish acclimated to 23°C recovered quickest after exposure to acute stress. Standard MR was highest and factorial aerobic scope was lowest for fish held at temperatures ≥20°C. Our findings demonstrate how molecular and physiological responses predict acclimation limits in a freshwater fish as the brook trout in the present study had a limited ability to acclimate to temperatures beyond 20°C.

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.

Hooking and Handling Mortality of Trout Captured in the Bald Eagle Creek Trout Tournament, Pennsylvania

AbstractFor many years bait has been banned in catch‐and‐release trout fisheries owing to anticipated high rates of hooking mortality. Recent studies that have been conducted in streams have found relatively low rates of hooking mortality. The objective of this study was to quantify the rates of hooking and handling mortality of stocked trout that were caught by recreational anglers using the terminal tackle of their choice during a 2‐d tournament for three consecutive years on a small stream in central Pennsylvania. Each year, we affixed T‐bar anchor tags to more than 800 Brook Trout Salvelinus fontinalis, Brown Trout Salmo trutta, Rainbow Trout Oncorhynchus mykiss, and golden Rainbow Trout and stocked them in an 11‐km stream reach. All of the tagged trout that were alive when they were checked in were eligible for cash prizes. After processing, the trout were monitored for 9 d in a hatchery. Anglers brought in 423–591 tagged trout each year. The rates for hooking and handling mortality among years ranged from 3.9% to 8.0%. Mortality of Rainbow Trout (7.4%) was the highest among the three species. The trout were caught on natural and manufactured baits (87.9%), artificial lures (10.8%), and flies (1.3%); mortality was not related to terminal tackle. Trout that had hooks left embedded in them or had blood in their holding container had the highest mortality. Time from capture to check‐in, holding method, hook type, or hook size did not influence mortality. This study demonstrated low mortality of trout that were caught primarily with bait and subjected to more handling stress than they would normally experience in catch‐and‐release waters. We suggest that these results support the notion that bait fishing can be allowed without negative population‐level effects in streams where regulations require that most or all angled trout are released.

Brook trout movement, survival and spawning redd sites in a central Wisconsin headwater stream vulnerable to low streamflow

AbstractBrook trout Salvelinus fontinalis populations inhabiting groundwater‐fed, headwater streams are sensitive to biotic and abiotic changes caused by anthropogenic actions in their native range but can be very resilient in their introduced range. Brook trout have maintained a self‐sustaining population in the Little Plover River, Wisconsin, despite fish kills during extreme low flows between 2005 and 2009 caused by groundwater pumping and limited precipitation. Increased understanding of brook trout sensitivity and resilience in headwater streams can aid restoration, conservation and eradication efforts. Therefore, we evaluated their movements, survival and spawning behaviours in the Little Plover River using a PIT antenna array (July 2016–July 2019) and spawning redd surveys (2017–2018) paired with estimated groundwater inputs. Tagged individuals often exhibited localised, nocturnal movements for most of the year. However, movements increased and shifted to a diurnal pattern with decreased photoperiod and water temperature beginning during spawning and continuing throughout winter (November–February). Spawning movements primarily (90%) occurred in the upstream direction, with consistent patterns of short (rkm <0.9, 64.8.9–70.7%), moderate (rkm =0.9 – 3.5, 20.0–30.2%) and long (rkm ≥4.5, 4.5–6.2%) distance movements across the three spawning periods. Monthly survival estimates ranged from 72.1 to 98.9% throughout the study (mean =91.5%) and were consistently lowest during winter and spring. Redd surveys indicated spawning peaked in mid‐November and redds were more concentrated in upstream reaches and in areas with higher estimated groundwater inflows in 2017 but not in 2018 when surface flows were higher. Our results increase understanding of brook trout daily and seasonal movements, monthly and seasonal survival, and spawning behaviours including relative to groundwater and surface flows in headwater streams, further informing management, conservation, and eradication efforts.

Differential gene expression associated with behavioral variation in ecotypes of Lake Superior brook trout (Salvelinus fontinalis)

Associations between behaviors and the development of different life history tactics have been documented in several species of salmon, trout, and charr. While it is well known that such behaviors are heritable the genes and molecular pathways connected to these behaviors remain unknown. We used an RNA-seq approach to identify genes and molecular pathways differentially regulated in brain tissue between “shy” and “bold” brook trout (Salvelinus fontinalis). A small number of genes were differentially expressed between the behavioral types at several months after hatching and two years of age. Pathway analysis revealed that EIF2 signaling differed consistently between shy and bold individuals suggesting large-scale differences in protein synthesis between behavioral types in the brain. Additionally, the RNA-seq data were used to find polymorphisms within the brook trout genome and a GWAS approach was used to test for statistical associations between genetic variants and behavior type. One allele located in a transcription factor (TSHZ3) contained a protein-coding non-synonymous SNP suggesting that functional variation within TSHZ3 is connected to the development of different behaviors. These results suggest that the molecular basis of behavioral development is complex and due to the differential expression of many genes involved in a wide-range of different molecular pathways.

Evaluation of different extractions for the metabolite identification of malachite green in brook trout and shrimp

Applications of mass spectrometry-based metabolomics in food science have developed fast in the last decade. Sample preparation and data processing are critical in non-target/metabolomic workflows but there is currently no standardized protocol for the development of these methods. The impact of data processing parameters or the inclusion of a different matrix is not often taken into account during the selection of an extraction. Thus, this study aimed to investigate the impact of different extractions, e.g., QuEChERS, and data processing on the determination of malachite green metabolites in two different organisms, brook trout and shrimp. The results obtained confirm the need for a harmonized approach for the validation of non-target workflows, as depending on the comparison criteria, the matrix, the mode of ionization or data processing, a different extraction could be chosen. This study also identified for the first time des-methylated leucomalachite green as another metabolite in the two organisms.

A Post-pastoral Reading of Ron Rash’s “Speckled Trout”

Although popularly known for his novels The World Made Straight (2006) and Serena (2008), Ron Rash has also committed himself to an unapologetic portrayal of the rural history and shifting cultures...

Condition factor and identification of amino acid composition of three trout species in the western region of Ukraine

Indicators of the condition factor, growth rate, and quality of the final products of cultivated objects are important parameters for the effective management of cold-water fish farming. These indicators are also used as a way to control the impact of environmental factors on fish, which requires constant research in the context of intensification of the aquaculture sector. The research is aimed at determining the condition factor and the amino acid composition of muscle tissues of Salmo trutta fario (Linnaeus, 1758), Oncorhynchus mykiss (Walbaum, 1792), and Salvelinus fontinalis (Mitchill, 1814) under the conditions of the western region of Ukraine. The results of the condition factor showed that S. fontinalis had the highest value with 1.52±0.0340, and O. mykiss and S. trutta showed the lowest value with 1.33±0.0361 and 1.26±0.0181, respectively. Food conversion ratios were similar for S. fontinalis and O. mykiss (1.0), whereas S. trutta showed higher values (1.4). The specific growth rate was highest in rainbow trout. The specific growth rate was higher for rainbow trout (1.4) compared to the brook trout (1.32) and brown trout (1.28). The maximum content of protein, total amino acids (TAA), total essential amino acids (TEAA) and nonessential amino acids (TNEAA) we registered in brook trout. The muscle tissue of the investigated fish species is a well-balanced source of the nutrition energy in terms of the ratio of total essential to total nonessential amino acids (TEAA:TNEAA ratio).

Genetic Structure of Maryland Brook Trout Populations: Management Implications for a Threatened Species

AbstractBrook Trout Salvelinus fontinalis have declined across their native range due to multiple anthropogenic factors, including landscape alteration and climate change. Although coldwater streams in Maryland (eastern United States) historically supported significant Brook Trout populations, only fragmented remnant populations remain, with the exception of the upper Savage River watershed in western Maryland. Using microsatellite data from 38 collections, we defined genetic relationships of Brook Trout populations in Maryland drainages. Microsatellite analyses of Brook Trout indicated the presence of five major discrete units defined as the Youghiogheny (Ohio), Susquehanna, Patapsco/Gunpowder, Catoctin, and Upper Potomac, with a distinct genetic subunit present in the Savage River (upper Potomac). We did not observe evidence for widespread hatchery introgression with native Brook Trout. However, genetic effects due to fragmentation were evident in several Maryland Brook Trout populations, resulting in erosion of diversity that may have negative implications for their future persistence. Our current study supplements an increasing body of evidence that Brook Trout populations in Maryland are highly susceptible to multiple anthropogenic stresses, and many populations may be extirpated in the near future. Future management efforts focused on habitat protection and potential stream restoration, coupled with a comprehensive assessment framework that includes genetic considerations, may provide the best outlook for Brook Trout populations in Maryland.

A Comparison of Brook Trout Passage at Road Culverts to Broadscale Assessment Criteria in a Pennsylvania Headwater Stream

AbstractRestoring stream connectivity by replacing road culverts is a high conservation priority, yet long‐term fish passage data aimed to “ground‐truth” culvert prioritization methods are lacking. One common tool for prioritizing culvert removals is the protocol developed by the North Atlantic Aquatic Connectivity Collaborative (NAACC), which uses culvert characteristics to estimate barrier severity and fish passage. To determine the degree to which NAACC scoring reflects trout passage, we monitored Brook Trout Salvelinus fontinalis movements through three culverts and a reference site (no culvert) in a central Pennsylvania watershed. Passage was nearly continuously monitored for 16 months using remote stationary PIT tag readers. We found that NAACC ranks underestimated Brook Trout passage through two of three culverts. Specifically, the culvert with a rank of “reduced aquatic organism passage (AOP)” experienced higher rates of upstream passage (up to 10 upstream movements per day) than all other sites combined, including the reference site. The reduced AOP site also had a similar proportion of the tagged population that moved upstream (20.9%) compared to the reference site (16.9%). Of the two remaining culverts, both box culverts rated as “no AOP,” one had almost no upstream passage (only two upstream movements over the entire study) and the other had passage rates similar to the reference stream (up to four upstream movements per day). Brook Trout tended to move during high flow and the fall spawning period. We suggest that, for the streams considered in our study, the NAACC protocol may better predict upstream passage if it emphasizes culvert type and adjusts measurement thresholds in the AOP coarse screening. If these patterns are supported by studies at other locations, a more nuanced treatment of culvert type and outlet characteristics in NAACC protocols may more accurately predict Brook Trout passage through culverts.

Cohort strength and body size in co-occurring salmonids in a small stream network: variation in space and time

Trout and salmon commonly coexist in stream networks. Exploring similarities and differences among species can help explain coexistence and invasive ability. Here, we describe spatial distribution, cohort strengths and size-at-age of three co-occurring species in a small stream network. Spatial distributions varied dramatically among species; native brook trout (Salvellinus fontinalis) occupied all stream reaches, naturalized brown trout (Salmo trutta) were found in the mainstem and lower portions of tributaries and fry-stocked Atlantic salmon (Salmo salar) were limited to the mainstem. Size-at-age also differed among species, Atlantic salmon were consistently the smallest, brook trout were intermediate in size and brown trout were the largest. Despite size differences, mean lengths of brook trout and brown trout were highly correlated among years. Cohort strengths varied considerably across years but were also highly correlated for the two trout species, suggesting strong environmental control on cohort strength and a reduced role for species interactions. At low densities, we observed strong negative effects of density on body sizes and weaker effects otherwise. Overall, these results suggest differences in spatial distribution combined with similarities in response to environmental variation contribute to species coexistence in this small steam network.

Comparison of Brook Trout Abundance and Distribution in Vermont's Streams between the 1950s and the 2000s

Salvelinus fontinalis (Mitchill) (Brook Trout) abundance and distribution have declined in much of their native range in the eastern United States, with most intact habitats concentrated in the northern states. We used stream electrofishing data from the 1950s (1952 to 1960) and the 2000s (2005 to 2016) to quantify changes in the abundance and distribution of Brook Trout in Vermont over the last half century. We also investigated whether Brook Trout's co-occurrence with Salmo trutta (Brown Trout) and Oncorhynchus mykiss (Rainbow Trout) in the 1950s influenced their abundance in the 2000s and, further, whether or not the distribution or abundance of non-native trout has changed appreciably since the 1950s. Overall, Brook Trout abundance was higher in the 2000s than in the 1950s. Increased abundance was driven by increases in young of year (YOY), which was not related to the occurrence of non-native trout. Although present at fewer sites in the 2000s, non-native trout densities remained unchanged. Brook Trout distribution at the HUC-12 watershed scale was essentially identical during both time periods. This study confirms previous modeling efforts, which indicated that Brook Trout have a higher probability of persisting in higher latitude, higher elevation, and less-developed regions.

Mechanisms of density dependence in juvenile salmonids: prey depletion, interference competition, or energy expenditure?

AbstractDensity dependence is a strong regulator of animal populations, operating primarily through intraspecific competition for a limiting resource. Because food is generally limited in natural environments, it is typically assumed that increasing animal density leads to reduced individual fitness through food depletion or monopolization. However, recent work demonstrates that density dependence can occur without apparent food depletion, or with virtually unlimited resources, suggesting that other mechanisms must also be important. Alternatively, density‐dependent regulation could be achieved through increasing energy costs rather than decreasing food abundance. The relative importance of these two processes (food depletion and energy costs) and their underlying mechanisms remains unclear. Here, we manipulated the density of juvenile stream‐dwelling brook trout (Salvelinus fontinalis) in three neighboring populations over two consecutive summers to relate food availability and consumption to density‐dependent growth, survival, and their trade‐off. Despite strong patterns of density dependence and evidence of food limitation, increasing fish density did not lead to detectable prey depletion in the environment. Instead, behavioral observations suggested that increasing densities resulted in higher energetic costs, primarily via increasing interference competition and the use of less suitable foraging microhabitats. These results highlight that animal populations may be regulated by density dependence without necessarily impacting prey communities.

Distribution of trout in the Upper Ob basin

Rainbow trout Oncorhynchus mykiss (Walbaum, 1792) and brown trout Salmo trutta Linnaeus, 1758 are popular aquaculture species worldwide. At the same time, it is known that when these species enter natural water bodies, they are able to form self-reproducing populations and cause significant damage to native fauna due to food competition, hybridization with native species, and predation. In the basin of the Upper Ob in the second half of the twentieth century, there was not only a large aquaculture farm specializing in trout but also work was carried out to introduce trout into natural water bodies: lakes in the basins of Lake Teletskoye and the Katun river. It is known about the formation of a self-reproducing population of brook trout in Lake Lebedinoe (in the basin of the Pervaya Koksha River, a second-order tributary of the lower reaches of the Katun River), which still exists. Currently, rainbow trout is a popular object of aquaculture in southern Siberia; it is grown mainly for the purpose of organizing recreational fishing, often in water bodies that are not isolated from the river network. This determines the regular ingress of this species into rivers. Nevertheless, currently no evidence of natural reproduction of trouts in natural water in the Upper Ob basin, except in Lake Lebedinoe. However, given the high risks associated with the potential invasiveness of trouts, it is necessary to recommend a cautious attitude towards the distribution of these species and to provide for an environmental impact assessment of projects related to their cultivation in water bodies of Western Siberia.

Riparian Timber Harvest Intensity Affects Diets of Appalachian Brook Trout

AbstractStream‐dwelling Brook Trout Salvelinus fontinalis rely heavily on terrestrial invertebrates, especially when aquatic prey is limited. We examined the effects of an experimental harvest of riparian timber on the diet and condition of Brook Trout in late summer. We evaluated the effects of two riparian harvest intensities (50% and 90% of the basal area harvest) in each of two streams on the diet, consumption, abundance, and condition of Brook Trout in summer. The diets and consumption patterns of Brook Trout were affected by the percentage of riparian timber harvest. Timber harvest increased the use of aquatic invertebrates—primarily via increased consumption of crayfish. In the 90% treatments, the use of terrestrial invertebrates by Brook Trout declined primarily due to the decreased use of Lepidoptera. Overall, consumption levels in the 50% treatments were nearly double those in the reference or 90% treatments. A common forestry best management practice is to limit riparian harvest to 50% of the basal area. Provided water quality and quantity are not affected, our study suggests that a 50% timber harvest limitation in the riparian area may provide at least a temporary boost in consumption due to an increase in the use of aquatic insects.