Sea Trout Salmo Trutta Research Articles

In situ infestation of sea trout Salmo trutta with salmon louse Lepeophtheirus salmonis reveals parasite-induced behavioral modifications.

In areas with high densities of salmon farming, spillover of the ectoparasitic salmon louse Lepeophtheirus salmonis poses a major threat to wild anadromous salmonids. By combining experimentally salmon louse infestation (mean ± standard deviation = 0.25 ± 0.25 lice g-1 fish) with acoustic telemetry, we studied the behavior of wild first-time migrating sea trout Salmo trutta (n = 58, fork length = 138-204 mm) from late June to September in a marine area with naturally low infestation pressure. We observed that a similar proportion of sea trout from the control and exposed groups returned to fresh water both temporarily and permanently. However, sea trout from the control group spent nearly twice the amount of time in the fjord before first freshwater detection compared to exposed individuals (32 vs. 17 days), and statistical models indicated a dose-response of louse burden on the timing of freshwater return. This effect was combined with evidence of negative impacts of salmon louse burden on overall marine residency. Sea trout predominantly utilized waters within their natal fjord during the marine migration, with exposed fish spending significantly more time close to their home river than sea trout from the control group. In summary, the behavioral modifications caused by salmon lice could reduce individual marine growth, increase long-term mortality, and ultimately harm recruitment at the population level.

Comparison of osteological characters of juveniles of freshwater and anadromous Black Sea trout Salmo trutta labrax and Atlantic salmon S. salar (Salmoniformes: Salmonidae)

A comparative analysis of juvenile anadromous and freshwater (stream) forms of the Black Sea brown trout Salmo trutta labrax Pallas, 1814 was conducted using 10 meristic and 62 morphometric characters of cranial bones. This analysis included the counts of teeth and pores in the bones, as well as measuring of their shape characters. As a basis for comparison, data on juvenile anadromous and freshwater Atlantic salmon Salmo salar Linnaeus, 1758 were used. The osteological differences between ecological forms were more pronounced in the brown trout than in the Atlantic salmon. In the brown trout, a greater number of meristic characters differentiated the forms compared to the salmon. However, for morphometric characters, the reverse pattern was observed. The freshwater forms exhibited characteristics intermediate to the anadromous forms of the two species, being more similar to the anadromous form of their species than to each other. Juvenile anadromous Black Sea trout typically had the fewest teeth, while juvenile Atlantic salmon had the most, with freshwater forms showing intermediate values. The most significant differences in the shape of cranial bones were also observed between the juvenile anadromous forms of two species. The characteristics pertaining to the number of pores in cranial bones did not reveal clear patterns when comparing the samples. Among the studied bones and characteristics, those showing the most significant differences between Black Sea trout and Atlantic salmon were identified, and species-specific features were noted. The results obtained show that juveniles of different ecological forms within the same species of the genus Salmo exhibit statistically significant osteological differences, suggesting a high genetic determination of these traits and the influence of selection within river systems on the divergence between freshwater and anadromous forms. Despite this, the variability in all studied characteristics indicates plasticity, resulting in the differences between the species and ecological forms within the genus Salmo typically not reaching the threshold for subspecies differentiation. These results align with previous studies on adult individuals and indicate that the freshwater form of the Atlantic salmon displays osteological characteristic of a more ancestral species, namely the brown trout.

CORRECTION: Temporal variation in sea trout Salmo trutta life history traits in the Erriff River, western Ireland

CORRECTION: Temporal variation in sea trout Salmo trutta life history traits in the Erriff River, western Ireland

Effect of an electromagnetic field generated by power infrastructure on the spatial orientation of developing sea trout embryos Salmo trutta Linnaeus, 1758

In recent decades, rapid technological advancements have led to a growing influence of anthropogenic electromagnetic fields on aquatic ecosystems. These fields predominantly stem from energy infrastructure facilities such as wind farms, high-voltage lines, underwater transmission cables, and power plants. As a result, there has been increasing interest in understanding the effects of heightened electromagnetic fields on aquatic ecosystems and their inhabitants, including developing fertilized eggs. This study focused on examining the effects of electromagnetic fields generated by high-voltage lines and power transformers, which are integral to transmission nodes and power plants, on the directional axis of symmetry in sea trout Salmo trutta (Linnaeus, 1758) embryos and their survival rates. The research was carried out at “PGE Dolna Odra in Nowy Czarnów”, one of Poland’s largest power plants (53°12′34′′ N, 014°28′16′′ E). Two experimental sites were selected, with electromagnetic field values ranging from 1.36 to 5.28 μT at the first site and 8.97 to 14.18 μT at the second site. A control sample was also established in an area unaffected by anthropogenic electromagnetic fields. The study findings revealed that electromagnetic fields originating from energy infrastructure facilities significantly affect the spatial orientation of sea trout embryos. The embryos’ response was influenced to be influenced by both the strength and direction of the electromagnetic fields. At the first test site, lower field values caused deviations from the natural alignment axis in the geomagnetic field (north-south), resulting in a shift towards the primary field source. In contrast, the second test site, with higher electromagnetic field values, showed no significant spatial orientation in embryo alignment. Additionally, the study highlighted that higher electromagnetic field values accelerated the rate of embryogenesis but also led to an increased mortality rate among sea trout embryos.

Digital Data Help Explain Drivers of Angler Satisfaction: An Example from Southern Norway

AbstractWe analyzed trip‐level self‐reports collected by a cell phone app to understand angler satisfaction of fishing for sea trout Salmo trutta (anadromous Brown Trout) in southern Norway. We found no clear support for a positive relationship between trip outcome (catch or no catch) and angler satisfaction level. In the cases where sea trout was caught, however, there was a positive relationship between fish size and angler satisfaction level. A total of 52% of the captured sea trout were voluntarily released, and releases were unrelated to fish size. In conclusion, digital data collected via a cell phone app are useful to reveal patterns of angler behavior and satisfaction.

Repeatability of migratory behaviour suggests trade‐off between size and survival in a wild iteroparous salmonid

AbstractRepeatable individual variation in behaviour has been demonstrated in all taxa, though few studies have explored the broader ecological consequences of such consistent behaviour.We tagged and tracked 401 individual sea troutSalmo truttawith passive integrated transponder telemetry over two to four spawning seasons as they migrated between freshwater and marine environments to spawn and feed respectively.We found the timing (time of river entry) and duration of migration (time spent in freshwater and time spent at sea) to be repeatable within individuals across years. In addition, we identified two peaks in return migration timing; a group of summer‐migrating fish and a group of fall‐migrating fish. At the time of first spawning, sea trout differed in size depending on how long the first marine phase was, but summer‐migrating fish were smaller in all subsequent spawnings. Furthermore, summer‐migrating fish had significantly better marine survival than fall‐migrating fish.Our study suggests that the timing of arrival in freshwater is an important fitness‐relevant trait, such that summer‐migrating fish have decreased fitness but remain in somewhat safer conditions, while fall‐migrating fish have increased fitness but are exposed to more risky conditions. Taken together, our findings suggest that migration timing and duration is determined via a trade‐off between size and survival, which resulted in two evolutionary stable strategies.A freePlain Language Summarycan be found within the Supporting Information of this article.

Identification of Environmental Factors that Influence the Upstream Migration of Sea Trout Salmo trutta in Shetland Waters

Migrating sea trout Salmo trutta L. in the waters of the Shetland Islands (UK) were once found in abundant numbers but they have been in decline since the mid-1980s. Therefore, it is becoming ever more critical to investigate sea trout behaviour with respect to the prevailing environmental conditions in the unique Shetland habitat so that we can determine how this prized and important species might be re-established to more sustainable levels. Here, during a period of four months (July to October) in 2015, environmental and fish catch rate data were collected for a small sample size of sea trout caught at six Shetland locations. We then looked for trends and correlations in the data that might help account for the migratory behaviour of the fish with respect to the environmental conditions at the time of capture. Our data showed that wind speed and pH correlated to the catch rate. However, no significant correlation was found between the water temperature, air temperature, barometric pressure, or humidity, and catch rate. Multivariate regression showed that wind speed and pH explained 26.3% of the variance in the catch rate. The sex ratio of the sea trout caught was skewed towards females at a ratio of 4.7 : 1.0 and the largest trout caught were all female. Recording biological data and understanding the migration patterns and behaviours of the remaining wild populations of sea trout are important for optimizing management plans to support current efforts to increase the numbers of this valuable anadromous species in Shetland waters.

Antioxidants, lysosomes and elements status during the life cycle of sea trout Salmo trutta m. trutta L.

The aim of our study was to elucidate the effects of both development stages (parr, smolt, adult, spawner), and kelt as a survival form and sex (male, female) on the functional stability of the lysosomal complex, biomarkers of oxidative stress, and element contents in the muscle tissue of the sea trout (Salmo trutta m. trutta L.) sampled in the Pomerania region (northern Poland). We have evaluated the maximal activities of lysosomal enzymes (alanyl aminopeptidase, leucyl aminopeptidase, β-N-acetylglucosaminidase, and acid phosphatase), lipid peroxidation level, and protein carbonyl derivatives as indices of muscle tissue degradation. The relationship between lysosomal activity and oxidative stress biomarkers estimated by the lipid peroxidation level and protein carbonyl derivatives was also assessed, as well as the relationships between element levels and oxidative stress biomarkers. Trends of the main effects (i.e., the development stages and sex alone, the interaction of the sex and development stage simultaneously) on oxidative stress biomarkers, lysosomal functioning, and element contents in the muscle tissue were evaluated. The study has shown sex-related relationships between the pro- and antioxidant balance and the tissue type in the adult stage as well as modifications in the lysosomal functioning induced by long-term environmental stress associated with changing the habitats from freshwater to seawater and intense migrations. The highest level of toxic products generated in oxidative reactions and oxidative modification of proteins was noted in both the spawner stage and the kelt form. The holistic model of analysis of all parameters of antioxidant defense in all development stages and sex demonstrated the following dependencies for the level of lipid peroxidation, oxidative modification of proteins, lysosomal activities, and element contents: TBARS > OMP KD > OMP AD > TAC, AcP > NAG > LAP > AAP and Cu > Fe > Ca > Mn > Zn > Mg, respectively.

System-specific salmon louse infestation thresholds for salmon farms to minimize impacts on wild sea trout populations

Salmon lice Lepeophtheirus salmonis from aquaculture can cause negative impacts on sea trout Salmo trutta and other wild salmonids. Long-term records from 5 Irish rivers were used to explore relationships between annual sea trout runs and estimated total number of lice on nearby salmon farms. It was hypothesised that local environmental conditions may result in system-specific differences in realised louse pressure on sea trout. Louse count was thus tested as an absolute number and as a relative pressure, i.e. standardised by farm. When the standardised total number of mobile lice on a given salmon farm in April was above baseline level (50th percentile of observed annual values on that farm), there was a high probability of a below-average sea trout run in the local river. Absolute louse counts did not show an important effect on runs. This finding suggests that salmon farm louse production in spring can have a strong system-specific regulating effect on wild sea trout populations. Total number of lice on a farm was most strongly driven by changes in individual infestation rate, with a lesser effect of stocking density. Thresholds for number of mobile lice per farmed salmon required to maintain total louse count below the baseline varied with stocking density and among systems: greater density required lower infestation rate. Regulations relying on a generic louse threshold to trigger treatment are not sufficient to protect sea trout populations—stocking density and site characteristics must be considered to evaluate system-specific infestation pressure and impacts on wild salmonids.

Modeling salmon lice effects on sea trout population dynamics using an individual-based approach

Salmon lice Lepeophtheirus salmonis infestation of sea trout Salmo trutta results in both additional marine mortality and behavioral changes which may contribute to sea trout population decline. For effective management of activities that increase exposure to salmon lice, such as salmon aquaculture, it is necessary to have a full understanding of how salmon lice may affect sea trout populations. An individual-based model (IBTRUTTA) was therefore developed to investigate the potential effects of salmon lice infestation on sea trout population abundance and dynamics based on data from the River Halselva and Altafjord system in northern Norway. This model allowed investigation of the effect of lice-induced mortality and also the compensatory salmonid behavioral mechanisms of premature return to freshwater, either persistent for overwintering or transitory after which sea trout could go back to sea. It was found that, in the absence of compensatory mechanisms, even low rates of lice infestation could lead to marked declines in sea trout abundance. Compensatory behavioral mechanisms had the potential to reduce these declines, but persistent premature return resulted in reduced body mass of returning adults. The shape of the stock-recruitment relationship was also shown to strongly affect how lice-induced mortality impacted the population.

Short-term homeostatic regulation of blood/interstitial fluid Ca2+ concentration by the scales of anadromous sea trout Salmo trutta L. during smoltification and migration.

The elasmoid scales of anadromous sea trout Salmo trutta L. represent a significant internal reservoir of Ca2+ . Although more is known about long-term remodelling of scales in response to calciotropic challenges encountered during smoltification and migration, very little is known about the contribution made by scales to the short-term, minute-to-minute regulation of Ca2+ homeostasis in the extracellular fluid (ECF) during these phases of the life cycle. This gap in the knowledge is partly due to the technical challenges involved in measuring small Ca2+ fluxes around the scales of live fish in real time. Here, this study describes exfoliating, mounting and culturing scales and their resident cells from parr, smolt and adult sea trout from a freshwater environment, as well as from adult sea trout caught in sea or brackish water. All the scales were then examined using an extracellular, non-invasive, surface-scanning Ca2+ -sensitive microelectrode. The authors quantified the Ca2+ fluxes, in the absence of any systemic or local regulators, into and out of scales on both the episquamal and hyposquamal sides under different extracellular calcemic challenges set to mimic a variety of ECF-Ca2+ concentrations. Scales from the life-cycle stages as well as from adult fish taken from sea, brackish or fresh water all showed a consistent efflux or influx of Ca2+ under hypo- or hypercalcemic conditions, respectively. What were considered to be isocalcemic conditions resulted in minimal flux of Ca2+ in either direction, or in the case of adult scales, a consistent but small influx. Indeed, adult scales appeared to display the largest flux densities in either direction. These new data extend the current understanding of the role played by fish scales in the short-term, minute-to-minute homeostatic regulation of ECF-Ca2+ concentration, and are similar to those recently reported from zebrafish Danio rerio scales. This suggests that this short-term regulatory response might be a common feature of teleost scales.

Effects of chronic exposure to microplastics of different polymer types on early life stages of sea trout Salmo trutta

The aim of the present study was to determine the effect of a long-term (113 days) exposure to microplastics on the development and induction of endocrine, geno- and cytotoxic responses in early life stages of sea trout Salmo trutta. Microplastic particles (3000 μm) of three most commonly mass-produced polymers (polystyrene - PS, polyethylene terephthalate - PET and polyethylene - PE) were applied in environmentally realistic concentrations (0.1% of sediment dry weight) in a laboratory experiment imitating the natural environment, typical for sea trout spawning grounds. The exposure of the sea trout, from fertilized eggs to mobile yolk-sac larvae, to microplastics did not affect the hatching success (the survival of embryos), hatching rate and the incubation period. Microplastics of any tested polymer type also had no adverse effect on the larvae survival, growth rate and the rate of yolk sack absorption. Similarly, no changes in frequencies of detected cytotoxicity endpoints compared to the control group were recorded. Exposure to polymer particles induced however the formation of genotoxicity endpoints (nuclear buds, micronuclei and blebbed nuclei cells). The level of total genotoxicity (ΣGentox) in fish larvae erythrocytes increased significantly in the following sequence: PS > PET > PE. No significant changes in the whole body corticosterone, dehydrocorticosterone and cortisone concentrations due to exposure to microplastics were recorded, while cortisol was detected in larvae exposed to PS. Our results show that long-term, non-ingestion related exposure to microplastics does not affect development of S. trutta early life stages but may lead to genotoxic responses. PS seems to be the most hazardous among all polymers studied. This is the first study demonstrating non-ingestion related toxicity of microplastics to the early life stages of fish.

Making the best of lousy circumstances: the impact of salmon louse Lepeophtheirus salmonis on depth preference of sea trout Salmo trutta

Sea trout are known for seeking out sources of freshwater to rid themselves of salmon lice. However, the effect of natural haloclines in fjords on parasite dynamics is not well understood. We tagged 48 naturally infested wild sea trout with acoustic depth sensors. The fish were kept inside a small net-pen (4 × 4 × 5 m), 12 at a time, in western Norway during 4 separate time periods in spring 2017. The sea trout were relatively highly infested with sea lice (prevalence: 100%, mean ± SD: 68 ± 58 lice fish-1), and a relatively large proportion of the individuals did not survive the trials (25% mortality). The results show that temperature and light were the 2 most important factors explaining the vertical behaviour of the surviving trout. Mobile lice also had a significant effect on depth distribution, where fish with higher abundances of lice were observed at shallower depths. During the 7 d periods in the net-pen, total sea louse abundance decreased from a mean of 68 to 35 fish-1. Surface salinity explained this reduction better than the experienced salinity of the individual fish, suggesting that short-time exposure to very low salinities, rather than long-term exposure to moderate salinities, is the driving force behind the effect of haloclines on reduction in sea lice numbers.

Trophic dynamics of anadromous brown trout and Arctic charr in NW Iceland and their correlation to salmon lice infection

Anadromous Arctic charr Salvelinus alpinus and sea trout Salmo trutta are commonly found in marine, estuarine and freshwater habitats across the Northern Hemisphere. The marine phase varies between populations but often involves summer foraging in nearshore waters while spawning and overwintering occur in freshwater. The dependence of anadromous salmonids on nearshore habitats makes them vulnerable to increased industrial activity, such as aquaculture developments, that may increase the risk of salmon lice Lepeophtheirus salmonis, infection. Lice infection in wild salmonids depends on farmed fish density but can also be correlated to environmental factors, including foraging ecology. In the current paper we examine niche use and trophic variation of co-occurring Arctic charr and sea trout in northwest Iceland, using stomach contents and stable isotope values of δ13C, δ15N and δ34S. We then test if these factors correlated to salmon lice infection. The salmonid species differed in niche use, for example, in time of marine foraging, with Arctic charr having a longer marine phase than was expected, and in the level of piscivory between both species. Moreover, we show that both environmental factors and individual trophic use are related to salmon lice infection in sea trout. This information may be useful in evaluating the risk and spatial management of sea farming.

Behaviour of adult sea trout Salmo trutta that survive or die at sea

We tagged 125 sea trout kelts (460–925 mm) in seven Danish rivers with positively buoyant DSTs. Fifty-three (42%) tags were recovered, enabling a comparison of behaviour in kelts that survived the marine period and kelts that did not. Data revealed an estimated mean survival time at sea of 14.3 days (range 1–65 days) for fish that died at sea. Fish that did not survive had lower weight/length ratios when tagged than survivors (P = 0.005) but exhibited a similar diel diving pattern while at sea. Both surviving and non-surviving fish gradually increased diving activity and the daily visited maximum depths after sea entry, but some performed fewer dives and resided in shallower depths than others. This difference was pronounced when comparing surviving fish (most active divers) with fish caught by anglers (least active divers). The results show that the first weeks at sea are critical for kelt survival and that physical status of kelts may affect behaviour and probability of survival. The preference for shallower waters and less diving activity in some individuals indicate that coastally based fisheries and recreational angling may select against specific behavioural phenotypes which should be investigated more intensively.

Behaviour of veteran sea trout Salmo trutta in a dangerous fjord system

Behaviour of veteran sea trout Salmo trutta in a dangerous fjord system

Combining empirical indicators and expert knowledge for surveillance of data-limited sea trout stocks

Abstract Inland and diadromous fish stocks can support important ecological, social and cultural functions. However, many of these stocks are data-limited and do not have formal state assessments or management reference points. Empirical surveillance indicators of relative abundance and population size-structure may provide an accessible first-step for monitoring such stocks. These indicators could be informed and interpreted via expert knowledge of specific systems and stock histories. The current study focused on an international scientific working group that met in 2017–2019. The group collated long-term monitoring data for sea trout Salmo trutta from six salmonid ‘index rivers’ in France, Ireland, Wales, Northern Ireland and Sweden. Indicators were selected, and time series of abundance- and length-based metrics for each river were presented on a new visual indicator plot. Expert knowledge from each system was elicited through one-to-one interviews to provide a corresponding stock narrative, in which indicator trends reflected known historical pressure-state events. The accessible presentation of simple empirical indicators supports elicitation of local expert knowledge, and provides an accessible framework for surveillance and reference-direction assessment of data-limited sea trout stocks. This approach could be applied to inland or diadromous stocks where available data are restricted to estimates of relative abundance and size-structure.

Formation of an antioxidant profile in the sea trout (Salmo trutta m. trutta L.) from the Slupia River

Using a stage- and sex-based multivariate significance tests on the sea trout Salmo trutta m. trutta L. model, we show dependencies in the balance between lipid peroxidation processes, levels of carbonyl derivatives, and activity of antioxidant enzymes (superoxide dismutase SOD, catalase CAT, glutathione reductase GR, and peroxidase GPx) in the processes of antioxidant profile formation during the fish growing process. The study was aimed at examination of the relationships between the biomarkers of oxidative stress estimated by the total antioxidant status as well as the dependencies between the sex (male, female) and developmental stage of the wild sea trout from the Slupia River and its catchment area rivers. Functioning of the pro/antioxidant balance of the liver tissue reflected the course of the individual developmental stages of the trout and was associated with significant intensification of lipoperoxidation, oxidative modification of proteins, and reduction of the total antioxidant capacity of fish along with age. Formation of a holistic model for the analysis of the involvement of all parameters of antioxidant protection in all stages of development and sex allowed us to obtain the following rank order for the level of lipoperoxidation processes, modified proteins, and antioxidant enzyme complex: CAT > SOD > GPx > GR and TBARS > OMP KD > TAC > OMP AD.

The effect of static magnetic field on melanophores in the sea trout (Salmo trutta m. trutta Linnaeus, 1758) embryos and larvae

AbstarctMagnetic field affects many living organisms, fishes included. The fish reactions are observed from the early stage of development, during embryogenesis and larval period, and into adult stage. Magnetic field affects, among other processes, water exchange in the eggs, embryo heart rate and respiration, directional reactions and spatial orientation. The few papers in this field published so far present melanophores morphology and development. Melanophores developing in embryos and in newly hatched sea trout (Salmo trutta m. trutta L.) larvae which had been incubated and kept under optimal conditions constituted the material for the study. The effect of static, generated magnetic field of intensity of 1, 3 and 5 mT on melanophores of sea trout embryos and larvae was studied. The control setting was kept under geomagnetic field. The appearance of melanophores in the trout embryos exposed to magnetic field was delayed. The number of melanophores was smaller, and the movement of melanin within the melanophores, visible as aggregation of pigment in the cells. Static magnetic field of relatively low intensity influences the reaction of melanophores of developing trout embryos and newly hatched larvae. Most probably, magnetite (Fe3O4) compounds, detected in many fish species, mainly migratory fishes such as trout, are responsible for such behaviour of melanophores.HighlightsStatic magnetic field delays the appearance of melanophores in the trout embryos and larvae.The largest aggregation of melanin in melanophores was found in larvae incubated in a 5 mT magnetic field.The largest number of melanophores was found in the embryos incubated in the geomagnetic field.

Temperature and depth preferences of adult sea trout Salmo trutta during the marine migration phase

Temperature and depth preferences of adult sea trout Salmo trutta during the marine migration phase