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Stocking can affect population density but may influence fish growth responses to changes in environmental conditions. In a multi‐year field experiment, we investigated the interactive effects of density and temperature on the growth of young‐of‐the‐year anadromous brown trout in streams stocked with wild‐origin hatchery‐reared brown trout. Fish origin was the predominant factor influencing growth rate, thereby highlighting the importance of discriminating between wild and hatchery‐reared individuals. Growth was positively related to temperature (degree‐days) and negatively related to density, with the growth response to temperature modulated by density. Temperature had a more pronounced effect on juvenile growth at low density than at high density. The reduced growth response to temperature caused by density could reduce population resilience and should be considered in management and conservation strategies. [ABSTRACT FROM AUTHOR]

ABSTRACT Sustainable management of recreational fisheries requires balancing angler attitudes and behaviour with fisheries' biological potential. Herein, we investigated the balance in the sea‐run brown trout (Salmo trutta) fishery around the Swedish island of Gotland using data collected through a creel survey, test fishing, and spawning returns to selected streams. Anglers accurately anticipated catches of large fish but underestimated the role of natural reproduction in supporting the stock. Female sea trout entering spawning streams and post‐spawn sea trout caught on the coast were significantly larger than spawning males and non‐spawned fish, and were particularly important for the fishery. Larger sea trout also faced a higher level of harvest pressure than other sizes. Small changes to angler preferences, harvest rates, or regulations could significantly influence characteristics and sustainability of this fishery. The scale and direction of these changes merit further investigation. [ABSTRACT FROM AUTHOR]

Dispersal is a ubiquitous ecological process that has been extensively studied in many plants and animals. Anadromous salmonids are an interesting system for examining dispersal, in part because of their well‐known philopatric behaviour, but also because of the conservation challenges related to the dispersal of hatchery‐origin fish. Building on earlier work, we provide an updated systematic review of dispersal and gene flow in anadromous salmonids. In particular, we compared studies on the dispersal of anadromous salmonids from wild and hatchery origins, including studies providing estimates of dispersal rates, observations of dispersal and results from modelling studies. We reviewed 228 studies and found these were unevenly distributed among species, with Atlantic salmon, Chinook salmon and sea trout being well‐represented. Our results showcase considerable variability in estimated dispersal rates within and across studies, which is likely related to the different methodologies, dispersal propensities across species and populations, and spatial extents considered. Overall, our results confirmed a higher tendency of hatchery fish to disperse relative to wild fish, but we also found some variation across species that warrants further study. Moreover, we found that dispersal propensity tended to decline exponentially with distance and that the drivers of dispersal varied considerably among studies. Additionally, we highlight various facets of dispersal captured across this suite of studies, including variation in terminology, methods and metrics for characterising dispersal, and the spatio‐temporal scales considered. Finally, our review revealed that few studies considered, and even fewer assessed, the implications of dispersal for the conservation and management of anadromous salmonids. [ABSTRACT FROM AUTHOR]

Genetic data have greatly increased means to understand fish marine migration behaviours at large spatial scale within a quantitative framework. The anadromous sea trout is a prized target of recreational fishery and an important ecosystem component in freshwater and marine coastal habitats in large parts of temperate northern Europe. Nonetheless, little is known about population distributions while feeding at sea. To reconcile notions about feeding migrations being predominantly locally restricted or not, we used SNP data for 3465 trout representing >100 rivers to identify population origins of 903 coastally feeding fish captured throughout the North Sea-Baltic Sea transition area. Across areas, coastal collections generally showed marked stock-mixing and overall 70:30% native:non-native fish with seasonal variation corresponding with spawning run timing. Data revealed strong spatial feeding segregation between trout from the Scandinavian Peninsula and the European continent. This is surprising given the short distances between areas, but is in alignment with strong genetic differentiation between populations in these areas. Estimation of stock complexity of coastal feeding aggregations showed no spatial trend through the North Sea-Baltic Sea transition area otherwise characterized by strong environmental clines. Analyses of scale samples collected in the 1950s indicate that stock-mixing was consistent over almost 70 years. [ABSTRACT FROM AUTHOR]

Sea trout, the anadromous ecotype of the species Salmo trutta, are subject to multiple threats, including exploitation and aquaculture impacts in the marine environment, habitat fragmentation and pollution in freshwaters, loss of genetic resilience due to interbreeding with hatchery strains and environmental change. Small streams contribute relatively little biomass to European sea trout stocks but are thought to be important in maintaining genetic diversity and therefore wider population resilience. The current study combined data from acoustic telemetry, stable isotopes, genetics and scalimetry to assess the current status of sea trout in the rivers Stiffkey and Glaven, two locally important chalkstreams in East Anglia, UK, to provide an evidence base for future management. The incidence of anadromy was low, and most sea trout were near migrants, residing in the lower reaches of rivers and close to the tidal outfalls. A small number migrated to the North Sea where they were vulnerable to exploitation in the coastal fishery, which comprises a mixed stock. Straying between the two rivers was recorded among 10% of sea trout, leading to apparent high gene flow. Nonetheless, genetic data also demonstrated structuring of River Glaven trout into two distinct groups. Quantification of patterns of freshwater and estuarine habitat use, and of passage at cross-channel obstructions, was used to identify where remedial measures such as habitat restoration would be most effectively targeted. Findings are discussed in the context of local supplementary stocking and the potential impact of the nearshore fishery on limited and vulnerable small stream anadromous trout populations. [ABSTRACT FROM AUTHOR]

As a predatory fish that migrates between freshwater and marine environments, the sea trout (Salmo trutta) is important in linking these systems. This study investigated movement patterns of sea trout in a coastal fjord at the Swedish Skagerrak region from August 2018 to January 2019, using acoustic telemetry, while assessing these against environmental variables across different spatial and temporal scales. Six acoustic receivers were deployed in the fjord and a river, which flows into the upper reaches of the fjord, with the aim of detecting 20 sea trout that had been tagged with acoustic transmitters. Sea surface temperature and winds (east–west) affected movement patterns of the sea trout the most, while changes in atmospheric pressure were also important, but to a lesser extent. Sea surface temperature and atmospheric pressure both had a positive relationship with the number of detections, whereas stronger winds from the east (i.e. from land) resulted in more detections than stronger winds from the west (i.e. from the ocean). In addition, interesting diel (day–night) movement patterns were observed for some fish. A significant positive correlation was also discovered between the weight of the fish and the number of detections. This study offers insight in movements of sea trout that use coastal habitats and how environmental conditions can affect movement patterns in a fjord system. To further our understanding of sea trout movement patterns and connectivity, tracking from river, through fjord, out to sea and at a longer time scale with more variation in fish size would be valuable to understand more about the complex movement dynamics of this important species. [ABSTRACT FROM AUTHOR]

The high plasticity, or the ability to differentiate into various cell types, and capacity to become both gametes of early-stage germ cells (eGCs) allows them to be used for the long-term storage and recovery of genetic information. In this study, species-specific protocols (isolation period, enzymatic separation solution, incubation period, appropriate cryoprotectant, and cryopreservation protocol) were established for the isolation and long-term preservation of Black Sea trout eGCs. In addition, the difference between the application of cryopreservation to the whole gonad tissue and to the enzymatically separated cells has been shown in terms of viability and the number of cells obtained. According to the cell count made from the histological sections of the testicular tissue throughout the year, the period with the highest concentration of eGCs in the tissue is between May and June. To identify the optimal enzymatic dissociation solution, we subjected testicular tissues to digestion using various combinations of trypsin (T) and collagenase (C) (0.3-0.5% T and 0.1-0.3% C). Our findings revealed that the 0.3% C provided the highest yield of viable cells (90.9%). We cryopreserved the enzymatically dissociated cells (EDCs) using six different cryoprotectants (Dimethyl sulfoxide, Glycerol, and CryoSOfree™, in both L-15 and phosphate-buffered saline -- PBS mediums). Additionally, whole tissue exclusively with CryoSOfree™. After storing the samples at -152 °C for two years, the group of EDCs cryopreserved in L15+Glycerol exhibited the highest viability at 93.3%. Meanwhile, the whole tissue group yielded the greatest number of cells per ml after thawing, with a count of 33 210 000 cells. When considering both the viability (91.11%) and the number of cells obtained (33 210 000 cells/ml), the whole tissue cryopreservation group outperformed all the other methods. [ABSTRACT FROM AUTHOR]

Populations of anadromous brown trout, also known as sea trout, have suffered recent marked declines in abundance due to multiple factors, including climate change and human activities. While much is known about their freshwater phase, less is known about the species' marine feeding migrations. This situation is hindering the effective management and conservation of anadromous trout in the marine environment. Using a panel of 95 single nucleotide polymorphism markers we developed a genetic baseline, which demonstrated strong regional structuring of genetic diversity in trout populations around the English Channel and adjacent waters. Extensive baseline testing showed this structuring allowed high‐confidence assignment of known‐origin individuals to region of origin. This study presents new data on the movements of anadromous trout in the English Channel and southern North Sea. Assignment of anadromous trout sampled from 12 marine and estuarine localities highlighted contrasting results for these areas. The majority of these fisheries are composed predominately of stocks local to the sampling location. However, there were multiple cases of long‐distance movements of anadromous trout, with several individuals originating from rivers in northeast England being caught in the English Channel and southern North Sea, in some cases more than 1000 km from their natal region. These results have implications for the management of sea trout in inshore waters around the English Channel and southern North Sea. [ABSTRACT FROM AUTHOR]

Habitat fragmentation may cut off anadromous salmonids from parts of their potential native habitat and separate previously connected populations. Understanding the consequences of this is vital for fish management and prioritization of restoration activities. Here, we show that there is a significant difference in the body morphology, physiological stress response, and aspects contributing to aerobic capacity between juvenile anadromous brown trout, Salmo trutta, collected at a downstream site and an upstream site, separated by 2 km and several challenging stream sections, in a small unfragmented stream system in western Sweden. Following a standardized stress test, there were significant differences between fish from the upstream and downstream sites (plasma cortisol concentration, plasma osmolality, hematocrit, hemoglobin concentration, and mean corpuscular hemoglobin concentration). Plasma glucose concentration did not significantly differ between fish from the two sites. Fish from the upstream site had larger spleen mass, although there was no evidence of differences in ventricle mass or proportion of compact ventricular myocardium. These physiological differences indicate local variation in stress response and highlight the importance of considering local trait variation in river management. If a section of the river becomes fragmented or degraded, and there are differences in the juveniles in different parts of the river, the consequence for the population might be larger than the proportional loss of habitat. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study investigates the effect of large woody debris (LWD) on the abundance of juvenile Atlantic salmon (Salmo salar, L.) and anadromous brown trout (Salmo trutta, L.) in semi‐alluvial side channels of the river Aurlandselva (Norway) using point electrofishing and microhabitat mapping. Not the presence of LWD, but stream bed shelter availability and the distance to spawning grounds affected the fish abundance (fish/point), independent of other habitat components. LWD showed only an effect on fish abundance when in interaction with other habitat components. This discrepancy can be explained by the availability of cavities in the shelter‐rich coarse substrate which provide sufficient cover and territory for juvenile fish at the given carrying capacity of river Aurlandselva. Whilst LWD may be most effective to provide shelter in lowland streams (bed slope <0.005), maintaining or restoring shelter‐rich coarse substrates should be considered a key priority in steeper salmonid rivers and associated semi‐fluvial streams. [ABSTRACT FROM AUTHOR]

Shallow coastal systems act as nursery habitat for many species of fish and macroinvertebrates. Juveniles of these species may show selective use of certain habitat types over others, but the degree of such selectivity is not well studied for many species. Analysis of habitat selectivity is often hindered by inherently different gear types used in the habitats examined, which may not allow for direct comparison between the habitats. Here, we carry out nekton catches in the fringing marsh, using fyke nets, and in the adjacent seagrass habitat, using trawls, in the northern Gulf of Mexico to assess the relative use of the two habitats by the juveniles of six widespread important species. To resolve issues of gear comparability between fyke nets and trawls, we develop a habitat use index (HUI S) . The results reveal a consistent trend where, in relation to pinfish, speckled sea trout shows slightly higher (from 8.4 to 66.9 times); American silver perch and brown shrimp show moderately higher (from 2.3 to 369.4 times); and blue crab and white shrimp show greatly higher (from 90.6 to 2366.4 times) use of marsh over seagrass habitat. Thus, while similar in direction, differences in the use of marsh over seagrass habitat in relation to pinfish were more pronounced in some sites. We propose an index that can resolve issues of gear comparability and improve our understanding of coastal habitat selectivity by fish and macroinvertebrates. [ABSTRACT FROM AUTHOR]

Salmonids are well known for their natal homing behaviour, meaning they return to breed in the same area where they originated. However, not all individuals return to their natal breeding grounds—a behavioural trait known as straying. The prevalence of straying is difficult to explore and therefore quantitative estimates for straying are seldom reported. In this study, otolith microchemistry and genetics were combined to investigate patterns of straying over ecological and evolutionary time, respectively, between neighbouring rivers flowing into Mariager fjord, Denmark. Otolith microchemistry was used to determine the river of origin for sea trout (Salmo trutta) upon their return to freshwater and 288 SNP markers were used to determine genetic structure among the rivers in the fjord. In this system, where the distance between rivers is short, otolith microchemistry achieved 80% accuracy in assigning juvenile brown trout to their natal river, thus allowing us to determine that approximately 43% of the adult sea trout had returned to non‐natal rivers to spawn, with a similar proportion of strayers and natal homers in all of the rivers. Genetic analysis further supported that there was substantial gene flow among individuals originating from different rivers, indicating that sea trout in Mariager fjord make up one population. The findings obtained from otolith microchemistry and genetics complement each other and provide further evidence that sea trout in this system migrate to non‐natal rivers and spawn there, which consequently affects the genetic structure of the population. [ABSTRACT FROM AUTHOR]

Several countries have implemented stocking programmes to enhance abundance and fish production by releases of hatchery-reared fish. However, due to fluctuations in population size, stocking history, and potential indirect effects of straying of hatchery-reared fish, it is often difficult to predict how these factors will affect genetic diversity and differentiation patterns among wild populations. This study characterized the population genetic structure and temporal variability of four Estonian sea trout populations by evaluating the degrees of direct and indirect genetic impacts of stocking over two decades using 14 microsatellite loci. Our results demonstrate considerable temporal change combined with weak genetic structuring among studied sea trout populations. We found a reduction of the overall level of genetic differentiation combined with the tendency for increased genetic diversity, and an effective number of breeders (Nb) over the study period. Furthermore, we found that immigration rates (m) from hatchery stocks were highest in the population subjected to direct stocking and in non-stocked populations that were located geographically closer to the stocked rivers. This work suggests that hatchery releases have influenced the genetic diversity and structuring of studied sea trout populations. However, the impact of hatchery releases on the adaptive variation and fitness-related traits in wild trout populations remains to be revealed by more informative genetic markers. This study illustrates the dynamic nature of the population genetic structure of sea trout and the value of long-term genetic monitoring for management and conservation. [ABSTRACT FROM AUTHOR]

Anadromous brown trout (Salmo trutta) in the northeastern Atlantic Ocean, and coastal cutthroat trout (Oncorhynchus clarkii clarkii) in the northeastern Pacific Ocean, are analogs in many ways. Both species display similar patterns of complex life histories and behavioral flexibility, are iteroparous and facultatively anadromous and occupy nearshore coastal marine habitats where numerous populations often mix. These characteristics create specific challenges for management and conservation that have been complicated by inadequate scientific attention in some areas. Both species are declining across their native range, and their ecology make them particularly vulnerable to habitat destruction, fishing, and climate change. Here, we review the available literature to compare the biology, ocean ecology, and management practices of these two species. We highlight ecological similarities and differences between the species and identify current knowledge gaps suggesting future research needs and management actions. Using a comparative approach, the review aims to promote and facilitate knowledge exchange between anadromous trout research communities from opposite sides of the globe to improve management and conservation of these species and stimulate the production of management plans specific to anadromous trout. [ABSTRACT FROM AUTHOR]

Every year, ulcerative dermal necrosis (UDN) affects salmonids that spend most of their lives in the sea during their migration to the rivers of northern Poland to spawn. The clinical form of the disease manifests itself in ulcerative skin lesions, which lead to significant weakening of the fish and, in most cases, result in their death. This study was carried out on samples taken from sea trout in the Słupia River in northern Poland. In order to identify the pathogen, experiments on the transmission of the disease were carried out, and additional histopathological, microbiological and electron microscopic examinations were performed. As a result of these studies, it was possible to experimentally transfer the disease from sick to healthy fish. The results indicate a complex etiology of the disease (lack of a clearly defined pathogen), in which the change in the environment from salty to freshwater triggers the related changes in skin physiology, which are the main causes of increased susceptibility to the development of the disease. [ABSTRACT FROM AUTHOR]

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The state of sea trout in 1251 Norwegian watercourses was assessed based on a scoring system for human pressures, abundance data, and local knowledge.Over 16,000 km of rivers and lakes were available to sea trout in these watercourses, spanning from the temperate to Arctic regions.Sea trout were classified to be in a good or very good state in fewer than 25% of the watercourses and in a poor or very poor state in almost 40%. Twenty‐nine watercourses had lost their sea trout populations.Salmon lice from aquaculture salmon farms had by far the largest adverse effect on sea trout among the human impact factors, both in the number of watercourses (83%) and river area affected (60%), and the total effect on sea trout abundance.Agriculture and hydropower production also had strong adverse impacts (35% and 19% of watercourses), but substantially lower than that caused by salmon lice. Culverts related to road crossings and other habitat alterations also had impacts on sea trout in many watercourses (27%).Exploitation of sea trout has been reduced in Norway in recent years, both in the marine and freshwater fisheries. Yet, the exploitation pressure was moderate or high in almost 14% of the watercourses where the state of sea trout was poor or very poor, suggesting a high potential for overexploitation in these.The state of sea trout was best in the northern sparsely populated areas. However, distribution of watercourses with sea trout in a poor or very poor state was more linked to aquaculture, agriculture, and hydropower production than human population density.The developed approach for large‐scale mapping of state and pressures, which is vital for prioritizing management measures, may inspire other nations in their conservation effort for this important species. [ABSTRACT FROM AUTHOR]

Abstract Background The balance of the intestinal commensal microbiome of fish and other animals plays an important role in the physiological processes of healthy animals, contributes to the defense against pathogens, stimulates the immune system and facilitates nutrient metabolism. In the last decade, the interest in the application of the insects in fish nutrition increased, although little is known regarding the effects of insect meals on the gastrointenstinal tract microbiome of the sea trout fingerlings. The aim of this study was to evaluate the effect of two diets containing mealworm (MW) and superworm (SW) on the microbiome of the digesta of sea trout fingerlings and the relative abundances of different taxa among communities under controlled conditions. Results The insect meals produced a similar weight gain and survival rate to sea trout fed fishmeal. The most abundant bacterial phylum in all the treatment groups was Firmicutes followed by Proteobacteria and Actinobacteria, and significant differences in the amount of Cyanobacteria were observed in the SW group. Conclusions The insect meals did not produce differences in the three most abundant phyla in the sea trout digesta. However, the effect of each type of meal on the lower taxonomic levels was evident, particularly in the case of the superworm meal. These microbiome differences indicated that mealworm meal was more related to fishmeal than superworm meal. Our results highlight the potential effects of insect meals, such as mealworm and superworm meals, on the microbiota of sea trout.

Juvenile salmonids often experience high mortality rates during migration and bird predation is a common source of mortality. Research suggests that hatchery‐reared salmonids are more prone to predation than wild salmonids, and that Atlantic salmon (Salmo salar) experience lower predation than Sea trout (Salmo trutta), yet telemetry studies have displayed equivocal results. Here, using a large data set on passive integrated transponder (PIT) tagged hatchery‐reared and wild juveniles of Atlantic salmon and Sea trout (25,769 individuals) we investigate predation probability by piscivorous birds (mainly Great Cormorants Phalarocorax carbo) on salmonids originating from River Dalälven in Sweden. Bird colonies and roosting sites were scanned annually (2019–2021), and the temporal dynamics of bird predation on salmonids released in 2017–2021 was assessed. Hatchery‐reared trout was clearly most susceptible to cormorant predation (0.31, 90% credibility interval [CRI] = 0.14–0.53), followed by wild trout (0.19, 90% CRI = 0.08–0.37), hatchery‐reared salmon (0.13, 90% CRI = 0.07–0.23), and wild salmon (0.08, 90% CRI = 0.04–0.14), in subsequent order. This order in predation probability was consistent across all studied tag‐ and release‐years, suggesting that the opportunistic foraging of cormorants affects the overall survival of juvenile salmonids, but that the inherent predation risk between different salmonid types differs systematically. [ABSTRACT FROM AUTHOR]

Brönmark et al. [[15]] discuss the importance of whole-lake studies and replicated pond systems as an innovative experimental infrastructure, to study animal movement and ecology. Fish tracking data are used to compare catchability, fine-scale movement, emigration from the lake and natural mortality of triploid and regular diploid fish, and coupled with data from traditional stock assessments. One of the most important tasks of ecology is to understand how animals use space and time. [Extracted from the article]

Many Norwegian rivers and lakes are regulated for hydropower, which affects freshwater ecosystems and anadromous fish species, such as sea trout (Salmo trutta). Lakes are an important feature of many anadromous river systems. However, there is limited knowledge on the importance of lakes as habitat for sea trout and how hydropower affects the behaviour of sea trout in lakes. To investigate this, we conducted an acoustic telemetry study. A total of 31 adult sea trout (532 ± 93 mm total length) were captured by angling in river Aurlandselva, Norway, and tagged between July 20 and August 12, 2021. The tags were instrumented with accelerometer, temperature, and depth sensors, which provided information on the sea trout's presence and behaviour in lake Vassbygdevatnet. Our results indicate that there was a large prevalence of sea trout in the lake during the spawning migration, and that the sea trout were less active in the lake compared to the riverine habitats. An increase in activity of sea trout in the lake during autumn might indicate that sea trout spawn in the lake. However, the discharge from the high-head storage plant into the lake did not affect the depth use or activity of sea trout in the lake. Furthermore, the large prevalence of spawners in the lake during autumn will likely cause an underestimation of the size of the sea trout population in rivers with lakes during annual stock assessment. In conclusion, our results could not find evidence of a large impact of the discharge on the behaviour of sea trout in the lake. [ABSTRACT FROM AUTHOR]

The aim of the study was to determine the influence of diets (factor D) and the time period (factor T) during which they were applied on the growth performance and physiological condition (blood plasma hematological and biochemical indicators of stress and immunity) in juvenile sea trout (Salmo trutta; initial body weight approximately 73 g). The diet of the fish that was used prior to the experiment (formulated feed; initial fish sample) was modified as follows: a different formulated feed (group B), mixed feed (feed B + prey fish; group B/N), prey fish exclusively (group N). The fish from group A were given the feed that was used prior to the beginning of the experiment. During the 28-day trial neither factors D nor T influenced absolute or relative fish growth rates. Factor D significantly influenced hematological indicators and leukograms, while the phagocytic index and cidal ability were determined by the time test (factor T). Myeloperoxidase (AMPO) was related significantly with the influence of factors D and T and also with the interaction of D×T. A significant decrease in AMPO was noted after two weeks of the test in groups B, N, and B/N, but after four weeks this indicator did not differ from that confirmed in the initial fish sample. The factors tested influenced stress indicators, i.e., cortisol (D and T) and glucose (D). Significant increases in cortisol (group B) and glucose (groups A, B, and B/N) concentrations were noted after two weeks of the test. After the subsequent two weeks (four weeks of the test) these indicators also stabilized. Sea trout from aquaculture readily accept prey fish; however, changes in diet cause stress reactions such as temporarily reduced immunity. Thus, the procedure for preparing sea trout stocking material for release, which is to change the feed from formulated to natural (live fish), should last approximately four weeks. [ABSTRACT FROM AUTHOR]

Proliferative kidney disease caused by the myxozoan parasite Tetracapsuloides bryosalmonae has been actively studied in juvenile salmonids for decades. However, very little is known about parasite prevalence and its geographical and intra‐host distribution at older life stages. We screened T. bryosalmonae among adult sea trout (Salmo trutta) (n = 295) collected along the Estonian Baltic Sea coastline together with juvenile trout from 33 coastal rivers (n = 1752) to assess spatial infection patterns of the adult and juvenile fish. The parasite was detected among 38.6% of adult sea trout with the prevalence increasing from west to east, and south to north, along the coastline. A similar pattern was observed in juvenile trout. Infected sea trout were also older than uninfected fish and the parasite was detected in sea trout up to the age of 6 years. Analysis of intra‐host distribution of the parasite and strontium to calcium ratios from the otoliths revealed that (re)infection through freshwater migration may occur among adult sea trout. The results of this study indicate that T. bryosalmonae can persist in a brackish water environment for several years and that returning sea trout spawners most likely contribute to the parasite life cycle by transmitting infective spores. [ABSTRACT FROM AUTHOR]

Since 2007 in Poland, skin lesions have been observed in salmon (Salmo salar L.) and sea trout (Salmo trutta L.) entering Pomeranian rivers to spawn. The clinical picture of affected fish resembled ulcerative dermal necrosis (UDN), a disease of unknown etiology affecting mainly the scalps of wild salmonids. The aim of the 2009-2012 study was to determine with microbiological tests the etiological agent of the skin lesions observed in salmonids entering the Pomeranian rivers. During the study, a total of 13 species of Gram-negative bacteria belonging mainly to the Yersiniaceae, Enterobacteriaceae, and Pseudomonadaceae families were isolated and identified from the skin and kidneys of diseased fish. The Gram-positive bacteria isolated were aerobic, hemolytic granules of the genus Streptococcus. Mycological examinations on damaged fish body surfaces revealed yeasts of the genus Rhodotorula and fungi of the family Saprolegniaceae. The results of our study did not permit us to identify unequivocally the direct cause of the fish diseases analyzed since all the bacteria isolated during the study are normally found in aquatic environments. Some of the isolated bacteria identified were assumed to be potentially pathogenic to fish. The fungal infections observed were probably secondary and only exacerbated ongoing disease processes.

Background: The balance of the intestinal commensal microbiome of fish and other animals plays an important role in the physiological processes of healthy animals, contributes to the defense against pathogens, stimulates the immune system and facilitates nutrient metabolism. In the last decade, the interest in the application of the insects in fish nutrition increased, although little is known regarding the effects of insect meals on the gastrointenstinal tract microbiome of the sea trout fingerlings. The aim of this study was to evaluate the effect of two diets containing mealworm (MW) and superworm (SW) on the microbiome of the digesta of sea trout fingerlings and the relative abundances of different taxa among communities under controlled conditions. Results: The insect meals produced a similar weight gain and survival rate to sea trout fed fishmeal. The most abundant bacterial phylum in all the treatment groups was Firmicutes followed by Proteobacteria and Actinobacteria, and significant differences in the amount of Cyanobacteria were observed in the SW group. Conclusions: The insect meals did not produce differences in the three most abundant phyla in the sea trout digesta. However, the effect of each type of meal on the lower taxonomic levels was evident, particularly in the case of the superworm meal. These microbiome differences indicated that mealworm meal was more related to fishmeal than superworm meal. Our results highlight the potential effects of insect meals, such as mealworm and superworm meals, on the microbiota of sea trout. [ABSTRACT FROM AUTHOR]

Anadromous brown trout display a continuum of life-history strategies with high intraspecific variability across their distribution range. While many of these strategies have been widely studied, some have received considerably less attention. In this study, we investigated intraspecific differences in two overlooked life-history strategies—outmigration phenology (spring vs. autumn migrants) and the prevalence of straying—in brown trout originating from four rivers flowing into the same fjord system. Juvenile brown trout (Salmo trutta) were tagged with passive integrated transponder (PIT) tags in their natal river, and were subsequently followed during their outmigration and subsequent return to freshwater. We found that patterns of outmigration (spring vs. autumn migrant, day of season) and return to freshwater (return likelihood, strayers vs. nonstrayers) differed between rivers, as did the factors (length, condition) affecting these outcomes. We also found evidence that outmigration phenology was linked to the likelihood of returning in a river-specific way. Our findings suggest that the costs and benefits of autumn migration and straying differ depending on an individual's home river. [ABSTRACT FROM AUTHOR]

Salmo caspius Kessler, 1877 is one of the most commercially important species of Salmonidae in the southern basin of the Caspian Sea. The occurrence of its wild populations has undergone sever reduction during the last years. In spite of the yearly restocking activity, still no progress on the recovery of its wild population has been observed. Hence, the present study was done in order to assess the efficiency of the current restocking activity in the southern Caspian basin in term of genetic diversity. DNA extracts of 32 S. caspius from four different groups were screened using 62621 genome-wide single nucleotide polymorphisms (SNP). The overal genetic diversity and Fst values were 0.18 and 0.08, respectively. Considering the observed admixture pattern and the positive values for inbreeding coeficient it seems that S. caspius suffers from its small effective population size. In order to obtain the maximum performance, alonside with expanding the size of brood stocks, rehabilitation of the habitats and spawning rivers of this nationally endangered species is of great importance. [ABSTRACT FROM AUTHOR]

This research determined the element values, selenium, and mercury balance of the large rainbow trout (Oncorhynchus mykiss) cultured in the Black Sea and the possible health risk for the consumer. By the end of the investigation, the concentration of components in these cultivated large rainbow trout in the Black Sea met the requirements specified by national and international legislation. According to analyses of the hazard risk associated with consuming, it has been determined that independent of nutritional quality, large rainbow trout produced on Turkey's Black Sea coast offers no risk to human consumption regarding element values and may be ingested safely. Health risks associated with the consumption of large rainbow trout in the Black Sea were assessed. Particularly Se had a protective effect against the effects of Hg on human health. EDI, THQ, and CRmm values did not pose a risk to human health. Biomagnification factors were low except Hg. [ABSTRACT FROM AUTHOR]

This work aims to present an historical review of the ecosystem services provided by anadromous fish (i.e., species that migrate from the sea to the river to spawn) throughout Human time, as well as of the main related threats, focusing on the Iberian Peninsula region. Anadromous fish provide important provision, cultural, regulatory and supporting ecosystem services across their distribution range and have been extensively exploited by humans since prehistoric times. In the Iberian Peninsula, sea lamprey, allis and twaite shads, sea trout, Atlantic salmon and European sturgeon were once abundantly present in several river basins covering what is now Portuguese and Spanish territory. These species have suffered a severe decline across their distribution range, mainly due to habitat loss and overexploitation. Considered regal delicacies, these fishes were once a statement on the tables of the highest social classes, a much appreciated bounty for the poorer population and are still an important part of the local gastronomy and economy. Such high economic and cultural interest encouraged intensive fishing. Currently, management efforts are being implemented, pairing habitat rehabilitation (e.g., construction of fish passes in obstacles to migration such as weirs and dams) with sustainable fisheries. Considering the present climate change scenario, these species are bound to endure increased pressures, demanding novel management approaches to ensure population numbers that are able to secure their sustainable exploitation. [ABSTRACT FROM AUTHOR]

Genetic identity analysis and PIT (passive integrated transponder) tagging were used to examine the freshwater return rates and phenotypic characteristics of n = 1791 downstream migrating juvenile Salmo trutta in the Burrishoole catchment (northwest Ireland) across the period September 2017 to December 2020. In this system, juveniles out‐migrate (move from freshwater into brackish or marine habitats) in every month of the year, with distinct seasonal peaks in spring (March through June; mostly silvered smolts) and autumn (September through December; mostly younger, unsilvered fry or parr). Both types exhibited a sex‐bias towards females, which was stronger in spring (78% females) than in autumn outmigrants (67%). Sixty‐nine returning fish were matched back to previous juvenile outmigrants, and similar return rates were found for spring outmigrants (5.0%), autumn outmigrants (3.3%) and fish that out‐migrated outside of spring or autumn (2.8%). Spring and autumn outmigrants returned at similar dates (typically mid to late July), but autumn fish were away for longer periods (median = 612 days; spring outmigrants = 104 days). Autumn outmigrants were 25% smaller than spring outmigrants at outmigration and 6% smaller on their return, and within both groups smaller/younger outmigrants spent longer away than larger/older outmigrants. Autumn outmigrants were more likely to return unsilvered as "slob" trout (84%) than spring outmigrants (31%), suggesting they make greater use of brackish habitats that might be safer, but less productive, than fully marine habitats. Nonetheless, both types also produced silvered "sea trout" (≥1+ sea‐age), implying neither is locked into a single life‐history strategy. The findings emphasise that autumn outmigrants and the transitional habitats that support their persistence should not be overlooked in salmonid management and conservation. [ABSTRACT FROM AUTHOR]

Brown trout (Salmo trutta L. 1758) and Arctic charr [Salvelinus alpinus (L. 1758)] tagged with acoustic transmitters migrated from fresh water to the sea mainly in May and June, but with large individual variation in migration timing. For S. trutta, large individuals (42–86 cm total length) migrated earlier in the season than small individuals (18–27 cm). For S. alpinus, no such pattern was found, likely because of the small size range of tagged fish (28–41 cm). S. trutta stayed longer at sea than S. alpinus (average 2 vs. 1 month). Early migrants of S. trutta stayed for a shorter period at sea than late migrants, whereas no such pattern was observed for S. alpinus. Large S. trutta moved quickly away from the river and spent average 3 days to reach a receiver line 20 km from the river mouth, whereas small S. trutta and S. alpinus migrating that far spent 2–3 weeks on the same distance. S. trutta utilized the entire fjord system and had a greater proportion of long‐distance migrants (>20 km, 78% and 59% of large and small S. trutta, respectively) than S. alpinus (29%). S. alpinus mostly stayed in the inner fjord areas, and none were recorded in the outermost part of the fjord. The difference in the use of marine areas may be caused by variation in prey choice and spatial distribution of the preferred prey groups. Stable isotope analysis showed that S. trutta had been feeding at a higher trophic level than S. alpinus. S. trutta had mainly fed on marine fish and shrimps, whereas S. alpinus had large proportions of freshwater invertebrates in the diet, suggesting that the estuary with benthos and amphipods drifting from the river was an important feeding habitat for S. alpinus. In conclusion, major differences in habitat use, migration patterns and feeding strategies were found between sympatric anadromous S. trutta and S. alpinus while at sea. [ABSTRACT FROM AUTHOR]

The longest Baltic River, the Vistula, historically hosted numerous sea trout populations. However, dam construction in the twentieth century drastically reduced the spawning migration rate. Reduced natural reproduction has resulted in a population collapse and, consequentially, a substantial reduction in catches. In response, like other Baltic countries, Poland has initiated an intensive stocking program, mainly involving smolt. Initially, stocking was conducted primarily with offspring of sea trout caught during spawning migration. Currently, due to difficulties in obtaining fish, most stocking involves fish from breeding stocks. Therefore, determining the proportion of fish derived from stocking has become an important issue. Experiments based on traditional tagging did not provide sufficient material for analysis; hence, we decided to use genetic methods based on analysis of relatedness. In this study, we performed parentage-based tagging and an analysis of the origins of parent animals used for artificial spawning in 2013, and offspring returning to the Vistula in subsequent years. We based the analysis on three different algorithms and compared the results, showing that the presented methods were effective for estimating mass stocking success. The study also indicated that a certain level of natural reproduction in the Vistula continues to occur. The proportion of sea trout from spawning in 2013 in Vistula sea trout catches from 2017 to 2018 was approximately 30%. [ABSTRACT FROM AUTHOR]

The increase in abundance of great cormorants (Phalacrocorax carbo sinensis) over the last decades has caused concern for the sustainability of fish populations. Cormorants are opportunistic piscivorous birds that eat fish from a wide range of species and sizes, in marine, lacustrine and riverine habitats. It has been documented that juvenile salmonids are under significant predation pressure by great cormorants, although knowledge on the predation of adult salmonids by cormorants is limited. In this study, adult anadromous brown trout (Salmo trutta) were tagged over multiple years with PIT tags during their spawning migration in a Danish lowland river. Two nearby cormorant colonies were subsequently scanned for PIT tags to estimate predation rate. It was estimated that by minimum 15.4% of tagged adult sea trout were predated by cormorants. The majority of the individuals were predated in the river, and females were more likely to be predated than males. Moreover, length had a significant effect on predation probability: individuals between 35 and 43 cm had the highest likelihood to be predated, while smaller and larger individuals were less likely to be predated. Our findings challenge the assumption that cormorants do not prey on reproductively mature salmonids. Furthermore, predation of mature individuals may have implications for the recruitment and sustainability of the population. [ABSTRACT FROM AUTHOR]

Anisakidosis is a foodborne zoonotic infection induced by members of the family Anisakidae via the consumption of raw or undercooked fish such as sushi and sashimi. Identifying anisakid larval species is critical for the epidemiology and diagnosis of diseases caused by them. This study aimed at identifying Anisakis larvae collected from marine fish in Egyptian waters based on morphological characteristics and molecular analysis. Thirty marine fish coral trout, Plectropomus areolatus, were collected from Hurghada, Red Sea, Egypt, to investigate larval nematodes of the genus Anisakis. The larvae were detected encapsulated in the peritoneal cavity and muscle of the fish host. This examination revealed that anisakid larvae naturally infected 19 fish specimens with a prevalence of 63.33% and a mean intensity of 4.1 ± 0.40. Most of them (68 larvae: 71.57%) were found in the musculature. Morphological and morphometric analyses using light and scanning electron microscopy revealed a head region with a prominent boring tooth, inconspicuous lips, and a characteristic protruded cylindrical mucron. All larvae in this study possessed the same morphology as Anisakis Larval type I. Molecular analysis based on ITS region using maximum likelihood and Bayesian phylogenetic methods confirmed them as Anisakis typica. This is the first study to identify A. typica larvae from the commercial fish coral trout P. areolatus in Egyptian waters using morphological and molecular methods. [ABSTRACT FROM AUTHOR]

In this study, radio telemetry was used to examine the upstream spawning migration behaviour of anadromous brown trout (sea trout), Salmo trutta L., in a boreal river system, the River Isojoki, western Finland. The aim was to study the movement activity and migration characteristics of trout during the upstream spawning migration, as well as to locate the important spawning habitats and study the spawning characteristics. Furthermore, the authors analysed how flow conditions and a hydropower dam, with adjacent fishways, affected the upstream spawning migration. Tagged trout spawned in both the main stem and four tributaries, with spawning taking place from early October to November. The movement activity of radio‐tagged trout was influenced by a hydropower dam (Perus dam), with spring migrators spending prolonged periods at the dam area, postponing the migration upstream. Flow conditions affected the total time spent at the dam area, as well as the movement activity in the free‐flowing sections above the dam, with increasing flow stimulating activity. In addition, time of river ascent and location of spawning area had a significant effect on the movement activity of tagged trout. These results are further evidence that synergistic effects of flow and migratory obstacles can negatively influence migrations of anadromous fish, regardless of constructed fishways. The management of flow regimes and the efficiency of fishways are vital, as climate change will likely influence the flow and increase the water temperature of boreal river systems, further aggravating issues caused by obstacles. [ABSTRACT FROM AUTHOR]

The rivers of southern England and northern France which drain into the English Channel contain several genetically unique groups of trout (Salmo trutta L.) that have suffered dramatic declines in numbers over the past 40 years. Knowledge of levels and patterns of genetic diversity is essential for effective management of these vulnerable populations. Using restriction site‐associated DNA sequencing (RADseq) data, we describe the development and characterisation of a panel of 95 single nucleotide polymorphism (SNP) loci for trout from this region and investigate their applicability and variability in both target (i.e., southern English) and non‐target trout populations from northern Britain and Ireland. In addition, we present three case studies which demonstrate the utility and resolution of these genetic markers at three levels of spatial separation:(a) between closely related populations in nearby rivers, (b) within a catchment and (c) when determining parentage and familial relationships between fish sampled from a single site, using both empirical and simulated data. The SNP loci will be useful for population genetic and assignment studies on brown trout within the UK and beyond. [ABSTRACT FROM AUTHOR]

Reproduction represents the most energetically demanding period of life for many organisms. Capital breeders, such as anadromous sea trout (Salmo trutta), provide a particularly interesting group of organisms to study within the context of reproduction because they rely on energy stores accrued before breeding to reproduce and sustain all phenotypic and behavioral changes related to reproduction. Energy allocation into current reproduction therefore cannot be mitigated via food intake, resulting in an important life history trade-off. For this reason, exploring indexes related to energetics in salmonids can provide powerful insights into the physiological costs of reproduction. In this study, we sampled blood from and PIT tagged 232 fish captured in the wild before the spawning season. We recaptured and resampled 74 individuals (53 females and 21 males) at the end of the spawning season. Females were further divided into spawning phases (nonspawned, partially spawned, and spawned individuals), though males could not be classified as such. We compared nutritional correlates (triglycerides, cholesterol, calcium, inorganic phosphorus, and total protein), stress correlates (cortisol, sodium, potassium, chloride, and glucose), and indexes of tissue damage (aspartate aminotransferase) between initial capture and recapture as well as among spawning phases in females. We found that nutritional status decreased in all fish throughout the spawning season but that it was substantially lower in females that had spawned. We further found that spawning itself appears stressful, with elevated glucose in partially spawned females and elevated cortisol in male sea trout at recapture. Our findings thus support the idea that the cost of reproduction is energetically high and that incurred stress and a decrease in nutritional status are important physiological costs. [ABSTRACT FROM AUTHOR]

The presently reported study intended to examine the effect of the oral administration of an immunomodulator ß-glucan and ß-glucan-containing product (BGN-2) on the levels of tumor necrosis factor-alpha (TNF-a), interleukin-6 (IL-6), fish heat shock protein 70 (HSP-70), and fish growth hormone (GH) as well as growth performance of cultured sea trout juveniles. The sea trout is a migratory sea-run brown trout, Salmo trutta Linnaeus, 1758. The fish (total of 15 000) were divided into four experimental and one control group including control (consisting of basal diet) (D1); basal diet + 1 g kg-1 ß-glucan (D2); basal diet + 3 g kg-1 ß-glucan (D3); basal diet + 6 g kg-1 BGN-2 (D4); basal diet + 14 g kg-1 BGN-2 (D5). The fish fed D4 and D5 diets showed significantly higher IL-6, HSP-70, and GH expression levels than other treatments (P < 0.05). Sea trout fed D4 and D5 diets showed significant improvements in growth performance compared to the fish fed the control diet. In conclusion, our results suggest that dietary supplementation with the product BGN-2 provides great immunostimulation and could be used as an effective measure to improve growth performance in juvenile sea trout. [ABSTRACT FROM AUTHOR]

The aims of this study were to compare male and female sea trout (Salmo trutta) with respect to their hypo-osmoregulatory ability over a simulated migration to seawater and their clinical and physiological response to salmon louse (Lepeophtheirus salmonis) infection in seawater and over a simulated pre-mature return to freshwater. For this purpose, 2-year-old hatchery-reared male and female brown trout (F1 offspring of wild caught anadromous fish) were infected with salmon lice and measured for changes in plasma ions, glucose, lactate and osmolality and relative heart, liver and gonad sizes during a simulated seawater migration and thereafter a premature return to freshwater after 4 weeks in seawater (pre-adult louse). Un-infected trout served as control. Male trout used longer time to develop full hypo-osmoregulatory ability in seawater and showed a stronger response in plasma glucose and lactate following simulated premature return to freshwater, compared to female trout. Response to salmon louse was stronger in female trout, shown by stronger osmotic stress by chalimus (plasma Cl−) and pre-adult louse (plasma osmolality) and elevated relative liver size (hepatosomatic index) by pre-adult louse in female compared to male trout. Moreover, high plasma cortisol in infected female and low plasma cortisol in infected male trout produced a significant treatment–sex interaction on plasma cortisol. Lice infection intensity was initially higher in male (0.18 lice g−1) compared to female trout (0.11 lice g−1) at the chalimus stage, but equal between sexes at the pre-adult stage (male 0.15 and female 0.17 lice g−1). This study showed that female trout were better adapted for changes in water salinity, while male trout were more robust against salmon louse infection. These results suggests that the elevated salmon louse infection pressure generated by salmon farming have strong and unexplored negative effects on wild sea trout populations. Further research on this topic is vital for the conservation of wild sea trout populations. [ABSTRACT FROM AUTHOR]

Simple Summary: Infectious pancreatic necrosis virus (IPNV) causes serious disease in salmonid species, especially in fry. In 2016, we identified an IPNV infected sea trout in Lake Vänern in Sweden. Lake Vänern hosts four small populations of landlocked Atlantic salmon and sea trout that each migrate annually to two different rivers to spawn. The virus was isolated and after sequencing placed it in genogroup 6. The pathogenicity of the virus was investigated in an infection trial in Atlantic salmon, sea trout, and rainbow trout. In the trial, the novel isolate was compared to an isolate of genogroup 5, that usually cause high mortalities. By the end of the trial, the Swedish genogroup 6 isolate only caused mild infection in all three species, suggesting a low pathogenicity. In addition, the prevalence of the virus was monitored by intensified field sampling and PCR analysis from 2016–2020. During this time, the virus was not detected once, thus suggesting a prevalence in the wild of 0.2–0.5%. The low pathogenicity of the local IPNV isolate means that the salmonid populations of fish in Lake Vänern are not immediately threatened. In November 2016, infectious pancreatic necrosis virus (IPNV) was isolated from a broodstock female of landlocked sea trout (Salmo trutta) in Lake Vänern in Sweden. VP2 gene sequencing placed the IPNV isolate in genogroup 6, for which pathogenicity is largely unknown. Lake Vänern hosts landlocked sea trout and salmon populations that are endangered, and thus the introduction of new pathogens poses a major threat. In this study we characterized the novel isolate by conducting an infection trial on three salmonid species present in Lake Vänern, whole genome sequencing of the isolate, and prevalence studies in the wild sea trout and salmon in Lake Vänern. During the infection trial, the pathogenicity of the Swedish isolate was compared to that of a pathogenic genogroup 5 isolate. Dead or moribund fish were collected, pooled, and analyzed by cell culture to identify infected individuals. In the trial, the Swedish isolate was detected in fewer sample pools in all three species compared to the genogroup 5 isolate. In addition, the prevalence studies showed a low prevalence (0.2–0.5%) of the virus in the feral salmonids in Lake Vänern. Together the data suggest that the novel Swedish IPNV genogroup 6 isolate is only mildly pathogenic to salmonids. [ABSTRACT FROM AUTHOR]

This research aims to minimize the environmental impact and promote the sustainability of aquaculture by optimizing nutrient dynamics, improving water quality and enhancing species growth performance through a land-based Integrated Multi-Trophic Aquaculture (IMTA) system. The study focused on Black Sea trout (Salmo labrax), Mediterranean mussel (Mytilus galloprovincialis), and sea lettuce (Ulva lactuca), reared in interconnected tanks using Black Sea water over 90 days. The Black Sea trout more than doubled in size to 333.92 ± 6.60 g and significant improvements were observed in the specific growth rate (SGR) at 0.85% and the feed conversion ratio (FCR) at 1.38. The fish's proximate composition included 19.19% protein, 2.31% lipid, 70.35% moisture, and 1.34% ash, with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) levels at 6.06% and 13.50%, respectively. The macroalgae showed substantial growth, with a SGR of 0.34% and a weight gain of 310 ± 3.50 g. Additionally, it increased protein content by 13.41% and demonstrated significant nutrient removal efficiencies: 41.4% for nitrate, 66.7% for nitrite, and 90.8% for ammonia. EPA and DHA levels increased by 45% and 70%, reaching 4.66% and 2.19%, respectively. In contrast, the mussels experienced a weight loss, with a weight gain of −1.20 ± 0.00 g and an SGR of −0.20%. Initially, wild mussels had a composition of 77.56% moisture, 13.79% protein, 1.54% lipid, and 1.77% ash. The presence of mussels and macroalgae significantly improved water quality, notably reducing ammonia by 92.2%, nitrate by 44.6% and nitrite by 75%, benefiting the overall ecosystem. This study concludes that a land-based IMTA system enhances sustainable aquaculture by improving product quality and bioremediation, with macroalgae playing a crucial role in nutrient absorption and growth within the system. • Ulva lactuca increased its protein and lipid content by 13.41% and 0.05% at the end of the experiment in the land-based IMTA. • Ammonia, nitrate and nitrite levels of the wastewater were reduced by 92.2%, 44.6% and 75%, respectively. • Mytilus galloprovincialis and Ulva lactuca mitigated ammonia, nitrate, nitrite by 15.6%, 5.4%, 25% and 90.8%, 41.4%, 66.7%. • Land-based IMTA system is not suitable for the feeding requirements of the Mytilus galloprovincialis in a long term study. [ABSTRACT FROM AUTHOR]

The current study assessed health risks posed by exposure to metals from the consumption of Baltic Sea trout (Salmo trutta L.). Concentrations of essential minerals in sea trout muscles were determined and compared with the physiological requirements of these minerals in Polish nutrition standards, recommended dietary allowances (RDA), and estimated average requirements (EAR). Chemical analyses indicated that sea trout was rich in phosphorus, calcium, magnesium, sodium, and potassium. The pattern significance gradation of the element concentrations was as follows: P>Ca>Mg>Na>K>Fe>Zn>Cu>Se>Mn>Co. Sea trout consumption can provide a considerable portion of the RDA of copper, magnesium, phosphorus, calcium, iron, and zinc. The ranking order of the mean toxic element concentrations in sea trout muscle tissues was As>Pb>Cd>Hg. Potential risk estimated with the hazard quotient (HQ) indicated that most metals posed no health risk because they did not exceed reference doses at HQ < 1. For carcinogenic and non-carcinogenic effects, the maximum allowable rates of sea trout consumption were sufficiently high to ensure human health. According to these data, the consumption of farmed sea trout from the Baltic Sea in the northern region of Pomerania, Poland did not pose a risk to human health.

Sperm motility is an important character for the assessment of milt quality and indicator to the expected rate of fertilization. Many factors can affect the sperm motility, including nature of water used as sperm activator medium after stripping the milt from the male fish. The aim of this study was to gain motility to spermatozoa and improve sperm kinematic parameters by applying a non‐chemical method. The effects of magnetic field on samples of hatchery water exposed to magnetic field of 2.71, 4.51 and 8.11 mT for the duration of 12, 24 and 36 hours on Salmo trutta labrax sperm motility were investigated with computer‐assisted sperm analysis (CASA) system; 4.51 mT exposure for 36 hours (A2H3) was greater in motility kinematic parameters (p < 0.05) and progressive kinematic parameters (VAP, VSL and VCL) with values of (93.1244 ± 37.222, 88.6111 ± 36.137, 96.8378 ± 35.396 μm/s) and (102.9167 ± 32.546, 100.9767 ± 31.894, 105.8778 ± 30.401 μm/s) respectively. But there was no (p ≥ 0.05) in the slow phase just in the VCL parameter had (p ≤ 0.05) (35.8789 ± 39.127 μm/s) among other parameters. There was (p ≤ 0.05) in starting motility time until vibration point (s) for 4.51 mT in 12 hour (A2H1) (27.3333 ± 1.527 s), but total time of motility was greater for 4.51 mT in 36 hour (A2H3) with (p ≤ 0.05) (49.6667 ± 2.081 s) compared with other treatments. [ABSTRACT FROM AUTHOR]

Natal homing, a strategy in which individuals return to breed in the same river as they were born, is prevalent among salmonids. However, some individuals may not return to their natal river, and instead stray to non-natal rivers. To date, there is limited documentation on patterns of straying among iteroparous salmonids that have returned to spawn over multiple years. In this study, 21538 out-migrating juvenile anadromous brown trout (Salmo trutta L.) were tagged over two years with passive integrated transponder (PIT) tags, and followed as they returned to either their natal or three non-natal rivers in a fjord system, over multiple years. In total, 206 individuals were detected returning for more than one year, of which 43% were strayers. A divergence in migratory strategies among strayers was documented: a smaller proportion of strayers were only detected in non-natal rivers, while the majority (67%) displayed high variability in their migratory patterns as they were detected in both their natal and non-natal rivers, sometimes within the same reproductive season. This study documents high variability in the migratory patterns of repeat spawners and high probability for them to stray, and suggests that straying is an important life-history strategy possibly affecting individual fitness. [ABSTRACT FROM AUTHOR]

The Sidnie Manton Award has recognised ECR excellence in research in multiple areas of animal ecology, including computer vision (Weinstein, 2018), macroimmunology (Becker et al., 2020) and most recently on animal-vectored spatial ecosystem subsidies (Ellis-Soto et al., 2021). Time is of the essence in ecology. Authors (particularly ECRs, and from regions and/or ecological systems not well represented) are welcome to contact our commissioning editor (Rob Salguero-Gómez; rob.salguero@biology.ox.ac.uk) to discuss their ideas and feasibility for the Sidnie Manton Award and our Journal. [Extracted from the article]