Anadromous red-spotted masu salmon (Oncorhynchus masou ishikawae), a southernmost sea-migration form of salmonid, displays low variation in both age at seaward migration and sea age

We examined variations in age at seaward migration and sea age for the anadromous form of red-spotted masu salmon (Oncorhynchus masou ishikawae) in two Japanese rivers. The anadromous form of red-spotted masu salmon expressed only two sea migration patterns in the two rivers: (a) the majority of the salmon (95%, n = 81) were of age-0, and age-1 migrants were rare (n = 4); and (b) all the salmon examined (n = 22) made a return migration within a year, with 23% of the salmon exhibiting potamodromy in the river. Owing to low variation in their sea migratory patterns, the anadromous form of red-spotted masu salmon is likely vulnerable to environmental fluctuations.

Ultra-acute exposure to cadmium does not impair whitefish sperm motility

Cadmium (Cd) exposure can impair the traits of aquatic animals associated with reproduction. In natural lakes Cd is typically detected at concentrations below 0.001 mg l^-1 . The authors investigated the impact of ultra-acute Cd exposure on sperm motility in European whitefish (Coregonus lavaretus). They activated sperm with water containing various nominal concentrations of Cd and recorded sperm motility parameters. Only the highest Cd concentration (500 mg l^-1 ) was associated with decreased sperm swimming velocity and increases in both the percentage of static cells and curvature of the sperm swimming trajectory. The results indicate that environmentally realistic concentrations of Cd during the sperm motility activation are not critically harmful to male C. lavaretus fertilization potential.

Response of European grayling, Thymallus thymallus, to multiple stressors in hydropeaking rivers

Rivers of the large Alpine valleys constitute iconic ecosystems that are highly threatened by multiple anthropogenic stressors. This stressor mix, however, makes it difficult to develop and refine conservation and restoration strategies. It is, therefore, urgent to acquire more detailed knowledge on the consequences and interactions of prevalent stressors on fish populations, in particular, on indicator species such as the European grayling Thymallus thymallus. Here, we conducted a multi-river, multi-stressor investigation to analyze the population status of grayling. Using explorative decision-tree approaches, we disentangled the main and interaction effects of four prevalent stressor groups: flow modification (i.e., hydropeaking), channelization, fragmentation, and water quality alteration. Moreover, using a modified variant of the bootstrapping method, pooled bootstrapping, we determined the optimal number of characteristics that adequately describe fish population status. In our dataset, hydropeaking had the strongest single effect on grayling populations. Grayling biomass at hydrological control sites was around eight times higher than at sites affected by hydropeaking. The primary parameters for predicting population status were downramping rate and peak amplitude, with critical ranges of 0.2-0.4 cm min^-1 and 10-25 cm. In hydropeaking rivers, river morphology and connectivity were the preceding subordinated parameters. Repeating the procedure with pooled bootstrapping datasets strengthened the hypothesis that the identified parameters are most relevant in predicting grayling population status. Hence, hydropeaking mitigation based on ecological thresholds is key to protect and restore already threatened grayling populations. In hydropeaking rivers, high river network connectivity and heterogenous habitat features can dampen the adverse effects of pulsed-flow releases by offering shelter and habitats for all life cycle stages of fish. The presented approach of explorative tree analysis followed by post-hoc tests of identified effects, as well as the pooled bootstrapping method, offers a simple framework for researchers and managers to analyze multi-factorial datasets and draw solid management conclusions.

Experimental study of ultrastructural mechanisms and kinetics of tegumental secretion in cestodes parasitizing fish (Cestoda: Diphyllobothriidea)

The structural response and plasticity of the cestode tegument in response to the influence of the host organism is not yet well understood. The main aims of our in vitro study were to analyse the ultrastructural mechanisms and kinetics of tegumental secretion in two cestode species, Dibothriocephalus dendriticus and Ligula interrupta, in response to the influence of fish host blood serum. The incubation of plerocercoids in the culture medium, which contained fish host blood serum, resulted in an increased number of secretory products on the tegumental surface. Our study is the first to experimentally demonstrate the formation of plerocercoid protective layers influenced by the host's internal environment factors. The mechanism of the generation of the protective layer included the following: the intensive formation of organelles in the tegumental cytons and their transfer to the distal cytoplasm of the tegument; increases in extracellular vesicles and vacuoles released on the tegumental surface; arrangement of secretory products and fine-dispersed extracellular matrix in layers; and formation of the protective layer. The structural tegumental response included increases in the glycocalyx layer and structural changes. Our study revealed that the universal mechanism of protective layer formation was intrinsic to different tapeworms. We hypothesize that plerocercoids of cestodes parasitizing fish may use tegumental secretion in the formation of a protective layer and in the release of immunoregulator molecules to evade the host's immune response.

Ultrasonic structural modification of myofibrillar proteins from Coregonus peled improves emulsification properties

This study evaluated the effects of high intensity ultrasonication (HIU, 100, 150, 200, and 250 W) and treatment time (0, 3, 6, 9, and 12 min) on the structure and emulsification properties of myofibrillar proteins (MPs) from Coregonus peled. These investigations were conducted using an ultrasonic generator at a frequency of 20 kHz (ultrasonic probe). Analysis of the carbonyl content and total number of sulfhydryl groups showed that HIU significantly improved the oxidative modification of MPs (P < 0.05). SDS-PAGE profiling showed significant degradation of the myosin heavy chain (P < 0.05). In addition, Fourier transformed infrared spectroscopy (FTIR) revealed that HIU altered these treated MP secondary structures, this was due to molecular unfolding and stretching, exposing interior hydrophobic groups. Particle size analysis showed that HIU treatment reduced particle sizes. Solubility, emulsification capacity, and emulsion stability were improved significantly, and each decreased with an increase in treatment time (up to 12 min), indicating aggregation with prolonged sonication. These results indicate that HIU could improve the emulsification properties of MPs from C. peled, demonstrating a promising method for fish protein processing.

Temperature effects on the contractile performance and efficiency of oxidative muscle from a eurythermal versus a stenothermal salmonid

We compared the thermal sensitivity of oxidative muscle function between the eurythermal Atlantic salmon (Salmo salar) and the more stenothermal Arctic char (Salvelinus alpinus; which prefers cooler waters). Power output was measured in red skeletal muscle strips and myocardial trabeculae, and efficiency (net work/energy consumed) was measured for trabeculae, from cold (6°C) and warm (15°C) acclimated fish at temperatures from 2 to 26°C. The mass-specific net power produced by char red muscle was greater than in salmon, by 2-to 5-fold depending on test temperature. Net power first increased, then decreased, when the red muscle of 6°C-acclimated char was exposed to increasing temperature. Acclimation to 15°C significantly impaired mass-specific power in char (by ∼40-50%) from 2 to 15°C, but lessened its relative decrease between 15 and 26°C. In contrast, maximal net power increased, and then plateaued, with increasing temperature in salmon from both acclimation groups. Increasing test temperature resulted in a ∼3- to 5-fold increase in maximal net power produced by ventricular trabeculae in all groups, and this effect was not influenced by acclimation temperature. Nonetheless, lengthening power was higher in trabeculae from warm-acclimated char, and char trabeculae could not contract as fast as those from salmon. Finally, the efficiency of myocardial net work was approximately 2-fold greater in 15°C-acclimated salmon than char (∼15 versus 7%), and highest at 20°C in salmon. This study provides several mechanistic explanations as to their inter-specific difference in upper thermal tolerance, and potentially why southern char populations are being negatively impacted by climate change.

Elevated river discharge enhances the immigration of juvenile catadromous and amphidromous fishes into temperate coastal rivers

Anthropogenic alterations to river flow regimes threaten freshwater biodiversity globally, with potentially disproportionate impacts on species that rely on flow cues to trigger critical life history processes, such as migration for diadromous fishes. This study investigates the influence of river discharge on the abundance of juvenile fish moving into rivers by four temperate catadromous or amphidromous species (common galaxias Galaxias maculatus, spotted galaxias Galaxias truttaceus, climbing galaxias Galaxias brevipinnis and the threatened Australian grayling Prototroctes maraena). Fyke netting or fishway trapping was used to catch juvenile fish moving from estuaries into freshwater in five coastal waterways in south-eastern Australia during the spring migratory period. There was a positive relationship between the probability of high catch rates and mean discharge in September. We also found a positive relationship between discharge and the number of recruits captured 22-30 days later in a flow stressed system. In addition, day-of-year had a strong influence on catch rates, with the peak abundance of juveniles for three species most likely to occur midway through the sampling period (spotted galaxias in October, climbing galaxias in late October and Australian grayling in late October and early November). Our study shows that higher magnitudes of river discharge were associated with increased catches of juvenile catadromous and amphidromous fishes. With a limited supply of environmental water, environmental flows used to enhance immigration of these fishes may be best targeted to maintain small amounts of immigration into freshwater populations in waterways or years when discharges are low and stable. When there are natural, large discharge volumes, relatively large numbers of juvenile fish can be expected to enter coastal waterways and during these times environmental flows may not be required to promote immigration.

Evaluation of muscle lipid extraction and non-lethal fin tissue use for carbon, nitrogen, and sulfur isotope analyses in adult salmonids

RATIONALE

Chemical lipid extraction or using alternative tissues such as fish fin as opposed to muscle may alter isotopic ratios and influence interpretations of δ¹³ C, δ¹⁵ N, and previously unassessed δ³⁴ S values in stable isotope analyses (SIA). Our objectives were to determine if lipid extraction alters these isotope ratios in muscle, if lipid normalization models can be used for lipid-rich salmonids, and if fin isotope ratios are comparable with those of muscle in adult salmonids.

METHODS

In six adult salmonid species (n = 106) collected from Lake Ontario, we compared three isotope ratios in lipid-extracted (LE) muscle with bulk muscle, and LE muscle with fin tissue, with paired t-tests and linear regressions. We compared differences between δ¹³ C values in LE and bulk muscle with predicted values from lipid normalization models and the log-linear model of best fit and determined model efficiency.

RESULTS

The δ¹⁵ N values in LE muscle increased (<1‰) relative to bulk muscle for most salmonids, with relationships nearing 1:1. There were either no differences or strong 1:1 relationships in δ³⁴ S values between species-specific bulk and LE muscle. One lipid normalization model had greater model efficiency (97%) than the model of best fit (94%). Fin had higher δ¹³ C values than LE muscle while δ¹⁵ N trends varied (<1‰); however, both isotope ratios had either no or weak linear relationships with fin and LE muscle within species. The δ³⁴ S values in fin were similar to those in LE muscle and had strong 1:1 relationships across species.

CONCLUSIONS

We recommend using the lipid normalization model to adjust for δ¹³ C values in lipid-rich muscle (C:N >3.4). LE muscle could be used without δ¹⁵ N or δ³⁴ S adjustments, but the minimal increase in δ¹⁵ N values may affect SIA interpretation. With high unexplained variability among adult species in fin-muscle δ¹³ C and δ¹⁵ N relationships, species-specific fin-muscle adjustments are warranted. No fin-muscle tissue adjustment would be required for δ³⁴ S values.

Heavy metal and metalloid accumulation in wild brown trout (Salmo trutta L., 1758 complex, Osteichthyes: Salmonidae) from a mountain stream in Sardinia by ICP-OES

 This paper reports heavy metal and metalloid accumulation in wild brown trout (Salmo trutta L., 1758 complex) raised in freshwater and uncontaminated Sardinia system (Italy). Metals are widespread pollutants of aquatic systems, and their contamination can originate from anthropogenic activities such as industrial waste, agricultural and domestic environments, and geochemical release. Fish has a relevant position within the human diet; moreover, fishes can accumulate metals, making them a valuable tool as biomarkers for risk assessment studies. The concentration of 22 metals and metalloids after chemical digestion was assessed by inductively coupled plasma-optic emission spectroscopy (ICP-OES) in both the guts and the edible part (EP, muscle + skin) of brown trout. The results, expressed as μg g-1, showed different levels of accumulation in the EP and guts, following the series Cu > Zn > Ba > Al > Sr > Fe > Pb and Fe > Al > Hg > As > Mn > Cu > Ba > B > Zn > Pb, respectively. PCA analysis showed a fairly good correlation between the total lipid and SAFA content and Cd, Hg, and Pb accumulation in the gut. Non-carcinogenic risk assessment, expressed as THQ (target hazard quotient), showed values far below 1 for all metals in muscles, while high As and Hg contamination of the gut draws attention to possible health risks which should be discarded from the fish before consumption. TR (target cancer risk) values showed alarmingly high values for As and Cd when the fish were consumed entirely (gut + EP), while Pb levels were far below the safety levels.

Double whammy: Nitrate pollution heightens susceptibility to both hypoxia and heat in a freshwater salmonid

Species persistence in a changing world will depend on how they cope with co-occurring stressors. Stressors can interact in unanticipated ways, where exposure to one stressor may heighten or reduce resilience to another stressor. We examined how a leading threat to aquatic species, nitrate pollution, affects susceptibility to hypoxia and heat stress in a salmonid, the European grayling (Thymallus thymallus). Fish were exposed to nitrate pollution (0, 50 or 200 mg NO₃^- L^-1) at two acclimation temperatures (18 °C or 22 °C) for eight weeks. Hypoxia- and heat-tolerance were subsequently assessed, and the gills of a subset of fish were sampled for histological analyses. Nitrate-exposed fish were significantly more susceptible to acute hypoxia at both acclimation temperatures. Similarly, in 18 °C- acclimated fish, exposure to 200 mg NO3- L- 1 caused a 1 °C decrease in heat tolerance (critical thermal maxima, CTMax). However, the opposite effect was observed in 22 °C-acclimated fish, where nitrate exposure increased heat tolerance by ~1 °C. Further, nitrate exposure induced some histopathological changes to the gills, which limit oxygen uptake. Our findings show that nitrate pollution can heighten the susceptibility of fish to additional threats in their habitat, but interactions are temperature dependent.

Acute warming in winter eliminates chemical alarm responses in threatened Qinling lenok Brachymystax lenok tsinlingensis

Knowledge of how temperature influences animal behavior is critical to understanding and predicting impacts of changing climate on individual species and biotic interactions. However, the effects of climate change, especially winter warming in freshwater systems, on fish behaviors and the use of chemical information have been largely unexplored. Qinling lenok Brachymystax lenok tsinlingensis, an endangered salmonid species endemic to the Qinling Mountain Range, China, is currently experiencing population decline and is a potential biological indicator of warming winter climate effects on freshwater fishes due to its temperature sensitivity and required habitat of small, cold-water streams. Our objective was to determine if transient winter warming (increases of ~4 °C) consistent with seasonal maxima in line with near-future climate projections will affect antipredator responses to damage-released chemical alarm cues in B. lenok tsinlingensis. Wild fish were collected during winter and held in captivity under food deprivation for four days, during which half were acclimated to a warmer temperature (6 °C) while the other half were maintained at ambient levels (2 °C). Individual acclimated fish were then exposed to injections of either conspecific alarm cues to simulate elevated predation risk or stream water as a control treatment. Focal fish demonstrated responses consistent with antipredator behaviors to alarm cues at ambient temperature, but no significant behavioral responses to alarm cues were found relative to controls at the warmer temperature. These results support our hypothesis that winter warming will negatively influence antipredator responses and indicate that projected warmer temperature patterns in winter may have significant impacts on chemically mediated predator-prey interactions in cold-water streams.

Effects of Maternally Transferred Egg Selenium on Embryo-Larval Survival, Growth, and Development in Arctic Grayling (Thymallus arcticus)

Selenium (Se) toxicity to fish is primarily manifested via maternal transfer to the eggs, which may result in adverse effects on larval survival and development. The present study assessed the effects of egg Se concentrations derived via maternal transfer on early life-stage development, survival, and growth of Arctic grayling (Thymallus arcticus), a salmonid species not previously assessed for Se sensitivity. Fish gametes were collected from 4 streams in Alaska known to exhibit a range of egg Se concentrations. Eggs were fertilized and reared in the laboratory from hatch through post-swim-up. Larvae were assessed for survival, length, and weight, as well as deformities (skeletal, craniofacial, fin-fold) and edema based on a graduated severity index. Eggs from a total of 47 females were collected, with egg Se concentrations ranging from 3.3 to 33.9 mg kg^-1  dry weight. No relationships were observed between larval endpoints evaluated and parent females' egg, muscle, or whole-body Se concentrations. Therefore, Se 10% effective concentrations (EC10s) were defined as the maximum measured Se concentrations: >33.9, >17.6, and >19.7 mg kg^-1  dry weight for eggs, muscle, and whole-body tissue, respectively. Collectively, these data indicate that Arctic grayling are relatively insensitive to maternally transferred Se compared to other fish species. Environ Toxicol Chem 2021;40:380-389. © 2020 SETAC.

Diet influences on growth and mercury concentrations of two salmonid species from lakes in the eastern Canadian Arctic

Diet, age, and growth rate influences on fish mercury concentrations were investigated for Arctic char (Salvelinus alpinus) and brook trout (Salvelinus fontinalis) in lakes of the eastern Canadian Arctic. We hypothesized that faster-growing fish have lower mercury concentrations because of growth dilution, a process whereby more efficient growth dilutes a fish's mercury burden. Using datasets of 57 brook trout and 133 Arctic char, linear regression modelling showed fish age and diet indices were the dominant explanatory variables of muscle mercury concentrations for both species. Faster-growing fish (based on length-at-age) fed at a higher trophic position, and as a result, their mercury concentrations were not lower than slower-growing fish. Muscle RNA/DNA ratios were used as a physiological indicator of short-term growth rate (days to weeks). Slower growth of Arctic char, inferred from RNA/DNA ratios, was found in winter versus summer and in polar desert versus tundra lakes, but RNA/DNA ratio was (at best) a weak predictor of fish mercury concentration. Net effects of diet and age on mercury concentration were greater than any potential offset by biomass dilution in faster-growing fish. In these resource-poor Arctic lakes, faster growth was associated with feeding at a higher trophic position, likely due to greater caloric (and mercury) intake, rather than growth efficiency.

Size-dependent escape risk of lumpfish (Cyclopterus lumpus) from salmonid farm nets

In the last decade, the salmon aquaculture industry has considerably increased the use of lumpfish juveniles as cleaner fish. Potential escape of reared lumpfish into the wild may spread diseases or genetically contaminate wild stocks. The guidelines for minimum sizes of cleaner fish to use in aquaculture cages are currently based on simple mesh penetration tests. However, these guidelines do not consider the potential compressibility of fish or changes in mesh state due to factors such as sea conditions and maintenance operations. This study shows that the industry-recommended minimum stocking sizes for a given mesh size may result in escape risk and that ignoring fish compressibility and mesh state can lead to underestimation of the lumpfish sizes that are able to escape. Our results can be used to develop new guidelines that will contribute to reduced escape of lumpfish from salmonid farms and lessen the potential environmental consequences.

Nanopore whole genome sequencing and partitioned phylogenetic analysis supports a new salmonid alphavirus genotype (SAV7)

Salmon pancreas disease virus, more commonly known as salmonid alphavirus (SAV), is a single-stranded positive sense RNA virus and the causative agent of pancreas disease and sleeping disease in salmonids. In this study, a unique strain of SAV previously isolated from ballan wrasse was subjected to whole genome sequencing using nanopore sequencing. In order to accurately examine the evolutionary history of this strain in comparison to other SAV strains, a partitioned phylogenetic analysis was performed to account for variation in the rate of evolution for both individual genes and codon positions. Partitioning the genome alignments almost doubled the observed branch lengths in the phylogenetic tree when compared to the more common approach of applying one model of substitution across the genome and significantly increased the statistical fit of the best-fitting models of nucleotide substitution. Based on the genomic data, a valid case can be made for the viral strain examined in this study to be considered a new SAV genotype. In addition, this study adds to a growing number of studies in which SAV has been found to infect non-salmonid fish, and as such we have suggested that the viral species name be amended to the more inclusive 'piscine alphavirus'.

Microplastics in brown trout (Salmo trutta Linnaeus, 1758) from an Irish riverine system

Rivers play an important role in the overall transport of microplastic pollution (1 μm to 5 mm), with fluvial dynamics expected to influence biotic interactions, particularly for fish. So far, there have been few assessments of microplastics in freshwater salmonids. The prevalence (i.e. percentage occurrence) and burden (i.e. abundance per fish) of microplastics were assessed in the gastrointestinal tracts (GITs) and stomach contents (SCs) of 58 brown trout Salmo trutta Linnaeus, 1758 sampled at six sites along the River Slaney catchment in south-east Ireland. Sites were divided into two classifications (high and low exposure) based on proximity to microplastic pollution sources, comprising three sites each. Analysis of biological traits (e.g. fish length) and diet was performed on the same fish to determine possible factors explaining microplastic burden. Microplastics were found in 72% of fish having been recovered from 66% of GITs (1.88 ± 1.53 MPs fish⁻¹) and 28% of SCs (1.31 ± 0.48 MPs fish⁻¹). Fibres were the dominant particle type recovered from GITs (67%) and SCs (57%) followed by fragments. No difference in median microplastic burden was observed between fish collected in high and low exposure sites. Microplastic burden was unrelated to fish fork length, while microplastic size distribution (100 ≤ 350 μm, 350 μm to ≤ 5 mm) was unrelated to S. trutta age class estimates. Furthermore, microplastic burden was not explained by dietary intake. Though further research is necessary, this study showed the presence of microplastics in wild S. trutta collected from an Irish riverine system, which could have further implications for top-level consumers that feed on the species, including humans. Further analysis is required to determine possible trophic linkages for the species, with respect to microplastics, and to assess the suitability of S. trutta for monitoring microplastics in river systems.

The bite force-gape relationship as an avenue of biomechanical adaptation to trophic niche in two salmonid fishes

All skeletal muscles produce their largest forces at a single optimal length, losing force when stretched or shortened. In vertebrate feeding systems, this fundamental force-length relationship translates to variation in bite force across gape, which affects the food types that can be eaten effectively. We measured the bite force-gape curves of two sympatric species: king salmon (Oncorhynchus tshawytscha) and pink salmon (Oncorhynchusgorbuscha). Cranial anatomical measurements were not significantly different between species; however, peak bite forces were produced at significantly different gapes. Maximum bite force was achieved at 67% of maximum gape for king salmon and 43% of maximum gape for pink salmon. This may allow king salmon to use greater force when eating large or elusive prey. In contrast, pink salmon do not require high forces at extreme gapes for filter feeding. Our results illustrate that the bite force-gape relationship is an important ecophysiological axis of variation.

Development and evaluation of a method for concentration and detection of salmonid alphavirus from seawater

Waterborne viral infections represent a major threat to fish health. For many viruses, understanding the interplay between pathogens, host and environment presents a major hurdle for transmission. Salmonid alphavirus (SAV) can infect and cause pancreas disease (PD) in farmed salmonids in seawater. During infection, SAV is excreted from infected fish to the seawater. We evaluated two types of filters and four different eluents, for concentration of SAV3. One L of seawater was spiked with SAV3, followed by filtration and virus elution from membrane filters. For the negatively charged MF hydrophilic membrane filter (MF-) combined with NucliSENS® lysis buffer the SAV3 recovery was 39.5 ± 1.8 % by RT-ddPCR and 25.9 ± 5.7 % by RT-qPCR. The recovery using the positively charged 1 MDS Zeta Plus® Virosorb® membrane filter (MD+), combined with NucliSENS® lysis buffer was 19.0 ± 0.1 % by RT-ddPCR and 13.3 ± 3.8 % by RT-qPCR. The limits of quantification (LOQ) and detection (LOD) were estimated to be 5.18 × 10³ and 2.0 × 10² SAV3 copies/L of natural seawater, by RT-ddPCR. SAV3 recovery from small volumes of seawater, and the requirement for standard laboratory equipment, suggest the MF-filter combined with NucliSENS® lysis buffer would be a candidate for further validation in experimental trials.

Comparison of 137Cs uptake, depuration and continuous uptake, originating from feed, in five salmonid fish species

The origin of ¹³⁷Cs contamination, contamination levels, and its effective ecological half-life can differ among fish species, but until recently it was unknown whether interspecific differences in radiocaesium metabolism existed. We compare the trophic transfer of ¹³⁷Cs in five salmonid species under controlled conditions. Fish were fed a diet containing 200 Bq kg^-1 wet wt concentration of ¹³⁷Cs for a fixed period of time. While there were almost no differences in contamination levels among individual fish within a species during fixed periods, the rate of ¹³⁷Cs uptake was statistically different among the species examined, for which the effective half-life of ¹³⁷Cs ranged 49-84 days. No significant difference in rate of decline in the quantity of ¹³⁷Cs was apparent among species in two experiments after correcting for differences in growth. The effective half-life was shortest in Oncorhynchus mykiss and O. masou-two species exhibiting the best growth rate in both experiments-indicating an influence of the dilution effect associated with growth. When continuously fed 200 Bq kg^-1 wet wt concentration of ¹³⁷Cs for a period of 209-294 days, contamination levels in the five species ranged 216-240 Bq kg^-1 wet wt, and reached a steady state value. Our results indicate metabolic rate, although accompanying a change of body size, did not affect ¹³⁷Cs contamination levels in fish, which implies that contamination levels in the diet strongly determined contamination levels in fish.

Identification of the Nrf2 in the fathead minnow muscle cell line: role for a regulation in response to H2O2 induced the oxidative stress in fish cell

The Nrf2 (nuclear factor erythroid 2-related factor 2) plays a central role in cell protection against a wide variety of environmental stressors through the Nrf2-Keap1 (Kelch-like ECH-associated protein 1) pathway, but its involvement in modulation of antioxidant system of fish cell is still largely unexplored. The present study focused on the molecular cloning and silencing of the Nrf2 in the fathead minnow muscle cell line (FHM) in response to the oxidative stress induced by H₂O₂. A full-length cDNA of coding Nrf2 was cloned from FHM cells by RT-PCR and RACE approaches. The obtained cDNA covered 2578 bp with an open reading frame (1770 bp) of encoding 589 amino acids. Sequence alignment and phylogenetic analysis revealed a high degree of conservation (51-86%) among 16 fishes. Based on the cloned Nrf2 sequence, the siRNA-242 of targeting Nrf2 with the best knocking down efficiency was designed and detected. Then, the mRNA levels of Keap1, Nrf2, Maf (musculoaponeurotic fibrosarcoma oncogene), and HO-1 (haemoxygenase-1); the activities of T-SOD (total superoxide dismutase), CAT (catalase), and GSH-PX (glutathione peroxidase); the levels of GSH (glutathione) and MDA (malonaldehyde); and the cell cycle and apoptosis were analyzed to investigate the molecular responses after H₂O₂ exposure. These results showed a coordinated transcriptional regulation of Keap1, Maf, and HO-1 and antioxidants (T-SOD, GSH, CAT, and GSH-PX) and MDA levels after H₂O₂ exposure, leading to oxidative damage and apoptosis. These findings provided an insight to understand the mechanisms of Nrf2 against oxidative stress in fish.

Quantifying expert opinion with discrete choice models: Invasive elodea's influence on Alaska salmonids

Scientific evidence should inform environmental policy, but rapid environmental change brings high ecological uncertainty and associated barriers to the science-management dialogue. Biological invasions of aquatic plants are a worldwide problem with uncertain ecological and economic consequences. We demonstrate that the discrete choice method (DCM) can serve as a structured expert elicitation alternative to quantify expert opinion across a range of possible but uncertain environmental outcomes. DCM is widely applied in the social sciences to better understand and predict human preferences and trade-offs. Here we apply it to Alaska's first submersed invasive aquatic freshwater plant, Elodea spp. (elodea), and its unknown effects on salmonids. While little is known about interactions between elodea and salmonids, ecological research suggests that aquatic plant invasions can have positive and negative, as well as direct and indirect, effects on fish. We use DCM to design hypothetical salmonid habitat scenarios describing elodea's possible effect on critical environmental conditions for salmonids: prey abundance, dissolved oxygen, and vegetation cover. We then observe how experts choose between scenarios that they believe could support persistent salmonid populations in elodea-invaded salmonid habitat. We quantify the relative importance of habitat characteristics that influence expert choice and investigate how experts trade off between habitat characteristics. We take advantage of Bayesian techniques to estimate discrete choice models for individual experts and to simulate expert opinion for specific environmental management situations. We discuss possible applications and advantages of the DCM approach for expert elicitation in the ecological context. We end with methodological questions for future research.

Experimental transmission of Caligus rogercresseyi between two different fish species

Caligus rogercresseyi is the dominant sea louse parasite affecting the salmon and trout industry in southern Chile. This parasite has a wide range of native and endemic fish hosts. The Patagonian blenny Eleginops maclovinus, which is parasitized mostly by the caligid species Lepeophtheirus spp. and C. rogercresseyi, is presumably responsible for the transmission of C. rogercresseyi to salmonids. The aim of this study was to characterize the transmission of parasites between different fish species and parasite cohort development under laboratory conditions. Parasite abundances and intensities were quantified. Transmission of parasites from Patagonian blenny to Atlantic salmon Salmo salar was lower (~9%, mainly corresponding to C. rogercresseyi) than from salmon to Patagonian blenny (14.7-26.9%, where only C. rogercresseyi were observed). This suggests that the transmission of C. rogercresseyi from salmon individuals is higher than the transmission from a native fish. Parasite cohorts developed successfully on both fish species, but apparently under different developmental rates. Water temperature, oxygen, and juvenile abundances were the variables that better explained cohort development success and variation in C. rogercresseyi adult abundances over time.