The study of acidic/basic nature of metallothioneins and other metal-binding biomolecules in the soluble hepatic fraction of the northern pike (Esox lucius).

Since fish metalloproteins are still not thoroughly characterized, the aim of this study was to investigate the acidic/basic nature of biomolecules involved in the sequestration of twelve selected metals in the soluble hepatic fraction of an important aquatic bioindicator organism, namely the fish species northern pike (Esox lucius). For this purpose, the hyphenated system HPLC-ICP-MS was applied, with chromatographic separation based on anion/cation-exchange principle at physiological pH (7.4). The results indicated predominant acidic nature of metal-binding peptides/proteins in the studied hepatic fraction. More than 90 % of Ag, Cd, Co, Cu, Fe, Mo, and Pb were eluted with negatively charged biomolecules, and >70 % of Bi, Mn, and Zn. Thallium was revealed to bind equally to negatively and positively charged biomolecules, and Cs predominantly to positively charged ones. The majority of acidic (negatively charged) metalloproteins/peptides were coeluted within the elution time range of applied standard proteins, having pIs clustered around 4-6. Furthermore, binding of several metals (Ag, Cd, Cu, Zn) to two MT-isoforms was assumed, with Cd and Zn preferentially bound to MT1 and Ag to MT2, and Cu evenly distributed between the two. The results presented here are the first of their kind for the important bioindicator species, the northern pike, as well as one of the rare comprehensive studies on the acidic/basic nature of metal-binding biomolecules in fish, which can contribute significantly to a better understanding of the behaviour and fate of metals in the fish organism, specifically in liver as main metabolic and detoxification organ.

Mercury and amino acid content relations in northern pike (Esox lucius) in subarctic lakes along a climate-productivity gradient.

Mercury is a highly toxic element for consumers, but its relation to amino acids and physiology of wild fish is not well known. The main aim of this study was to evaluate how total mercury content (THg) of northern pike (Esox lucius) is related to amino acids and potentially important environmental and biological factors along a climate-productivity gradient of ten subarctic lakes. Linear regression between THg and sixteen amino acids content [nmol mg-1 dry weight] from white dorsal muscle of pike from these lakes were tested. Lastly, a general linear model (GLM) for age-corrected THg was used to test which factors are significantly related to mercury content of pike. There was a positive relationship between THg and proline. Seven out of sixteen analysed amino acids (histidine, threonine, arginine, serine, glutamic acid, glycine, and aspartic acid) were significantly negatively related to warmer and more productive lakes, while THg showed a positive relationship. GLM model indicated higher THg was found in higher trophic level pike with lower cysteine content and inhabiting warmer and more productive lakes with larger catchment containing substantial proportion of peatland area. In general, THg was not only related to the biological and environmental variables but also to amino acid content.

The time course of metabolic plasticity and its consequences for growth performance under variable food supply in the northern pike.

Many species up- or downregulate their resting metabolic rate (RMR) when they encounter favourable or unfavourable feeding conditions, respectively. This is thought to promote faster growth when food is abundant and conserve energy reserves when food is scarce. The time it takes to express metabolic plasticity remain little studied. Here, we develop a conceptual model showing how rapid or slow metabolic plasticity alter growth trajectories in response to changes in food supply. We test predictions from the model in a food manipulation experiment with young-of-the-year northern pike, Esox lucius, a species that experience drastic changes in food supply in nature. We find that metabolic plasticity is expressed gradually over several weeks in this species. Rapid changes in food supply thus caused apparent trait-environment mismatches that persisted for at least five weeks. Contrary to predictions, pike grew faster at high food levels when they had previously experienced low food levels and downregulated their RMR. This was not owing to increases in food intake but probably reflected that low RMRs increased the energetic scope for growth when feeding conditions improved. This highlights the important but complex effects of metabolic plasticity on growth dynamics under variable resource levels on ecologically relevant time scales.

Inactivation of the Anti-Müllerian Hormone Receptor Type 2 (amhrII) Gene in Northern Pike (Esox lucius) Results in Male-To-Female Sex Reversal.

BACKGROUND: The anti-müllerian hormone (Amh) pathway is crucial for sexual development in teleosts. A male-specific duplicate of anti-müllerian hormone (amhby) was previously identified as the northern pike (Esox lucius) master sex determination gene. However, the role of its putative cognate receptor, i.e., the anti-müllerian hormone receptor type 2 (amhrII) was unclear in this species. OBJECTIVE: Here, we investigated the role of amhrII during sexual development of northern pike. METHOD: We generated stable mutants with deletions in exon 9 of amhrII, inactivating the AmhrII protein using a CRISPR-Cas9-mediated gene knockout strategy. RESULT: The inactivation of amhrII in northern pike results in a high level of male-to-female sex reversal. CONCLUSION: This result demonstrates that amhrII is necessary for male sexual development in northern pike and supports the idea that AmhrII is a conserved regulator of the teleosts sex differentiation network.

Metal-binding biomolecules in the liver of northern pike (Esox lucius Linnaeus, 1758): The first data for the family Esocidae.

Metal-handling strategies of various fish species are known to vary significantly in association with their intracellular metal behaviour. Thus, to better understand the possible consequences of increased metal exposure in fish it is important to perform comparative studies on metal-binding biomolecules in organs of different species. This study was the first of this kind on a liver of an esocid fish (northern pike, Esox lucius), and the gathered information were compared to fish belonging to three other families, Leuciscidae, Cyprinidae and Salmonidae. Distributions of ten elements among cytosolic biomolecules of different molecular masses were studied by size exclusion HPLC combined offline with high resolution ICP-MS. The results indicated predominant association of Co, Fe and Mo to high molecular mass biomolecules (>100 kDa), of Zn and Bi to both high and medium molecular mass biomolecules (>30 kDa), of Mn and Se to medium molecular mass biomolecules (30-100 kDa), and Ag, Cd and Cu to low molecular mass biomolecules (10-30 kDa), presumably metallothioneins. Evident binding to metallothioneins was also detected for Zn and Bi. For several metals, distinct differences were observed when cytosolic metal distributions of northern pike were compared to leuciscids, salmonids and cyprinids. More pronounced Zn binding to metallothioneins was recorded in leuciscids and cyprinids than both esocids and salmonids, whereas cytosolic Mn and Se distributions clearly differed between all studied fish families. Accordingly, in assessment of metal pollution it is vital to consider the exposed species, which requires prior comprehensive comparative research on numerous aquatic organisms.

The effect of caspase-3 in mitochondrial apoptosis activation on degradation of structure proteins of Esox lucius during postmortem storage.

This study aimed to investigate the effect of caspase-3 inhibitor in mitochondrial apoptosis activation on structure protein degradation during postmortem storage. Mitochondrial dysfunction, apoptotic factors, structure protein degradation and the myofibrillar rupture index between the control and caspase-3 inhibitor groups were determined. The results show caspase-3 inhibitor repressed the mitochondrial membrane permeability and mitochondrial swelling, as well as increased mitochondrial membrane potential, causing a decrease in the release of cytochrome c from mitochondria to cytoplasm and caspase-9/3 activities (P < 0.05). Subsequently, small myofibrillar proteins (desmin and troponin-T) were susceptible to degradation, initiating texture deterioration. By contrast, giant structure proteins (titin and nebulin) were degraded during later postmortem storage, predominantly contributing to fish softening. The results further suggest that caspase-3 is involved in degradation of structure proteins during postmortem through mitochondrial apoptosis pathways.

Environmental exposure of northern pike to a primary wastewater effluent: Impact on the lipidomic profile and lipid metabolism.

Lipids play important roles in growth, reproduction, locomotion, and migration of fish. Municipal effluents, which are complex mixtures of biological and chemical compounds including flame retardants, have been shown to alter lipid metabletabolism in environmentally and experimentally exposed fish. Down-regulation of several genes coding for fatty acid metabolism enzymes has previously been reported in male northern pike (Esox lucius) collected in the St. Lawrence River (QC, Canada) downstream of a major primary wastewater treatment plant (WWTP) point of discharge. The main objective of this study was to investigate the effects of exposure to the Montreal's WWTP effluent on the lipidomic profile (i.e., fatty acids, acylcarnitines, and phospholipids) as well as the transcription of genes related to lipid metabolism in the liver of northern pike collected upstream and downstream of this WWTP effluent. Halogenated flame retardant concentrations were also determined in pike liver and used as markers of exposure to this effluent. Greater concentrations of saturated and monounsaturated lysophosphatidylcholines (LPCs) and lower concentrations of polyunsaturated LPCs were determined in the liver of pike collected downstream of the WWTP compared to those collected upstream. Lower mRNA levels of peroxisome proliferator-activated receptor alpha (pparα), a major regulator of lipid metabolism, were also measured in pike exposed to Montreal's WWTP effluent. In addition, the relative contributions (%) of LPC 18:2 and LPC14:0, compounds used as markers of obesity and inflammation, were significantly correlated with halogenated flame retardant concentrations and fish girth. Results of the present study suggest that chronic environmental exposure to a primary WWTP effluent can modulate the transcription of genes related to lipid metabolism, and hence affect the hepatic phospholipid composition of pike from the St. Lawrence River.

Suspect screening of plastic-related chemicals in northern pike (Esox lucius) from the St. Lawrence River, Canada.

Environmental contaminant monitoring traditionally relies on targeted analysis, and very few tools are currently available to monitor "unexpected" or "unknown" compounds. In the present study, a non-targeted workflow (suspect screening) was developed to investigate plastic-related chemicals and other environmental contaminants in a top predator freshwater fish species, the northern pike, from the St. Lawrence River, Canada. Samples were extracted using sonication-assisted liquid extraction and analyzed by high performance liquid chromatography coupled with quadrupole time of flight mass spectrometry (HPLC-QTOF-MS). Ten bisphenol compounds were used to test the analytical performances of the method, and satisfactory results were obtained in terms of instrumental linearity (r2 > 0.97), recoveries, (86.53-119.32%), inter-day precision and method detection limits. The non-targeted workflow data processing parameters were studied, and the peak height filters (peak filtering step) were found to influence significantly the capacity to detect and identify trace chemicals in pike muscle extracts. None of the ten bisphenol analogues were detected in pike extracts suggesting the absence of accumulation for these chemicals in pike muscle. However, the non-targeted workflow enabled the identification of diethyl phthalate (DEP) and perfluorooctanesulfonic acid (PFOS) in pike extracts. This approach thus can be also applied to various contaminants in other biological matrices and environmental samples.

Parasites and Metals in Walleye (Sander vitreus) and Northern Pike (Esox lucius) from Boreal Montreal Lake (Saskatchewan, Canada): Assessment of Human Health Risks.

Industrial activities conducted in Northern Canada have raised concerns among Indigenous communities regarding wildlife contamination and potential consequences for human health. Therefore, an investigation on the chemical (metals/metalloids) and biological (parasite) burden of adult walleye (Sandervitreus) and northern pike (Esoxlucius) from Montreal Lake, Saskatchewan, was conducted to assess health risks related to fish consumption. Dissection revealed that both fishes displayed typical parasite communities, with Eubothrium sp. (Cestoda) and Raphidascarisacus (Nematoda) occurring the most frequently. None of the identified parasite species were infectious to humans. Concentrations of most inorganic contaminants in fish muscle were low and both walleye and pike can be considered healthy components of a balanced diet. However, due to slightly elevated mercury concentrations, excessive daily consumption of these fishes is not recommended, as mercury exposure over time may lead to adverse health effects.

Factors influencing fish mercury concentrations in Iowa rivers.

Fish mercury concentrations have received considerable attention due to human health implications. Fish mercury concentrations are variable within and among systems due to a suite of biotic and abiotic influences that vary among regions and are difficult to predict. Understanding factors associated with variability in fish mercury concentrations would help guide consumption advisories. Mercury concentrations in channel catfish (Ictalurus punctatus, n = 205), flathead catfish (Pylodictis olivaris, n = 123), northern pike (Esox lucius, n = 60), smallmouth bass (Micropterus dolomieu, n = 176), and walleye (Sander vitreus, n = 176) were assessed in ten Iowa rivers and relationships with land use, water chemistry, and fish characteristics were explored. Mercury concentrations were generally low (mean among all species = 0.17 mg/kg, n = 740) but higher in flathead catfish, northern pike, smallmouth bass, and walleye than channel catfish and were positively related to fish length, age, trophic position, and δ13C signatures. Phosphorus, sulfate, and percent open water and grassland were negatively related to fish mercury concentrations, whereas water hardness, nitrogen-ammonia, Human Threat Index, and percent wetland and forest were positively related to fish mercury concentrations. Fish collected from the Paleozoic Plateau ecoregion in northeast Iowa had higher mercury concentrations than other ecoregions in Iowa. Combined, these factors explained 70% of the variation in fish mercury concentrations. This study provides a comprehensive analysis of abiotic and biotic factors influencing fish mercury concentrations in lotic ecosystems at the individual and system scale that will help guide fish consumption advisories.

Environmental exposure to a major urban wastewater effluent: Effects on the energy metabolism of northern pike.

Municipal wastewater effluents (MWWEs) consist of dynamic and complex mixtures of chemical and biological compounds that can alter the health of exposed aquatic organisms. Disturbance of energy metabolism has been reported in fish exposed to MWWEs. However, there is a scarcity of knowledge on the physiological events leading to perturbation of energy balance and thyroid regulation, and associated lipid metabolism. The objective of the present study was to use a set of biomarkers, from gene transcription to body condition, to investigate the effects of a chronic environmental exposure to a major primary MWWE on fatty acid metabolism and thyroid hormone levels in northern pike (Esox lucius) collected from the St. Lawrence River near Montreal (QC, Canada). The exposure of pike to MWWE was examined through determination of a suite of persistent and bioaccumulative halogenated flame retardants in liver as this effluent is a known regional source for these chemicals. Greater hepatic concentrations of polybrominated diphenyl ethers (PBDEs, range: 29.6-465ng/g w.w. and 88.8-823ng/g w.w. in females and males, respectively) and other halogenated flame retardants (e.g., dechlorane-related compounds) were determined in fish collected downstream of the MWWE's point of discharge relative to the upstream site. This exposure in male pike was associated with decreased acyl-coA oxidase (acox1) and fatty acid synthase (fasn) mRNA levels as well as a decreased acyl-coA oxidase (ACOX) activity in liver. In female pike, MWWE exposure was associated with lower circulating free and total triiodothyronine (T3) levels and a tendency for greater total lipid percentages in liver. Present findings provide evidence that chronic exposure of a top predator fish to MWWE can be related to gender-specific effects on fatty acid metabolism and thyroid hormone homeostasis, and highlight the need for further investigation.

Age-dependent accumulation of (137)Cs by pike Esox lucius in the Yenisei River.

Age-dependent accumulation of (137)Cs in the muscles and bodies of the pike Esox lucius (aged two to seven years) inhabiting a section of the Yenisei River polluted with artificial radionuclides has been studied. The content of (137)Cs in muscles varied from 0.5 to 7.0 Bq/kg of fresh weight. The maximum content of the radionuclide has been found in juveniles. The content of (137)Cs in pike muscles and body decreased considerably with age. The high content of (137)Cs in the muscles of juveniles is probably a consequence of their higher intensity of feeding as compared to older individuals, which is due to the intense growth of juveniles.

Behaviour in a standardized assay, but not metabolic or growth rate, predicts behavioural variation in an adult aquatic top predator Esox lucius in the wild.

This study tested for links among behaviour, state and life-history variables as predicted by the pace-of-life hypothesis in adult pike Esox lucius. First, a standardized open-field behavioural assay was developed to assess individual behaviour of wild-captured adult E. lucius. Behaviour within the standardized assay predicted swimming behaviour in the lake, providing an ecological validation of the assay. There was no relationship between standardized behaviour and any of the life-history and state variables, including metabolism, body condition, juvenile growth rate and adult growth rate in contrast to predictions from the pace-of-life hypothesis. This study demonstrates that it is possible to assess ecologically relevant behavioural variation in a large-bodied top predator using a standard open-field assay, but it is noteworthy that this standardized behaviour is not systematically related to standard metabolism or growth.

A study on the levels of radioactivity in fish samples from the experimental lakes area in Ontario, Canada.

To better understand background radiation levels in country foods, a total of 125 fish samples were collected from three lakes (Lake 226, Lake 302 and Lake 305) in the Experimental Lakes Area (ELA) in Ontario of Canada during the summer of 2014. Concentrations of naturally occurring radionuclides ((226)Ra, (210)Pb and (210)Po) as well as anthropogenic radionuclides ((134)Cs and (137)Cs) were measured. This study confirmed that (210)Po is the dominant contributor to radiation doses resulting from fish consumption. While concentrations of (210)Pb and (226)Ra were below conventional detection limits, (210)Po was measured in almost all fish samples collected from the ELA. The average concentration was about 1.5 Bq/kg fresh weight (fw). None of the fish samples analysed in this study contained any detectable levels of (134)Cs. An average (137)Cs level of 6.1 Bq/kg fw was observed in freshwater fishes harvested in the ELA, almost twice that of samples measured in the National Capital Region of Canada in 2014 and more than 20 times higher than the levels observed in marine fish harvested from the Canadian west coast in 2013 and 2014. However, it is important to note that the concentrations of (137)Cs in fish samples from these inland lakes are considered very low from a radiological protection perspective. The resulting radiation dose for people from fish consumption would be a very small fraction of the annual dose from exposure to natural background radiation in Canada. The results indicate that fishes from inland lakes do not pose a radiological health concern.

[Ecological and Biochemical Aspects of Parasite-Host Interactions in Transformed Aquatic Bodies: A Case Study of the Cestode Triaenophorus nodulosus and Its Host, the Northern Pike Esox lucius].

The lysosomal enzyme activities of the cestode Triaenophorus nodulosus and its host, the pike, in-aquatic bodies with different degrees of technogenic transformation (Northern Karelia, Russia) have been studied. As has been shown, iron-ore waste causes an increase in the acid phosphatase, nuclease, and beta-galactosidase activities of the host and a decrease in its beta-glucosidase and cathepsin D activities. As a rule, the changes in the same cestode enzyme activities are the opposite. With a decrease in the technogenic load, most of the studied characteristics display the trend of approaching the corresponding values observed in a clean lake. It is assumed that the host plays a leading role in the biochemical adaptation of the parasite and its host to mineral environmental pollution.

Bioaccumulation of Heavy Metals and Microelements in Silver Bream (Brama brama L.), Northern Pike (Esox lucius L.), Sterlet (Acipenser ruthenus L.), and Common Carp (Cyprinus carpio L.) From Tisza River, Serbia.

The aim of this study was to determine the concentrations of Al, As, B, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Sr, and Zn in liver, gills, gonads, and brain of four ecologically different fish species in Serbia: piscivorous northern pike, benthivorous sterlet and silver bream, and omnivorous common carp. Fish were caught at four sites along the stretch of the River Tisza in the Pannonian part of Serbia during October 2010. Results revealed that heavy metals and microelements with the highest values in fish samples were Fe, Al, and Zn. The highest concentration of heavy metals and microelements was recorded in omnivorous common carp, and organs that most intensively accumulated the greatest number of metals were liver and gills, whereas the locality did not exert a marked impact on level of bioaccumulation.

Spatio-temporal trends of PCBs in the Swedish freshwater environment 1981-2012.

Polychlorinated biphenyls (PCBs) have been monitored in perch (Perca fluviatilis), pike (Esox lucius), and Arctic char (Salvelinus alpinus) in reference lakes since the late 1960s. Temporal trends and spatial patterns are currently monitored in nine and 32 lakes, respectively. Overall, PCB concentrations are decreasing. However, this is not consistent for all congeners across all lakes and species. Perch has comparatively low PCB concentrations relative to suggested target levels, but individual congener concentrations in some lakes are concerningly high. No temporal trend is seen for CB-118 and CB-153 in perch, but significant decreasing trends exist for Arctic char and pike, for which monitoring started earlier than for perch. The lower/higher chlorinated congener ratio decreased over time in most lakes, indicating fewer new emissions. CB-118 and CB-153 concentrations in perch show spatial gradients across Sweden, with higher concentrations found near urban/industrial areas.

Modification by UV radiation of the surface of thin films based on collagen extracted from fish scales.

Collagen was extracted from fish scales (Esox lucius) through demineralization process. Thin films by solvent evaporation from collagen extracted from fish scales were prepared. The surface of thin films made of fish scales collagen was modified by ultraviolet (UV)-irradiation with the wavelength λ = 254 nm. The amino acid composition of the Esox lucius scale collagen was analyzed before and after UV-irradiation by means of high-pressure liquid chromatography. The surface properties of films were investigated using the technique of atomic force microscopy (AFM) and by means of contact angle measurements allowing the calculation of surface free energy. Measurements of the contact angle for diiodomethane (D) and glycerol (G) on the surface of fish collagen films were made and surface free energy was calculated. The structure of collagen before and after UV-irradiation was studied using Fourier-transform infrared spectroscopy. It was found that after UV-irradiation the amount of all amino acids present in collagen molecule decreased. It was found also that the contact angle and the surface free energy were altered by UV-irradiation of collagen film. AFM showed that the surface roughness of collagen films was also altered by UV-irradiation. UV-irradiation caused the decrease of surface roughness due to photochemical processes, which occurred in the top layer of collagen film. The formation of collagen fibrils after solvent evaporation was observed using AFM. The diameter of collagen fibrils was bigger for irradiated collagen film than the diameter of collagen fibrils before UV-irradiation.

Metabolic enzymes activity and histomorphology in the liver of whitefish (Coregonus lavaretus L.) and pike (Esox lucius L.) inhabiting a mineral contaminated lake.

The effects of wastewater from a mining and ore-dressing mill on fish in Lake Kostomukshskoe, which is used as a cesspool of circulating water and for storage of industrial wastes produced by the Kostomuksha mining and ore-dressing mill in northwest Russia, were studied. The lake is characterized by heavy mineralization, high pH, elevated levels of K(+), Li(+), SO4 (2-), NO(2-), Cl(-), Li, Mn, and Ni, and the presence of a fine-dispersed mechanical suspension. To assess the impact of contamination on fish and determine the mechanisms of their adaptation, we investigated the biochemical indices and histology of the liver of whitefish (Coregonus lavaretus L.) and pike (Esox lucius L.) inhabiting Lake Kostomukshskoe, downstream Lake Koyvas (64° 47' 30° 59'), and Lake Kamennoe, which is located in a nature preserve and has not been affected by anthropogenic activity (64° 28' 30° 13'). Changes were detected in the activity of metabolic enzymes (cytochrome c oxidase (COX), lactate dehydrogenase, and glucose-6-phosphate dehydrogenase) in the liver. Specifically, the COX activity in the liver of both fish species from the contaminated lake decreased, indicating a low level of aerobic metabolism. Lipid infiltration was the most visible and widespread change observed in the liver of both fish species; therefore, it can be considered a marker of such long-term contamination. Lesions in pike liver demonstrated a wider range of severity than in those of whitefish. In summary, metabolic enzyme activity and histomorphology of the liver of whitefish and pike differed among lakes in a species-specific manner. The changes in enzyme activity and histomorphological alterations in fish that were observed can be applied for evaluation of freshwater systems that may be subjected to mineral pollution.