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The expansion of northern Pike Esox lucius outside its native range into the western states of North America is a growing problem due to their negative effects on fish communities. Illegally introduced E. lucius were first detected in Box Canyon Reservoir in northeast Washington in 2004. By 2010, the E. lucius population was estimated at more than 10,000 individuals. Between 2012 and 2019, a gillnet suppression programme was conducted, which reduced the E. lucius catch per unit effort in Box Canyon Reservoir by 97% and their biomass by 98%. Between 2004 and 2019, four standardized surveys were conducted to characterize changes in the Box Canyon Reservoir fish community. Even after E. lucius were effectively suppressed, native species showed no signs of recovery during the study. The relative abundance of all native species decreased 82% in total number and 56% in total biomass between 2004 and 2019. Conversely, the relative abundance of non‐native species increased 26% in total number and 33% in total biomass over the same period. As an apex predator, E. lucius had a significant impact on the fish community in Box Canyon Reservoir over a relatively short period of time (7 years), and appeared to act as a catalyst to increase the rate of replacement of native species with non‐native species, which likely increased the pace of taxonomic homogenization in the reservoir. [ABSTRACT FROM AUTHOR]

The northern pike Esox lucius is a freshwater fish with low genetic diversity but ecological success throughout the Northern Hemisphere. Here, we generate an annotated chromosome-level genome assembly of 941 Mbp in length with 25 chromosome-length scaffolds. We then genotype 47 northern pike from Alaska through New Jersey at a genome-wide scale and characterize a striking decrease in genetic diversity along the sampling range. Individuals west of the North American Continental Divide have substantially higher diversity than those to the east (e.g. Interior Alaska and St. Lawrence River have on average 181 and 64K heterozygous SNPs per individual, or a heterozygous SNP every 5.2 and 14.6 kbp, respectively). Individuals clustered within each population with strong support, with numerous private alleles observed within each population. Evidence for recent population expansion was observed for a Manitoba hatchery and the St. Lawrence population (Tajima's D = −1.07 and −1.30, respectively). Several chromosomes have large regions with elevated diversity, including LG24, which holds amhby , the ancestral sex determining gene. As expected amhby was largely male-specific in Alaska and the Yukon and absent southeast to these populations, but we document some amhby (−) males in Alaska and amhby (+) males in the Columbia River, providing evidence for a patchwork of presence of this system in the western region. These results support the theory that northern pike recolonized North America from refugia in Alaska and expanded following deglaciation from west to east, with probable founder effects resulting in loss of both neutral and functional diversity (e.g. amhby). [ABSTRACT FROM AUTHOR]

Abstract Eustrongylides excisus is a fish-borne zoonotic parasite known to infect various fish species, including Northern pike (Esox Lucius). This nematode, belonging to the family Dioctophymatidae, has a complex life cycle involving multiple hosts. This study aimed to investigate the occurrence of Eustrongylides nematodes in Northern pike (E. Lucius) collected from Mijran Dam (Ramsar, Iran). Between June and October 2023, an investigation was conducted on Northern pike from Mijran Dam in Ramsar, Iran, following reports of reddish parasites in their muscle tissues. Sixty fish were examined at the University of Tehran, revealing live parasites in the muscles, which were then analyzed microscopically and preserved for a multidisciplinary study. The skeletal muscle tissues of 85% (51/60) of fish specimens were infected by grossly visible larvae which were microscopically identified as Eustrongylides spp. In histopathological examination, the lesion was composed of encapsulated parasitic granulomatous myositis. Microscopically, the cystic parasitic granulomas compressed the adjacent muscle fibers, leading to their atrophy and Zenker’s necrosis. Moreover, epithelioid macrophages, giant cells and mononuclear inflammatory cells were present around the larvae and between the muscle fibers. Finally, a molecular analysis by examining the ITS gene region, revealed that they belong to the species E. excisus. Eustrongylidiasis in northern Iran necessitates further research into the biology, epidemiology, and control of Eustrongylides nematodes, focusing on various hosts. This study is the first to comprehensively characterize E. excisus in Northern pike in Ramsar, Iran, raising concerns about possible zoonotic transmission.

Eustrongylides excisus is a fish-borne zoonotic parasite known to infect various fish species, including Northern pike (Esox Lucius). This nematode, belonging to the family Dioctophymatidae, has a complex life cycle involving multiple hosts. This study aimed to investigate the occurrence of Eustrongylides nematodes in Northern pike (E. Lucius) collected from Mijran Dam (Ramsar, Iran). Between June and October 2023, an investigation was conducted on Northern pike from Mijran Dam in Ramsar, Iran, following reports of reddish parasites in their muscle tissues. Sixty fish were examined at the University of Tehran, revealing live parasites in the muscles, which were then analyzed microscopically and preserved for a multidisciplinary study. The skeletal muscle tissues of 85% (51/60) of fish specimens were infected by grossly visible larvae which were microscopically identified as Eustrongylides spp. In histopathological examination, the lesion was composed of encapsulated parasitic granulomatous myositis. Microscopically, the cystic parasitic granulomas compressed the adjacent muscle fibers, leading to their atrophy and Zenker's necrosis. Moreover, epithelioid macrophages, giant cells and mononuclear inflammatory cells were present around the larvae and between the muscle fibers. Finally, a molecular analysis by examining the ITS gene region, revealed that they belong to the species E. excisus. Eustrongylidiasis in northern Iran necessitates further research into the biology, epidemiology, and control of Eustrongylides nematodes, focusing on various hosts. This study is the first to comprehensively characterize E. excisus in Northern pike in Ramsar, Iran, raising concerns about possible zoonotic transmission. [ABSTRACT FROM AUTHOR]

The White-Tailed Eagle (WTE) Haliaeetus albicilla is a top avian predator that has rapidly increased in numbers and range in large parts of Europe in recent decades. In Poland, over the past 30 years, it has recolonized previously abandoned areas. In 1991, the first breeding pair in a large forest complex, the Augustów Forest (Northeast (NE) Poland), was recorded. In 2022, there were 13 breeding pairs. We analyzed changes in the diet composition of WTE in 2000–2023, divided into three periods: 2000–2005, 2009–2017, and 2018–2023. Throughout the 24 years of study, birds were the most frequently recorded food item, accounting for an average of 58% of food items, followed by fish (34%) and mammals (7%). During the study period, the most numerous food items were the Northern Pike Esox lucius, Coot Fulica atra, Common Bream Abramis brama, Mallard Anas platyrhynchos, and storks Ciconia sp. These species together accounted for 52% of food items. We recorded a long-term increasing share of Northern Pike, storks, and Great Crested Grebe Podiceps cristatus. Opposite changes, with declining frequency, were found for Coots and ducks. The share of the Coot, ducks, and Great Crested Grebe, as well as the total share of food connected with lakes in the WTE's diet, increased along the growing area of lakes in the territory of the WTE. The proportion of fish in the food did not show a relationship with the increase in the area of lakes, while the most frequently eaten fish species changed. Observed changes in food composition appear related to the settlement of the habitat-diverse areas by individual breeding pairs and changes the availability of main food categories. [ABSTRACT FROM AUTHOR]

Diet plays a critical role in the composition and development of the gut microbiome and benefits of a healthy gut microbiome are well understood in humans; similar symbiotic functions likely exist in fish. We examined the link between northern pike (Esox lucius) initial diet and gut microbiome during the first 4 weeks of fish development by manipulating feed type and characterizing microbial communities of fish guts, water, and diet samples via next generation sequencing of the 16s rRNA gene. Swim-up fry received one of two 'initial' diets (Artemia sp. or zooplankton) for 2 weeks before transitioning to a dry pellet diet. We observed differences in gut microbiota between diet treatments and within treatments across time. In particular, differences were detected between weeks three and four in Artemia sp. and zooplankton treated fish despite transition to a dry pellet diet. Late sampled fish (weeks 3 and 4) exhibited a pattern of decreased microbial diversity compared to fish from weeks 1 and 2. Despite fish being shifted to the same diet, these divergent paths indicate a strong influence of initial diet on gut microbiome structure later in life. Overall, diet showed a deterministic influence on the presence/absence of certain bacteria in the fish gut microbiome. [ABSTRACT FROM AUTHOR]

Abstract Invasive species are a major threat to global biodiversity, yet also represent large‐scale unplanned ecological and evolutionary experiments to address fundamental questions in nature. Here we analyzed both native and invasive populations of predatory northern pike (Esox lucius) to characterize landscape genetic variation, determine the most likely origins of introduced populations, and investigate a presumably postglacial population from Southeast Alaska of unclear provenance. Using a set of 4329 SNPs from 351 individual Alaskan northern pike representing the most widespread geographic sampling to date, our results confirm low levels of genetic diversity in native populations (average 𝝅 of 3.18 × 10−4) and even less in invasive populations (average 𝝅 of 2.68 × 10−4) consistent with bottleneck effects. Our analyses indicate that invasive northern pike likely came from multiple introductions from different native Alaskan populations and subsequently dispersed from original introduction sites. At the broadest scale, invasive populations appear to have been founded from two distinct regions of Alaska, indicative of two independent introduction events. Genetic admixture resulting from introductions from multiple source populations may have mitigated the negative effects associated with genetic bottlenecks in this species with naturally low levels of genetic diversity. Genomic signatures strongly suggest an excess of rare, population‐specific alleles, pointing to a small number of founding individuals in both native and introduced populations consistent with a species' life history of limited dispersal and gene flow. Lastly, the results strongly suggest that a small isolated population of pike, located in Southeast Alaska, is native in origin rather than stemming from a contemporary introduction event. Although theory predicts that lack of genetic variation may limit colonization success of novel environments, we detected no evidence that a lack of standing variation limited the success of this genetically depauperate apex predator.

We evaluated a wetland habitat modification strategy to contrast fish assemblage structure and the production of young‐of‐the‐year (YOY) fish between different engineered habitats (i.e., spawning pool complexes and connectivity channels) relative to unmodified lateral channels in a large drowned river mouth tributary of the St Lawrence River. Prior to habitat modifications, the coastal wetland was impaired by water level regulations and dominance of the invasive hybrid cattail, Typha × glauca, which collectively replaced or created barriers to seasonally flooded spawning habitats important to fish. Connectivity enhancements provided fish access along a wetland habitat gradient from sedge‐meadows to the deeper water robust emergent main channel. Across an 8‐year fish emigration dataset (2012, 2013, 2016–2021) more than 90% of all captured fish (Ntotal = 218,086 fish) were YOY and modified habitats outperformed the unmodified channels in total fish catch‐per‐unit‐effort (CPUE) per year (both YOY and non‐YOY). Spawning pool complexes had higher YOY species richness than unmodified channel habitats. Fish assemblage structure differed between the modified habitats, where connectivity channels and unmodified channels shared a more similar fish assemblage than spawning pool complexes. Modified habitats, however, supported warmer water and higher dissolved oxygen than the unmodified channels. Redundancy analysis and linear mixed‐effect modelling with abiotic variables (hydrology, temperature and dissolved oxygen) showed significant effects on fish assemblage structure, species richness and CPUE of fish emigrating from the modified and unmodified habitats. Historic flooding in 2017 and 2019 was a primary driver of YOY fish production and fish assemblage structure, but also appeared to be associated with near anoxic conditions systemwide. YOY fish for several species was inversely affected by floods at spawning pool complexes, but CPUE of YOY fish for these species appeared unaffected at the connectivity channels despite low dissolved oxygen. Diversified habitat structure (i.e., connectivity channels and spawning pool complexes) offers a management option to enhance habitat for fish that allowed compensatory effects on the capture of YOY fish of several species during floods. This multifaceted outcome from the habitat modifications resulted in unique fish assemblages between the channelized and spawning pool habitat. A connectivity‐based habitat enhancement strategy provides adaptability for an uncertain climatic and regulatory future for the Laurentian Great Lakes and St Lawrence River. [ABSTRACT FROM AUTHOR]

Abstract The core‐microbiome hypothesis postulates that key fish gut microbiota develop independently from the environment they exist in. Fish nursery habitats serve as critical environments early in ontogeny that support fish growth and development, but their relationship to the development of gut microbiota is poorly understood. We compared gut microbiota of first growing season northern pike (Esox lucius) and source water from two spatially distinct nursery wetlands to examine their potential association and as a field test of the core‐microbiome hypothesis. Microbial communities within the pike hindguts and associated water column samples were characterized through metabarcoding and sequencing of the 16S rRNA gene. As expected, community level non‐metric multidimensional scaling analysis revealed significant separation in microbial community composition between fish and water samples. Unifrac distances indicated no significant dissimilarity among fish gut and source water combinations compared to fish gut samples pairwise tested with non‐source water samples, suggesting similar patterns of in vivo selection of the gut microbiome. This was consistent among habitats for three of four dominant hindgut bacterial genera (Aeromonas spp., Clostridium sensu stricto, and Plesiomonas spp.). Cetobacterium spp. was an exception, where they dominated fish guts in one wetland system. Because these four‐core gut microbiota were only minor components of the source water environment, it is possible that environmental exposure is a selective process in the developing fish gut. Further experimental and field research with examination of the influence of diet is needed to isolate mechanisms involved in gut microbiome development in freshwater fishes.

Invasive species are a major threat to global biodiversity, yet also represent large‐scale unplanned ecological and evolutionary experiments to address fundamental questions in nature. Here we analyzed both native and invasive populations of predatory northern pike (Esox lucius) to characterize landscape genetic variation, determine the most likely origins of introduced populations, and investigate a presumably postglacial population from Southeast Alaska of unclear provenance. Using a set of 4329 SNPs from 351 individual Alaskan northern pike representing the most widespread geographic sampling to date, our results confirm low levels of genetic diversity in native populations (average 흅 of 3.18 × 10−4) and even less in invasive populations (average 흅 of 2.68 × 10−4) consistent with bottleneck effects. Our analyses indicate that invasive northern pike likely came from multiple introductions from different native Alaskan populations and subsequently dispersed from original introduction sites. At the broadest scale, invasive populations appear to have been founded from two distinct regions of Alaska, indicative of two independent introduction events. Genetic admixture resulting from introductions from multiple source populations may have mitigated the negative effects associated with genetic bottlenecks in this species with naturally low levels of genetic diversity. Genomic signatures strongly suggest an excess of rare, population‐specific alleles, pointing to a small number of founding individuals in both native and introduced populations consistent with a species' life history of limited dispersal and gene flow. Lastly, the results strongly suggest that a small isolated population of pike, located in Southeast Alaska, is native in origin rather than stemming from a contemporary introduction event. Although theory predicts that lack of genetic variation may limit colonization success of novel environments, we detected no evidence that a lack of standing variation limited the success of this genetically depauperate apex predator. [ABSTRACT FROM AUTHOR]

French rivers are subject to winter floods. The northern pike (Esox lucius) needs these, as it performs lateral migrations for breeding. On the contrary, the allochthonous European catfish (Silurus glanis) is known to be less active in winter. However, very few studies have focused on the behaviour of these two predatory fishes during winter floods. Thus, we propose to characterize their respective responses to high waters, using a radio telemetry approach: thirty northern pikes and seven European catfish were tagged with radio transmitters in the Aisne River (northern France) and monitored between October 2020 and May 2021. As a result, some northern pikes and at least one catfish were recorded in the major bed, in various habitats, during two major floods. A "preferential zone" was identified for the northern pike and defined from the pre-flood positions; three types of behaviour were identified: "sedentary" pikes never left these zones, "returned" pikes left during floods but returned when the water level dropped, and "departed" pikes did not come back at all. Individuals from the departed group were significantly larger than those from the other two groups (5% threshold), and those in the sedentary group significantly smaller (10% threshold), suggesting a greater exploration capacity in experienced northern pikes. Meanwhile, the supposed winter quiescence of the European catfish can be questioned, as our observations highlight an adaptability to various conditions. These results also underline the importance of taking the major bed into account in riverine management policies. [ABSTRACT FROM AUTHOR]

Mercury (Hg) is a toxic environmental contaminant associated with oxidative stress in freshwater fish. A known antagonist to Hg, selenium (Se), may reduce the toxic effects of Hg. In this study, the relation among Se, methylmercury (MeHg), inorganic mercury (IHg), total mercury (THg), and the expression of biomarkers of oxidative stress and metal regulation in livers of northern pike were examined. Livers from northern pike were collected from 12 lakes in Isle Royale National Park, Pictured Rocks National Lakeshore, Sleeping Bear Dunes National Lakeshore, and Voyageurs National Park. The concentrations of MeHg, THg, and Se were measured in liver tissue, and the expression of superoxide dismutase (sod), catalase (cat), glutathione s-transferase (gst), and metallothionein (mt) was assessed. There was a positive relationship between the concentrations of THg and Se, with a Hg:Se molar ratio less than one in all livers examined. There was no significant relation between sod, cat, gst, or mt expression and Hg:Se molar ratios. cat and sod expression were significantly related to increases in percent MeHg, relative to THg; however, gst and mt expression were not significantly altered. This suggests that incorporating biomarkers containing Se may be a better indicator than non-selenium-containing proteins of assessing the long-term effect of Hg and the interactions between Hg and Se in the livers of fish, such as northern pike, especially when molar concentrations of Se are greater than Hg. [ABSTRACT FROM AUTHOR]

We assayed the fatty acid composition of muscles of the northern pike Esox lucius Linnaeus, 1758 inhabiting the Gyda River, Siberia, Russia using gas-liquid chromatography. Of 43 fatty acids identified in the pike samples, 23 fatty acids accounted for 99.3% of the total content. The most abundant saturated fatty acids (SFA, 31.6%) were palmitic (C16:0, 20.0%) and stearic (C18:0, 7.3%) acids. Among monounsaturated fatty acids (MUFA, 15.1%), oleic acid (C18:1n9, 10.2%) and palmitoleic acid (C16:1, 4.1%) demonstrated the highest levels. The most represented polyunsaturated fatty acids (PUFA, 53.3%) were arachidonic acid (C20:4n-6, 7.6%), eicosapentaenoic acid (EPA, C20:5n-3, 7.3%), and docosahexaenoic acid (DHA, C22:6n-3, 26.3%). The fatty acid profile of specimens from the Gyda River was different in comparison to profiles found in other pike populations, most likely due to different diets. Pike flesh has good nutrition quality in terms of a low n-6/n-3 ratio (0.36), low atherogenic (0.39), and thrombogenic (0.22) indices, and a high ratio of hypocholesterolemic to hypercholesterolemic fatty acids (2.83), and this species can be recommended as a replacement or alternative to other fish sources in traditional diets. [ABSTRACT FROM AUTHOR]

Being a valuable fish specie for aquaculture, the pike is getting more attention from the scientists and the farmers. Normally, intensive pike farming involves the feeding of pikes with pellets up to the size of 250-300 grams, followed by culture in traditional policulture in earth ponds. In intensive pike farming, having the fingerlings sooner means that the pike will have a bigger size at the end of the growing season. Therefore out-of-season propagation for this specie is important if we need large size pike at the age of one summer. In current practice, out-of-season propagation for pike involves quick wintering followed by thermal shocks. We propose a simple method which consists in lack of wintering and allows the farmer to artificially reproduce the pike almost in any period of winter or spring

The White-Tailed Eagle (WTE) Haliaeetus albicilla is a top avian predator that has rapidly increased in numbers and range in large parts of Europe in recent decades. In Poland, over the past 30 years, it has recolonized previously abandoned areas. In 1991, the first breeding pair in a large forest complex, the Augustów Forest (Northeast (NE) Poland), was recorded. In 2022, there were 13 breeding pairs. We analyzed changes in the diet composition of WTE in 2000–2023, divided into three periods: 2000–2005, 2009–2017, and 2018–2023. Throughout the 24 years of study, birds were the most frequently recorded food item, accounting for an average of 58% of food items, followed by fish (34%) and mammals (7%). During the study period, the most numerous food items were the Northern Pike Esox lucius, Coot Fulica atra, Common Bream Abramis brama, Mallard Anas platyrhynchos, and storks Ciconia sp. These species together accounted for 52% of food items. We recorded a long-term increasing share of Northern Pike, storks, and Great Crested Grebe Podiceps cristatus. Opposite changes, with declining frequency, were found for Coots and ducks. The share of the Coot, ducks, and Great Crested Grebe, as well as the total share of food connected with lakes in the WTE’s diet, increased along the growing area of lakes in the territory of the WTE. The proportion of fish in the food did not show a relationship with the increase in the area of lakes, while the most frequently eaten fish species changed. Observed changes in food composition appear related to the settlement of the habitat-diverse areas by individual breeding pairs and changes the availability of main food categories.

Ferritin, as an iron storage protein, regulates iron metabolism and delivers bioactive substances. It has been regarded as a safe, new type of natural iron supplement, with high bioavailability. In this paper, we extracted and purified ferritin from northern pike liver (NPLF). The aggregation stabilities, assemble properties, and structural changes in NPLF were investigated using electrophoresis, dynamic light scattering (DLS), circular dichroism (CD), UV–Visible absorption spectroscopy, fluorescence spectroscopy, and transmission electron microscopy (TEM) under various thermal treatments. The solubility, iron concentration, and monodispersity of NPLF all decreased as the temperature increased, and macromolecular aggregates developed. At 60 °C and 70 °C, the α-helix content of ferritin was greater. The content of α-helix were reduced to 8.10% and 1.90% at 90 °C and 100 °C, respectively, indicating the protein structure became loose and lost its self-assembly ability. Furthermore, when treated below 80 °C, NPLF maintained a complete cage-like shape, according to the microstructure. Partially unfolded structures reassembled into tiny aggregates at 80 °C. These findings suggest that mild thermal treatment (80 °C) might inhibit ferritin aggregation while leaving its self-assembly capacity unaffected. Thus, this study provides a theoretical basis for the processing and use of NPLF. [ABSTRACT FROM AUTHOR]

This work reports the first data on the content of plutonium (239+240Pu) in the muscle tissues of the Northern pike (Esox lucius) and the Siberian dace (Leiciscus baicalensis) inhabiting the middle reaches of the Yenisey River in the vicinity of the radioactive discharge site. An increase in the content of 239+240Pu and radiocaesium (137Cs) in pike muscles followed an increase in the volume of controlled discharges of these radionuclides to the Yenisey in 2018. The content of 239+240Pu in the muscles of pike (2–11 mBq/kg dry weight) and dace (1–4 mBq/kg dry weight) of the Yenisey fall within the range of values obtained by other authors for the ichthyofauna from water bodies contaminated with radioactive discharges from nuclear power plants and spent nuclear fuel processing plants. The ratio of the activity concentrations 239+240Pu/137Cs in fish muscles, compared with the similar ratios in other hydrobionts, indicates a significantly lower bioavailability of plutonium for fish. The obtained preliminary results make it possible to consider the Northern pike as a more prospective indicator of biologically available plutonium in the Yenisey than the dace. [ABSTRACT FROM AUTHOR]

The monitoring of species in a habitat is important to ensure biological diversity. Environmental DNA (eDNA) can infer the presence-absence of species and enable rapid action to avoid threatening factors in ecosystems in the case of non-indigenous species. Loop-mediated isothermal amplification (LAMP) assays for molecular amplification are rapidly gaining popularity in species detection, but LAMP remains an underutilized method for eDNA-based monitoring practices. The most effective combination for successful species monitoring may be the collection of eDNA or biological traces collected by nanofiltration followed by LAMP-based species detection initiatives. Here, we used LAMP analysis to detect the eDNA of Esox lucius (Northern Pike), Anguilla anguilla (European Eel), and Salmo salar (Atlantic Salmon) in Borre Lake and in the Drammen River. The selection of species is based on the categories of regionally invasive species, endangered species, and species of least concern. Two target genes were considered for each species and LAMP primers were designed. Our study showed that LAMP is an effective tool for discovering specific fish eDNA (analysis) to maintain aquatic ecosystems.

Internal seiches are common in stratified lakes, with significant effects on stratification patterns, hydrodynamics and vertical nutrient transport. In particular, seiches can change the vertical distribution of the thermocline and the cold hypolimnetic and warm epilimnetic water masses by several metres on a timescale of a few hours, leading to rapid and strong changes in temperature profiles and oxygen availability, with profound effects on mobile and sessile organisms. This could affect fish communities directly, through physiological stress and elevated mortality, and indirectly, through prey distribution.The aim of this study was to analyse the effects of internal seiche dynamics on lacustrine fish behaviour, and to characterise fish reaction patterns, with the main focus on vertical movement of fish in the vicinity of a shifting thermocline, and avoidance of cold hypolimnetic water.The analysis was based on acoustic telemetry data from Lake Milada, a post‐mining lake in the Czech Republic, with a total of 61 tracked individuals of four species: northern pike (Esox lucius), wels catfish (Silurus glanis), tench (Tinca tinca) and rudd (Scardinius erythropthalmus).The effects of seiche dynamics on the four species studied were weak but significant during the day, while at night they affected only rudd. Upward seiches elicited stronger responses in fish than downward seiches, and the impacts occurred only during the strongest seiche events.Thermocline shifting during seiche events may induce a transient reduction in habitat for seiche‐reacting species, and thus affect predation and other inter‐ and intra‐specific interactions, as well as fish community dynamics. [ABSTRACT FROM AUTHOR]

Understanding whether fishes feed selectively is important for informing conservation and management actions such as selecting receiving waters for stocked fishes and prioritizing nursery habitats for preservation or restoration. We conducted a laboratory experiment to determine if (1) age-0 muskellunge (Esox masquinongy) and northern pike (E. lucius), two primarily piscivorous congeners in the Laurentian Great Lakes, fed selectively among four prey species (bluntnose minnow [ Pimephales notatus ], johnny darter [ Etheostoma nigrum ], rock bass [ Ambloplites rupestris ], and yellow perch [ Perca flavescens ]) with different anti-predator behaviors and morphologies, and (2) prey selection and time to consumption differed between predators. Muskellunge strongly selected bluntnose minnow and avoided the other prey species. Northern pike also strongly selected bluntnose minnow and avoided johnny darter and rock bass, but exhibited slight avoidance to neutral selection of yellow perch. Mean time to consumption differed between species, with northern pike feeding more quickly than muskellunge. Further controlled experimentation is needed to reveal whether growth and survival differs when these predators consume preferred vs. non-preferred prey. In the interim, we recommend managers presume nursery habitats with soft-rayed, fusiform, non-demersal prey fishes are most likely to support growth and survival of age-0 muskellunge and northern pike. [ABSTRACT FROM AUTHOR]

Complex life history behaviours like spawning migrations can complicate population assessments. However, predictable aggregation of populations at certain times of year (e.g. at spawning grounds) presents an effective way to sample species that are otherwise spatially widespread. From 2014 to 2019, a mark‐recapture study on Green Bay northern pike (Esox lucius) entering a spawning wetland was used to estimate apparent survival and population size using Bayesian inference and the Cormack–Jolly–Seber model. Population estimates and apparent survival varied from 446 to 1949 and 0.22 (males in 2017) to 0.63 (males in 2015), respectively, among years. Apparent survival also increased with maximum mean daily water temperature. Estimated capture probability was consistently low across years (<30%) despite a sampling method with high capture efficiency of fish present at the wetland, suggesting Green Bay northern pike may be exhibiting low spawning site fidelity or other life history behaviours, like skipped spawning, which reduce their capture probability at a single wetland over time. Further, spawning site selection and timing may respond to water temperatures. Surveying multiple sites could further elucidate important life history traits while refining estimates of population size and structure in large systems. [ABSTRACT FROM AUTHOR]

Abstract Background Salmonids are of major importance both as farmed and wild animals. With the changing environment comes changes in pathogenic pressures so understanding the immune system of all salmonid species is of essence. Major histocompatibility complex (MHC) genes are key players in the adaptive immune system signalling infection to responding T-cells populations. Classical MHC class I (MHCI) genes, defined by high polymorphism, broad expression patterns and peptide binding ability, have a key role in inducing immunity. In salmonids, the fourth whole genome duplication that occurred 94 million years ago has provided salmonids with duplicate MHCI regions, while Northern Pike, a basal sister clade to salmonids, represent a species which has not experienced this whole genome duplication. Results Comparing the gene organization and evolution of MHC class I gene sequences in Northern pike versus salmonids displays a complex picture of how many of these genes evolved. Regional salmonid Ia and Ib Z lineage gene duplicates are not orthologs to the Northern pike Z lineage sequences. Instead, salmonids have experienced unique gene duplications in both duplicate regions as well as in the Salmo and Oncorhynchus branch. Species-specific gene duplications are even more pronounced for some L lineage genes. Conclusions Although both Northern pike as well as salmonids have expanded their U and Z lineage genes, these gene duplications occurred separately in pike and in salmonids. However, the similarity between these duplications suggest the transposable machinery was present in a common ancestor. The salmonid MHCIa and MHCIb regions were formed during the 94 MYA since the split from pike and before the Oncorhynchus and Salmo branch separated. As seen in tetrapods, the non-classical U lineage genes are diversified duplicates of their classical counterpart. One MHCI lineage, the L lineage, experienced massive species-specific gene duplications after Oncorhynchus and Salmo split approximately 25 MYA. Based on what we currently know about L lineage genes, this large variation in number of L lineage genes also signals a large functional diversity in salmonids.

The field of stable isotope ecology is moving away from lethal sampling (internal organs and muscle) towards non‐lethal sampling (fins, scales and epidermal mucus). Lethally and non‐lethally sampled tissues often differ in their stable isotope ratios due to differences in metabolic turnover rate and isotopic routing. If not accounted for when using non‐lethal tissues, these differences may result in inaccurate estimates of resource use and trophic position derived from stable isotopes. To address this, the authors tested whether tissue type, season and their interaction influence the carbon and nitrogen stable isotope ratios of fishes and whether estimates of species trophic position and resource use are affected by tissue type, season and their interaction. This study developed linear conversion relationships between two fin types and dorsal muscle, accounting for seasonal variation. The authors focused on three common temperate freshwater fishes: northern pike Esox lucius, yellow perch Perca flavescens and lake whitefish Coregonus clupeaformis. They found that fins were enriched in 13C and depleted in 15N compared to muscle in all three species, but the effect of season and the interaction between tissue type and season were species and isotope dependent. The estimates of littoral resource use based on fin isotope ratios were between 13% and 36% greater than those based on muscle across species. Season affected this difference for some species, suggesting the potential importance of using season‐specific conversions when working with non‐lethal tissues. Fin and muscle stable isotopes produced similar estimates of trophic position for northern pike and yellow perch, but fin‐based estimates were 0.2–0.4 trophic positions higher than muscle‐based estimates for lake whitefish. The effect of season was negligible for estimates of trophic position in all species. Strong correlations existed between fin and muscle δ13C and δ15N values for all three species; thus, linear conversion relationships were developed. The results of this study support the use of non‐lethal sampling in stable isotope studies of fishes. The authors suggest that researchers use tissue conversion relationships and account for seasonal variation in these relationships when differences between non‐lethal tissues and muscle, and seasonal effects on those differences, are large relative to the scale of isotope values under investigation and/or the trophic discrimination factors under use. [ABSTRACT FROM AUTHOR]

In the context of global change, the aim of this study was to investigate the effects of temperature on the survival rate and various variables (development time, morphometric measures, energy values) for both embryos and post-hatch stages until first food intake of northern pike (Esox lucius). We applied five constant temperatures (8, 10, 12, 14 and 16 °C) and their effects were analyzed during the entire endogenous feeding period at three stages: hatching, emergence and first food intake. Around 80,000 eggs from five females and five males were used. As expected, the development time was three times longer at 8 than at 16 °C. The survival rate of well-formed post-hatch stages at the end of the endogenous feeding period was similar between temperatures: 76% (10 °C), 73% (12 °C), 72% (14 °C), 72% (16 °C), except at 8 °C (70%). Also at 16 °C, post-hatch stages were larger and had the highest energy value when starting feeding exogenously. These results are in accordance with current models that predict an increase of the distribution area of northern pike in France in coming decades associated with climate change projections (1 to 5 °C increase by 2100 for France). [ABSTRACT FROM AUTHOR]

Mercury (Hg) is a toxic environmental contaminant associated with oxidative stress in freshwater fish. A known antagonist to Hg, selenium (Se), may reduce the toxic effects of Hg. In this study, the relation among Se, methylmercury (MeHg), inorganic mercury (IHg), total mercury (THg), and the expression of biomarkers of oxidative stress and metal regulation in livers of northern pike were examined. Livers from northern pike were collected from 12 lakes in Isle Royale National Park, Pictured Rocks National Lakeshore, Sleeping Bear Dunes National Lakeshore, and Voyageurs National Park. The concentrations of MeHg, THg, and Se were measured in liver tissue, and the expression of superoxide dismutase (sod), catalase (cat), glutathione s-transferase (gst), and metallothionein (mt) was assessed. There was a positive relationship between the concentrations of THg and Se, with a Hg:Se molar ratio less than one in all livers examined. There was no significant relation between sod, cat, gst, or mt expression and Hg:Se molar ratios. cat and sod expression were significantly related to increases in percent MeHg, relative to THg; however, gst and mt expression were not significantly altered. This suggests that incorporating biomarkers containing Se may be a better indicator than non-selenium-containing proteins of assessing the long-term effect of Hg and the interactions between Hg and Se in the livers of fish, such as northern pike, especially when molar concentrations of Se are greater than Hg.

We assayed the fatty acid composition of muscles of the northern pike Esox lucius Linnaeus, 1758 inhabiting the Gyda River, Siberia, Russia using gas-liquid chromatography. Of 43 fatty acids identified in the pike samples, 23 fatty acids accounted for 99.3% of the total content. The most abundant saturated fatty acids (SFA, 31.6%) were palmitic (C16:0, 20.0%) and stearic (C18:0, 7.3%) acids. Among monounsaturated fatty acids (MUFA, 15.1%), oleic acid (C18:1n9, 10.2%) and palmitoleic acid (C16:1, 4.1%) demonstrated the highest levels. The most represented polyunsaturated fatty acids (PUFA, 53.3%) were arachidonic acid (C20:4n-6, 7.6%), eicosapentaenoic acid (EPA, C20:5n-3, 7.3%), and docosahexaenoic acid (DHA, C22:6n-3, 26.3%). The fatty acid profile of specimens from the Gyda River was different in comparison to profiles found in other pike populations, most likely due to different diets. Pike flesh has good nutrition quality in terms of a low n-6/n-3 ratio (0.36), low atherogenic (0.39), and thrombogenic (0.22) indices, and a high ratio of hypocholesterolemic to hypercholesterolemic fatty acids (2.83), and this species can be recommended as a replacement or alternative to other fish sources in traditional diets.

© 2015 Elsevier Ltd. The biogeography of freshwater fish species during and after late-Pleistocene glaciations relate to how these species are genetically organized today, and the management of these often disjunct populations. Debate exists concerning the biogeography and routes of dispersal for Northern pike (Esox lucius) after the last glaciation. A hypothesis to account for the relatively low modern genetic diversity for E. lucius is post-glacial radiation from refugia, including lakes from within the un-glaciated portions of eastern Beringia. We report the remains of a Northern pike (E. cf. lucius) skull, including bones, teeth, bone collagen and ancient DNA. The remains were preserved at a depth of between 440 and 446cm in a 670cm long core of sediment from Quartz Lake, which initiated at ~11,200calyr BP in interior Alaska. A calibrated accelerator mass spectrometer (AMS) radiocarbon age of the collagen extracted from the preserved bones indicated that the organism was dated to 8820calyr BP and is bracketed by AMS values from analyses of terrestrial plant macrofossils, avoiding any potential aquatic reservoir effect that could have influenced the radiocarbon age of the bones. Scanning electron microscope images of the specimen show the hinged tooth anatomy typically of E.lucius. Molar C:N (3.5, 1σ=0.1) value of the collagen from the specimen indicated well-preserved collagen and its mean stable nitrogen isotope value is consistent with the known predatory feeding ecology of E.lucius. Ancient DNA in the bones showed that the specimen was identical to modern E.lucius. Our record of E.lucius from interior Alaska is consistent with a biogeographic scenario involving rapid dispersal of this species from glacial refugia in the northern hemisphere after the last glaciation.

© 2015 Elsevier Ltd. The biogeography of freshwater fish species during and after late-Pleistocene glaciations relate to how these species are genetically organized today, and the management of these often disjunct populations. Debate exists concerning the biogeography and routes of dispersal for Northern pike (Esox lucius) after the last glaciation. A hypothesis to account for the relatively low modern genetic diversity for E. lucius is post-glacial radiation from refugia, including lakes from within the un-glaciated portions of eastern Beringia. We report the remains of a Northern pike (E. cf. lucius) skull, including bones, teeth, bone collagen and ancient DNA. The remains were preserved at a depth of between 440 and 446cm in a 670cm long core of sediment from Quartz Lake, which initiated at ~11,200calyr BP in interior Alaska. A calibrated accelerator mass spectrometer (AMS) radiocarbon age of the collagen extracted from the preserved bones indicated that the organism was dated to 8820calyr BP and is bracketed by AMS values from analyses of terrestrial plant macrofossils, avoiding any potential aquatic reservoir effect that could have influenced the radiocarbon age of the bones. Scanning electron microscope images of the specimen show the hinged tooth anatomy typically of E.lucius. Molar C:N (3.5, 1σ=0.1) value of the collagen from the specimen indicated well-preserved collagen and its mean stable nitrogen isotope value is consistent with the known predatory feeding ecology of E.lucius. Ancient DNA in the bones showed that the specimen was identical to modern E.lucius. Our record of E.lucius from interior Alaska is consistent with a biogeographic scenario involving rapid dispersal of this species from glacial refugia in the northern hemisphere after the last glaciation.

One of the predators of the ichthyofauna of the Lower Tobol is Esox lucius (Linnaeus, 1758) (Esociformes, Esocidae). The purpose of this work is to study the current state of the E. lucius parasite fauna in the lower reaches of the Tobol River. In the present study 47 individuals of the northern pike of different sex aged from 2+ to 8+ years were examined by the method of complete parasitological dissection. As a result of the research, 23 types of parasites were found in the pike. The largest number of species of parasitic organisms – 20 – were found in May, 12 were found in December and 11 in September. Of these, 10 species are specific to northern pike: Haemogregarina esoci (Nawrotzky, 1914), Chloromyxum esocinum (Dogiel, 1934), Myxidium lieberkuhni (Biitschli, 1882), Myxosoma anurum (Cohn, 1895), Henneguya psorospermica (Thelohan, 1995), Tetraonchus monenteron (Wagener, 1857), Gyrodactylus lucii (Kulakowskaja, 1951), Triaenophorus nodulosus (Pallas, 1781), Azygia lucii (Miiller, 1776), Raphidascaris acus (Bloch, 1779). For the first time an intraerythrocyte parasite – H. esoci – was found in pike in the Lower Tobol, the extensiveness of invasion was 18.7% in December, and 6.2% in May. Epistylis sp. and Trichodinella epizzotica parasitized on the surface of the body of fish only in May, whereas members of the genus Trichodina were found in winter and spring. In all seasons, parasitization by M. anurum and H. psorospermica was established on the gills. The greatest occurrence of spores of M. lieberkuhni and C. esocinum was observed in the spring. Myxosporidia parasitized in the kidneys and T. monenteron parasitized on the gills during all periods of the study (the latter with an extensivity of invasion of 100.0%). All examined fish are infected with T. nodulosus 100.0% of cases. In May, other types of cestodes were found: P. esocis and Dibothriocephalus latus. Three pike were infected with proteocephalis. The larval stage of diphyllobothriid was found in one fish in the liver and gonads in an amount of 139 individuals. In the pikes’ stomach, during all periods of the study, A. lucii was found in all the fish examined. In the autumn period of the study immature R. campanula were found in in the intestine of 4 fish specimens. The nematode R. acus was found in pike only in spring. This nematode was found in fish aged 4+–8+. In May, glochidia with a high intensity of invasion were found on fins, gill covers and gills of fish. E. sieboldi copepods were found on the gills; in May, one specimen was found in one pike and in September in 6 with AI of 0.7. Tetraonchus monenteron was a dominant species, in May its degree of dominance decreased with the greatest uniformity of species in this study period. Having considered the age dynamics of pike infection by various types of parasites, it was found that in the age group 4+–5+ the number of species of parasites was greatest (20), while in groups 2+–3+ and 6+–8+ it was 14. In the pike, the core parasitic fauna were M. anurum, H. psorospermica, T. monenteron, T. nodulosus, A. lucii. Seasonality has virtually no effect on the degree of infection with specific parasites. The age of fish largely determines the qualitative and quantitative composition of the parasite fauna.

Ferritin, as an iron storage protein, regulates iron metabolism and delivers bioactive substances. It has been regarded as a safe, new type of natural iron supplement, with high bioavailability. In this paper, we extracted and purified ferritin from northern pike liver (NPLF). The aggregation stabilities, assemble properties, and structural changes in NPLF were investigated using electrophoresis, dynamic light scattering (DLS), circular dichroism (CD), UV–Visible absorption spectroscopy, fluorescence spectroscopy, and transmission electron microscopy (TEM) under various thermal treatments. The solubility, iron concentration, and monodispersity of NPLF all decreased as the temperature increased, and macromolecular aggregates developed. At 60 °C and 70 °C, the α-helix content of ferritin was greater. The content of α-helix were reduced to 8.10% and 1.90% at 90 °C and 100 °C, respectively, indicating the protein structure became loose and lost its self-assembly ability. Furthermore, when treated below 80 °C, NPLF maintained a complete cage-like shape, according to the microstructure. Partially unfolded structures reassembled into tiny aggregates at 80 °C. These findings suggest that mild thermal treatment (80 °C) might inhibit ferritin aggregation while leaving its self-assembly capacity unaffected. Thus, this study provides a theoretical basis for the processing and use of NPLF.

Northern pike (Esox lucius L.) is of great importance to inland commercial and recreational fisheries in Poland. Thanks to northern pike's substantial size, strength, the possibility of using a variety of fishing methods and techniques and various baits, and many other values, lake anglers value this species above all others. Additionally, for over a decade, northern pike has been the most widely stocked species in Polish inland waters of lakes, rivers and dam reservoirs. The aim of this work was to analyze in detail the size and characteristics of northern pike commercial fisheries and angling catches in Polish inland waters over the long term. The analyses were based on a compilation of traditional scientific papers, primarily analyses of commercial catches, and a review of the results of more than 40 years of studies on the size of northern pike angling catches. The analysis of research material indicated a steady decrease in commercial catches of this species in the years State Fisheries Enterprises (SFE) were in operation followed by relative stability in catches over the past two decades. The paper describes the methods used to estimate angling catches, namely questionnaire and catch-return (the so-called register) research. An increasing disproportion between the sizes of pike catches made with angling and commercial fishing gear was documented. Despite the problems presented in the paper related to estimating total pike catches, the analysis revealed that anglers catch eightfold more northern pike than do commercial fishers. [ABSTRACT FROM AUTHOR]

Concentrations of total mercury (THg) in the axial musculature of northern pike (Esox lucius), walleye (Sander vitreus), lake whitefish (Coregonus clupeaformis), and sauger (Sander canadensis) were analyzed from several regions of Lake Winnipeg and three main inflows, focusing on Mossy Bay in the North Basin of the lake. Length-standardized means (standard means) indicated THg concentrations in pike of 550 mm fork length (0.44 ppm) and walleye measuring 400 mm (0.38 ppm) from Mossy Bay were highest in 1971 and declined to 0.13 and 0.22 ppm, respectively, by 1974. Standard means of both these species have been similar since 2010 (walleye; approximately 0.11 ppm) and 2013 (pike; approximately 0.17 ppm), except for a significant increase to 0.15 ppm in walleye in 2019, potentially related to concurrent changes in trophic interactions with invasive fish and invertebrate species. Standard means of 300 mm long sauger (0.23–0.29 ppm) did not decline significantly between 1971 and 1974, and those of 350 mm long whitefish ranged from 0.006 to 0.028 ppm from 1983 to 2016 with no clear temporal trend. In concert with data from other areas of Lake Winnipeg and the three inflows for 2000–2019, these results indicate higher contemporary concentrations in the South Basin of the lake. This latitudinal gradient in fish THg is assumed to be a result of continuous mercury inputs from the Red and the Winnipeg River, whereas a former point source of industrial mercury in the Saskatchewan River is no longer relevant. According to human consumption limits based on tolerable daily intake calculations and current THg concentrations of fish from Mossy Bay, substantial quantities of whitefish, pike, and walleye fish can be safely eaten. [ABSTRACT FROM AUTHOR]

Aim: The factors that set range limits for animal populations can inform management plans aimed at maintaining regional biodiversity. We examine abiotic and biotic drivers of the distribution of finescale dace (Chrosomus neogaeus) in two Great Plains basins to identify limiting factors for a threatened freshwater fish population at the edge of their range. Location: Great Plains, Nebraska, South Dakota and Wyoming, USA. Methods: We investigated abiotic and biotic factors influencing the contemporary distribution of finescale dace in the Belle Fourche and Niobrara River basins with Random Forests classification models using fish surveys from multiple agencies spanning 2008–2019 and GIS‐derived environmental data. Results: In both basins, finescale dace occurrence exhibited a nonlinear response to mean August water temperature. Abiotic covariates, including streamflow, water temperature and channel slope, were important limiting factors in the final model fit with Belle Fourche River basin surveys (n = 131). In contrast, a biotic covariate, native minnow richness, was the most important predictor of finescale dace occurrence in the Niobrara River basin model (n = 27). In the Niobrara River, native minnow richness was lower at sites with non‐native northern pike (Esox lucius). Main conclusions: Basin‐specific analyses revealed context dependencies for species–environment relationships, which can inform targeted restoration actions. Similar relationships between water temperature and finescale dace occurrence across both basins suggest summer thermal habitat as a regional limiting factor. The importance of biotic interactions in the Niobrara River highlights an emergent threat from invasive predators to a distinct assemblage of native prairie fishes. [ABSTRACT FROM AUTHOR]

Major histocompatibility complex (MHC) genes are key players in the adaptive immunity providing a defense against invading pathogens. Although the basic structures are similar when comparing mammalian and teleost MHC class II (MHCII) molecules, there are also clear-cut differences. Based on structural requirements, the teleosts non-classical MHCII molecules do not comply with a function similar to the human HLA-DM and HLA-DO, i.e., assisting in peptide loading and editing of classical MHCII molecules. We have previously studied the evolution of teleost class II genes identifying various lineages and tracing their phylogenetic occurrence back to ancient ray-finned fishes. We found no syntenic MHCII regions shared between cyprinids, salmonids, and neoteleosts, suggesting regional instabilities. Salmonids have experienced a unique whole genome duplication 94 million years ago, providing them with the opportunity to experiment with gene duplicates. Many salmonid genomes have recently become available, and here we set out to investigate how MHCII has evolved in salmonids using Northern pike as a diploid sister phyla, that split from the salmonid lineage prior to the fourth whole genome duplication (4WGD) event. We identified 120 MHCII genes in pike and salmonids, ranging from 11 to 20 genes per species analyzed where DB-group genes had the most expansions. Comparing the MHC of Northern pike with that of Atlantic salmon and other salmonids species provides a tale of gene loss, translocations, and genome rearrangements. [ABSTRACT FROM AUTHOR]

The Esox genus belongs to the family Esocidae. It is a freshwater fish that can be found in different parts of Europe, Asia, and North America. The Northern Pike, is a carnivorous fish, member of the only remaining genus of the Esocidae. This fish prefers to lead a solitary life due to the disadvantages of the presence of individuals of the same species which compete for food resources and territory. Waiting for a suitable situation to catch prey is a favoured hunting method, which means this specific species is a lie-in-wait predator. The elongated body and the broad snout are the most striking features used for the identification of this species. This lie-in-wait carnivorous predator mostly feeds on invertebrates and fishes. The species spawns annually. The special living conditions of this species and their endangered environment have made it necessary to avoid any acts that can affect their life quality. [ABSTRACT FROM AUTHOR]

This paper documents changes in three villages of the Ponoy River region, Murmansk, Russia between 2006 and 2020. Two keystone species—the Atlantic salmon (Salmo salar) and northern pike (Esox lucius) as well as an introduced species, the pink salmon (Oncorhynchus gorbuscha), were studied to determine changes to fish and fisheries. Oral histories, community-based observations and literature data are used to establish key messages on river health from the 1800s to 2020, including temperature data from 1864 to present. Climate change becomes increasingly evident and impacts the Ponoy River system from 1980s onwards with system-relevant changes becoming more pronounced in late 2010s. This coincides with proliferation of pink salmon from 2006 onwards. The species was introduced from the Russian Far East in the 1930s. Very few long-term community-based observation processes have taken place in the Russian North and this paper corrects this to certain extent. Ponoy River and region are important as the last major roadless wilderness area of the European North. Societal and climate changes are rapidly impacting the river and its catchment area as well as the available biological resources and consequently the local culture. This study shows the value of local communities to determine base lines and highlight ongoing changes when establishing climate change impacts and impacts of an alien species. [ABSTRACT FROM AUTHOR]

Biotelemetry is a central tool for fisheries management, with the implantation of transmitters into animals requiring refined surgical techniques that maximize retention rates and fish welfare. Even following successful surgery, long‐term post‐release survival rates can vary considerably, although knowledge is limited for many species. The aim here was to investigate the post‐tagging survival rates in the wild of two lowland river fish species, common bream Abramis brama and northern pike Esox lucius, following their intra‐peritoneal double‐tagging with acoustic transmitters and passive integrated transponder (PIT) tags. Survival over a 2‐year period was assessed using acoustic transmitter data in Cox proportional hazards models. Post‐tagging survival rates were lowest in the reproductive periods of both species, but in bream, fish tagged just prior to spawning actually had the highest subsequent survival rates. Pike survival was influenced by sex, with males generally surviving longer than females. PIT tag detections at fixed stations identified bream that remained active, despite loss of an acoustic transmitter signal. In these instances, loss of the acoustic signal occurred up to 215 days post‐tagging and only during late spring or summer, indicating a role of elevated temperature, while PIT detections occurred between 18 and 359 days after the final acoustic detections. Biotelemetry studies must thus always consider the date of tagging as a fundamental component of study designs to avoid tagged fish having premature end points within telemetry studies. [ABSTRACT FROM AUTHOR]

Translocation into a novel environment through common fisheries management practices, such as fish stocking, provides opportunities to study behavioural and fitness impacts of translocations at realistic ecological scales. The process of stocking, as well as the unfamiliarity with novel ecological conditions and the interactions with resident fish may affect translocated individuals, leading to alterations of behaviours and causing fitness impacts.Our objectives were to investigate how aquatic top predators behaviourally establish themselves and compete with resident individuals following introduction in a novel lake environment and to investigate the resulting fitness consequences.Using high‐resolution acoustic telemetry, we conducted whole‐lake experiments and compared the activity, activity‐space size and fate of translocated and resident individuals in two model top predators, the northern pike Esox lucius (n = 160) and European catfish Silurus glanis (n = 33). Additionally, we compared the reproductive success of translocated and resident northern pike. The experiment was conducted with large (adult) individuals of different origins, resilient to predation, but subject to agonistic interactions and competition with resident fish.Over a period of several months, the translocated catfish exhibited consistently larger activity‐space sizes than resident catfish, but did not differ from residents in activity and survival. The pike from one of the two translocated origins we tested also showed elevated space‐use, and both translocated origins revealed higher mortality rates than their resident conspecifics, indicating maladjustment to their novel environment. When non‐resident pike reproduced, they overwhelmingly produced hybrid offspring with resident fish, indicating that introductions fostered gene flow of non‐native genes.Our study indicates that fish introductions result in behavioural and fitness impacts even in large‐bodied top predators that experience low levels of natural predation risk. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the endogenous cathepsin activity in each subcellular fraction and the effect of this activity on myofibrillar protein and texture during refrigeration and partial freezing storage of northern pike (Esox lucius) fillets. The results showed that fillets stored under the refrigerated condition were more susceptible to oxidation than partial freezing. Endogenous cathepsin activity indicated that partial freezing destroys the integrity of lysosomes more effectively than refrigeration and inhibits the increase in cathepsin B and B + L in lysosomes. The activity of cathepsin B and B + L in lysosomes, mitochondria and myofibrils under the partial freezing conditions was always lower than that under refrigeration. Texture analysis showed that refrigeration had a negative impact on hardness and springiness. In conclusion, the cathepsin activity in each subcellular fraction was effectively inhibited and better textural characteristics were obtained with partial freezing than refrigeration. [ABSTRACT FROM AUTHOR]

Northern pike are an invasive species in southcentral Alaska and have caused the decline and extirpation of salmonids and other native fish populations across the region. Over the last decade, adaptive management of invasive pike populations has included population suppression, eradication, outreach, angler engagement, and research to mitigate damages from pike where feasible. Pike suppression efforts have been focused in open drainages of the northern and western Cook Inlet areas, and eradication efforts have been primarily focused on the Kenai Peninsula and the municipality of Anchorage. Between 2010 and 2020, almost 40,000 pike were removed from southcentral Alaska waters as a result of suppression programs, and pike have been successfully eradicated from over 20 lakes and creeks from the Kenai Peninsula and Anchorage, nearly completing total eradication of pike from known distributions in those areas. Northern pike control actions are tailored to the unique conditions of waters prioritized for their management, and all efforts support the goal of preventing further spread of this invasive aquatic apex predator to vulnerable waters. [ABSTRACT FROM AUTHOR]

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Individual variability in dispersal strategies, where some individuals disperse and others remain resident, is a common phenomenon across many species. Despite its important ecological consequences, the mechanisms and individual consequences of dispersal remain poorly understood. Here, riverine Northern pike (Esox lucius) juveniles (age 0+ (young‐of‐the‐year) and 1+ years) were used to investigate the influence of body size and trophic position (at capture) on the dispersal from off‐channel natal habitats and the subsequent consequences for body sizes, specific growth rate and trophic position (at recapture). Individuals that dispersed into the river ("dispersers") were not significantly different in body size than those remaining on nursery grounds ("stayers"). For trophic position, 0+ dispersers were of significantly lower trophic position than stayers, but with this not apparent in the 1+ fish. Following dispersal into the river, the dispersers grew significantly faster than stayers and, on recapture, were significantly larger, but with no significant differences in their final trophic positions. Early dispersal into the river was, therefore, not associated with early dietary shifts to piscivory and the attainment of larger body sizes of individuals whilst in their natal habitats, contrary to prediction. These results suggest that despite an increasing risk of mortality for individuals dispersing early from natal areas, there are long‐term benefits via elevated growth rates and, potentially, higher fitness. Such early dispersal behaviour could be driven by early competitive displacement. [ABSTRACT FROM AUTHOR]

Understanding the spatial ecology of juvenile freshwater fish beyond summer months is an essential component of their life history puzzle. To this end, declines in the natural populations of sympatric Muskellunge (Esox masquinongy) and Northern Pike (Esox lucius) in the upper St. Lawrence River prompted study of spatiotemporal patterns and habitat requirements associated with earlier life stages of these congeneric, freshwater predators in fall and overwinter periods. Over 75 age‐0 esocids were tagged and passively monitored using acoustic telemetry in four nursery embayments in fall and winter months from 2015 and 2017 months to elucidate spatiotemporal ecology and test hypotheses related to emigration. Presence, residency, space and habitat use were assessed and modelled against key environmental (i.e. water temperature and level) and biological (total length) covariates using mixed effect models. Muskellunge were found to spend more time in deeper, littoral regions with canopy‐forming, submerged aquatic vegetation while Northern Pike aggregated in the deepest, highly vegetated region of their nursery embayment. Results suggest fish may exhibit transitionary movements in fall months and may span outwards into nearshore regions along the main river channel. Studies informing coastal restoration initiatives to increase Muskellunge production are encouraged to assess sympatric habitat use relative to prominent embayment structures and further explore depth partitioning by these young predators. With a substantial influence from water‐level regulation on use of nursery habitat, future studies must work in concert with management plans aimed at producing more natural riverine cycles and thus increased recruitment of Esox species. [ABSTRACT FROM AUTHOR]

The effect of different treatment agents, namely, carp pituitary homogenate (CPH), Ovaprim ([D-Arg6, Pro9NEt]-sGnRH + domperidone) and a dopamine-receptor antagonist (metoclopramide), on the stimulation of northern pike (Esox lucius) spermiation was tested under controlled conditions. To carry out the experiment, males (n = 84) were divided into four groups: control (n = 21); CPH (n = 21); Ovaprim (n = 21); metoclopramide (n = 21). The control group was given 0.9% NaCl but no hormonal treatment. After 24 h, sperm was collected from seven males belonging to control (n = 7), CPH (n = 7), Ovaprim (n = 7) and metoclopramide (n = 7). This procedure was repeated after 48 and 72 h post-treatment. At each time, sperm was collected from seven males from each group only once. After collection, the quantity and quality of sperm were determined. It was confirmed that the treatment agent and latency time (the time between treatment and sperm collection) are two factors affecting the quantity and quality of northern pike sperm collected under controlled conditions. The highest total sperm volume and total sperm production (TSP) were noted in the CPH group compared to the Ovaprim, metoclopramide and control groups. In contrast, the time of sperm collection affected the sperm concentration (SC), TSP and sperm pH. With increasing time, SC and TSP decreased, which indicated the occurrence of sperm hydration being part of the final sperm maturation process. Sperm maturation is in turn a consequence of increases in sperm pH and seminal plasma osmotic pressure between 48 and 72 h post-treatment. Sperm motility and sperm kinetic parameters were affected by treatment agent and the time of sperm collection. This indicates that the sperm's ability to move that is achieved in the optimal environment (in spermatic ducts) is dependent on both factors which determine sperm maturation in northern pike under controlled condition. • Treatment agent and latency time are two major factors affecting the quantity and quality of sperm collected in captivity. • The largest and lowest amount of mature sperm was collected after 48 h in CPH group, and 24 h in Ovaprim group respectivelly. • A dopamine-receptor antagonist, metoclopramide, was not beneficial in the reproductive performance of pike male. • Interactions between treatment agent and time of sperm collection significantly affected the sperm kinetic parameters of pike. [ABSTRACT FROM AUTHOR]

Across the globe, dozens of species of invasive fish are now found in fresh as well as marine waters, where they alter habitats, compete with native fish for food, and prey on native fishes, exerting both indirect and direct effects on ecosystems and economies. While efforts to understand and control these species are growing, most are still in their infancy; however, a few examples stand out. This special issue is comprised of 11 notable articles on freshwater invasive fish and is the first to address this topic. This introductory article serves as an introduction to these articles which focus on 5 topics on invasive freshwater fish: (1) the damage they cause (one article); (2) techniques to ascertain their presence (one article); (3) techniques to restrict their movement (one article); (4) strategies to control them (three articles); and (5) lessons learned from ongoing management efforts (five articles). This introduction notes that successful management efforts share a few approaches: (1) they develop and use a deep understanding of local species and their abundance as well as distribution; (2) they focus on reducing reproductive success; (3) they use multiple complimentary control strategies; and (4) they use a long-term approach.

Otolith microchemistry has emerged as a powerful technique with which to identify the natal origins of fishes, but it relies on differences in underlying geology that may occur over large spatial scales. An examination of how small a spatial scale on which this technique can be implemented, especially in water bodies that share a large proportion of their flow, would be useful for guiding aquatic invasive species control efforts. We examined trace isotopic signatures in northern pike (Esox lucius) otoliths to estimate their provenance between two reservoirs in the Upper Yampa River Basin, Colorado, USA. This is a challenging study area as these reservoirs are only 11-rkm apart on the same river and thus share a high proportion of their inflow. We found that three isotopes (86Sr, 137Ba, and 55Mn) were useful in discriminating between these reservoirs, but their signatures varied annually, and the values overlapped. Strontium isotope ratios (87Sr/86Sr) were different between sites and relatively stable across three years, which made them an ideal marker for determining northern pike provenance. Our study demonstrates the usefulness of otolith microchemistry for natal origin determination within the same river over a relatively small spatial scale when there are geologic differences between sites, especially geologic differences underlying tributaries between sites.

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. [ABSTRACT FROM AUTHOR]

Abstract Spawning habitat structure may protect demersal eggs of broadcast spawning species from depredation. Egg predation by round goby (Neogobius melanostomus) is commonly referenced as a concern associated with their invasion of the Laurentian Great Lakes. Whereas nest-building species have received some attention in egg predation studies, broadcast spawning species may be particularly vulnerable as they do not guard their eggs. This study used a 2 × 7 factorial experiment to investigate how substrate characteristics influenced the rate that fertilized eggs are lost when exposed to round goby. Eggs for two recreationally important broadcast spawning species, northern pike (Esox lucius) and muskellunge (Esox masquinongy), were placed within spawning habitat treatments (bare, silt, sand, rubble, gravel, filamentous algae, and submerged aquatic vegetation) representing a range (least to most complex) of habitat complexity. Regardless of substrate type, egg loss was similar between the two esocid species. Across all substrates and species, the number of eggs lost varied two-fold over the 24-hour experiment, with the lowest rate of egg loss observed in the most complex substrate (submerged aquatic vegetation) and the highest over the least complex substrates (bare and silt). Both northern pike and muskellunge are known to spawn over structurally complex submerged aquatic vegetation and filamentous algae. Although eggs spawned over these substrates likely offer some protection from predation, eggs that settle over less complex ancillary habitats may face higher predation risk. [ABSTRACT FROM AUTHOR]

The invasion of non-native fishes is a leading cause of extinction and imperilment of native freshwater fishes. Evidence suggests that introduced species with generalist diets have the potential for greatest impacts through competition and predation even though populations are often comprised of specialist individuals. The northern pike (Esox lucius), a predatory fish, has been widely introduced outside its native range for recreational fishing purposes, especially in western North America, and it has been implicated in declines and extirpations of native fishes. We synthesized over 2900 individual northern pike diet records across 31 waterbodies from the native and introduced ranges in Alaska to quantify the extent of diet specialization and generalization relative to freshwater prey communities. To control for effects of ontogenetic diet shifts, we separately analyzed major size classes of northern pike and inferred and visualized trophic plasticity from prey-specific abundance indices and ordination. Diet generalization was common in northern pike among waterbodies and usually consisted of individuals consuming macroinvertebrates. However, when available, individual northern pike diets showed specialization on fishes, amphibians, small mammals, and dragonflies. The reliance on macroinvertebrate prey by northern pike from small, isolated lakes in the native and invasive ranges suggests that dietary plasticity facilitates persistence of these predators in the absence of preferred fish prey. Broadly, this synthesis supports the hypothesis that trophic plasticity and diet generalization widely occur among invasive and native populations of northern pike which is likely to enhance the probability of introduction success, exacerbate their environmental impacts, and complicate management of this potentially invasive freshwater predator. [ABSTRACT FROM AUTHOR]