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In many ways, globalization is beneficial, but in one way, it promotes the spread of alien (invasive) species through international trade and transport. In different habitats, Esox lucius (northern pike) can be considered a regionally alien species, and this fish tends to establish a higher density population than desired in fresh water. Early identification of such invasive species using sensitive and quick methods is important to be able to take immediate measures and avoid environmental problems. Loop-mediated isothermal amplification (LAMP) has emerged as the best DNA/RNA detection technique, without any expensive equipment and could be used to detect environmental DNA (eDNA). However, the reagents for amplification are not stable at ambient temperature for field applications. Therefore, this work aims to lyophilize the entire reaction mixture as a single microbead, with enzyme, and LAMP primers towards the detection of mitochondrial cytochrome B (Cyt B), a housekeeping gene in Esox lucius. Analytical and molecular techniques were performed to characterize and validate the lyophilized beads, respectively. The lyophilized beads were stored at two different temperatures, at 20 °C and 4 °C, and tested for biological activity after different time intervals. The result shows that lyophilized beads are bioactive for almost 30 days when stored at 20 °C, while beads at 4 °C did not lose their bioactivity after storage for up to one year. This study will be particularly useful for conducting on-site LAMP analyses in the field, where resources for freezing and storage are limited. [ABSTRACT FROM AUTHOR]

Northern pike (Esox lucius L.) is one of the fish species whose production in freshwater aquaculture may increase in the next few years. One method of producing this species is to create monosex stocks of pike, as females grow faster, mature later and gain larger body sizes. They can be obtained in the process of gynogenesis. The aim of this research was to determine and optimize the conditions of UV irradiating European perch (Perca fluviatilis L.) spermatozoa to inactivate them genetically (first experiment). The aim of this study was also to confirm whether perch spermatozoa can be used to induce northern pike gynogenesis using thermal shock (second experiment). During first experiment the highest rate of haploid larvae (29.9 ± 0.85%) was noted in the group inseminated with perch sperm irradiated for 6 min (1548 J m-2). No viable embryos were observed in groups of eggs inseminated with sperm irradiated for more than 10 minutes (2580 J m-2). The heat shock applied 12 or 14 min after gamete activation, for 3 or 5 min at 34.0°C, resulted in obtaining of gynogenetic specimen due to retention of the second polar body in all experimental groups. The most efficient was heat shock applied 14 min after gamete activation and lasting 3 min, and resulted in 18.5 ± 1.3% of gynogenetic larvae for female B. Heat shock applied 12 min after gamete activation, lasting 3 min was also effective in the case of female A, resulting in obtaining of 16.5 ± 2.1% gynogenetic specimen.

To improve stocking success in threatened populations, captive-reared animals are often familiarized to natural environment. However, whether such actions improve the ability to cope with multiple biological interactions, such as competition, predation, and parasitism that impose contradicting pressures on decision-making, is not well understood. Here, we explored short-term (4 weeks) and long-term (10 months) effects of enriched rearing on fitness-related traits of Atlantic salmon (Salmo salar). Salmon with different backgrounds of enrichment and parasite infection (eye fluke Diplostomum pseudospathaceum) were released to semi-natural ponds and monitored for activity, growth, and predation susceptibility. Fish from enriched rearing showed lower short-term activity and higher short-term growth, suggesting that they coped better with novel conditions. However, predation susceptibility and longer-term growth and survival were unaffected by rearing treatment. Importantly, parasitism did not remove the positive effect of enrichment on growth, although the infection decreased both short-term and long-term growth and survival. These results suggest that enriched rearing can enhance fitness-related traits, such as growth, of stocked fish, particularly during the critical early days, which can have important implications for stock enhancement activities. [ABSTRACT FROM AUTHOR]

Objective: Anglers typically use stringers to keep fish intended for harvest from spoiling or for high‐grading purposes (i.e., culling). However, relatively few studies have examined the effects of temporary stringer retention on the physical condition and postrelease mortality of fish. In this study, our objective was to investigate the lethal and sublethal effects of temporarily retaining Northern Pike Esox lucius on stringers. Methods: We evaluated the blood physiology, reflex impairment, injury, and fate of 168 Northern Pike that were exposed for 2 h on one of five treatments: (1) cord stringer through the operculum, (2) cord stringer through the lower jaw, (3) metal stringer through the operculum, (4) metal stringer through the lower jaw, and (5) aerated tank control. Result: Immediately after retention, blood lactate concentrations of stringer treatments were on average 42% greater relative to controls. Fish from the stringer treatments exhibited injuries of varying severity, most of which (e.g., gill lesions, expanded puncture wounds, swelling) were still present on surviving fish 48 h later. Reflexes were impaired for all stringer fish, whereas control fish tended to have all reflexes intact. No fish died during the treatment period. The highest occurrence of mortality was within the first 8 h following retention for the cord–operculum (48%), metal–jaw (15%), and metal–operculum (19%) treatments. Stringers placed through the operculum had a higher mortality rate (37%) compared with stringers placed through the lower jaw (17%), regardless of stringer type. Overall, 27% of fish placed on stringers died and 68% of the remaining fish showed injuries related to stringers, while control fish showed low mortality (7%) and no meaningful injuries. Conclusion: Our results suggest that holding fish on stringers causes stress and injury levels that can result in postrelease mortality. As such, fisheries managers should consider restricting the release of fish placed on stringers, and once placed on a stringer, fish should be regarded as part of the daily harvest limit for a given angler. Impact statementThis research highlights the detrimental effects of releasing Northern Pike off stringers during culling. We discovered that this practice results in stress, injury, and frequently death in released fish. We encourage fisheries managers to consider implementing regulations explicitly disallowing this practice to avoid negative impacts on fish populations. [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.

Twelve specimens of northern pike (Esox lucius (Linnaeus, 1758)) were caught from the Maritsa River during 2020- 2021 and examined for parasites. Helminth parasites were found in 50% of the examined northern pikes (6 specimens) from the Maritsa River. Two species of parasites were fixed: one trematode species (Bunodera luciopercae (Müller, 1776)) and one nematode species (Raphidascaris acus (Bloch, 1779)). The dominant structure of the established species is represented at the level of component communities and infracommunities. R. acus is a core species for the component community of Esox lucius from the Maritsa River. B. luciopercae is an accidental parasite species for northern pike helminth communities. The data for the infracommunities were used to determine the basic biotic indices. The bioindicator significance of the established parasite species was discussed for an ecological assessment of the studied river ecosystem. As a result of the conducted research, new data on the parasite fauna of E. lucius from the Maritsa River have been presented. [ABSTRACT FROM AUTHOR]

In this study, the quality (sensory evaluation, microbial enumerate, color, tvb-n (total volatile basic nitrogen), tca-soluble peptide (trichloroacetic acid-soluble peptide), muscle glucose, lactate, total sugar, Bas (Biogenic amines), VOCs (volatile organic compounds) and the microbial dynamic structure in samples stored at 4 °C were evaluated, and the relationship between VOCs and the diversity structure of microorganisms was also discussed. It was determined by sensory evaluation that the shelf life of samples was around 8 days. Protein and sugar were detected in large quantities by microorganisms in the later stage. At the same time, this also caused a large amount of Bas (biogenic amines) (tyramine, cadaverine, and putrescine). According to high-throughput amplicon sequencing, the initial microbiota of samples was mainly composed of Pseudomonas, Acinetobacter, Planifilum, Vagococcus, Hafnia, Mycobacterium, Thauera, and Yersinia. Among them, Pseudomonas was the most advantageous taxon of samples at the end of the shelf life. The minor fraction of the microbial consortium consisting of Vagococcus, Acinetobacter and Myroides was detected. The substances 3-methyl-1-butanol, ethyl acetate, and acetone were the main volatile components. The glucose, lactic acid, and total sugar were negatively correlated with Yersinia, Hafnia-Obesumbacterium, Thauera, Mycobacterium, and Planifilum; the proportion of these microorganisms was relatively high in the early stage. TVB-N and TCA-soluble peptides were positively correlated with Pseudomonas, Shewanella, Brochothrix, Vagococcus, Myroides, and Acinetobacter, and these microorganisms increased greatly in the later stage. The substance 3-methyl-1-butanol was positively correlated with Pseudomonas and negatively correlated with Mycobacterium. Ethyl acetate was associated with Hafnia-Obesumbacterium, Thauera, and Yersinia. Acetone was positively correlated with Acinetobacter. [ABSTRACT FROM AUTHOR]

Eustrongylides excisus is a parasitic nematode species whose life cycle requires two intermediate hosts, an aquatic oligochaete and a benthophagous fish. In the present study, 100 specimens of Esox lucius Linnaeus weighing 550800 g were collected from Freidoonkenar, south of the Caspian Sea (Mazandaran province, Iran) and were examined for the presence of Eustrongylides. The bright red nematode larvae were found in the testes and encapsulated in the body musculature of 90% of E. lucius fish. The larvae were diagnosed as Eustrongylides excisus. Tissue samples were collected from the muscles and testes for histopathological examination of the lesions caused by the parasitic larvae. For molecular analysis, the nematode larvae genomic DNA was extracted and molecular characterisa-tion of Eustrongylides and comparison with the corresponding sequences available in the GenBank was done. The histopathological damages caused by parasites in the muscle included external nod-ules, inflammation, necrosis, and granulomas. Granulomas containing multi-nucleated giant cells, epithelioid cells, lymphoid cells, macrophages and necrotic debris were observed. Microscopic ex-amination of the testes revealed mild vacuolar degeneration in some Sertoli cells. Molecular analysis confirmed obtained larvae as E. excisus. Comparison of DNA sequences showed that isolated nema-todes were very similar to those obtained from freshwater fish in China. The present study reported Eustrongylides nematodes in Esox lucius, and inflammatory lesions caused by E. excisus larvae in the muscle and testis of this species of fish for the first time. In addition, molecular characterization and phylogenic analysis of recovered larvae showed presence of microvarients.

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]

Predatory fish species play a key role in aquatic ecosystems by exerting top‐down control on the food web. Also, their intra‐guild trophic interactions (i.e. competition) are crucial for the stability of the community. However, most studies focus on adult stages, while juveniles remain poorly studied, although their recruitment is the basis for the maintenance of predator populations.We analysed carbon and nitrogen stable isotopes ratios of the young‐of‐year of four coexisting widespread predatory fish species (northern pike Esox lucius, European perch Perca fluviatilis, pikeperch Sander lucioperca, and European catfish Silurus glanis), sampled over 3 years in a shallow natural lake.We found that the hierarchy in trophic position between species was consistent across years and similar to that known for adults, but with large variations around a general pattern: pike and pikeperch tended to occupy the highest trophic positions while perch occupied the lowest, and catfish had very varying positions.Species partitioned their niches to decrease interspecific competition, but with some occasional overlaps, contributing to preserving their body condition. Depending on density, which was particularly impacted by harsh environmental conditions, niche overlap fluctuated across years, leading to niche enlargement of densely populated species, except for catfish.These mechanisms enabled species coexistence, allowing the co‐occurrence of alien and native predators within the same ecosystem.This work advocates for time‐integrated studies of trophic webs because they capture the variability of their dynamics better than a static picture. This is particularly true for juveniles whose survival strongly depends on their capacity to cope with competition. Information from trophic mid‐term studies of juveniles provides valuable guidance for optimised management of species. [ABSTRACT FROM AUTHOR]

Eustrongylides excisus is a parasitic nematode species whose life cycle requires two intermediate hosts, an aquatic oligochaete and a benthophagous fish. In the present study, 100 specimens of Esox lucius Linnaeus weighing 550-800 g were collected from Freidoonkenar, south of the Caspian Sea (Mazandaran province, Iran) and were examined for the presence of Eustrongylides. The bright red nematode larvae were found in the testes and encapsulated in the body musculature of 90% of E. lucius fish. The larvae were diagnosed as Eustrongylides excisus. Tissue samples were collected from the muscles and testes for histopathological examination of the lesions caused by the parasitic larvae. For molecular analysis, the nematode larvae genomic DNA was extracted and molecular characterisation of Eustrongylides and comparison with the corresponding sequences available in the GenBank was done. The histopathological damages caused by parasites in the muscle included external nodules, inflammation, necrosis, and granulomas. Granulomas containing multi-nucleated giant cells, epithelioid cells, lymphoid cells, macrophages and necrotic debris were observed. Microscopic examination of the testes revealed mild vacuolar degeneration in some Sertoli cells. Molecular analysis confirmed obtained larvae as E. excisus. Comparison of DNA sequences showed that isolated nematodes were very similar to those obtained from freshwater fish in China. The present study reported Eustrongylides nematodes in Esox lucius, and inflammatory lesions caused by E. excisus larvae in the muscle and testis of this species of fish for the first time. In addition, molecular characterization and phylogenic analysis of recovered larvae showed presence of microvarients. [ABSTRACT FROM AUTHOR]

The ratio of the body length of trematodes Azygia lucii and the body length of pikes in the population of the Rybinsk Reservoir has been studied. The material was collected in September–October from 2018 to 2021. A total of 386 pikes are divided into seven size classes according to body length (range 4.7–83 cm). The prevalence of A. lucii increases from 14.2% in underyearlings to 46.2% in pikes 9+. The distribution of the trematodes in all size classes is aggregated. The usual intensity of invasion is 1–3 trematodes in all classes; the proportion of fish with this intensity of invasion varies from 62.5 to 83.3%. A total of 259 worms are measured. The body length of the worms ranges from 0.49 to 3.5 cm. The average length of A. lucii increases with host size from 1.39 cm in underyearlings to 2.39 cm in older pikes. The largest trematodes (3–3.5 cm long) are found in the largest pikes. Distribution/redistribution of trematodes in the pike population occurs due to pike cannibalism. Due to this, a group of trematodes is formed in large pikes, consisting of worms of different ages and sizes. An important role in the formation of such groups of trematodes is played by paratenic hosts. Their significance depends on their infection rate and the proportion in diet of pike in a particular reservoir. The features of the biology of A. lucii (large body size and short contact of trematodes with mollusks) suggest a long lifespan of marites. [ABSTRACT FROM AUTHOR]

The aim of this research is to analyse trends of anglers’ total catches of the most important fish species caught by angling in different parts of the Sava River Basin in Croatia (Cyprinus carpio, Silurus glanis, Esox lucius and Sander lucioperca). In all investigated counties, with the exception of Vukovar-Sirmium, common carp is the dominant fish species, usually present in significantly higher quantities compared to the other three species. Only in Vukovar-Sirmium county, northern pike is the dominant species caught. In most counties there are no dramatic changes in the catches of these four fish species, apart from the usual oscillations. Due to high fishing pressure and possibly inflow of polluted water from the Bosna River, Vukovar-Sirmium county is also particularly characterised by the trend of declining catches of all four species. The significant negative correlation between the average catch and the respective value of the coefficient of variation (CV) was also found for all data.

The effect of size grading on rearing effectiveness in pike larvae and juvenile was evaluated. Three separate experiments (I, II, and III) were conducted in groups of fish with initial mean body weights of 0.047 g, 0.135 g, and 1.17 g (at corresponding ages of 29, 46, and 68 days post hatching). Before the start of each part of the experiment, the fish were graded into the following groups: small fish (group S), large fish (group L), and ungraded fish (group U). In experiment I, the mean body weights of pike in the small (SI), large (LI), and ungraded (UI) groups were 0.041 g, 0.054 g, and 0.047 g, respectively. In experiment II, the body weights in groups SII, LII, and UII were 0.098 g, 0.170 g, and 0.137 g, respectively, and in experiment III in groups SIII, LIII, and UIII were 0.99 g, 1.32 g, and 1.19 g, respectively. The stocking density in experimental I, II, and III was 450, 300, and 150 individuals per tank, respectively. Three replications were performed for each group. The duration of each experiment was 14 days and the fish were reared in a recirculating aquaculture system (20 °C, 24L:0D). The fish were fed with commercial sinking feed in the amount of 20% of the fish biomass per day in experiment I, 15% in experiment II, and 10% in experiment III. The results of the study showed that the size grading resulted in a two-fold reduction in cannibalism among large fish compared to the small and ungraded fish, which resulted in the highest survival of large pikes in experiment I. The biomass gain was significantly higher in small fish compared to large fish only in experiment III. When the growth performances obtained for the graded groups were analyzed together (groups S + L) and then compared with the results obtained for the ungraded fish (group U), only significant differences were observed in pike cannibalism for experiments I and II. The level of cannibalism in these experiments was lower in the graded fish. Ultimately, size grading does not improve the survival and biomass gain of graded fish compared to ungraded fish. [ABSTRACT FROM AUTHOR]

Micron fish bone (MFB) is an ideal food material for low-salt surimi gel. The gel properties and the 3D printing performance quality of Esox lucius surimi involved by MFB at various additions were investigated. The MFB promoted the unfolding of the surimi protein structure, catalyzed the covalent cross-linking within or between protein molecules, and boosted the formation of the surimi gel. MFB can be embedded into the gel network, increasing the strength of the gel network structure, making the surimi gel more self-supporting, and improving the thermal stability of the 3D-printed surimi gel products. The results showed that 4.0 g/100 g MFB could sustain the printing accuracy (95.22%), reduce the shrinkage rate and cooking loss rate (7.39% and 11.31%), maintain the shape stability, improve the whiteness value and water holding capacity (80.12% and 68.92%), enhance the gel strength (444.07 g cm), and improve the texture of the 3D printing product. The 4.0 g/100 g MFB also increased the hydrogen bond content and the P 21 value (the peak area ratio of the bound water) and shaped a denser mesh structure with smaller pores inside the surimi gel printed samples. This study could encourage the high-value applications of MFB and supply guidance for the subsequent progression of low-salt surimi products. • Fish bone meal was used in 3D-printed surimi gel products as a functional ingredient. • Micron fish bone can embed into myofibrillar protein gel mesh without damaging the gelling ability. • Micron fish bone promote the unrolling of the surimi protein structure and formation of surimi gel. • Micron fish bone catalyze the covalent cross-linking within or between protein molecules. [ABSTRACT FROM AUTHOR]

The paper presents the results obtained in the artificial breeding process and the stages of embryonic and postembryonic development to the pike (Esox lucius), under the conditions of Fish Culture Research and Development Station Nucet, Dâmbovita, Romania. Artificial breeding and embryonic development in pike is carried out in the temperature range of 8-12oC with an optimum of 10oC. Fecundity is variable, and depends on the size of the female, but also on water temperature, food availability, density, inter and intraspecific interactions. The number of eggs per gram is between 104 and 148, depending on the size of the females. The embryonic development period lasts 7-9 days at 11-12oC. The postembryonic development period begins on the first day of hatching, larvae ranging in length from 7.5-9 mm, present a nearly spherical yolk sac. The larval period starts when the transition to exogenous nutrition occurs; the end of this phase is marked by the axial skeleton formation and ossification. The larval period ends when the appearance of the body resembles that of adult fish. The results are essential for knowing the pike requirements and factors that influence growth and development at these stages in order to substantiate technological processes.

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 181K and 64K heterozygous SNPs per individual, or a heterozygous SNP every 5.2 kbp 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)., (© The Author(s) 2024. Published by Oxford University Press on behalf of The Genetics Society of America.)

In this study, the quality (sensory evaluation, microbial enumerate, color, tvb-n (total volatile basic nitrogen), tca-soluble peptide (trichloroacetic acid-soluble peptide), muscle glucose, lactate, total sugar, Bas (Biogenic amines), VOCs (volatile organic compounds) and the microbial dynamic structure in samples stored at 4 °C were evaluated, and the relationship between VOCs and the diversity structure of microorganisms was also discussed. It was determined by sensory evaluation that the shelf life of samples was around 8 days. Protein and sugar were detected in large quantities by microorganisms in the later stage. At the same time, this also caused a large amount of Bas (biogenic amines) (tyramine, cadaverine, and putrescine). According to high-throughput amplicon sequencing, the initial microbiota of samples was mainly composed of Pseudomonas, Acinetobacter, Planifilum, Vagococcus, Hafnia, Mycobacterium, Thauera, and Yersinia. Among them, Pseudomonas was the most advantageous taxon of samples at the end of the shelf life. The minor fraction of the microbial consortium consisting of Vagococcus, Acinetobacter and Myroides was detected. The substances 3-methyl-1-butanol, ethyl acetate, and acetone were the main volatile components. The glucose, lactic acid, and total sugar were negatively correlated with Yersinia, Hafnia-Obesumbacterium, Thauera, Mycobacterium, and Planifilum; the proportion of these microorganisms was relatively high in the early stage. TVB-N and TCA-soluble peptides were positively correlated with Pseudomonas, Shewanella, Brochothrix, Vagococcus, Myroides, and Acinetobacter, and these microorganisms increased greatly in the later stage. The substance 3-methyl-1-butanol was positively correlated with Pseudomonas and negatively correlated with Mycobacterium. Ethyl acetate was associated with Hafnia-Obesumbacterium, Thauera, and Yersinia. Acetone was positively correlated with Acinetobacter.

The aim of this research is to compare the average individual weight of the four most important fish species in fisheries (Cyprinus carpio, Silurus glanis, Esox lucius and Sander lucioperca), caught by angling in different parts of the Sava River catchment in Croatia. Significant differences were expressed between the counties along the Sava River catchment, with the smallest specimens (p˂0.05) caught in Vukovar-Sirmium county. Artisanal fishery is mostly developed in that part of the Sava River, along with angling in both countries – Croatia and Bosnia and Herzegovina. Furthermore, the inflow of the River Bosna passes through urban and industrial cities of Bosnia and Herzegovina. It can be concluded that implementing recreational fishing surveys with the specific aim of obtaining data on average individual weight is useful for fishery management.

Abstract Northern pike (Esox lucius) was widely distributed in the high latitudes of the northern hemisphere. In China, northern pike was originally distributed only in the upper reaches of the Irtysh River in Xinjiang and has appeared in many water bodies outside the Irtysh River Basin in Northern Xinjiang. A total of four populations were collected from north to south in Xinjiang, including Irtysh River (RIR), Ulungu Lake (LUL), a small lake nearby Ulungu River (LJD), and Bosten Lake (LBO). We estimated population genomic parameters, performed gene flow analysis, and estimated the effective population size of each population. The proportion of individuals with high inbreeding coefficient (F ≥ 0.0625) accounted for 36.4% (44/121) of all sequenced individuals, approximately 4.5% (1/22) in LUL, 25.9% (7/27) in LBO, 42.9% (18/42) in RIR, and 60% (18/30) in LJD. RIR had the highest mean of genomic relatedness (coancestry coefficient = 0.025 ± 0.040, IBD = 0.036 ± 0.078). Gene flow results showed that the population spreading was from RIR into two branches, one was LBO, and the other continued to split into LUL and LJD, and migration signal from LBO to LUL was detected. Our results suggested that the extinction risk of northern pike was very low in Xinjiang of China, and the controlled capture fishery of northern pike could be developed reasonably.

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The spread of aquatic invasive species typically occurs through a combination of natural and human mediated dispersal. For many aquatic invasive species, natural dispersal is limited to aquatic corridors connecting habitat. In contrast, human transport may facilitate more distant dispersal and transport among disconnected waterbodies. Genetic information can serve as a powerful tool to track invasion histories and identify both the sources and mechanisms of invasive species dispersal. We used genetic information to understand invasion history and dynamics of expanding northern pike invasion in the Columbia River basin. Results indicate that the initial introduction of northern pike into the Pend Oreille River (in eastern Washington State) resulted from human transport of fish, not dispersal from established populations upstream. Subsequent reproduction and natural dispersal from the Pend Oreille River resulted in downstream expansion of northern pike into Lake Roosevelt, a reservoir within the mainstem Columbia River. These results highlight the need for a holistic approach to suppression of invasive species. Immediate efforts must address the biological mechanisms of natural dispersal. Sustained suppression and eradication must take a broad approach that includes coordination between management agencies, as well as policy and public outreach aimed at prevention of repeated human transport events. The genetic database created from this study has already been used to eliminate potential source populations for new northern pike invasions in Washington State outside the Columbia River basin. This highlights the utility of genetic monitoring for both immediate and long-term applications to managing aquatic species invasions. [ABSTRACT FROM AUTHOR]

Understanding how eco‐evolutionary processes and environmental factors drive population differentiation and adaptation are key challenges in evolutionary biology of relevance for biodiversity protection. Differentiation requires at least partial reproductive separation, which may result from different modes of isolation such as geographic isolation (allopatry) or isolation by distance (IBD), resistance (IBR), and environment (IBE). Despite that multiple modes might jointly influence differentiation, studies that compare the relative contributions are scarce. Using RADseq, we analyse neutral and adaptive genetic diversity and structure in 11 pike (Esox lucius) populations from contrasting environments along a latitudinal gradient (54.9–63.6°N), to investigate the relative effects of IBD, IBE and IBR, and to assess whether the effects differ between neutral and adaptive variation, or across structural levels. Patterns of neutral and adaptive variation differed, probably reflecting that they have been differently affected by stochastic and deterministic processes. The importance of the different modes of isolation differed between neutral and adaptive diversity, yet were consistent across structural levels. Neutral variation was influenced by interactions among all three modes of isolation, with IBR (seascape features) playing a central role, wheares adaptive variation was mainly influenced by IBE (environmental conditions). Taken together, this and previous studies suggest that it is common that multiple modes of isolation interactively shape patterns of genetic variation, and that their relative contributions differ among systems. To enable identification of general patterns and understand how various factors influence the relative contributions, it is important that several modes are simultaneously investigated in additional populations, species and environmental settings. [ABSTRACT FROM AUTHOR]

The diversity of predatory species plays a key role in ecosystem functioning but our understanding of the mechanisms underlying their coexistence is limited, particularly in freshwater ecosystems. Northern pike Esox lucius, European perch Perca fluviatilis and pikeperch Sander lucioperca are three widespread predatory species in European lakes, where they often coexist. As potential competitors, we hypothesised that partitioning habitat is a determinant of species coexistence. This was tested by quantifying the variability of their habitat use in tracking adult individuals in the Bariousses reservoir (France, 86.6 ha, mean depth 7.1 m). Specifically, we investigated their distribution along the littoral–pelagic and depth axes along the daily cycle and across seasons. From littoral to pelagic waters were first found pike, then perch and finally pikeperch. Pike was the closest to the surface while pikeperch was the deepest. This general pattern was, however, variable across seasons with the three species located in the upper layer in summer during reservoir stratification. Individuals were more evenly distributed along the littoral–pelagic axis and closer to the bottom when water was mixing (autumn, winter). In summer, perch used more intensively in the pelagic zone during the daytime. Other species did not show any diel change of habitats. Our results highlighted that species coexistence is associated with habitat partitioning among these three predators, with perch showing a more variable behaviour regarding habitat characteristics. Now more than ever, in the context of global change which modifies habitats, it is of crucial importance to understand the coexistence mechanisms of species that shape ecosystems. [ABSTRACT FROM AUTHOR]

Information on the effects of silver nanoparticles (AgNPs) in fish has mostly been generated from standard laboratory species and short‐term toxicity tests. However, there is significant uncertainty regarding AgNP toxicity to native species of concern in North America, particularly in northern freshwater ecosystems. We assessed the chronic toxicity of AgNPs in early life stages of three North American fish species: rainbow trout (Oncorhynchus mykiss), lake trout (Salvelinus namaycush), and northern pike (Esox lucius). Newly fertilized embryos were exposed to nominal aqueous concentrations of 0.1, 0.3, 1.0, 3.0, 10.0, or 30.0 nM AgNPs for 126 (rainbow trout), 210 (lake trout), and 25 (northern pike) days. Endpoints included cumulative developmental time (°C × day or degree‐days to 50% life‐stage transition), mortality, fork length, embryonic malformations, cumulative survival, and histopathology of gill and liver in larvae/alevins. The results showed life stage–specific differences in responses, with endpoints during the embryonic stage occurring more often and at lower concentrations compared to larval/alevin and juvenile stages. Sensitivities among species were highly dependent on the endpoints measured, although developmental time appeared to be the most consistent endpoint across species. At embryonic and larval/alevin stages, northern pike was the most sensitive species (lowest observable effect concentration of 0.1 nM using developmental time). Rainbow trout displayed similar responses to lake trout across multiple endpoints and therefore seems to be an adequate surrogate for trout species in ecotoxicology studies. Moreover, while mortality during individual life stages was not generally affected, the cumulative mortality across life stages was significantly affected, which highlights the importance of chronic, multi‐life‐stage studies. Environ Toxicol Chem 2021;40:3337–3350. © 2021 SETAC [ABSTRACT FROM AUTHOR]

The long-term dynamics (over more than 70 years) of pike infection by cestodes Triaenophorus crassus and T. nodulosus in the Rybinsk Reservoir (the Volga River) has been studied in a comparative aspect. Cestode T. crassus is an invasive species that has entered the reservoir together with vendace Coregonus albula (the second intermediate host) from Lake Beloe; T. nodulosus is a native species that develops with the involvement of perch as a second intermediate host. Climate warming in the Rybinsk Reservoir manifests itself in a consistently growing average water temperature. This has led to a gradual decrease in the rate of pike infection by cestode T. crassus as a result of disturbances in the set of complex ecological relationships between the parasite and its hosts: a decrease in the abundance of large pike, fluctuations in the reservoir water level, and mass death of vendace in years with abnormally hot summers and the alternation of strong and weak year-classes in this short-cycle species (age 1+ to 3+). The long-term dynamics of pike infection by T. nodulosus is characterized by its consistently high rates and slight fluctuations. The abundance of perch population in the Rybinsk Reservoir remains high, and its age composition is stable, which contributes to a high rate of infection of both perch and pike by T. nodulosus. Cestode T. crassus occurs only in large pike (30 cm long or more); the rate of infection increases with age; T. nodulosus parasitizes mainly young pike (starting from young of the year), with the infection rate decreasing in large pike. [ABSTRACT FROM AUTHOR]

© 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.

Ladik Lake (Samsun, Turkey) is a natural landscape under the threat of pollution because of urban, agricultural and industrial activities. In this study, accumulation of heavy metals (Al, Ba, Cr, Cu, Fe, Mn, Pb and Zn) in the tissues (muscle, liver and gill) of sediment dwelling pike fish and in different substrates of Ladik Lake were investigated. Seasonal haematological, biochemical and histopathological parameters of the carp are also reported. In general, heavy-metal levels in water and sediment samples were found in the highest level in summer and the lowest in autumn. Histopathologic changes in the tissues of the fish (liver and gill) were at the minimum in winter while it was highest in summer. Blood biochemical parameters exhibited higher level in summer in comparison with other seasons. Al, Ba, Cr, Mn and Zn levels in the tissues of the fish were in the order gill>liver>muscle in all seasons. The levels of Cu, Fe and Pb were in the sequence liver>gill>muscle. Cr, Cu, Pb and Zn levels were determined to be in high level in the tissues of the fish with respect to the literature values. The heavy-metal levels in Ladik Lake and the fish health need to be regularly monitored for a sustainable environmental health. [ABSTRACT FROM AUTHOR]

Northern pike (Esox lucius) was widely distributed in the high latitudes of the northern hemisphere. In China, northern pike was originally distributed only in the upper reaches of the Irtysh River in Xinjiang and has appeared in many water bodies outside the Irtysh River Basin in Northern Xinjiang. A total of four populations were collected from north to south in Xinjiang, including Irtysh River (RIR), Ulungu Lake (LUL), a small lake nearby Ulungu River (LJD), and Bosten Lake (LBO). We estimated population genomic parameters, performed gene flow analysis, and estimated the effective population size of each population. The proportion of individuals with high inbreeding coefficient (F ≥ 0.0625) accounted for 36.4% (44/121) of all sequenced individuals, approximately 4.5% (1/22) in LUL, 25.9% (7/27) in LBO, 42.9% (18/42) in RIR, and 60% (18/30) in LJD. RIR had the highest mean of genomic relatedness (coancestry coefficient = 0.025 ± 0.040, IBD = 0.036 ± 0.078). Gene flow results showed that the population spreading was from RIR into two branches, one was LBO, and the other continued to split into LUL and LJD, and migration signal from LBO to LUL was detected. Our results suggested that the extinction risk of northern pike was very low in Xinjiang of China, and the controlled capture fishery of northern pike could be developed reasonably. [ABSTRACT FROM AUTHOR]

Pike (Esox lucius) is a large freshwater species with a wide distribution in Eurasia and North America that has been exploited since prehistoric times as is shown by the skeletal remains found on numerous archaeological sites. The role the species played in the subsistence of inland human settlements can be documented by its proportion within the spectrum of exploited fish and by reconstructing the body lengths of the pike and the amount of meat they represent. Osteometrical data in the literature allow size and, sometimes, meat weight reconstructions on the basis of the measurements of isolated cranial bones, but little attention has been paid thus far to the use of vertebrae for such reconstructions. Using a series of 27 dry skeletons of modern pike, here, we provide regression equations that allow an accurate estimation of the body length and weight of the fish on the basis of each of the first five vertebrae. Analysis of the size variation of the height, width and length of all the vertebral centra along the vertebral column, through the construction of the so-called Global Rachidian Profile, showed that only the length measurements can be of potential use for a rather crude estimation of body length. Finally, a case study is provided, using a large assemblage of Early Neolithic pike vertebrae, to show the potential of the new osteometrical data. [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]

This paper connects the concept of involvement with recreational fishing and decision rules, namely regret-minimizing vs. utility-maximizing when making choices related to the activity. We hypothesized that people who are more involved show regret-minimizing rather than utility-maximizing behavior. In support, we found that behavioral commitment, measured as avidity in fishing, and psychological involvement (measured by centrality of angling in the lifestyle of the respondent) was significantly related to the decision rule, correlating with regret-minimizing behavior, while skill, specific attitudes toward the catch and place attachment were unrelated to the decision rules that respondents followed. In our sample, regret-minimizers were dominant and preferred more restrictive harvest policies (i.e., lower daily bag limits or harvest slots over minimum-size limits). Welfare estimates of policy changes were sensitive to the decision rule and were substantially lower when assuming regret minimizing behavior than when assuming utility maximization. We conclude that regret-minimizing behavior may be a characteristic of more involved anglers, with relevant implications for welfare estimation and derivation of policy advice. • The random regret minimization model is applied to the recreational fishing context. • We conceptually and empirically connect involvement and regret minimization. • More involved anglers are more likely to be regret minimizers compared to utility maximizers. • Regret minimizing is associated with more conservation-oriented behavior. • Large difference in welfare changes between utility maximizers and regret minimizers. [ABSTRACT FROM AUTHOR]

Abstract Background In the wake of climate change many environments will be exposed to increased and more variable temperatures. Knowledge about how species and populations respond to altered temperature regimes is therefore important to improve projections of how ecosystems will be affected by global warming, and to aid management. We conducted a common garden, split-brood temperature gradient (4.5 °C, 9.7 °C and 12.3 °C) experiment to study the effects of temperature in two populations (10 families from each population) of anadromous pike (Esox lucius) that normally experience different temperatures during spawning. Four offspring performance measures (hatching success, day degrees until hatching, fry survival, and fry body length) were compared between populations and among families. Results Temperature affected all performance measures in a population-specific manner. Low temperature had a positive effect on the Harfjärden population and a negative effect on the Lervik population. Further, the effects of temperature differed among families within populations. Conclusions The population-specific responses to temperature indicate genetic differentiation in developmental plasticity between populations, and may reflect an adaptation to low temperature during early fry development in Harfjärden, where the stream leading up to the wetland dries out relatively early in the spring, forcing individuals to spawn early. The family-specific responses to temperature treatment indicate presence of genetic variation for developmental plasticity (G x E) within both populations. Protecting between- and within-population genetic variation for developmental plasticity and high temperature-related adaptive potential of early life history traits will be key to long-term viability and persistence in the face of continued climate change.

Parasite communities of pike (Esox lucius L. 1758) were calculated in Anzali Wetland along with evaluating their impacts on biometric characticties of the fish host. A total of 4338 parasites from 11 diferent species were identified including: Ichthyophthirius mutifiliis (21.88%); Trichodina sp. (8.59%); Henneguya sp. (0.78%); Tetraonchus monenteron (60.94%); Diplostomum spathaceum (23.44%); Rhipidocotyle illense (9.37%); Posthodiplostomum cuticola (0.78%); Raphidascaris acus (41.41%); Rhabdochona helichi (8.59%); Eustrongylides excisus (2.34%) and Lernea cyprinacea (3.13%). The occurrence of P.cuticola in E. lucius is reported for the first time from Anzali Wetland. By increasing total length, the average weight of the infected fish raised from 26.54 ± 12.94 g to 472.39 ± 68.38 g, the condition factor (K) from 0.64 ± 0.11 to 0.66 ± 0.06 and the gonadosomatic index (GSR) from 0.15±0.55 to 0.75±1.88. In healthy fish, the instantaneous growth rate (G) in the age groups of 1+ to 0+ years old was higher (0.617) than in the other groups, while in infected fish, the instantaneous growth factor had fluctuations in different age groups. On the other hand, the age groups of 3+ to 2+ years old had the highest growth rate (0.773). There were significant differences between the prevalence of parasites and some biometric characticties in infected fish (p

This study investigated the effects of a six-week starvation period on the fatty acid profile, body composition and blood parameters of intensively reared pike (Esox lucius). 150 pike were stocked in an experimental recirculating aquaculture system (RAS) and feed was completely withdrawn. Body composition, fatty acid composition and blood parameters (serum protein, albumin, triacylglycerol, cholesterol concentration and Lactate dehidrigenase and alkaline phosphatase activity) were measured and somatic indices were calculated. A significant decline in bodyweight, crude fat content and somatic indices was accompanied by a significant decrease of blood triacylglycerol content. The relative proportion of saturated fatty acids in the fillet decreased, while polyunsaturated fatty acids increased. There was also a significant increase in the average chain length and unsaturation index of fatty acids found in the fillet flesh. [ABSTRACT FROM AUTHOR]

У роботі з’ясовано основні проблеми, що виникають під час вирощування риб у лабораторних умовах. Вирощування риб необхідне для проведення екологічних досліджень, вивчення морфогенезу систем органів та інших досліджень, де потрібен постійний контроль за рибами на різних стадіях розвитку. Під час інкубації ікри в лабораторії виникають проблеми, які пов’язані передусім із неможливістю забезпечити постійну проточність інкубаторів з ікрою. Під час вирощування щуки звичайної (Esox lucius) через велику щільність ікри важливим є своєчасна і швидка боротьба з грибами роду Saprolegnia, забезпечення постійної заміни води в інкубаторах. Особливістю щуки є нерест за низьких температур, тому важливим є контроль за температурою води, де розвиваються ікра та личинки.

Population genetic studies reveal biodiversity patterns and inform about drivers of evolutionary differentiation and adaptation, including gene flow, drift and selection. This can advance our understanding and aid decision making regarding management and conservation efforts. Microsatellites have long been used in population genetic studies. Thanks to the development of newer techniques, sequencing approaches such as restriction site associated DNA sequencing (RADseq) are on their way to replace microsatellites for some applications. However, the performance of these two marker types in population genetics have rarely been systematically compared. We utilized three neutrally and adaptively differentiated populations of anadromous pike (Esox lucius) to assess the relative performance of microsatellites and RADseq with respect to resolution and conclusiveness of estimates of population differentiation and genetic structure. To this end, the same set of individuals (N = 64) were genotyped with both RADseq and microsatellite markers. To assess effects of sample size, the same subset of 10 randomly chosen individuals from each population (N = 30 in total) were also genotyped with both methods. Comparisons of estimated genetic diversity and structure showed that both markers were able to uncover genetic structuring. The full RADseq dataset provided the clearest detection of the finer scaled genetic structuring, and the other three datasets (full and subset microsatellite, and subset RADseq) provided comparable results. A search for outlier loci performed on the full SNP dataset pointed to signs of selection potentially associated with salinity and temperature, exemplifying the utility of RADseq to inform about the importance of different environmental factors. To evaluate whether performance differences between the markers are general or context specific, the results of previous studies that have investigated population structure using both marker types were synthesized. The synthesis revealed that RADseq performed as well as, or better than microsatellites in detecting genetic structuring in the included studies. The differences in the ability to detect population structure, both in the present and the previous studies, are likely explained by the higher number of loci typically utilized in RADseq compared to microsatellite analysis, as increasing the number of markers will (regardless of the marker type) increase power and allow for clearer detection and higher resolution of genetic structure.

Abstract Background The Northern pike, Esox lucius, is a large, long-lived, top-predator fish species and occupies a broad range of aquatic environments. This species is on its way to becoming an important model organism and has the potential to contribute new knowledge and a better understanding of ecology and evolutionary biology. Very few studies have been done on the intestinal pathology of pike infected with helminths. The present study details the first Italian record of adult Acanthocephalus lucii reported in the intestine of E. lucius. Results A total of 22 pike from Lake Piediluco (Central Italy) were examined, of which 16 (72.7%) were infected with A. lucii. The most affected areas of gastrointestinal tract were the medium and distal intestine. The intensity of infection ranged from 1 to 18 parasites per host. Acanthocephalus lucii penetrated mucosal and submucosal layers which had a high number of mast cells (MCs) with an intense degranulation. The cellular elements involved in the immune response within the intestine of pike were assessed by ultrastructural techniques and immunohistochemistry using antibodies against met-enkephalin, immunoglobulin E (IgE)-like receptor (FCεRIγ), histamine, interleukin-6, interleukin-1β, substance P, lysozyme, serotonin, inducible-nitric oxide synthase (i-NOS), tumor necrosis factor-α (TNF-α) and the antimicrobial peptide piscidin 3 (P3). In intestines of the pike, several MCs were immunopositive to 9 out of the 11 aforementioned antibodies and infected fish had a higher number of positive MCs when compared to uninfected fish. Conclusions Pike intestinal tissue response to A. lucii was documented. Numerous MCs were seen throughout the mucosa and submucosal layers. In infected and uninfected intestines of pike, MCs were the dominant immune cell type encountered; they are the most common granulocyte type involved in several fish-helminth systems. Immunopositivity of MCs to 9 out of 11 antibodies is of great interest and these cells could play an important key role in the host response to an enteric helminth. This is the first report of A. lucii in an Italian population of E. lucius and the first account on positivity of MCs to piscidin 3 and histamine in a non-perciform fish.

We address the problem of optimal size‐selective exploitation in an age‐structured fish population model by systematically examining how density and size dependency in growth, mortality and fecundity affect optimal harvesting patterns when judged against a set of fisheries objectives. The study offers five key insights. First, while minimum‐length limits often maximize the biomass yield, exploitation using harvest slots (i.e. regulations that protect both immature and very large individuals) can generate within 95% of maximum yield; harvest slots also generally maximize the number of fish that are harvested. Second, density dependence in growth and size‐dependent mortality predict more liberal optimal size limits than those derived under assumptions of no density and size dependence. Third, strong density dependence in growth maximizes the catch of trophy fish only when modest harvest is introduced; the same holds for numbers harvested, when the stock–recruitment function follows the Ricker type. Fourth, the inclusion of size‐dependent maternal effects on fecundity or egg viability has only limited effects on optimal size limits, unless the increase in fecundity with mass ("hyperallometry") is very large. However, large hyperallometry in fecundity shifts the optimal size limit for biomass yield from the traditional minimum‐length limit to a harvest slot. Fifth, harvest slots generally provide the best compromises among multiple objectives. We conclude that harvest slots, or more generally dome‐shaped selectivity to harvest, can outperform the standard minimum‐length selectivity. The exact configuration of optimal size limits crucially depends on objectives, local fishing pressure, the stock–recruitment function, and the density and size dependency of growth, mortality and fecundity. [ABSTRACT FROM AUTHOR]

The increasing popularity of pike in angling and fish farming has created a need to increase pike production. However, intensive pike farming is subject to limitations due to diseases and pathogens. Sodium chloride (NaCl) could be a good alternative to chemotherapeutics, especially for protecting the fish against pathogens and parasites at early life stages. However, the impact of high salinity on the symbiotic bacteria inhabiting freshwater fish is still unclear. Therefore, our objective was to analyze the gut microbiome to find possible changes caused by salinity. In this study, the influence of 3‰ and 7‰ salinity on pike fry was investigated. High-throughput 16S rRNA gene amplicon sequencing was used to profile the gut microbiome of the fish. It was found that salinity had a statistically significant influence on pike fry mortality. Mortality was highest in the 7‰ salinity group and lowest in the 3‰ group. Microbiological analysis indicated that Proteobacteria and Actinobacteria predominated in the pike gut microbiome in all examined groups, followed by lower percentages of Bacteroidetes and Firmicutes. There were no statistically significant differences in the percent abundance of bacterial taxa between the control group and groups with a higher salinity. Our results suggest that salinity influences the gut microbiome structure in pike fry, and that 3‰ salinity may be a good solution for culturing pike at this stage in their development. [ABSTRACT FROM AUTHOR]

A decline in northern pike (Esox lucius) abundance in the upper St. Lawrence River is thought to be related to hybrid cattail invasion and disruption of natural water-level periodicity leading to spawning and nursery habitat degradation. Channel-connectivity and spawning-pool excavations were implemented in a tributary to the upper St. Lawrence River to enhance spawning and nursery site complexity. We assessed the effects of excavations on pike by comparing percent survival (from advanced larvae to fall emigration), water quality factors, and larval diets at excavated and non-excavated sites. Lab-reared pike, 16 days post-hatch and 14 mm in length, were released at three site types: non-excavated, spawning pool, and channel. Percent survival in channels and spawning pools after a minimum of 26 days was nearly identical (2.4%), and greater than non-excavated sites (0.13%). Spawning pools displayed higher water temperatures and dissolved-oxygen concentrations than either channel or non-excavated sites. Larvae primarily consumed zooplankton and diets of larvae from spawning pools and non-excavated sites were similar, whereas larvae in channels consumed different taxa. Differences in diet were not reflected in survival, suggesting larvae were not prey-limited. Observed differences in percent survival among sites demonstrates created spawning pool and channel-connectivity sites enhanced conditions for pike. [ABSTRACT FROM AUTHOR]

Population genetic studies reveal biodiversity patterns and inform about drivers of evolutionary differentiation and adaptation, including gene flow, drift and selection. This can advance our understanding and aid decision making regarding management and conservation efforts. Microsatellites have long been used in population genetic studies. Thanks to the development of newer techniques, sequencing approaches such as restriction site associated DNA sequencing (RADseq) are on their way to replace microsatellites for some applications. However, the performance of these two marker types in population genetics have rarely been systematically compared. We utilized three neutrally and adaptively differentiated populations of anadromous pike (Esox lucius) to assess the relative performance of microsatellites and RADseq with respect to resolution and conclusiveness of estimates of population differentiation and genetic structure. To this end, the same set of individuals (N = 64) were genotyped with both RADseq and microsatellite markers. To assess effects of sample size, the same subset of 10 randomly chosen individuals from each population (N = 30 in total) were also genotyped with both methods. Comparisons of estimated genetic diversity and structure showed that both markers were able to uncover genetic structuring. The full RADseq dataset provided the clearest detection of the finer scaled genetic structuring, and the other three datasets (full and subset microsatellite, and subset RADseq) provided comparable results. A search for outlier loci performed on the full SNP dataset pointed to signs of selection potentially associated with salinity and temperature, exemplifying the utility of RADseq to inform about the importance of different environmental factors. To evaluate whether performance differences between the markers are general or context specific, the results of previous studies that have investigated population structure using both marker types were synthesized. The synthesis revealed that RADseq performed as well as, or better than microsatellites in detecting genetic structuring in the included studies. The differences in the ability to detect population structure, both in the present and the previous studies, are likely explained by the higher number of loci typically utilized in RADseq compared to microsatellite analysis, as increasing the number of markers will (regardless of the marker type) increase power and allow for clearer detection and higher resolution of genetic structure. [ABSTRACT FROM AUTHOR]

Patterns of animal migration and the ecological forces that shape them have been studied for centuries. Yet ecological impacts caused by the migration, such as altered predator–prey interactions and effects on community structure, remain poorly understood. This is to a large extent due to the scarcity of naturally replicated migration systems with negative controls, that is, ecosystems without migration. In this study, we tested whether partial migration of certain species within the overall prey community affects foraging ecology of top predators and thereby alters energy pathways in food webs. We carried out the study in independent replicated freshwater lake systems, four with and four without opportunity for prey migration. Specifically, we compared predator foraging mode in lakes where cyprinid prey fish perform seasonal partial migrations into connected streams with lakes lacking migratory opportunities for prey fish. We found clear seasonal bottom-up effects of prey migration on predators, including changes in size structure and total biomass of ingested prey, size-specific changes in littoral versus pelagic origin of diet, and a higher degree of feast-and-famine for predators in systems with migratory prey. Our analyses further showed that partially migratory prey species constitute a larger part of the prey community in systems that allow migration. Hence, prey migrations have important implications for predator foraging ecology and may cause seasonal shifts in the importance of their supporting energy pathways. We suggest that such bottom-up effects of partial migration may be a widespread phenomenon both in aquatic and in terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Efforts to positively influence ecological processes and water quality by manipulating the fish community (biomanipulation) are of particular importance in drinking water reservoirs. One of the principle measures employed is to increase the abundance of predatory fish species as a means of reducing planktonophagous and benthophagous cyprinids. However, there is little information available on the effectiveness of different predatory fish in biomanipulation exercises. We examined the diet of the five dominant predatory species (pike Esox lucius, zander Sander lucioperca, asp Leuciscus aspius, European catfish Silurus glanis, and perch Perca fluviatilis) in five representative reservoirs in the Morava River drainage basin (Czech Republic). Fish prey made up 75% of total food intake, with undesirable small cyprinids dominant by biomass (40%). European catfish and asp were not taken as prey and showed no sign of cannibalism. On the other hand, predation on conspecific predatory species (including cannibalism) was relatively high in perch, pike and zander, thereby reducing their net benefit overall. This little-considered aspect of predatory feeding needs to be taken into consideration in future biomanipulation stocking strategies. [ABSTRACT FROM AUTHOR]