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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]

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]

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]

Copyright of Ege Journal of Fisheries & Aquatic Sciences (EgeJFAS) / Su Ürünleri Dergisi is the property of Ege Journal of Fisheries & Aquatic Sciences (EgeJFAS) / Su Urunleri Dergisi and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

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]

Morphological differentiation may allow individuals to cope with prevailing environmental conditions. Morphological differentiation in fish characterized by sagittiform shape and ambush predator behaviour, such as northern pike ( Esox lucius L., 1758), has rarely been addressed. Morphological differentiation was assessed in two rivers exhibiting contrasting flow regimes: a hydropeaking river characterized by large and frequent fluctuations in flow rates and an unregulated river. An increase in northern pike movement rate was observed in the hydropeaking river. Therefore, morphological features enhancing sustained and burst swimming, as well as manoeuvrability, were expected. Our objectives are to ( i) compare morphology between the two rivers and ( ii) assess morphological differentiation between sexes. Using geometric morphometrics, shape significantly diverged between rivers irrespective of sex and between sexes in the hydropeaking river. Individuals from the hydropeaking river had more elongated heads, deeper bodies and caudal peduncles, and longer dorsal fin insertions than individuals from the unregulated river. Caudal fin differences between rivers were not consistent between sexes. Morphological differentiation suggested a trade-off among adaptations for sustained and burst swimming, as well as manoeuvrability, to cope with variable flows in a hydropeaking river. Morphological differentiation may allow the exploitation of spatially and temporally variable environmental conditions, including those stemming from river flow regulation. [ABSTRACT FROM AUTHOR]

After a fish snaps an angler’s line, the hook(s) still embedded in its mouth, the question arises: what will the encounter cost the fish? The consequences of retained gear on the physiology and behaviour of fish is not well understood. This study aimed to quantify the impact of prolonged exposure to a retained lure (simulated break off in recreational angling) to the physiology and behaviour of northern pike ( Esox lucius ) was studiedin a laboratory setting. A combination of blood-based physiological metrics and metabolic rate measurements were used to provide a comprehensive overview of the physiological consequences of lure retention in this species using two different treble hook sizes on metal casting spoons in three different hooking locations. Fine-scale video observations of pike following simulated break off were collected to assess pike interaction with a retained lure and to quantify activity patterns. We found that the retention of a lure did not significantly affect metabolic rate, blood physiology or locomotor activity of pike. However, gill ventilation rate was found to be elevated in pike hooked deeply in the throat suggesting that lures in obstructive locations may somewhat challenge recovery from exercise. Elevated cortisol levels in these fish compared to wild controls suggests that confinement produced prolonged stress in all treatments that may have affected the physiological and behaviour responses that we observed. Our findings provide important observations about the interpretation of stress-oriented laboratory studies using northern pike and the extrapolation of these results to the wild. Despite our negative findings in relation to lure impacts on pike physiology and behaviour, avoiding break offs would still be advisable for fish welfare reasons. [ABSTRACT FROM AUTHOR]

Little is known about the effect of short-term flow changes on the movement of northern pike ( Esox lucius L.). We conducted a comparative study in two rivers with different flow regimes (i.e. one regulated and one unregulated) to evaluate the extent to which adult northern pike movement is influenced by short-term river flow conditions. Data on northern pike hourly movement were collected in northeastern Ontario on 40 individuals in the Mississagi River, a river subjected to extreme daily flow variations associated with hydro-electric operations (i.e. hydropeaking), and the Aubinadong River, an unregulated river. Using manual tracking by radio-telemetry, we found that northern pike moved at a higher rate in the river subjected to short-term changes in river flow than in the unregulated river. Results also show that the relationship between movement of northern pike and flow can vary among rivers. In the Mississagi River, flow had a significant positive effect on northern pike activity, while the effect of flow in the Aubinadong River depended on water temperature. Moreover, fish in the Mississagi River utilized a restricted river section and travelled more laterally in comparison to fish inhabiting the Aubinadong River, where longer upstream-downstream movements were more common. The present study contributes to our understanding of the effects of short-term changes in flow on fish movement. This constitutes the first step towards assessing the effect of flow on fish habitat use, and eventually developing flow management strategies to mitigate impacts on fish. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Understanding how individuals are distributed in space and time, as well as how they interact with dynamic environmental conditions, represent fundamental knowledge gaps for many fish species. Using acoustic telemetry tags, we monitored the temperatures and depths used by northern pike ( Esox lucius L., 1758) and largemouth bass ( Micropterus salmoides (Lacepède, 1802)) in Toronto Harbour (Lake Ontario). Northern pike and largemouth bass had similar thermal experiences throughout the year, except during summer, when northern pike were observed in cooler waters than largemouth bass. Both species used different depths throughout the year, with northern pike occupying deeper depths. Statistical modelling indicated that depth usage was influenced by all variables (season, species, and body size) and interactions between them, whereas thermal preferences were influenced by the main effects and interactions between species:season and species : body size. Both species were observed at temperatures warmer than those in the vicinity of nearby telemetry stations, but as station temperatures exceeded 20 °C, northern pike moved into cooler water, indicating active thermoregulation. These data will be useful for refining our understanding of the spatial ecology of fish and for informing fisheries and habitat management in this and other urban harbours of the Laurentian Great Lakes. [ABSTRACT FROM AUTHOR]

The pike population in the Løpsjøen reservoir and the accessible 21 km section of the inflowing River Rena was investigated from 2003 to 2013. Telemetry and mark-recapture with Floy tags demonstrated that most fish had an annual home range of less than 2 km, while some fish performed quite extensive migrations (up to 14.4 km). Of fish radio-tagged in the reservoir, 57% were positioned in the river at least once. The population of pike ≥25 cm was estimated at 1002 fish, or 3.9 fish (3.17 kg) ha −1 . Mean length at age was significantly larger for pike caught in the river than in the reservoir for almost all age groups. CPUE during boat electro-fishing indicated significantly lower population densities and a lower proportion of juvenile fish in the river than in the reservoir. Diet analysis revealed that almost all available prey fish species were taken by pike, and that there was a clear diet differentiation between pike size classes, and between fish from the river and reservoir habitats. Small pike (<25 cm) in the reservoir had eaten mainly invertebrates, whereas smaller pike and Alpine bullhead ( Cottus poecilopus ) dominated in small pike from the river. Nine prey fish species were identified in the stomachs of medium sized pike (25–50 cm) in the reservoir, with brook lamprey ( Lampetra planeri ) and brown trout ( Salmo trutta ) as dominant. Medium sized pike in the river had taken mainly lamprey and Alpine bullhead. Larger pike (>50 cm) in the reservoir had taken brown trout as well as a number of other prey fish, while river pike of this size had taken burbot ( Lota lota ), lamprey and brown trout. Species like perch ( Perca fluviatilis ), roach ( Rutilus rutilus ) and in particular grayling ( Thymallus thymallus ) were rarely found in pike stomachs. The construction of the reservoir in a fast-flowing river caused the establishment of a healthy pike population and additional predation pressure on the rheophilic salmonids in the system, both in the reservoir and in the inflowing river. [ABSTRACT FROM AUTHOR]

The northern pike ( Esox lucius) is a fresh water species belonging to the Esocidae family. It is a carnivorous fish feeding mostly on invertebrates and fishes. Due to the scantiness of relevant literature regarding the morphology of the tongue in fish we carried out this study with the aim of providing information on the dorsal surface morphology and histological structures of the tongue in E. lucius. The tongues of five E. lucius were examined using light- and scanning electron- microscopy (SEM) techniques. The SEM studies revealed the presence of numerous teeth, longitudinal mucosal strands and scattered taste buds spread on the tongue surface. Histological studies using hematoxylin and eosin and Masson's trichrome staining showed that the musculature was not visible in the tongue of E. lucius. The tongue is composed of mucosa, and submucosa supported by osteocartilagionous skeleton. The mucosa consists of several layers of unicellular mucous cells interrupted by numerous teeth. The derivation of teeth from the underlying bronchial skeleton was visible in longitudinal section. The scattered taste buds with a typical onion shape were also present. Overall, the morphological features of the E. lucius tongue together suggested its mechanical and sensory roles. The findings of this study together with morphological and physiological data from other fishes contribute to the knowledge of the nutrition and feeding behavior in aquaculture species. [ABSTRACT FROM AUTHOR]

Our objective was to identify characteristics of aquatic vegetative communities used as larval northern pike nursery habitat in Rainy and Kabetogama lakes, glacial shield reservoirs in northern Minnesota. Quatrefoil light traps fished at night were used to sample larval northern pike in 11 potential nursery areas. Larval northern pike were most commonly sampled among floating-leaf burreed Sparganium fluctuans, common burreed Sparganium eurycarpum, sedges Carex spp., hybrid cattail Typha × glauca and wild rice Zizania palustris. A negative binomial model of light-trap catches using the presence/absence data for 2012 from all 11 bays included water elevation and the presence of cattail as significant variables. Ultimately, the species of vegetation may not be as important as the physical quality or form of the vegetation in supplying feeding and hiding cover. The aquatic plant species and structural forms encountered by larval northern pike suggest they use nearly any vegetated cover available in early spring. Water-level regulations that change availability of aquatic vegetation are likely to influence recruitment of northern pike to larger sizes. [ABSTRACT FROM AUTHOR]

We examined the long-term effects on prey fish communities of introducing Northern Pike (Esox lucius), a top predator fish, into small, Boreal Shield lakes lacking natural piscivore populations. During 1987-1994, Northern Pike were introduced into Lakes 110, 221, and 227 in the Experimental Lakes Area in northwestern Ontario, Canada. In Lake 227, prey fish were undetectable three years after the addition of Northern Pike. Although Northern Pike were removed from the lake by 1996, multiple independent visual and trapping surveys have yielded no evidence of any fish in Lake 227 since then. In 1994-1995, 85% of the Northern Pike were removed from Lake 221. In 2012, despite intensive sampling efforts using baited minnow traps, fyke nets, trap netting, gill netting, angling, and visual observation, no forage fish of any species was observed or caught in Lake 110 or 221. In all three lakes where Northern Pike were added, prey fish populations were extirpated or too small to detect. In Lake 221, we estimated the current population of Northern Pike to be 49 ± 37, a 59% decrease since 2000 when prey fish were still present. The mean total length and body condition of Northern Pike in Lake 221 had not changed since the prey community collapsed. Our findings suggest that the introduction of Northern Pike into lakes without natural piscivore populations has long-lasting effects on fish community structure, to the detriment of both Northern Pike and prey fish populations. [ABSTRACT FROM AUTHOR]

A pilot study of bioindicators of environmental health was performed in a non-industrial region of Poland in April 2008. Twenty wild-caught northern pike Esox lucius Linnaeus, 1758 were used. Established biomarkers of environmental stress were studied in these fish, including condition factor, macroscopic lesions, morphometry of hepatic melanomacrophage cells, follicular atresia, and histopathology of liver and gonads. Body weight, total body length, and gender were recorded; livers, gonads, and organs with macroscopic lesions were collected for histopathology. H&E-stained paraffin-embedded sections were studied by light microscopy. All fish appeared in good health and had no macroscopic lesions except for two fish with gut trematodes. Microscopic lesions were minimal and included peribiliary fibrosis and cholangitis, focal hepatic necrosis and vasculitis, biliary myxozoanosis, intestinal metazoan parasites, and post-spawning peritonitis. Very low levels of hepatic MMC and ovarian follicular atresia were found. The data constitute the first report of biomarkers of environmental stress in northern pike from northeastern Poland and can be used as a reference for future monitoring of fish health and aquatic pollution in this region. [ABSTRACT FROM AUTHOR]

In recent decades, wetlands have been constructed or restored around the Baltic sea to counteract the eutrophication of its coastal waters. Some of these wetlands could also be suitable spawning and nursery areas for anadromous northern pike ( Esox lucius L.). We studied juvenile pike production in three coastal wetlands along the south-eastern coast of Sweden that were restored in different ways. Where terrestrial vegetation was temporarily flooded, pike larval/juvenile emigration increased from a few thousand individuals before restoration to over a hundred thousand afterwards. We suggest that vegetation was the key to this successful reproduction, as wetlands where vegetation was removed or reduced saw no similar increase in pike production. Flooded vegetation in shallow waters offers optimal spawning conditions, increased food resources, and refuge from predation. The growth and emigration of larvae and juveniles were followed over time, revealing that 80–95% of individuals left the wetlands within 1 month (at a size <6 cm). This emigration probably represents an adaption to seasonally decreasing water levels but may also be a way to avoid cannibalism. [ABSTRACT FROM AUTHOR]

The article reports on a study related to the identification of testicular tumour in a northern pike through ecotoxicological monitoring. It notes that the composition of tubular structures of the tumour has been determined through histological tests. It mentions that fibrovascular stromal cells have separated glandular formations with Sertoli cells.

Highlights: [•] First step towards an integrated spatially explicit model for describing pike populations in rivers. [•] Calibration and validation of the individual-based model for pike in the river Yser, Belgium. [•] It is shown how a trustworthy initial condition can be established from which the IBM is evolved. [ABSTRACT FROM AUTHOR]

Background: The ability to produce physiologically critical LC-PUFA from dietary fatty acids differs greatly among teleost species, and is dependent on the possession and expression of fatty acyl desaturase and elongase genes. Atlantic salmon, as a result of a recently duplicated genome, have more of these enzymes than other fish. Recent phylogenetic studies show that Northern pike represents the closest extant relative of the preduplicated ancestral salmonid. Here we characterise a pike fatty acyl elongase, elovl5, and compare it to Atlantic salmon elovl5a and elovl5b duplicates. Results: Phylogenetic analyses show that Atlantic salmon paralogs are evolving symmetrically, and they have been retained in the genome by purifying selection. Heterologous expression in yeast showed that Northern pike Elovl5 activity is indistinguishable from that of the salmon paralogs, efficiently elongating C18 and C20 substrates. However, in contrast to salmon, pike elovl5 was predominantly expressed in brain with negligible expression in liver and intestine. Conclusions: We suggest that the predominant expression of Elovl5b in salmon liver and Elovl5a in salmon intestine is an adaptation, enabled by genome duplication, to a diet rich in terrestrial invertebrates which are relatively poor in LC-PUFA. Pike have retained an ancestral expression profile which supports the maintenance of PUFA in the brain but, due to a highly piscivorous LC-PUFA-rich diet, is not required in liver and intestine. Thus, the characterisation of elovl5 in Northern pike provides insights into the evolutionary divergence of duplicated genes, and the ecological adaptations of salmonids which have enabled colonisation of nutrient poor freshwaters [ABSTRACT FROM AUTHOR]

Copyright of Canadian Field-Naturalist is the property of Ottawa Field Naturalists' Club and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study examined mercury levels in northern pike ( Esox lucius) from the Twin Valley Reservoir in southern Alberta, 2 years after construction in 2003. The hypothesis was tested that mercury concentrations in pike from the reservoir are significantly higher than in pike from the nearby Oldman River. Mercury concentrations in muscle tissue (0.37–1.54 ppm) generally exceeded the consumption guideline of 0.5 ppm total mercury (THg), and were significantly higher (3.5-fold) than northern pike mercury concentrations in the Oldman River. In addition, these levels exceeded (up to 2-fold) previously published data from other reservoirs of the northern hemisphere. Gill-netting followed by stomach contents and stable isotope analysis revealed a very simple food web. No zooplanktivorous fish species were present, and the benthic fish community contained only few white sucker ( Catostomus commersoni). Thus, the reservoir almost completely lacked forage fish, and the pike fed primarily on amphipods ( Gammarus lacustris and Hyalella azteca), whose average mercury concentrations were 0.21 ppm. An observed low growth trajectory of northern pike in this reservoir may reflect low growth efficiency as a result of their invertebrate diet. [ABSTRACT FROM AUTHOR]

Removal of piscivores may affect population size structure, abundance and growth rates of the remaining fish community. A total of 572 northern pike, Esox lucius L., was removed from 25-ha West Long Lake, Nebraska from 2003 to 2006. The northern pike population was reduced from 36 fish ha−1 and 22 kg ha−1 in 2002 to 20 fish ha−1 and 9 kg ha−1 in 2006. The northern pike population shifted to dominance by smaller individuals. Relative abundance increased for bluegill, Lepomis macrochirus Rafinesque, but remained similar between years for largemouth bass, Micropterus salmoides (Lacepède), and yellow perch, Perca flavescens (Mitchill). Bluegill and yellow perch size structure increased probably because of reduced predation by northern pike. The effects of reduced northern pike density on largemouth bass were less evident. The largemouth bass population may be returning to higher density with smaller size structure observed before pike were introduced. The sport fish community responded positively to the removal of northern pike in this small lake. [ABSTRACT FROM AUTHOR]

The efficiency of northern pike ( Esox lucius Linnaeus) fry production via hormonal treatment of wintered broodstock is, in general, relatively low due to low egg fertilization percentage. It has been experimentally demonstrated that administration of acetone-dried carp pituitary extract in a slow-release vehicle of aqueous dispersion of Carbopol 971 P resin (CP) resulted in a higher mean fertilization percentage, possibly because the gradual hormone action could optimally control ovarian follicle maturation and ovulation. This new method of hormonal induction of ovulation was tested in a large-scale hatchery production of northern pike fry. In the present study, data on fertilization percentage collected between 2002 and 2006 at two prominent hatcheries in Hungary were analyzed. Administration of acetone-dried carp pituitary in a 2.5% CP vehicle resulted in higher fertilization (76.4 ± 7.7%; mean ± SD) compared to the saline vehicle group (59.3 ± 10.8%). The vehicle used did not affect the ovulation ratio. According to these results from large-scale production, the new method could be suitable to have wide application for induced breeding of northern pike. [ABSTRACT FROM AUTHOR]

Abstract: We hypothesized that exposure to metal mining effluent would reduce the ability of young-of-the-year fishes to accumulate energy reserves to survive the overwinter period (known as “winter stress syndrome”) in a Canadian boreal forest watershed. Northern pike (Esox lucius) and burbot (Lota lota) were collected immediately before and after winter from a reference lake and two lakes receiving effluent. Unexpectedly, total body lipid and triglyceride, and liver triglyceride levels were greater in effluent-exposed pike and burbot in both fall and spring. However, there were no lake or season differences in growth indices of length, weight, muscle RNA/DNA ratio, or muscle protein levels in pike. In addition, total lipids and triglycerides in burbot were greater in spring compared to fall, while no seasonal differences were observed in pike, suggesting that burbot continued to feed during winter. Findings do not support the winter stress syndrome hypothesis and suggest possible direct and indirect effects of metal mining effluent on lipid dynamics of juvenile fishes. [Copyright &y& Elsevier]

We performed a tagging study on one of the spawning populations of northern pike ( Esox lucius L.) of the River Kajaaninjoki in Finland. Northern pike is the main predator in many lakes and rivers in the northern hemisphere. Previous tagging studies have shown a general tendency to sedentary behaviour by pike. Whether individuals in a fish population adapt a sedentary or moving strategy may affect population persistence. To study if the spawning population consists of sedentary or moving individuals and the pattern of movements, we tagged 40 pike with radio transmitters and followed them from May 2002 to June 2003. Pike were caught and tagged during the spawning season in the mouth of the River Kajaaninjoki which flows into one of the largest lakes in Finland, Lake Oulujärvi. Our results suggest that the pike spawning population consisted of sedentary pike ( N = 16) dwelling the whole year in the river, and moving pike ( N = 24) which moved to Lake Oulujärvi after the spawning period. Pike exhibited homing behaviour, as most of the migrating pike returned to the same spawning area in the following year. Large pike had a higher movement rate than small pike during the summer and seasonally the movement rate was lowest during the spring and highest during the summer. [ABSTRACT FROM AUTHOR]

An individual-based early life history model demonstrated that the timing and distribution of St Lawrence River northern pike ( Esox lucius) spawning could affect subsequent young-of-year (YOY) production during nursery and influence year-class formation. Three different spawning patterns have emerged from empirical studies, where egg deposition occurred along the entire littoral gradient beginning in seasonally flooded emergent habitats in tributaries, progressing to submerged aquatic vegetation in shallow bays, and ending in deep water littoral habitats (up to 6 m). The spawning period is protracted, and typically lasts 6–8 weeks due to the presence of a strong thermal gradient. The model used temperature as the driving variable to predict egg abundance, stage-specific development, growth, survival, and ultimately relative production of YOY northern pike within 1-ha plots representative of the three habitats. Earlier spawning (mean 21 days) and higher mean daily survival and growth yielded higher YOY net production for tributaries (mean = 3095.4 g ha−1, SD = 2028.6) relative to the shallow bay habitat (202.5 g ha−1, SD = 125.7). In contrast, deep littoral habitat represented an ecological sink with little production (<0.9 g ha−1). The results demonstrate the importance of the linkage between spawning and nursery processes in determining reproductive success. [ABSTRACT FROM AUTHOR]

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Griffiths RW, Newlands NK, Noakes DLG, Beamish FWH. Northern pike ( Esox lucius) growth and mortality in a northern Ontario river compared with that in lakes: influence of flow. Ecology of Freshwater Fish 2004: 13: 136–145. © Blackwell Munksgaard, 2004 We measured the growth and mortality characteristics of northern pike ( Esox lucius) in a northern Ontario river and examined the influence of flow on these characteristics by comparing our measurements with those estimated for a lake at the same latitude based on published studies. Pike ranged in total length from 229 to 784 mm, in mass from 70 to 4250 g, and in age from 1 to 10 years. The population showed a preponderance of 2–5-year olds, with few fish surviving beyond 7 years of age. Growth, in terms of length increase, was similar to that reported for circumpolar populations. Mean total length at 5 years of age was 577 mm, growth rate of young adults was 62.5 mm year−1, growth was isometric, longevity was 10 years of age, and the adult annual mortality rate was 49%. Growth and mortality characteristics of this riverine population were similar to those estimated for a lacustrine population at the same latitude. Flow thus had little measurable effect on the growth or mortality of pike possibly because of the overwhelming effect of other abiotic variables such as temperature, length of growing season and productivity. Consequently, growth characteristics of lacustrine populations can be used to assess the health and condition of riverine populations. [ABSTRACT FROM AUTHOR]

The broad-spectrum antibacterial drug oxytetracycline (OTC) is used in the U.S. to treat certain diseases in salmonids and catfish. This study was conducted to support an extension of the OTC label to include all cool-water fish species cultured at U.S. public aquaculture facilities by satisfying human food safety requirements. Juvenile northern pike (Esox lucius; mean weight: 117 g) and walleye (Stizostedion vitreum; mean weight: 59 g) were fed OTC-medicated diets near the maximum legal treatment rate (82.7 mg OTC-HCl/kg fish/day for 10 days) and near the lower limit of the water temperature range for most disease outbreaks in these species (14 and 16 °C, respectively). Two trials were conducted simultaneously with northern pike, one using commercially medicated feed and the other using on-site OTC top-coated feed. A third trial was performed with walleye using on-site OTC top-coated feed. Fillet tissues were collected and OTC free base (OTC-base) concentrations were determined by high performance liquid chromatography. The maximum mean OTC-base concentrations in the fillet tissue were 319 ng/g in northern pike (skinless) and 721 ng/g in walleye (skin-on), both well below the current tolerance limit of 2000 ng/g OTC-base. The log-linear loss of OTC-base from the fillet tissues was monophasic, with terminal phase half-lives of 5.9 days in northern pike fed commercial medicated feed, 6.7 days in northern pike fed top-coated feed, and 10.5 days in walleye fed top-coated feed. The data supported a zero withdrawal time in juvenile northern pike and walleye fed OTC at the approved dose level for 10 days at water temperatures down to 14 and 16 °C respectively. [Copyright &y& Elsevier]

Eyeing and hatching rates with regard to sperm: egg ratio, the length of time eggs remain viable post-activation in water, and duration of storage time in testicular and stripped sperm were determined in northern pike Esox lucius. In a trial of seven sperm: egg ratios, we found 4 × 105 to be the minimum tested number of spermatozoa per egg to produce an acceptable hatching rate (66 ± 4%). To determine the period of time that eggs remain viable after activation, eggs were placed in hatchery water and fertilized at 0, 15, 30, 45, 60, 90, 120, 240, and 480 s post-activation. With elapsed time, the eyeing and hatching rates decreased significantly (P <.05), dropping from 83 ± 8% and 73 ± 1% at time 0 to 69 ± 7% and 62 ± 1%, respectively, after 30 s. At 480 s post-activation, the eyeing and hatching values were 23 ± 8% and 15 ± 4%. Produced eyeing and hatching rates and sperm motility parameters of testicular and stripped sperm were compared over the course of 48 h storage. Testicular sperm remained viable for 24 h compared with 3 h for stripped sperm. The obtained data clarified important biological characteristics and interaction of gametes for use in developing optimal techniques for artificial reproduction of northern pike under controlled conditions. • The minimum spermatozoa to egg ratio in effective artificial fertilization of northern pike is 400-000 spermatozoa per egg. • The eggs of northern pike retain their fertilizing ability after activation with activation solution for at least 30s. • Testicular sperm could be successfully stored for 24 h while the stripped sperm retained the fertilizing ability only for 3 h after the sperm storage. [ABSTRACT FROM AUTHOR]

Mercury pollution is a global environmental problem that threatens ecosystems, and negatively impacts human health and well-being. Mercury accumulation in fish within freshwater lakes is a complex process that appears to be driven by factors such as individual fish biology and water chemistry at the lake-scale, whereas, climate, and land-use/land-cover conditions within lake catchments can be influential at relatively larger scales. Nevertheless, unravelling the intricate network of pathways that govern how lake-scale and large-scale factors interact to affect mercury levels in fish remains an important scientific challenge. Using structural equation models (SEMs) and multiple long-term databases we identified direct and indirect effects of lake-scale and larger-scale factors on mercury levels in Walleye and Northern Pike - two species that are valued in inland fisheries. At the lake-level, the most parsimonious path models contained direct effects of fish weight, DOC, and pH, as well as an indirect effect of DOC on fish mercury levels via fish weight. Interestingly, lakeshed-, climate-, and full-path models that combine the effects of both lakeshed and climate revealed indirect effects of surrounding landscape conditions and latitude via DOC, pH, and fish weight but no direct effects on fish mercury levels. These results are generally consistent across species and lakes, except for some differences between stratified and non-stratified lakes. Our findings imply that understanding climate and land-use driven alterations of water chemistry and fish biology will be critical to predicting and mitigating fish mercury bioaccumulation in the future. Image 1 • Mercury bioaccumulation in fishes is a complex mutli-scale process that is driven by individual fish biology and lake water chemistry as well as large-scale climate and surrounding landscape conditions • Untangling the intricate network of pathways that determine large-scale inter-lake variations in fish mercury levels remains a key scientific challenge • Using structural equation models, the study identifies direct and indirect effects of several lake-scale and large-scale drivers on mercury levels in Walleye and Northern Pike. • Landscape conditions around lake and latitude affected mercury levels in both species, but almost always indirectly via lake water chemistry variables and fish weight • Understanding how large-scale drivers interact with fine-scale factors to shape individual fish-level responses is thus critical to mitigating fish mercury levels in the future [ABSTRACT FROM AUTHOR]

Northern pike (Esox lucius) sperm equilibration and cryopreservation were conducted using a simple cryopreservation extender (CE) containing 185 mM trehalose, 40 mM KCl, 20 mM Tris at pH 8.5 and supplemented with 10% of methanol. Sperm was diluted tenfold (1:9; sperm:CE), and a subset of the samples was equilibrated (over 15 min) and stored on crushed ice (+4 °C). The remainder of the samples were drawn into French straws of 250 μl capacity and subsequently frozen. Thawing of sperm was carried out in a hot water bath at 40 °C for five seconds. The control group was fresh sperm that was neither diluted in CE nor frozen. After equilibration and cryopreservation, sperm motility parameters were analyzed using a Computer-Assisted Sperm Analysis system. Fertilization using different sperm:egg ratios (i.e. 400, 200, 100, 50, 25 and 10 thousand sperm per egg) was performed to determine the fertilization capacity of sperm. Sperm motility parameters of northern pike remain at the same level in fresh, equilibrated and cryopreserved samples. On the other hand, average sperm longevity was longest in equilibrated (118.0 s.) and cryopreserved (124.5 s.) sperm in comparison to fresh sperm (84.7 s.). Sperm samples equilibrated in CE achieved higher (n = 4. P <.05) hatching rate at sperm:egg ratios equal to 25,000 and 10,000:1 (85.3 and 77.2%, respectively) as compared to fresh (67.7 and 61.2%, respectively) or cryopreserved (73.5, 65.5%, respectively) samples. This indicated that CE may be a promising option not only for cryopreservation but also for northern pike sperm storage and fertilization capacity improvement under controlled conditions. • Dilution of northern pike sperm in cryopreservation extender improves sperm longevity and fertilization success. • Our cryopreservation protocol allows to achieve post-thaw fertility, at the same level as measured for the fresh sperm. • Use of the proposed extender could have positive implications for pike reproduction and hatchery management. [ABSTRACT FROM AUTHOR]