Climate change vulnerability of Arctic char across Scandinavia.

Climate change is anticipated to cause species to shift their ranges upward and poleward, yet space for tracking suitable habitat conditions may be limited for range-restricted species at the highest elevations and latitudes of the globe. Consequently, range-restricted species inhabiting Arctic freshwater ecosystems, where global warming is most pronounced, face the challenge of coping with changing abiotic and biotic conditions or risk extinction. Here, we use an extensive fish community and environmental dataset for 1762 lakes sampled across Scandinavia (mid-1990s) to evaluate the climate vulnerability of Arctic char (Salvelinus alpinus), the world's most cold-adapted and northernly distributed freshwater fish. Machine learning models show that abiotic and biotic factors strongly predict the occurrence of Arctic char across the region with an overall accuracy of 89 percent. Arctic char is less likely to occur in lakes with warm summer temperatures, high dissolved organic carbon levels (i.e., browning), and presence of northern pike (Esox lucius). Importantly, climate warming impacts are moderated by habitat (i.e., lake area) and amplified by the presence of competitors and/or predators (i.e., northern pike). Climate warming projections under the RCP8.5 emission scenario indicate that 81% of extant populations are at high risk of extirpation by 2080. Highly vulnerable populations occur across their range, particularly near the southern range limit and at lower elevations, with potential refugia found in some mountainous and coastal regions. Our findings highlight that range shifts may give way to range contractions for this cold-water specialist, indicating the need for pro-active conservation and mitigation efforts to avoid the loss of Arctic freshwater biodiversity.

Finotypic plasticity: Predator-induced plasticity in fin size, darkness and display behaviour in a teleost fish.

Fish fins are remarkable devices of propulsion. Fin morphology is intimately linked to locomotor performance, and hence to behaviours that influence fitness, such as foraging and predator avoidance. This foreshadows a connection between fin morphology and variation in predation risk. Yet, whether prey can adjust fin morphology according to changes in perceived risk within their lifetime (a.k.a. predator-induced plasticity) remains elusive. Here, we quantify the structural size of five focal fins in crucian carp (Carassius carassius) following controlled manipulations to perceived predation risk (presence/absence of pike Esox lucius). We also assess if crucian carp respond to increased predation risk by shifts in dorsal fin colouration, and test for differences in how fish actively use their dorsal fins by quantifying the area of the fin displayed in behavioural trials. We find that crucian carp show phenotypic plasticity with regards to fin size as predator-exposed fish consistently have larger fins. Individuals exposed to perceived predation risk also increased dorsal fin darkness and actively displayed a larger area of the fin to potential predators. Our results thus provide compelling evidence for predator-induced fin enlargement, which should result in enhanced escape swimming performance. Moreover, fin-size plasticity may evolve synergistically with fin colouration and display behaviour, and we suggest that the adaptive value of this synergy is to enhance the silhouette of deep-bodied and hard-to-capture prey to deter gape-limited predators prior to attack. Together, our results provide new perspectives on the role of predation risk in development and evolution of fins.

Iron-binding biomolecules in the soluble hepatic fraction of the northern pike (Esox lucius): two-dimensional chromatographic separation with mass spectrometry detection.

Iron plays vital roles in important biological processes in fish, but can be toxic in high concentrations. The information on metalloproteins that participate in maintenance of Fe homeostasis in an esocid fish, the northern pike, as an important freshwater bioindicator species, are rather scarce. The aim of this study was to identify main cytosolic constituents that sequester Fe in the northern pike liver. The method applied consisted of two-dimensional HPLC separation of Fe-binding biomolecules, based on anion-exchange followed by size-exclusion fractionation. Apparent molecular masses of two main Fe-metalloproteins isolated by this procedure were ~360 kDa and ~50 kDa, with the former having more acidic pI, and indicated presence of ferritin and hemoglobin, respectively. MALDI-TOF-MS provided confirmation of ferritin subunit with a m/z peak at 20.65 kDa, and hemoglobin with spectra containing main m/z peak at 16.1 kDa, and smaller peaks at 32.1, 48.2, and 7.95 kDa (single-charged Hb-monomer, dimer, and trimer, and double-charged monomer, respectively). LC-MS/MS with subsequent MASCOT database search confirmed the presence of Hb-ß subunits and pointed to close relation between esocid and salmonid fishes. Further efforts should be directed towards optimization of the conditions for metalloprotein analysis by mass spectrometry, to extend the knowledge on intracellular metal-handling mechanisms.

Morphological and molecular characterization of Stomachicola muraenesocis Yamaguti, 1934 (Digenea: Hemiuridae) from the daggertooth pike conger Muraenesox cinereus (Forsskål).

Hemiurid digeneans conspecific with Stomachicola muraenesocis Yamaguti, 1934 (the type species of the genus Stomachicola Yamaguti, 1934) were collected from the stomach of the daggertooth pike conger Muraenesox cinereus (Forsskål) off the Persian Gulf of Iran. This study aimed to provide a detailed characterization of Stom. muraenesocis, including measurements, illustrations and scanning electron microscopy (s.e.m.) representations. Comparisons with the original and previous descriptions revealed morphological and metrical variations in several features (i.e. body size and shape, arrangement of reproductive organs, soma to ecsoma length ratio, position of genital opening, number of vitelline tubules and extension of uterine coils) between Stom. muraenesocis from different hosts and localities. This study presents the first molecular sequence data associated with the small (18S) and large (28S) subunit nuclear ribosomal RNA genes (rDNA) for Stom. muraenesocis. Phylogenetic analyses of the 18S dataset placed Stom. muraenesocis as sister lineage to a clade formed of a group of species of Lecithaster Lühe, 1901 (Lecithasteridae Odhner, 1905). In contrast, phylogenetic analyses based on the 28S consistently recovered a sister relationship between Stom. muraenesocis and representatives of the Hemiuridae Looss, 1899. Further comprehensive phylogenetically based classification in light of morphology and taxonomic history of the Hemiuridae and Lecithasteridae is required to infer phylogenetic affinities and historical biogeography of Stomachicola. A comprehensive list of previously reported species of Stomachicola together with their associated hosts, localities and morphometric data is provided.

Histopathological, morphological, and molecular characterization of fish-borne zoonotic parasite Eustrongylides Excisus infecting Northern pike (Esox lucius) in Iran.

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

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

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

Reproductive ecology of muskellunge (Esox masquinongy), an introduced predator, in the lower Wolastoq/Saint John River, New Brunswick, Canada.

Introduced predators can have harmful top-down effects on their newly colonized system through competition with and direct predation on native species. Following an initial introduction of muskellunge in Lac Frontière, Québec in the 1970s at the headwaters of the Wolastoq/Saint John River, the species rapidly migrated downstream, expanding its range by ~500 km over ~20 years. Despite this expansive colonization and concern over possible threats to native species, little is known about the basic ecology of muskellunge in this system. The last downstream barrier is the hydroelectric facility, Mactaquac Generating Station (MGS), 150 km upstream of the sea. While there are no downstream fish passage facilities at MGS, adult muskellunge have been recorded downstream. In this study, muskellunge (n = 23) were surgically tagged with very-high-frequency (VHF) radio or combined acoustic radio telemetry (CART) tags and tracked over two spawning seasons. We sought to determine if there was a reproducing population downstream of MGS and tracked Tagged muskellunge over two spawning seasons. We tracked fish to locate and confirm spawning sites, and followed up with egg and/or juvenile sampling surveys. Tagged muskellunge (90%) moved upstream towards the MGS during the spawning period in each year (2016 and 2017), where they remained throughout the entire spawning period. No spawning or nursery sites were confirmed near MGS, but in 2016 three distinct spawning locations and six distinct nursery sites were confirmed 10-12 km downstream amongst a chain of flooded islands. In 2016, eggs, sac-fry and juveniles were collected and confirmed as muskellunge by genetic sequencing, providing the first empirical observation of successful spawning downstream of MGS.

The role of predation risk in structuring life-history traits of crucian carp (Carassius carassius) in a series of small boreal lakes.

Predation is a major evolutionary force determining life-history traits in prey by direct and indirect mechanisms. This study focuses on life-history trait variation in crucian carp (Carassius carassius), a species well known for developing a deep body as an inducible morphological defence against predation risk. Here, the authors tested variation in growth and reproductive traits in 15 crucian carp populations in lakes along a predation risk gradient represented by increasingly efficient predator communities. Lakes were located in south-eastern Norway and were sampled in summer 2018 and 2019. The authors expected crucian carp to attain higher growth rate, larger size, and later age at maturity with increasing predation risk. In the absence of predators, they expected high adult mortality, early maturity and increased reproductive effort caused by strong intraspecific competition. They found that the life-history traits of crucian carp were clearly related to the presence of piscivores: with increasing predation risk, fish grew in body length and depth and attained larger asymptotic length and size at maturity. This growth was evident at young age, especially in productive lakes with pike, and it suggests that fish quickly outgrew the predation window by reaching a size refuge. Contrary to the authors' predictions, populations had similar age at maturity. High-predation lakes also presented low density of crucian carp. This suggests that fish from predator lakes may experience high levels of resource availability due to reduced intraspecific competition. Predation regulated life-history traits in crucian carp populations, where larger size, higher longevity and size at maturity were observed in lakes with large gaped predators.

Comparative evaluation of loop-mediated isothermal amplification and PCR for detection of Esox lucius housekeeping genes for use in on-site environmental monitoring.

Esox lucius (northern pike) is an invasive species in fresh water and causes extreme impacts in the local habitat. Northern pike easily replaces the local native species and disrupts the regional ecosystem. Traditionally, in connection with environmental monitoring, invasive species are identified using PCR through species-specific DNA. PCR involves many cycles of heating to amplify the target DNA and requires complex equipment; on the contrary, loop-mediated isothermal amplification (LAMP) entails isothermal amplification, which means the target needs to be heated to only one temperature between 60 and 65°C. In this study, the authors conducted a LAMP assay and a conventional PCR assay to determine which technique is less time consuming, more sensitive and reliable for use in real-time and on-site environmental monitoring. Mitochondrial gene cytochrome b, an essential factor in electron transport; histone (H2B), a nuclear DNA responsible for the chromatin structure; and glyceraldehyde 3-phosphate dehydrogenase involved in energy metabolism are taken as the reference genes for this article. The results show that LAMP is more sensitive and less time consuming than the conventional PCR, and thus it can be used for the detection of northern pike in aquatic ecosystems related to environmental monitoring.

Expanding non-invasive approaches for fish-health monitoring: A survey of the epidermal mucous metabolomes of phylogenetically diverse freshwater fish species.

There is a pressing need for more-holistic approaches to fisheries assessments along with growing demand to reduce the health impacts of sample collections. Metabolomic tools enable the use of sample matrices that can be collected with minimal impact on the organism (e.g., blood, urine, and mucus) and provide high-throughput, untargeted biochemical information without the requirement of a sequenced genome. These qualities make metabolomics ideal for monitoring a wide range of fish species, particularly those under protected status. In the current study, we surveyed the relative abundances of 120 endogenous metabolites in epidermal mucus across eight freshwater fish species belonging to seven phylogenetic orders. Principal component analysis was used to provide an overview of the data set, revealing strong interspecies relationships in the epidermal mucous metabolome. Normalized relative abundances of individual endogenous metabolites were then used to identify commonalities across multiple species, as well as those metabolites that showed notable species specificity. For example, taurine was measured in high relative abundance in the epidermal mucus of common carp (Cyprinus carpio), northern pike (Esox lucius), golden shiner (Notemigonus crysoleucas), rainbow trout (Oncorhynchus mykiss), and rainbow smelt (Osmerus mordax), whereas γ-amino butyric acid (GABA) exhibited a uniquely high relative abundance in flathead catfish (Pylodictis olivaris). Finally, hierarchical cluster analysis was used to evaluate species relatedness as characterized by both the epidermal mucous metabolome (phenotype) and genetic phylogeny (genotype). This comparison revealed species for which relatedness in the epidermal mucous metabolome composition closely aligns with phylogenetic relatedness (e.g., N. crysoleucas and C. carpio), as well as species for which these two measures are not well aligned (e.g., P. olivaris and Polyodon spathula). These, and other findings reported here, highlight novel areas for future research with fish, including development of epidermal mucous-based markers for non-invasive health monitoring, sex determination, and hypoxia tolerance.

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

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

Drivers of neutral and adaptive differentiation in pike (Esox lucius) populations from contrasting environments.

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.

Identification of the master sex determining gene in Northern pike (Esox lucius) reveals restricted sex chromosome differentiation.

Teleost fishes, thanks to their rapid evolution of sex determination mechanisms, provide remarkable opportunities to study the formation of sex chromosomes and the mechanisms driving the birth of new master sex determining (MSD) genes. However, the evolutionary interplay between the sex chromosomes and the MSD genes they harbor is rather unexplored. We characterized a male-specific duplicate of the anti-Müllerian hormone (amh) as the MSD gene in Northern Pike (Esox lucius), using genomic and expression evidence as well as by loss-of-function and gain-of-function experiments. Using RAD-Sequencing from a family panel, we identified Linkage Group (LG) 24 as the sex chromosome and positioned the sex locus in its sub-telomeric region. Furthermore, we demonstrated that this MSD originated from an ancient duplication of the autosomal amh gene, which was subsequently translocated to LG24. Using sex-specific pooled genome sequencing and a new male genome sequence assembled using Nanopore long reads, we also characterized the differentiation of the X and Y chromosomes, revealing a small male-specific insertion containing the MSD gene and a limited region with reduced recombination. Our study reveals an unexpectedly low level of differentiation between a pair of sex chromosomes harboring an old MSD gene in a wild teleost fish population, and highlights both the pivotal role of genes from the amh pathway in sex determination, as well as the importance of gene duplication as a mechanism driving the turnover of sex chromosomes in this clade.

A new species of Myxidium (Cnidaria: Myxosporea: Myxidiidae) from the gallbladder of pickerels, Esox spp. (Esociformes: Esocidae), from southwestern Arkansas, USA.

During April 2016 and again in November 2021, four Chain Pickerels, Esox niger were collected from Union (n = 3) and Nevada (n = 1) counties, Arkansas, USA, and 65 Grass Pickerels, Esox americanus vermiculatus were collected between January 2015 and December 2021 from four counties of Arkansas (n = 31) and McCurtain County, Oklahoma, USA (n = 34), and examined for myxozoans. Gallbladders of an individual E. niger from Nevada County, Arkansas, as well as a single individual of E. a. vermiculatus from Sevier County, Arkansas, were infected with a new myxozoan, Myxidium whippsi n. sp. Qualitative and quantitative morphological data were from formalin-fixed preserved myxospores while molecular data (SSU rRNA gene) consisted of 2031bp (host: E. niger) and 1723 bp (host: E. a. vermiculatus) partial sequences of the small subunit ribosomal RNA gene. Phylogenetic analysis placed M. whippsi n. sp. in a clade with two other myxozoans, Zschokkella nova and Myxidium truttae, previously reported from cyprinids and salmonids, respectively. We document the first report of a myxozoan from E. a. vermiculatus. This article was registered in the Official Register of Zoological Nomenclature (ZooBank) as urn:lsid:zoobank.org:pub:A50FCEB3-68C3-428E-A04E-37A16790F1EB.

Comparative Study of Plutonium and Radiocaesium Content in the Muscle of Fish of the Yenisey River.

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

Fate of MHCII in salmonids following 4WGD.

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.

Environmental DNA detection of endangered and invasive species in Kejimkujik National Park and Historic Site.

The use of environmental DNA (eDNA) allows the early detection of aquatic species at low densities (e.g., elusive and invasive species), which otherwise could be challenging to monitor using conventional techniques. Here, we assess the ability of eDNA sampling to detect the presence or absence of one species at risk (Blanding's turtle) and two invasive species (chain pickerel and smallmouth bass) in Kejimkujik National Park and National Historic Site, Nova Scotia, where the aquatic system is highly acidic and rich in organic compounds. Five replicates of 1 L water samples were taken per sampling site. Water filtration and eDNA extractions were performed on-site, while qPCR reactions were performed in the laboratory using species-specific assays. Samples were treated with an inhibition removal kit and analyzed pre- and post-inhibition removal. Despite the low pH and PCR inhibitors in water samples, our results showed positive eDNA detections in almost all expected positive sites (except in one site for Blanding's turtle). Detections of the target species were also observed at sites where their presence was previously unknown. Our study supports the advantage of eDNA to monitor species at low densities, revealing new distributions or recently invaded areas. We also demonstrate how eDNA can directly instruct management strategies in Kejimkujik.

Impacts of Oxazepam on Perch (Perca fluviatilis) Behavior: Fish Familiarized to Lake Conditions Do Not Show Predicted Anti-anxiety Response.

A current theory in environmental science states that dissolved anxiolytics (oxazepam) from wastewater effluents can reduce anti-predator behavior in fish with potentially negative impacts on prey fish populations. Here, we hypothesize that European perch (Perca fluviatilis) populations being exposed to oxazepam in situ show reduced anti-predator behavior, which has previously been observed for exposed isolated fish in laboratory studies. We tested our hypothesis by exposing a whole-lake ecosystem, containing both perch (prey) and northern pike (Esox lucius; predator), to oxazepam while tracking fish behavior before and after exposure in the exposed lake as well as in an unexposed nearby lake (control). Oxazepam concentrations in the exposed lake ranged between 11 and 24 µg L-1, which is >200 times higher than concentrations reported for European rivers. In contrast to our hypothesis, we did not observe an oxazepam-induced reduction in anti-predator behavior, inferred from perch swimming activity, distance to predators, distance to conspecifics, home-range size, and habitat use. In fact, exposure to oxazepam instead stimulated anti-predator behavior (decreased activity, decreased distance to conspecifics, and increased littoral habitat use) when using behavior in the control lake as a reference. Shoal dynamics and temperature changes may have masked modest reductions in anti-predator behavior due to oxazepam. Although we cannot fully resolve the mechanism(s) behind our observations, our results indicate that the effects of oxazepam on perch behavior in a familiar natural ecosystem are negligible in comparison to the effects of other environmental conditions.

Production and outmigration of young-of-year northern pike Esox lucius from natural and modified waterways connected to Lower Green Bay, Wisconsin.

Production and outmigration of young-of-year (YOY) northern pike from natal sites in Lower Green Bay, WI, USA, were documented over three consecutive years (2013-2015). We tested the hypothesis that spawning success and outmigration characteristics of YOY northern pike would vary among natural and anthropogenically modified habitats. Sixteen focal study locations were surveyed, including a restored natural wetland, agricultural drainage ditches, a flooded forested wetland and several unimpounded tributaries. We collected 1469 YOY northern pike with most individuals (N = 1163) originating from a flooded forested wetland on the east shore. Most sites produced YOY in all years (range N = 2-1145 individuals among study years). Outmigration ranged between 1 and 40 days during 2013-2015. Greater production and extended outmigration times occurred at most sites in 2014 (range 17-40 days) when the region experienced a late spring with heavy precipitation. In contrast, the lowest production and shortest outmigration period occurred at most sites in 2015 (range 14-23 days) when environmental conditions reflected regional averages. Outmigration began nearly 3 weeks earlier in 2015 (5/8) than in other study years (8 June 2013 and 25 May 2014). Total length (TL) of outmigrating northern pike ranged between 17 and 138 mm. Total length of YOY was significantly different among sites in 2013 and 2014, with the smallest fish (17 mm TL) outmigrating from agricultural ditches in both years. There were no significant variations in size among sites in 2015 (range 21-95 mm TL). Our results indicate significant variation in YOY northern pike outmigration characteristics within Lower Green Bay that may reflect the interplay between adult spawning site selection and annual weather patterns. Our findings highlight the importance of quantifying overlooked habitats in regions of mixed development.

Widespread Seropositivity to Viral Hemorrhagic Septicemia Virus (VHSV) in Four Species of Inland Sport Fishes in Wisconsin.

Serological assays were conducted for anti-viral hemorrhagic septicemia virus (VHSV) antibodies in four species of fish in Wisconsin (Bluegill Lepomis macrochirus, Brown Trout Salmo trutta, Northern Pike Esox lucius, and Walleye Sander vitreus) to examine spatial and temporal distributions of exposure. Sera were tested for non-neutralizing anti-nucleocapsid antibodies to VHSV by blocking enzyme-linked immunosorbent assay (ELISA). Results (percent inhibition [%I]) were analyzed for differences among species, across geographic distance, and among water management units. Positive fish occurred in 37 of 46 inland water bodies tested, including in water bodies far from reported outbreak events. Using highly conservative species-specific thresholds (mean %I of presumptive uninfected fish + 2 SDs), 4.3% of Bluegill, 13.4% of Brown Trout, 19.3% of Northern Pike, and 18.3% of Walleye tested positive for VHSV antibodies by ELISA. Spatial patterns of seropositivity and changes in %I between sampling years were also analyzed. These analyses explore how serology might be used to understand VHSV distribution and dynamics and ultimately to inform fisheries management.