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Due to the increasing prevalence and variety of underwater anthropogenic noise sources, and the growing human population, anthropogenic noise has the potential to negatively impact aquatic organisms. With this growing threat, the question of how fishes respond to this stressor in their natural environments becomes more urgent. The current study used behavioral trials with bluegill sunfish Lepomis macrochirus, pumpkinseed sunfish Lepomis gibbosus, and rock bass Ambloplites rupestris, both in isolation and in a heterospecific trial, to determine how behaviors indicative of stress were influenced by interspecific interactions when exposed to recordings of pure tones and boat motors. Regardless of social context, all three species experienced an increase in fin beats per second, an increase in time spent at the bottom of the pen, and a decrease in time spent swimming when exposed to boat noise. Fishes in heterospecific trials experienced more fin beats per second and spent less time swimming, but there was no significant difference when comparing time spent at the bottom of pen with fish in individual trials. Our findings of behavioral changes when exposed to acoustic stimuli, in two social contexts, allow for a deeper understanding of interspecific effects and provide insight into how varied field studies can be useful in studying fish behavior when encountering acoustic stressors. [ABSTRACT FROM AUTHOR]

The objective of this study was to assess the growth rates and general body condition of two common game fishes (largemouth bass Micropterus nigricans and bluegill Lepomis macrochirus) in a productive midwestern USA lake, Lake Winona, 20+ years after one of its two separate basins was partially dredged. We also used historical lake survey data spanning 19 years before and 15 years after dredging to assess the pre- and post-dredging growth of these species. Dredging was expected to improve the growth rates and conditions (relative weights) of both species due to post-dredging changes to lake habitats (more open water and reduced macrophyte beds) and the fish community structure in the dredged basin. Both species displayed significantly faster growth in the dredged basin, with the bluegill by age 3 and the bass by age 6. The mean relative weights of both species were significantly higher in the non-dredged basin (bass were in good condition: 106% versus 100%; bluegill were in fair condition: 84% versus 80%), although both bluegill and largemouth bass exhibited significant declines in relative weight with increasing lengths in the non-dredged basin. The growth rates for largemouth bass have declined from historical levels, especially in the non-dredged basin, whereas bluegill growth rates have remained stable or improved, especially in the dredged basin. Overall, largemouth bass and bluegill growth rates and relative weights are responding to differences in habitat and fish communities between dredged and non-dredged basins, indicating that the two lake basins are isolated enough from one another to allow for separate biological responses to occur in each. [ABSTRACT FROM AUTHOR]

Concentrations of toxic metals (Hg, Pb, and Cd) were determined in the muscles of Lepomis macrochirus, Barbus callensis, and Barbus nasus caught from the Moulouya River of Morocco by graphite furnace (for Pb and Cd) and cold vapour (for Hg) atomic absorption spectrometry, after acid digestion. Although the concentration of metals in some species was relatively high, no health risk has been identified in comparison to the maximum limits as set by the European Commission. The order of increasing concentrations was Cd < Hg < Pb. Calculated Target Hazard Quotients and Hazard Indices were below 1, indicating that the intake of metals via consumption of the muscles of both fish species does not represent a hazard to human health. [ABSTRACT FROM AUTHOR]

The objective of this study was to assess the growth rates and general body condition of two common game fishes (largemouth bass Micropterus nigricans and bluegill Lepomis macrochirus) in a productive midwestern USA lake, Lake Winona, 20+ years after one of its two separate basins was partially dredged. We also used historical lake survey data spanning 19 years before and 15 years after dredging to assess the pre- and post-dredging growth of these species. Dredging was expected to improve the growth rates and conditions (relative weights) of both species due to post-dredging changes to lake habitats (more open water and reduced macrophyte beds) and the fish community structure in the dredged basin. Both species displayed significantly faster growth in the dredged basin, with the bluegill by age 3 and the bass by age 6. The mean relative weights of both species were significantly higher in the non-dredged basin (bass were in good condition: 106% versus 100%; bluegill were in fair condition: 84% versus 80%), although both bluegill and largemouth bass exhibited significant declines in relative weight with increasing lengths in the non-dredged basin. The growth rates for largemouth bass have declined from historical levels, especially in the non-dredged basin, whereas bluegill growth rates have remained stable or improved, especially in the dredged basin. Overall, largemouth bass and bluegill growth rates and relative weights are responding to differences in habitat and fish communities between dredged and non-dredged basins, indicating that the two lake basins are isolated enough from one another to allow for separate biological responses to occur in each.

The scales and skin mucus of bony fishes are both proposed to have a role in beneficially modifying the hydrodynamics of water flow over the body surface. However, it has been challenging to provide direct experimental evidence that tests how mucus and fish scales change the boundary layer in part due to the difficulties in working with live animal tissue and difficulty directly imaging the boundary layer. In this manuscript, we use direct imaging and flow tracking within the boundary layer to compare boundary layer dynamics over surfaces of fish skin with mucus, without mucus, and a flat control surface. Our direct measurements of boundary layer flows for these three different conditions are repeated for two different species, bluegill sunfish (Lepomis macrochirus) and blue tilapia (Oreochromis aureus). Our goals are to understand if mucus and scales reduce drag, shed light on mechanisms underlying drag reduction, compare these results between species, and evaluate the relative contributions to hydrodynamic function for both mucus and scales. We use our measurements of boundary layer flow to calculate shear stress (proportional to friction drag), and we find that mucus reduces drag overall by reducing the velocity gradient near the skin surface. Both bluegill and tilapia showed similar patterns of surface velocity reduction. We also note that scales alone do not appear to reduce drag, but that mucus may reduce friction drag up to 50% compared to scaled surfaces without mucus or flat controls. [ABSTRACT FROM AUTHOR]

The addition of coarse woody habitat (CWH) is often used to mitigate the loss of natural structure in aging waterbodies. Ecosystem‐scale effects of large‐scale CWH additions and their influence on fish productivity have been assessed in oligotrophic, natural lakes, but need to be assessed in more ecosystems. Therefore, we tested the effects of an ecosystem‐scale addition of CWH to a eutrophic reservoir using a reference reservoir and data from 4 years before and 4 years after habitat enhancement. Zooplankton and benthic macroinvertebrates did not respond to the addition of CWH, but bluegill (Lepomis macrochirus) reproductive productivity and largemouth bass (Micropterus salmoides) size structure increased. Positive fish responses that contrasted with a lack of fish population‐level responses after a similar CWH addition in an oligotrophic, natural lake highlight the importance of assessing the efficacy of CWH addition across diverse ecosystems. [ABSTRACT FROM AUTHOR]

Growing demand for water requires resource managers to be innovative to minimise impacts on aquatic ecosystems. There are increasing concerns about fish damage and losses at water intakes, but few studies have examined the effectiveness of different screening material for excluding New Zealand fishes. We experimentally tested six screens (50–100 and 100–200 mm rock bunds, 3 mm woven mesh, 1.5, 2 and 3 mm wedge-wire), on two introduced and five native fish species. Bluegill bully (> 32 mm), common bully (> 30 mm), Canterbury galaxias (> 47 mm) and rainbow trout (> 40 mm) were screened effectively by 3 mm woven mesh and wedge-wire. Chinook salmon (> 43 mm) and īnanga whitebait (> 46 mm) were excluded by 2 mm wedge-wire, but shortfin elvers (< 80 mm) penetrated 3 and 2 mm wedge-wire, and glass eels (< 63 mm) penetrated 1.5 mm wedge-wire. Rock bunds were effective barriers for rainbow trout but were ineffective, and acted as habitat, for bluegill bully, Canterbury galaxias and shortfin eels. We recommend that 1.5 mm wedge-wire screens are used in the tidal zone of New Zealand rivers, 2 mm screens are used beyond this zone with an upstream transition to 3 mm screens dependent on catchment-specific fisheries values. [ABSTRACT FROM AUTHOR]

Duoculture has been reported to increase growth rates of some fishes when reared in combination, due to "shading" effects between the species. Two experiments, one involving outdoor cage-rearing in a reservoir, and the other, indoor tank-rearing, were conducted within each of three temperatures ranges (means of ~18.0°C, ~22.0°C and ~26.5°C), to determine whether duoculture of bluegill (BG) Lepomis macrochirus and yellow perch (YP) Perca flavescens would lead to improved growth relative to when the two species were reared separately. Juvenile bluegill and yellow perch were reared in triplicated groups each involving monoculture sets of 100% BG and 100% YP, and a duoculture set of 50% BG + 50% YP. Experiments in cages (Exp. 1) ran for 150 days while those in tanks ran for 126 days (Exp. 2). In Experiment 1, bluegill exhibited significantly greater (P<0.05) mean weight (P<0.05) in duoculture than in monoculture, under the high summer-like range of temperature (~26.5°C) over most of the experiment, whereas yellow perch showed no significant difference in mean weight in duoculture versus monoculture. By the end of a 150-d experiment, bluegill in duoculture outweighed those in monoculture by 62.5%. In Experiment 2, yellow perch in duoculture grew significantly larger than in monoculture (P<0.05) under the warm thermal regime (mean of ~22°C), while no significant differences were detected in mean weight of bluegill in monoculture versus duoculture. Yellow perch in duoculture outweighed those in monoculture by 33.1% at the end of the experiment. Yellow perch performed better in duoculture than in monoculture under the low thermal regime (mean of ~18°C) in both experiments. A significantly greater reduction of CVwt was observed for both bluegill and yellow perch in duoculture than in monoculture in Experiment 1, while no differences in CVwt reduction were detected for bluegill in Experiment 2. Feed conversion ratios (FCR) of bluegill and yellow perch reared in duoculture were significantly lower than for both fishes reared in monoculture in Experiment 1, while there were no significant differences in FCR among the three groups throughout most of Experiment 2. Findings indicate that duoculture of yellow perch and bluegill holds good potential to improve growth and FCR, and to reduce size variation by diminishing social interaction costs. [ABSTRACT FROM AUTHOR]

We investigated disease trends of concern for fish or public health in a 5-y (2017–2021) prospective survey of fish in Cook County, IL, inland lakes. Lesions were assessed in relation to fish species, lake type and location, season and collection year, and lake water chemistry parameters. Fish included bullheads (n = 98), common carp (n = 99), bluegill (n = 114), and largemouth bass (n = 118). Annually, fish collection and point-source water sampling were conducted in spring, summer, and fall from both seepage and impoundment lakes. Examinations included autopsy, wet-mount cytologic assessment for ectoparasites, and histopathology. No lesions of public health concern were detected. The most common abnormalities were branchitis (261 of 429; 60.8%) and endoparasitism (312 of 429; 72.7%). Branchitis was mild in most cases (189 of 261; 72.4%) and concurrent with branchial parasitism in 175 of 261 (67%) cases. Monogeneans were the most common gill parasites but did not influence branchitis severity (Kruskal–Wallis, p = 0.484). Using generalized ordered logistic regression, predictors of branchitis severity included fish species (p < 0.001), the interaction of lake or location and alkalinity (p < 0.001), and water temperature or season (p < 0.001). Endoparasites included tissue larval trematodes (metacercaria), nematodes, and cestodes (plerocercoids), enteric acanthocephalans, gastric trematodes, renal myxosporidia, biliary and gall bladder myxosporidia, enteric cestodes, and tissue microsporidia. Using generalized ordered logistic regression, variables influencing endoparasitism severity included species (p < 0.001), year (p < 0.001), chloride level (p = 0.009), and the interaction of year and chloride level (p < 0.001). Our results suggested overall good health of fish in sampled Cook County inland lakes and provide a foundation for continued monitoring of ecosystem and public health in the urban environment. [ABSTRACT FROM AUTHOR]

The shy-bold behavioral continuum is an element of animal behavior which is often studied for its ecological relevance, particularly in the context of predation risk. How individuals respond to various predation cues is well studied at the individual level, but relatively little is known about how these responses can differ among closely related species. We exposed individual wild-caught juvenile bluegill (Lepomis macrochirus) and pumpkinseed (L. gibbosus) to kairomones of a common predator (Northern pike, Esox lucius), conspecific alarm cues, or a lake water control in a Z-maze trial commonly used to assess relative levels of bold and exploratory behaviors. Neither species exhibited any significant behavioral responses to either predation cue, but bluegill consistently displayed more bold-type behaviors than pumpkinseed. Although the lack of a behavioral response to predation cues in this study is equivocal, we identify clear differences in boldness between these two congeners and discuss the possibility of ecological niche differentiation driving these behavioral differences. Significance Statement: Closely related species exposed to similar predator guilds may differ in their behavioral responses to predation risk, particularly during different life-history stages. We exposed juveniles of two co-occurring sunfish congeners (Lepomis spp.) to chemical predation cues (predator kairomones or conspecific alarm cues) in a Z-maze assay to assess relative levels of bold and exploratory behaviors. Bluegill (L. macrochirus) were consistently bolder and more proactive than pumpkinseed (L. gibbosus). Ontogenetic ecological niche differentiation between these species may be the cause of these observed differences and life-history trajectories should be considered in the design of future research questions. [ABSTRACT FROM AUTHOR]

Microplastic (<5 mm) pollution has been documented globally throughout freshwater and marine ecosystems. Exposure to and ingestion of microplastics presents a threat to the health of aquatic and marine organisms and humans through the consumption of fish and crustaceans. Understanding the factors which influence microplastic ingestion by fish is a key step in predicting the potential health risks. Drivers of microplastic consumption have been studied in lab settings, but there has been limited ability to confirm in field studies. Here we examine the roles and contributions of feeding guild, pelagic microplastic concentrations, and fish length to microplastic consumption by three species of fish across four lake ecosystems in Minnesota, United States. Fish samples were collected in the summers of 2019 and 2020 and processed to determine variability in microplastic ingestion. Identifying particles between 0.18 and 5 mm, plastic ingestion ranged from 0.6 microplastics fish-1 in Elk Lake (low surface water microplastics) bluegill to 1.09 microplastics fish-1 in White Iron Lake (moderate surface water microplastics) cisco. Results indicate that microplastic consumption by filter feeding cisco is driven by surface water microplastic concentrations, while microplastic consumption by visual feeding bluegill and yellow perch is not. Additionally, the high variability of ingestion between lake ecosystems coupled with the complex behavior of some fish species presents difficulties in identifying primary drivers of microplastic consumption that would be broadly applicable across ecosystems and species. [ABSTRACT FROM AUTHOR]

Freshwater habitats display a high degree of heterogeneity in both space and time. This heterogeneity is a result of the hierarchical interplay of hydrology and geomorphology, producing the physical habitat template to which biological communities respond and interact. Thus, it follows that any effort to fully understand the complexity of these systems requires a spatial and temporal perspective of heterogeneity at multiple scales within a hierarchical framework. In this study we 1) test if fish assemblage structure differs between hydrogeomorphically distinct, off-channel patches of the Upper Mississippi River, USA, 2) identify which species are driving differences in assemblages between patch types and, 3) assess which hydrogeomorphic variables are associated with fish assemblages and if these are the same suite of variables responsible for the physical differentiation of patches. Different fish assemblages were associated with hydrogeomorphically distinct patches, importantly, sub-groups of backwaters. Species including the Bluegill Lepomis macrochirus Rafinesque, 1819, the Black Crappie Pomoxis nigromaculatus (Lesueur in Cuvier and Valenciennes, 1829), and the Gizzard Shad Dorosoma cepedianum (Lesueur, 1818) were influential in driving differences in assemblages. Fish assemblages did not respond to the same suite of hydrogeomorphic variables responsible for the physical character of patches, although there was some overlap. Instead, they responded to patch-scale characteristics and long-term hydrology and, in the case of backwaters, which navigation pool they were located in. We suggest that classification of hydrogeomorphic character across multiple spatio-temporal scales is critical. This classification should be done prior to sampling so patches can be targeted based on their physical character to draw out key habitat-assemblage relationships. We also contend that broad classification of habitats (e.g., floodplain lake vs backwater) may be too simplistic. Instead, individual characteristics defining the physical nature of a habitat need to be linked to biological responses across scales. A more nuanced understanding of these relationships is needed to improve restoration and management outcomes with respect to increasing or maintaining heterogeneity in the landscape. [ABSTRACT FROM AUTHOR]

Perrion MA, Lebsock JR, Werner JP, Blank AJ, Miller BT. 2024. Comparing bluegill growth among newly constructed, renovated, and established flood-control reservoirs in southeastern Nebraska. Lake Reserv Manage. 40:57–65. Multiple reservoirs have been constructed in the last 10 yr in southeastern Nebraska for flood control and recreational purposes. In addition, other existing reservoirs have undergone major renovations in the same time period to remove sediment and aquatic invasive species. This situation created the opportunity to compare bluegill (Lepomis machrochirus) growth between newly constructed, renovated, and established reservoirs. This study analyzed bluegill growth data from 8 different flood-control reservoirs in southeastern Nebraska in 2021 and 2022. The study objectives were to (1) determine aging precision of scales and otoliths in bluegill and (2) evaluate bluegill growth among new, renovated, and established flood-control reservoirs. For all bluegill collected during the study, exact percent agreement for otolith ages between 2 readers was 89.6%, and percent agreement was 99.1% within 1 yr of age. For scales, exact percent agreement was 48.0% and 84.3% within 1 yr. Mean lengths at age for all reservoir types were similar for age-2 bluegill, whereas age-3 bluegill had longer mean lengths in renovated reservoirs than in either new or established reservoirs. Mean lengths of age-4 bluegill from new and renovated reservoirs were similar, but greater than mean lengths of age-4 bluegill in established reservoirs. Results of this study further demonstrate the greater precision of whole view otolith aging for bluegills compared to scale estimates and will benefit future managers making management decisions for bluegills. Managers can also use information ascertained from bluegill growth metrics to further manage bluegill populations based on reservoir age and management objectives. [ABSTRACT FROM AUTHOR]

Background: Since the late 1990s, bigheaded carps (largely silver carp [Hypophthalmichthys molitrix] but also bighead carp [H. nobilis]) have established throughout the lower Mississippi River basin. Using previously studied oxbow lakes in the lower White River basin, Arkansas, we compared current (2017, "post-carp" establishment) fish assemblages to historical (2002, "pre-carp" establishment) fish assemblages. Fish assemblages were comprehensively assessed using multiple gears, including boat electrofishing, mini-fyke nets, and experimental small-mesh gill nets. Results: T-tests suggested that fish assemblage indices of richness, diversity, evenness, and dominance were often greater (P < 0.05) during the post-carp period as reflected by boat electrofishing and experimental gill nets. However, all indices were generally similar (P > 0.05) between the pre-carp and post-carp period with fish assemblages depicted using mini-fyke nets. Nonmetric multidimensional scaling analyses indicated that fish assemblages differed structurally between pre-carp and post-carp periods. Assemblage differences were linked to both small and large abundance changes for more than 20 species. Abundances of gizzard shad (Dorosoma cepedianum), emerald shiner (Notropis atherinoides), pugnose minnow (Opsopoeodus emiliae), crappies (Pomoxis spp.), bluegill (Lepomis macrochirus), orangespotted sunfish (L. humilis), and yellow bass (Morone mississippiensis) declined between the pre-carp and post-carp periods. Conversely, abundances of weed shiner (N. texanus), pallid shiner (Hybopsis amnis), longear sunfish (L. megalotis), buffalofishes (Ictiobus spp.), and gars (Lepisosteus spp.) generally increased during the same period. Conclusions: Although not possible to conclude assemblage shifts were entirely related to bigheaded carps due to the absence of an appropriate reference system where carps did not establish, the wide establishment of these carps is one of the most pervasive changes to have occurred in the lower White River ecosystem during the past two decades. Thus, it is probable to conclude that post-carp establishment observations from this study were at least, in part, attributable to bigheaded carp establishment. Impacts of further range expansions by bigheaded carps in the White River and other lower Mississippi River sub-basins are unclear, though this study suggests probable effects on native fish assemblages, underscoring the need for further research and monitoring. [ABSTRACT FROM AUTHOR]

Objective: The Bluegill Lepomis macrochirus, which utilizes colony spawning, has been introduced globally, and in Japan it is considered one of the worst invasive species. However, a detailed examination of the factors driving male guarding behavior and brood predation in the invaded habitat is lacking. The removal of guarding males, a common management technique in Japan, is thought to be effective in controlling Bluegill. However, the colony spawning strategy may influence the effectiveness of selective male removal through brood protection from neighbor males. Methods: Bluegill spawning was studied in Lake Nojiri, Nagano, Japan, using underwater video recording and experimental removal of guarding males. Result: Bluegill were found spawning in shallow habitat during June–July, and nests were constructed in loosely aggregated colonies, with many solitary nests. Males utilized a variety of guarding behaviors, such as rim circling and predator chases, as well as paternal investment behaviors, such as tail fanning. Males that preyed upon their own eggs defended their nests less aggressively and invested less time in nourishing behaviors. Removal of guarding males revealed that brood predators were primarily conspecific Bluegill, but other fishes, such as invasive Smallmouth Bass Micropterus dolomieu and Largemouth Bass M. nigricans as well as native Japanese Dace Pseudaspius hakonensis, preyed on broods. Conclusion: In concurrence with the colony spawning theory, nests that were located closer to other nests with active guarding males experienced decreased brood predation and increased predator arrival time after male removal. In addition, nests where males had been guarding more aggressively prior to removal experienced reduced brood predation after male removal. These results provide insights into the factors driving male guarding behavior and brood predation of colony‐spawning Bluegill in an invasive habitat and indicate that the removal of guarding males—a common management strategy in Japan—may have reduced effectiveness due to colony spawning. Impact statementBluegill, an invasive species in Japan, were found to have very few native brood predators in a lake where they are thought to be increasing. In addition, the colony spawning strategy appeared to be beneficial in that nests located closer to other active nests experienced reduced brood predation even after the guarding males were removed. [ABSTRACT FROM AUTHOR]

Objective: Reducing Largemouth Bass Micropterus salmoides recruitment and therefore population density could benefit recreational fisheries in small impoundments by improving individual growth rates and increasing the average size and condition of Largemouth Bass. To achieve these effects, methods of controlling Largemouth Bass recruitment should avoid reducing the productivity of their primary prey species, the Bluegill Lepomis macrochirus. Methods: We tested this hypothesis by evaluating the effects of shoreline rotenone application on the density of Bluegill and the density, growth, and survival of age‐0 and age‐1 Largemouth Bass in 15 Alabama small impoundments. Result: After treatment, Largemouth Bass age‐0 densities declined and mean age‐1 length increased, whereas Bluegill populations were not significantly reduced. Conclusion: Our study indicates that shoreline rotenone application may be a valuable method for reducing Largemouth Bass recruitment and increasing the growth of age‐1 Largemouth Bass in small impoundments. However, further research is needed to understand the effects of treatment on nontarget fishes and to better assess the effects of factors such as impoundment surface area and treatment frequency and duration on the ultimate utility of the approach. Impact statementSmall impoundment management could benefit from reducing Largemouth Bass recruitment. We found that shoreline rotenone application improved age‐1 Largemouth Bass growth rates while Bluegill densities were unaffected. Shoreline rotenone application appears to immediately enhance Largemouth Bass populations in impoundments ≤11 ha. [ABSTRACT FROM AUTHOR]

Studies of marine fish have revealed distant relatives of viruses important to global fish and animal health, but few such studies exist for freshwater fish. To investigate whether freshwater fish also host such viruses, we characterized the viromes of five wild species of freshwater fish in Wisconsin, USA: bluegill (Lepomis macrochirus), brown trout (Salmo trutta), lake sturgeon (Acipenser fulvescens), northern pike (Esox lucius), and walleye (Sander vitreus). We analyzed 103 blood serum samples collected during a state-wide survey from 2016 to 2020 and used a metagenomic approach for virus detection to identify known and previously uncharacterized virus sequences. We then characterized viruses phylogenetically and quantified prevalence, richness, and relative abundance for each virus. Within these viromes, we identified 19 viruses from 11 viral families: Amnoonviridae, Circoviridae, Coronaviridae, Hepadnaviridae, Peribunyaviridae, Picobirnaviridae, Picornaviridae, Matonaviridae, Narnaviridae, Nudnaviridae, and Spinareoviridae, 17 of which were previously undescribed. Among these viruses was the first fish-associated coronavirus from the Gammacoronavirus genus, which was present in 11/15 (73%) of S. vitreus. These results demonstrate that, similar to marine fish, freshwater fish also harbor diverse relatives of viruses important to the health of fish and other animals, although it currently remains unknown what effect, if any, the viruses we identified may have on fish health. [ABSTRACT FROM AUTHOR]

Heat shock proteins are natural biomarker that plays a vital role in genetic variability and adaptive survival in organisms under environmental stress. We assessed the effect of the stressor using Heat shock protein 70 in Hemibarbus labeo and Lepomis macrochirus at three geological points of Juam and Yedang lake. The study focused on the stress-relieving effect of heat shock protein 70 expressed in fish associated with physicochemical factors in the lake ecosystem. We recorded significant upregulation (p < 0.05) of the heat shock protein 70 gene in L. macrochirus in Juam (0.99-fold) and Yedang (1.44-fold). The upregulation in H. labeo indicated 0.83-fold in Juam and 1.21-fold in Yedang. The water quality index determined using physicochemical factors was low in the middle regions of both lakes. However, the maximum gene expression distribution was found in Yedang. The two-way clustering analysis revealed ammonia, total phosphorus, and suspended solids with maximum stress threshold. Dissolved oxygen, pH, nitrate, and organic carbon were the stress factors with minimal concentrations induced expression. The key observations are (i) the vital influence of molecular markers regulated tolerance at initial stress levels, (ii) the synergistic effect of the stressors and Heat shock protein 70 induction impacted adaptive strategy in fishes to regain tolerance (iii) fish population (L. macrochirus) with elevated response exhibited maximum distribution, correlating with the practical scenario. Heat shock protein 70 expressions through metabolic compensation strategy thus influenced the size of inhabited fish population retarding biodiversity of the lake ecosystem. [ABSTRACT FROM AUTHOR]

Managing impounded river systems is a recurring challenge for aquatic resource professionals because reservoirs serve multiple functions with different ecological and socioeconomic outcomes. However, research on fishes in reservoirs has disproportionally focused on recreationally and economically important species, with less attention directed toward fish assemblages despite the potential for management at the assemblage level. As such, evaluation of relationships between reservoir fish assemblages and biotic and abiotic factors and testing whether assemblage structure is affected by changing environmental conditions may deepen ecological understanding and provide insights for reservoir fisheries management. Our overall objective was to assess these relationships in 11 reservoirs from North Carolina, USA. We sampled fish assemblages in the reservoirs, which spanned five river basins representing a range of habitat conditions, using experimental gillnets and pulsed DC nighttime electrofishing. Multivariate statistical analyses indicated that taxonomic differences in fish assemblage composition among river basins followed a gradient of productivity. The top contributing species to reservoir dissimilarity were bluegill (Lepomis macrochirus), gizzard shad (Dorosoma cepedianum), black crappie (Pomoxis nigromaculatus), and white perch (Morone americana). These four species were positively associated with factors that reflect increasing eutrophic conditions in the 11 reservoirs and could, therefore, serve as indicators of reservoir productivity, anthropogenic influence, and fish assemblage structure, in addition to their key role in reservoir fisheries management. Whereas -fisheries research has historically focused on assessing fish -populations, our results illustrate the ecological and management insights derived from simultaneously collecting assemblage- and population-level data. Research on reservoir fish assemblages in relation to biotic and abiotic conditions may help advance fish ecology and management alike. Reservoir research has disproportionally focused on individual species of recreational and socioeconomic importance, rather than fish assemblages. Simultaneous collection of assemblage- and population-level fisheries data may generate both ecological and management insights that species-specific sampling cannot. As anthropogenic influences on reservoirs continue to increase, integrating environmental (biotic and abiotic conditions) and fish-assemblage data may be helpful for advancing our understanding of fish ecology and management alike. [ABSTRACT FROM AUTHOR]

The Northern Sunfish (Lepomis peltastes Cope, 1870) is threatened in New York state, USA, but this was not the case before 1940 when the NY Biological Survey documented the species at scattered, specialized habitats in six watersheds in the central and western parts of the state. After 1940 the historic populations could not be detected, but a new population was discovered in 1974 in lower Tonawanda Creek and the nearby Erie Canal. Northern Sunfish, and a few of their hybrids with other Lepomis species, were caught at these locations during irregular sampling through 2009, but no Northern Sunfish were caught after 2009. The objectives of our study were to: (1) Determine the extent of Northern Sunfish hybridization with other Lepomis species, and (2) Evaluate how well identifications of Lepomis species and their hybrids agreed among field keys, morphometric measurements and meristic counts, and genetic methods. In 2013, we collected Northern Sunfish (descended from fish captured in lower Tonawanda Creek from 2006-2009) from NY State Department of Environmental Conservation rearing ponds, plus wild Green Sunfish (L. cyanellus Rafinesque, 1819), Pumpkinseed (L. gibbosus Linnaeus, 1758), Bluegill (L. macrochirus Rafinesque, 1819), and suspected Lepomis hybrids from lower Tonawanda Creek. Ultimately, 91 fish were identified using field keys, morphometric-meristic analysis, and mtDNA and nuclear DNA analysis. Assuming genetic analysis provided accurate identification, we found 7 Bluegill × Northern Sunfish, 8 Bluegill × Pumpkinseed, 13 Bluegill × Green Sunfish, and 3 Green Sunfish × Pumpkinseed hybrids in our sample (female parent listed second in these crosses). Keyed and morphometric-meristic identifications did not differ in accuracy and averaged 81% of genetic identification accuracy. After Northern Sunfish stocking (not in our study area) and sampling from 2008 to 2018 in several watersheds with appropriate habitat and no recaptures after 2014, we conclude that the Northern Sunfish is extirpated in western New York state. While populations of Northern Sunfish (Lepomis peltastes) existed in several New York state watersheds before 1940, only one, discovered in 1974, persisted in small areas of lower Tonawanda Creek and the nearby Erie Canal. Despite high effort, no Northern Sunfish were captured after 2009 in the places they had occupied since 1974. Because many Northern Sunfish, all descended from wild fish in lower Tonawanda Creek and the Erie Canal, exist in two New York state hatchery ponds, we recommend attempting restoration in their former habitat by stocking. [ABSTRACT FROM AUTHOR]

Locomotion is essential for the survival and fitness of animals. Fishes have evolved a variety of mechanisms to minimize the cost of transport. For instance, bluegill sunfish have recently been shown to employ intermittent swimming in nature and in laboratory conditions. We focused on the functional properties of the power‐producing muscles that generate propulsive forces in bluegill to understand the implications of intermittent activity. We used in vivo aerobic or red muscle activity parameters (e.g., oscillation frequency and onset time and duration of activation) in muscle physiology experiments to examine muscle power output during intermittent versus steady swimming in these fish. Intermittent propulsion involves swimming at relatively slow speeds with short propulsive bursts alternating with gliding episodes. The propulsive bursts are at higher oscillation frequencies than would be predicted for a given average swimming speed with constant propulsion. The work‐loop muscle physiology experiments with red muscle demonstrated that intermittent activity allows muscle to produce sufficient power for swimming compared with imposed steady swimming conditions. Further, the intermittent muscle activity in vitro reduces fatigue relative to steady or continuous activity. This work supports the fixed‐gear hypothesis that suggests that there are preferred oscillation frequencies that optimize efficiency in muscle use and minimize cost of transport. [ABSTRACT FROM AUTHOR]

Channa argus (Northern Snakehead) was first discovered in Pennsylvania and the Delaware River watershed in 2004 in Franklin Delano Roosevelt Park (FDRP), Philadelphia, PA. We monitored this population by boat and/or backpack electrofishing from 2005 to 2021. Our objective was to summarize common population characteristics and compare these with other non-native Northern Snakehead populations. Length-at-age data indicated the FDRP population was slower growing and lacked larger individuals relative to other populations. Data from stomach dissection documented feeding on Anguilla rostrata (American Eel), Lepomis macrochirus (Bluegill), Lepomis gibbosus (Pumpkinseed), Fundulus diaphanus (Banded Killifish), and Micropterus salmoides (Largemouth Bass), suggesting potential impacts to these species. Backpack electrofishing in 2005 and 2008 showed significant decreases in the densities of American Eel and Banded Killifish which may be due to predation by Northern Snakehead. [ABSTRACT FROM AUTHOR]

Invasion biologists have attempted to reveal intraspecific variability of biological traits of non-native species at large spatial scales, but the knowledge of the intraspecific variability of invasive species within a single population (such as resource polymorphism) is still limited. In this study, we report the intraspecific variability in life-history traits of a non-native largemouth bass (LMB) population in a subtropical reservoir and discuss the causes and mechanisms of this novel resource polymorphism in relation to ontogenetic diet shift (ODS) and growth rate of prey fish. A polymorphic LMB population was characterized as the sympatric occurrence of "normal" and "dwarf" forms. The normal form showed evident ODS in their diet from smaller gobies to larger prey such as bluegill (BG). In contrast, the majority of dwarfs preyed on gobies throughout their life, because the BG population rapidly grew out of the predation window of dwarfs under the subtropical warm climate. Analysis of the first-year life-history of LMB suggested that the shift of individuals to normal form is irreversibly determined by first-year growth and that the largest size class of the young-of-the-year cohort reaching 180–200 mm standard length and experiencing ODS can shift to the normal form. In conclusion, scarcity of alternative prey and rapid escape of BG from the predation window prevents ODS in dwarfs, creating distinct resource use patterns and diverging life-history traits between the two forms. Novel resource polymorphism in LMB is likely a response to food limitation, and whether this response is based on phenotypic or genetic plasticity should be clarified. [ABSTRACT FROM AUTHOR]

Organisms can exhibit plasticity in phenotypic responses to environmental stimuli but the response can vary based on the evolutionary history of a population. Numerous studies have found that prey will express adaptive responses when subjected to various predators in experimental settings. For species with a large distribution, such as Ambystoma maculatum (spotted salamander), it is not surprising that phenotypic variance can be high across their range. This variance has been hypothesized to be because of different predator regimes of populations. While A. maculatum preferentially oviposit eggs in low-risk ponds (temporary fishless) to decrease egg and larval mortality, Missouri populations still use high-risk ponds (permanent with fish) for reproduction. Using a series of experiments, we investigated how A. maculatum population risk influenced adaptive responses to both native and novel predator kairomones. For natural predators, we used larval A. opacum (marbled salamanders) and Lepomis macrochirus (bluegill) and for novel predators we used Siren intermedia (lesser siren). We found that larval salamanders generally responded with no differences in morphological traits to all three predators. However, head width was larger for low-risk populations. One hypothesized benefit of larger heads (increased foraging efficiency) was not fully supported. All larval salamanders also increased refuge use with predators but this decreased over time. Our results suggest that predation risk of a population may influence the degree of phenotypic expression in response to larval predators. Overall, local adaptation may dictate the ability of prey to respond to environmental conditions within a life stage. [ABSTRACT FROM AUTHOR]

Western mosquitofish, Gambusia affinis , have been introduced around the world, and can affect native fish through competition and predation. The diet of G. affinis may therefore determine the extent of their interactions with native species. We examined stomach contents of G. affinis from two ponds in central Ohio in 2010, 2015, and 2016. In Olde Minnow Pond, we collected diet data before and after the introduction of the native sunfish, Lepomis megalotis , in 2014. We also collected data for G. affinis for the same period in Wood Duck Pond that has contained G. affinis and Lepomis macrochirus for years prior to the study period. The most important prey were zooplankton, especially Chydorus sp. and Alona sp. Aquatic insects, especially chironomid larvae, were often found in stomachs, with their importance varying by year. The relative consumption of zooplankton increased dramatically in G. affinis , especially females, in Olde Minnow Pond from 2010 to 2015 but then dropped in 2016. In addition, the relative consumption of aquatic insects increased in Olde Minnow Pond after the arrival of L. megalotis compared to 2010. In contrast, the diets of G. affinis in Wood Duck Pond remained relatively similar across the study period. Male and female G. affinis in Olde Minnow Pond had different diets, whereas the diets of males and females in Wood Duck Pond were generally similar. In conclusion, the results of this natural experiment provide circumstantial evidence that the arrival of L. megalotis in Olde Minnow Pond affected the diet of G. affinis. [ABSTRACT FROM AUTHOR]

Biomechanics research often revolves around understanding traits impacting suction feeding performance in fishes, using freshwater ray‐finned sunfishes (Family Centrarchidae) as models. However, simultaneous feeding and locomotion kinematics during prey capture are not recorded for many species and there is less information on how these kinematics vary within a species and within individuals. To (1) add to existing data on the prey capture kinematics of centrarchids, (2) assess variation in a species both within and across individuals, and (3) compare morphology and prey capture kinematics of well‐sampled centrarchids, we filmed five redbreast sunfish (Lepomis auritus) at 500 fps−1 approaching and striking non‐evasive prey. Redbreast approach prey at ~30 cm s−1 and use approximately 70% of their maximum gape size. Traits related to feeding are more repeatable than traits related to locomotion. However, the Accuracy Index (AI) was consistent across individuals (AI = 0.76 ± 0.07). Functionally, redbreast sunfish are more similar to bluegill sunfish but morphologically they fall in the intermediate morphospace alongside green sunfish when compared with other centrarchids. These data show that whole organism outcomes (AI) are similar despite variation present both within and across individuals and demonstrate the importance of considering both interspecific and intraspecific differences in the functional diversity of ecologically and evolutionarily important behaviors such as prey capture. Research Highlights: Intraspecific variation was constrained for feeding traits and flexible for locomotion traits, however strike accuracy remained high.Morphologically, redbreast are close to largemouth bass and green sunfish but functionally similar to bluegill. [ABSTRACT FROM AUTHOR]

We integrated stomach content analysis (SCA) and stable isotope analysis (SIA) to understand ontogenetic niche shifts in the invasive freshwater fish, bluegill, Lepomis macrochirus, inhabiting the Yedang Reservoir in Korea. Based on the total length (TL), we classified L. macrochirus as small (23–57 mm), medium (61–99 mm), or large (100–163 mm). Across all study sites, the index of relative importance (IRI) of zooplankton was high for small individuals, whereas those of benthic macroinvertebrates were high for the medium and large groups. Isotopic niche width estimates based on carbon and nitrogen isotope ratios (δ space) also increased with growth, indicating an ontogenetic niche shift in L. macrochirus. In particular, the δ space and diet plasticity of large fish was higher in the littoral population, implying L. macrochirus are generalist feeders as adults. Individuals classified as small showed confined and constant δ space, regardless of habitat condition. Thus, together with the results on the significantly high IRI of zooplankton, these individuals seem to have strong specialistic feeding ecology. Our study demonstrates the applicability strength of combining SCA and SIA for ecological niche research by providing clear evidence of an ontogenetic niche shift in L. macrochirus and elucidates their feeding ecology. [ABSTRACT FROM AUTHOR]

We compared three methods of boat driving and pedal operation using 600‐s transects: these were the parallel continuous (PC), parallel intermittent (PI), and arc‐intermittent (AI) methods for surveying warmwater fishes in reservoirs. We tested differences in total time and distance per transect, CPUE (fish/h, fish/m), and length frequencies of captured fish among methods. The PC method took the least amount of time, while the AI method took the least amount of distance to complete a transect. The AI method provided slightly higher CPUE (fish/h, fish/m) for Bluegill Lepomis macrochirus and Yellow Bass Morone mississippiensis and higher CPUE (fish/m) for Common Carp Cyprinus carpio, Green Sunfish L. cyanellus, and Largemouth Bass Micropterus salmoides. Each method caught similar size ranges of fish; however, there were slight differences in proportions of sizes for Gizzard Shad Dorosoma cepedianum, Largemouth Bass, and Bluegill. Overall, the AI method performed slightly better for a few species; however, difference in the methods were minor. Any technique should work well for monitoring reservoir fish populations when fish/h is the effort metric. [ABSTRACT FROM AUTHOR]

Objective: The first objective of the study aimed to detect the presence of Lactococcus petauri, L. garvieae, and L. formosensis in fish (n = 359) and environmental (n = 161) samples from four lakes near an affected fish farm in California during an outbreak in 2020. The second objective was to compare the virulence of the Lactococcus spp. in Rainbow Trout Oncorhynchus mykiss and Largemouth Bass Micropterus salmoides. Methods: Standard bacterial culture methods were used to isolate Lactococcus spp. from brain and posterior kidney of sampled fish from the four lakes. Quantitative PCR (qPCR) was utilized to detect Lactococcus spp. DNA in fish tissues and environmental samples from the four lakes. Laboratory controlled challenges were conducted by injecting fish intracoelomically with representative isolates of L. petauri (n = 17), L. garvieae (n = 2), or L. formosensis (n = 4), and monitored for 14 days postchallenge (dpc). Result: Lactococcus garvieae was isolated from the brains of two Largemouth Bass in one of the lakes. Lactococcus spp. were detected in 14 fish (8 Bluegills Lepomis macrochirus and 6 Largemouth Bass) from 3 out of the 4 lakes using a qPCR assay. Of the collected environmental samples, all 4 lakes tested positive for Lactococcus spp. in the soil samples, while 2 of the 4 lakes tested positive in the water samples through qPCR. Challenged Largemouth Bass did not show any signs of infection postinjection throughout the challenge period. Rainbow Trout infected with L. petauri showed clinical signs within 3 dpc and presented a significantly higher cumulative mortality (62.4%; p < 0.0001) at 14 dpc when compared to L. garvieae (0%) and L. formosensis (7.5%) treatments. Conclusion: The study suggests that qPCR can be used for environmental DNA monitoring of Lactococcus spp. and demonstrates virulence diversity between the etiological agents of piscine lactococcosis. Impact statementSalmonids are a keystone species in the Pacific Northwest, given their key role in nutrient cycling and as a vital food source for humans and animals. Gaining a better understanding of the distribution, prevalence, virulence, and diversity of emerging pathogens in wild and captive fish is important for the development of containment and preventative protocols. [ABSTRACT FROM AUTHOR]

Purpose: Bluegill sunfish (Lepomis macrochirus) are a North American sport fish that exhibit two different male morphotypes. Alpha-males are large, colorful, territorial, and have significant parental investment, while β-males are small, drab, and have two reproductive phenotypes, neither of which involves parental investment. Due to the two different reproductive strategies, the level of interaction between congenerics varies, which may impact parasites that are spread via close contact, such as Monogenoidea that infect the gills. Monogeneans are ectoparasites on the gills and skin of fish hosts that may cause significant pathology in high numbers and be an indicator of host behavior and interaction between hosts. Methods: In this study, 328 L. macrochirus (106 α-males, 92 β-males, and 130 females) were necropsied from 8 lakes and ponds in northwestern Virginia to identify and enumerate monogenean parasites from the gills. Results: Alpha-males had a significantly greater parasite abundance and species richness compared to β-males. This may be due to the increased size and surface area of gills in α-males, increased interaction with females during mating, and stationary behavior when guarding nests, which enhanced the chances of α-males contracting the parasites. This also led to significant differences in the monogenean communities infecting the two morphotypes, which were also significantly influenced by the size of the hosts. Conclusions: It is important in future studies regarding parasitism that behavioral morphotypes within a sex, such as α-male and β-male L. macrochirus in this study, be treated separately as behavioral and morphometric differences between them can potentially lead to differences in parasitism. [ABSTRACT FROM AUTHOR]

There exists a wealth of knowledge on hearing ability in individual fish species, but the role of interspecific variation, and drivers behind it, remains understudied, making it difficult to understand evolutionary drivers. The current study quantified hearing thresholds for three species of sunfish in the family Centrarchidae [bluegill sunfish (Lepomis macrochirus), pumpkinseed sunfish (Lepomis gibbosus), and rock bass (Ambloplites rupestris)] using auditory evoked potentials and behavioral trials and saccular otolith size and hair cell density. In auditory physiological experiments, 10-ms tone bursts were played and responses monitored to measure hearing. In behavioral experiments, fish were exposed to the same tone bursts for 1 s, and changes in fish behaviors were monitored. Saccular otolith morphology and hair cell densities were also quantified. Physiological thresholds varied between species, but behavioral thresholds did not. Rock bass had larger S:O ratio (percentage of the saccular otolith surface occupied by the sulcus), but no differences in hair cell densities were found. Our study allows for a direct comparison between confamilial species, allowing a deeper understanding of sound detection abilities and possible mechanisms driving differential hearing. Using both approaches also allows future research into how these species may be impacted by increasing levels of anthropogenic noise. [ABSTRACT FROM AUTHOR]

Simple Summary: The aquaculture industry suffers large financial losses every year to a bacterial disease known as columnaris. Columnaris can be treated with antibiotics in the feed, but this is expensive and can lead to antibiotic resistance. Alternative inert substances that are inexpensive and that would not lead to antibiotic resistance are needed. One such alternative is kaolin clay. This clay is added to the water and has been shown to bind to columnaris bacteria in laboratory studies. This study used kaolin clay on several species of game and sportfish stocked at commercial rates. When added to the water as a prophylactic treatment, the kaolin clay bound to columnaris. The kaolin clay did not damage the organs of the fish, nor did it cause mortalities. We have shown that kaolin clay is safe to use as a prophylactic treatment in several freshwater fish species raised in Arkansas, USA. Aquaculture farms in Arkansas, USA routinely battle columnaris disease caused by Flavobacterium covae. Columnaris is prevalent during stressful events such as feed training and when fish are stocked at high densities in holding vats before sale. Kaolin clay was effective in laboratory trials as a treatment for columnaris in catfish. As a result, fish farmers are interested in applying kaolin products but were hesitant as they feared that the high doses of kaolin clay in vats might negatively affect the gills and overall health of fish. Therefore, we evaluated potential clay concentrations that might be used to prophylactically treat fish in vats. The effects of low to excessively high doses (0, 1, 2, 4, or 8 g/L) of kaolin clay (AkuaProTM, Imerys, GA, USA) were evaluated using a 72 h bioassay conducted in static tanks using Micropterus salmoides, Pomoxis nigromaculatus, Lepomis macrochirus, Ictalurus punctatus, Notemigonus crysoleucas, and Pimephales promelas. Results of these trials revealed a 100% survival rate across all six fish species exposed to kaolin clay at concentrations of up to 8 g/L for 48 h (followed by a 24 h recovery period in clean water) with no adverse effects to eyes, skin, gastrointestinal tract, or liver histology noted at any treatment. In addition, Micropterus salmoides analyzed for heavy metals due to exposure to the clay indicated that concentrations did not differ from control fish. [ABSTRACT FROM AUTHOR]

Invasive crayfish (family Cambaridae) displace native crayfish species and alter aquatic habitat, community structure, and ecosystem function. We evaluated whether chemical control can be a reliable control agent for crayfish to ensure that shipments from fish hatcheries did not result in new infestations of invasive crayfish. A series of acute (≤1 h) toxicity tests were conducted to evaluate the toxicity of cypermethrin and pyrethrin to crayfish, freshwater mussels, and fish; chemical concentrations in test organisms; effectiveness of carbon‐block filters to remove cypermethrin from test waters; and the cost of chemical control relative to extra handling of fish. Cypermethrin dosed at 75 μg/L for 15 min resulted in 100% mortality of adult white river crawfish Procambarus acutus and virile crayfish Faxonius virilis but did not cause >20% mortality in adult pondmussel Ligumia subrostrata, juvenile fatmucket Lampsilis siliquoidea, fingerling Bluegill Lepomis macrochirus, hybrid sunfish (Bluegill × Green Sunfish L. cyanellus), hybrid Striped Bass (White Bass Morone chrysops × Striped Bass M. saxatilis), yearling Paddlefish Polyodon spathula, or ready‐to‐eat Bluegill, hybrid sunfish, and Channel Catfish Ictalurus punctatus. Behavioral effects, such as loss of equilibrium or head shaking, were generally limited to 1 h postexposure. Mean concentrations of cypermethrin increased in fish fillets (4–26 μg/g) and whole fish (5–1,770 μg/g); therefore, regulations limiting harvest for up to 7 d following stocking may be required. A carbon‐block filtration system was effective in reducing (<90%) cypermethrin concentrations and thus reducing potential effects to nontarget species in receiving waters. Extra handling of fish was more cost‐effective for all fish tested except for Paddlefish, where the cost of chemical control was half that for extra handling. For all other fish tested, chemical control was 4–10 times more expensive than extra handling. Special use permits or chemical registration are needed before chemical control for crayfish could be routinely used at fish hatcheries. [ABSTRACT FROM AUTHOR]

Barotrauma can lead to physical injury and physiological disturbance (elevated stress hormones, and depleted energy stores during post‐release struggling) in angled fish. Effectiveness of methods for reducing effects of barotrauma on fish has not been tested on fish subjected to ice‐angling. We examined post‐release behavior and re‐descension of bluegill Lepomis macrochirus and black crappie Pomoxis nigromaculatus. Barotrauma was mitigated for fish either during capture by slow retrieval or following capture by venting or re‐descension with weights, before observation in a behavioral arena or using small acceleration and depth biologgers. Black crappie spent less time in the center of the behavioral arena and were less likely to successfully re‐descend than bluegill. Depth increased over time during the post‐release monitoring period, with control fish less likely to descend to depth as fish for which barotrauma was mitigated. Our results demonstrate species‐specific effects of ice‐angling to inform anglers on the effectiveness of barotrauma mitigation strategies to improve welfare of fish after release. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) has recently been developed for detecting the distribution of macroorganisms in aquatic systems and for estimating biomass/abundance. Although positive relationships between eDNA concentrations of species and biomass/abundance have been observed in previous studies, estimation of total biomass in a particular ecosystem based on eDNA concentration has not been investigated.To test this, we sampled eDNA from the littoral and pelagic zones of eight small ponds in Japan. Then, we drained ponds to capture all fish inhabiting each pond. We compared the eDNA copies measured by quantitative real‐time polymerase chain reaction analysis with the captured biomass of three dominant fish species (common carp, bluegill sunfish, and largemouth bass) obtained by direct capture. Differences in eDNA concentrations were compared between the littoral and pelagic zones of each pond.We found positive relationships between the eDNA copies and the whole captured biomass of all target species using Type II logarithmic equations, and the eDNA copies appeared to be saturated at a higher total biomass.We found positive correlations between the total number of eDNA copies and the total captured biomass of three fish species. This demonstrated the first step in estimating the population biomass of target fish species under natural conditions using eDNA measurement. [ABSTRACT FROM AUTHOR]

Juvenile stages of fishes are frequently bottlenecks to recruitment. Habitat use of early life stages and the extent to which fish rely on local resources may affect how they respond to habitat loss and alterations, with important implications for habitat management. To investigate the potential for prolonged reliance on local resources, we quantified stable isotope ratios (δ13 carbon, δ15 nitrogen, δ18 oxygen and δ2 hydrogen) of young‐of‐year (YOY) largemouth bass Micropterus salmoides and isotope ratios of locally collected water and potential prey across three study components, a controlled pond experiment, a multi‐lake survey and a detailed single‐lake survey. Across study components, we observed habitat and site fidelity of YOY largemouth bass in mid‐summer, demonstrated by distinct spatial differences in young bass stable isotope ratios. Additionally, we observed significant, positive correlations between δ13C of YOY largemouth bass and δ13C of locally collected invertebrates and small bluegill Lepomis macrochirus in the single lake survey, suggesting localised foraging. Later in summer, spatial differences in largemouth bass stable isotope ratios were not apparent, indicating a transition to more spatially integrated foraging. Prior to switch to piscivory, YOY largemouth bass rely on local resources indicating that they may be more susceptible, both positively and negatively, to hyper‐local changes in forage availability or disturbances. This study demonstrates that stable isotope ratios allow for differentiating environmental experiences among young fish in relatively close proximity in small freshwater systems. Moreover, high spatial variation of consumer stable isotope ratios demonstrates the importance of considering spatial heterogeneity in stable isotope studies. [ABSTRACT FROM AUTHOR]

Prolactin and 11‐ketotestosterone (11‐KT) are important reproductive hormones in fishes, which may also influence immunocompetence. The immunocompetence handicap hypothesis states that higher androgen concentrations that support secondary sex traits are traded off against a decrease in immune system function. To test the relationships between these hormones and immunocompetence, we experimentally manipulated 11‐ketotestosterone and prolactin in the freshwater fish, bluegill (Lepomis macrochirus) during parental care using implants that contained either 11‐KT, prolactin, or an inert control. We vaccinated individuals to stimulate the acquired immune response, then measured immunocompetence as the number of granulocytes, lymphocytes and monocytes, and the expression of interleukin 8 in each sample. We did not observe any significant differences in the immune measures among the hormone treatments. Our results indicate that in bluegill, there is no trade‐off between androgens or prolactin and immunocompetence. Research Highlights: Prolactin or androgen (11‐KT) treatment did not affect immune responses in bluegill sunfish.We find no support the immunocompetence handicap hypothesis in fish.Increased 11‐KT affected behavior, but not the immune response to a vaccine. [ABSTRACT FROM AUTHOR]

North American sunfishes (Family Centrarchidae) are among the most popular sportfish throughout the United States and Canada. Despite the popularity of sunfishes, their ecological importance, and their extensive stocking and aquacultural history, few molecular studies have examined the evolutionary relationships and species boundaries among members of this group, many of which are known to hybridize. Here, we describe a chromosome-scale genome assembly representing Bluegill (Lepomis macrochirus), one of the most widespread centrarchid species. By combining long-read, Oxford Nanopore sequencing data with short-insert, whole-genome and HiC sequence reads, we produced an assembly (Lm_LA_1.1) having a total length of 889 Mb including 1,841 scaffolds and having a scaffold N50 of 36 Mb, L50 of 12, N90 of 29 Mb, and L90 of 22. We detected 99% (eukaryota_odb10) and 98% (actinopterygii_odb10) universal single-copy orthologs (BUSCOs), and ab initio gene prediction performed using this new assembly identified a set of 17,233 genes that were supported by external (OrthoDB v10) data. This new assembly provides an important addition to the growing set of assemblies already available for spinyrayed fishes (Acanthomorpha), and it will serve as a resource for future studies that focus on the complex evolutionary history of centrarchids. [ABSTRACT FROM AUTHOR]

Purpose: Behavioral variation among conspecific organisms can have substantial ecological impacts, particularly affecting parasite infection. Bluegill sunfish (Lepomis macrochirus) exhibit multiple male reproductive morphotypes that differ in their size, feeding dynamics, and reproductive behavior. This study investigated how these morphological and ecological differences contribute to the patterns of infection by strigeid trematodes. Methods: A total of 1961 L. macrochirus was collected from 14 lakes and ponds in northwestern Virginia, USA, and were necropsied to identify and enumerate three common strigeid parasites, white grub (Posthodiplostoum spp.), black grub (Uvulifer ambloplitis), and yellow grub (Clinostomum marginatum) infecting the fish and determine if there were different infection patterns among sexes and morphotypes. Results: Strigeid infections in L. macrochirus α-males were in greater abundance compared to females and β-males. Additionally, α-males had greater strigeid infection in the kidneys and fins, while females and β-males accumulated more parasites in the liver and body tissues. Conclusions: Increased nesting responsibilities and potential interaction with snail intermediate hosts by α-males may lead to the differences in infection patterns. The distinction of morphotypes revealed significant differences in abundance and distribution of parasite infections between the sexes of L. macrochirus, trends that were masked when male morphotypes are combined. [ABSTRACT FROM AUTHOR]

Fluoranthene (FLU) has gained much attention in recent years because of its continuous discharge in natural waters and toxicity to aquatic ecosystems. However, it is difficult to control and manage FLU pollution because of the lack of a rational and scientific water quality criteria (WQC) of FLU. To solve these data gaps, the US EPA established an interspecies correlation estimation (ICE) model, which can be utilized to develop the SSD and HC5 (hazardous concentration, 5th percentile). Moreover, an improved model was developed using a combination of North American ICE models supplemented with China-specific species. In this study, to verify the applicability of the two ICE models, measured acute toxicity data for FLU were obtained from 9 acute toxicity tests using indigenous Chinese aquatic species from different taxonomic levels. Original and improved ICE-based SSD curves, which were generated using 3 surrogate species (Daphnia magna, Oncorhynchus mykiss, and Lepomis macrochirus), were compared with SSD curves based on measured data. The results showed that HC5 was 1.838, 1.062, and 0.570 mg/L for the original ICE, improved ICE, and measured data, respectively. The improved ICE-based HC5 value for FLU was within twofold of the HC5 value based on measure data, while the original ICE-based HC5 value was threefold higher than the HC5 value based on measure data. This indicated that the improved ICE had better predictability in extrapolating data with acceptable deviation than the original ICE. Furthermore, their differences between HC5 derived from two SSD curves were not significant. Generally, the improved ICE model was verified as a valid approach for generating SSDs with limited toxicity data and for deriving WQC for FLU. [ABSTRACT FROM AUTHOR]

Research on Bluegills, Lepomis macrochirus R., is abundant but typically focuses on water bodies with similar environmental conditions. We assessed Bluegill density, relative abundance (catch per unit effort [CPUE] by electrofishing), growth, and size structure in 60 lakes with wide-ranging surface areas (2–12,412 ha), trophic states (oligotrophic–hypereutrophic), and macrophyte abundances (0.3–100 percent of lake volume inhabited [PVI]) across Florida, USA. Bluegill density and CPUE increased with lake productivity and decreased with macrophyte abundance. Bluegill growth increased with lake productivity and CPUE of stock-length Florida Bass, Micropterus floridanus L., a Bluegill predator. Bluegill size structure increased with lake productivity and decreased with Bluegill density. Results indicate that Bluegill fisheries with abundant individuals of quality size (≥150 mm) require productive (>25 μg/L chlorophyll-a concentration) lakes with moderate to high macrophyte coverage (PVI 50–100), abundant stock-length Florida Bass (>40 fish/h of electrofishing), and Bluegill densities <300 fish/ha. This study provides an approach to predict Bluegill population demographics based on abiotic and biotic factors, establish fisheries management expectations, and develop regional and lake-specific management tools. [ABSTRACT FROM AUTHOR]

Simultaneously defending against predators, stymieing competitors, and generating immune responses can impose conflicting demands for host species caught in the entanglement of a food web. Host immunity is not only shaped by direct interactions among species, but also many indirect cascading effects. By reducing competition, predators in particular can affect resource acquisition necessary for hosts to mount energetically costly immune responses. However, identifying the links between predators and host immune responses determined by resource acquisition is a complex affair, because predators can (1) reduce host density and thus competition among hosts, (2) exert non-consumptive trait-mediated effects on host resource acquisition behavior, and (3) generate natural selection on host resource acquisition behavior. To examine the relative contributions of these potential predator driven density- and trait-mediated effects on a key aspect of immune function (total phenoloxidase activity, total PO), we conducted mesocosm and field experiments with larval damselflies (Enallagma signatum) and their dominant fish predator (Lepomis macrochirus). Although we expected to observe declines in total PO activity with increases in damselfly density, we found no relationship between density and total PO activity. We also found no support for the prediction that total PO activity would vary as a result of either non-consumptive trait-mediated effects or selection on damselfly foraging activity underlying resource acquisition. Despite the lack of trait- or density-mediated effects, we did find that total PO activity increased with damselfly prey density among lakes, implying resource limitation for this aspect of immune function. These unexpected results point to the need to better understand the ecological conditions whereby predators and competitors constrain immune functions necessary for species to defend themselves in complex food webs. [ABSTRACT FROM AUTHOR]

During spawning activity, fish release large amounts of sperm and eggs into the water, which has been assumed to cause an increase in environmental DNA (eDNA) levels and nuclear DNA/mitochondrial DNA ratios. To test whether these assumptions are valid and whether nuclear and mitochondrial eDNA analysis can be used to monitor the spawning activity of freshwater fish, we conducted field eDNA surveys and traditional surveys using common carp (Cyprinus carpio), largemouth bass (Micropterus salmoides) and bluegill sunfish (Lepomis macrochirus) as model species.Fish spawning periods were estimated based on age, as estimated using the body lengths of juveniles collected in the Miharu reservoir in Fukushima, Japan. The results showed that the main spawning periods of largemouth bass and bluegill sunfish were from April to July and from July to August, respectively.Field eDNA surveys were conducted in the Hebisawagawa front reservoir, which is connected to the Miharu reservoir. From March to August 2019 and 2020, weekly eDNA sampling was conducted at three sites, and daily sampling was conducted at six sites from 23 June to 3 July 2020. The eDNA concentrations of the nuclear internal transcribed spacer 1 (ITS1) and mitochondrial cytochrome B (CytB), as well as the ITS1/CytB ratio, were measured for each of the three fish in each water sample. Water temperature had a statistically significant effect on eDNA concentration, probably reflecting the relationship between water temperature and spawning.We created generalised additive mixed models to estimate spawning activity periods based on weekly eDNA data. The estimated periods of spawning activity for common carp, largemouth bass and bluegill sunfish were March to May, May to July, and May to August, respectively. The estimated spawning periods coincided with known fish ecology or the results of traditional methods. This method also has been applied to daily eDNA samples, showing the feasibility of high‐resolution estimation of spawning activity.For common carp and bluegill sunfish, we were able to estimate the spawning period using this method. Although the method is affected by biomass and the diffusion and degradation of eDNA, it has the potential to accurately estimating spawning activities. These then can be estimated without conducting laborious traditional surveys, facilitating the monitoring of reproduction by rare, invasive or important fishery species. Further research on the diffusion distance and degradation time of the eDNA concentration peak caused by fish spawning activity may improve the accuracy of monitoring. [ABSTRACT FROM AUTHOR]

Elevated levels of anthropogenic noise, especially those observed through boating activity, can negatively impact fish species, but it remains unclear which species are most affected and which behavioural metrics are best used in assessing fish responses to underwater noise. The effects of boat sounds on freshwater species are of particular interest because freshwater environments are less studied than the marine realm despite comparably high levels of biodiversity.In the current study, we examine the behavioural responses to boat noise in two freshwater species that differ in their hypothesised response to sound inputs: the spottail shiner (Notropis hudsonius), a species with known hearing specialisations, and the bluegill sunfish (Lepomis macrochirus), a species with more generalised hearing capabilities. Fish were presented with boat noise in a laboratory setting, and their swimming, escape and foraging behaviours were assessed to examine differential responses in relation to hypothesised hearing abilities.Both species showed a decrease in general swimming behaviours but an increase in erratic movements in response to boat noise, indicative of stress responses for both species. Despite the similarities in response based on swimming behaviours however, only spottail shiners exhibited true escape responses to the onset of the noise stimulus, suggesting a more extreme reaction in the species with a more refined hearing ability.Taken together, these results show that freshwater fish can respond to increased levels of anthropogenic noise, but that the severity of the response may differ based on auditory structures and therefore presumed hearing ability. The differences seen between behavioural metrics used (swimming vs. escape responses) also demonstrate how care must be taken in choosing a metric when developing exposure guidelines for underwater sound exposures, as different metrics could lead to differential impact assessments. [ABSTRACT FROM AUTHOR]

Control and prevention of invasive alien species (IAS) are important issues for the environmental management of dam reservoirs. Recently, environmental DNA (eDNA) analysis has been used for monitoring IAS in aquatic ecosystems. In this study, as a simple and user-friendly eDNA method for monitoring IAS, we developed an eDNA chip analysis for monitoring three IAS, largemouth bass Micropterus salmoides, smallmouth bass Micropterus dolomieu and bluegill sunfish Lepomis macrochirus, in dam reservoirs. The eDNA chip analysis using each IAS-specific primer and probe only amplified and detected the target species. The developed eDNA chip detected three IAS from water samples collected in five dam reservoirs, indicating that eDNA chip analysis can be used as a monitoring tool for IAS. However, IAS were not detected by the eDNA chip at some survey sites where the qPCR assays showed low eDNA concentrations, indicating a lower sensitivity of the eDNA chip at low eDNA concentrations. For the establishment of an eDNA chip for biomonitoring, some challenges faced by other techniques like qPCR and metabarcoding remain, such as sensitivity at low target concentrations and "real-time" detections in the field and further improvement of performance in eDNA chip will be required. [ABSTRACT FROM AUTHOR]

The Korean Demilitarized Zone (DMZ) was established in 1953 during the cessation of the Korean War, which divided the Korean Peninsula into North and South Korea. The DMZ is a representative biodiversity resource because it limits human activities. The current status of faunal diversity in adjacent areas of the DMZ was investigated in five regions at 91 sites from 2015 to 2019. A total of 19,562 individuals were collected and identified, including 81 species, 19 families, and 11 orders. Zacco koreanus was the most abundant fish species (relative abundance of 21.9%), while other key species were Zacco platypus (18.2%), Rhynchocypris oxycephalus (5.2%), Rhynchocypris steindachneri (4.9%), and Pungtungia herzi (3.7%). Notably, twenty-nige endemic and seven Red Data Book species were recorded, and three exotic species, Carassius cuvieri, Micropterus salmoides, and Lepomis macrochirus were found at five sites. Human activities and disturbances were found at 34.0% of all sampling sites, and the highest disturbance factors were river dredging and agricultural use (seven sites), sewage (five sites), and fisheries and development (two sites). We recommend that the governments of South and North Korea collaboratively manage the DMZ to protect ecological diversity and maintain its status as a symbol of peace. [ABSTRACT FROM AUTHOR]

• The eDNA method exhibits higher taxonomic resolution and detection rates compared with traditional gillnet methods. • Gillnetting and eDNA survey methods resulted in significantly different fish communities. • The spatial distribution of fish species sampled by gillnetting was more dispersed than that using eDNA method. • The eDNA reads can to some extent indicate the abundance and biomass of fish assemblage. Environmental DNA (eDNA) technology, as an alternative to traditional gillnet surveys, has attracted widespread attention. However, comparisons between eDNA and traditional methods regarding biodiversity and community structure have not yet been fully elucidated. This study compared the ability of eDNA and gillnets for fish monitoring in a large deep reservoir (Qiandao Lake) in East China. The results showed that eDNA exhibited higher taxonomic resolution and detection rates, and significantly larger species diversity and richness indices compared with traditional gillnetting methods. Using abundance and biomass datasets from gillnets revealed significant differences in fish community composition between gillnetting and eDNA survey methods. Gillnet abundance was dominated by small-sized fish species, while gillnet biomass was dominated by larger-sized ones, and the prevailing species detected in eDNA reads included the dominant species from gillnet abundance and biomass, as well as a medium-sized invasive alien fish (Lepomis macrochirus). Non-metric multidimensional scaling (NMDS) showed that the spatial distribution in abundance of fish species sampled by gillnetting was more dispersed than that using eDNA. The explanatory power with the gillnet abundance and biomass together as predictor variables of the eDNA reads increased moderately compared with taking them separately, and the fitting degree of quadratic functions was also improved somewhat compared to linear equations when using biomass to predict eDNA reads. Furthermore, the key environmental factors affecting fish communities differed between the two methods. Current research indicates that eDNA has advantages over gillnets in detecting fish species diversity, and it is recommended to combine it with traditional sampling methods. Under natural aquatic ecosystem conditions, the eDNA reads may comprehensively reflect the biomass and abundance information obtained through gillnetting, but their relationship is complex and requires further research. This study will provide guidance for biodiversity monitoring. [ABSTRACT FROM AUTHOR]