Smallmouth Bass Research Articles

Relative effects of electro-immobilisation and chemical anaesthesia on in situ post-release behaviour and reproductive success in nesting smallmouth bass (Micropterus dolomieu)

In fisheries science, chemical anaesthesia and electrical immobilisation are often studied in laboratory or aquaculture settings with little focus on post-release behaviours of fish in the wild. We used nest-guarding smallmouth bass (Micropterus dolomieu) as a model species to investigate the relative impacts of chemical anaesthesia, electroanaesthesia with a TENS unit and conductive gloves, and electrostunning on natural behaviours and reproductive success in situ. Electrostunned fish had higher rates of failure to return to nests within 1 h and showed greater behavioural impairment in terms of both pre-release reflex assessments and capacity to resume parental care behaviours compared to other experimental treatments and control groups. The gloves failed to adequately reduce involuntary movements relative to controls but those fish returned to the nest quickly, suggesting potential opportunities for further refinement of methods. However, ultimate nest fate (i.e., abandonment rates) was similar across groups. We discuss the likely drivers for observed treatment effects, or lack thereof, as well as the implications of variation in biotic and abiotic environmental factors to our results. We end with recommendations regarding the use and development of anaesthetic and electro-immobilisation options for research on wild fishes.

Evaluating harvest incentives for suppressing a socially‐valued, but ecologically‐detrimental, invasive fish predator

AbstractThe legacy of intentional freshwater fish introductions across the western United States has fostered social tensions over the control of nonnative species in some contexts. Overcoming tensions and implementing effective control programs is important for mitigating impacts to native species. We modeled the efficacy of incentivized harvest for controlling nuisance smallmouth bass (Micropterus dolomieu) using empirical responses measured during fishing tournaments on two reservoirs that are sources of nonnative predators to critical habitat of native species. Simulations demonstrated that anglers could suppress adult smallmouth bass by 90%–99% in under 30 years, but were contingent on program participation and density dependence in harvest efficiency (i.e., catchability) and population demographics. Catchability differed between systems and varied temporally within the same system, thereby suggesting tournament structure could be adapted to increase harvest rates. Incentivized harvest should not be dismissed as a viable control strategy alone or in tandem with other methods in small lentic systems.

Effects of poor recruitment on riverine Smallmouth Bass population dynamics

AbstractObjectiveAltered flow regimes pose significant risks to the stability of populations of riverine Smallmouth Bass Micropterus dolomieu. Periods of poor recruitment, due to early life stage mortality resulting from high‐flow events, can cause size‐structure and density alterations of populations. The aim of this study was to opportunistically test for changes in dynamic rates of a riverine Smallmouth Bass population using a long‐term data set that spanned a period of poor recruitment.MethodsOur study evaluated size‐specific CPUE (fish/h), mortality, growth, and condition and tested for recruitment determinants of Smallmouth Bass through three consecutive years of poor age‐0 recruitment in the South Branch Potomac River, West Virginia. We used fall nighttime boat electrofishing surveys during 2009–2022 to monitor this population before and after the poor‐recruitment time frame (2016–2018).ResultAge‐0 CPUE was greater during the time frame prior to the poor‐recruitment time frame. However, there was no difference in the CPUE of quality‐length Smallmouth Bass between the two time frames and CPUE of preferred‐length fish was greater during the poor‐recruitment time frame. Growth and relative weight increased during the poor‐recruitment time frame. There was no significant difference detected in mortality between the recruitment time frames. Streamflow during the spawning period was a significant factor influencing fall recruitment of age‐0 Smallmouth Bass. A Ricker density‐dependent model with an added streamflow term performed as well as a basic, log‐linear streamflow model and a density‐independent model that also incorporated a streamflow term.ConclusionOur results provide evidence of density‐dependent structuring in this population. Decreases in population density increased population dynamic rates that maintained or improved size structure. High adult biomasses did not increase age‐0 recruitment. Many riverine Smallmouth Bass populations may display favorable density‐dependent responses to declines in juvenile recruitment. Thus, management agencies should better understand the resiliency of these populations prior to establishing expensive programs or regulations, which may be ineffective, to combat alterations in juvenile recruitment.

Pesticides in small volume plasma samples: Method development and application to smallmouth bass (Micropterus dolomieu) from the Chesapeake Bay watershed, USA

Nontarget organisms are exposed to pesticides following applications in agricultural and urban settings, potentially resulting in deleterious effects. Direct measurements of pesticides in biological tissues may aid in characterizing exposure, accumulation, and potential toxicity versus analyses in environmental media alone (e.g., water, soil, and air). Plasma represents a nonlethal sampling medium that can be used to assess recent exposures to contaminants. Herein, a method was developed to test the extraction of 210 pesticides and their transformation products in small volume plasma samples (100 μL). Plasma samples were protein precipitated with 0.5 % formic acid in acetonitrile added to the sample (ratio of 3.5:1). Pass-through solid phase extraction was used for sample matrix and lipid removal and samples were analyzed by liquid chromatography and gas chromatography with tandem mass spectrometry. Recoveries of 70.0–129.8 % were achieved for 182 pesticides and degradates across the low (25 ng mL−1), medium (100 ng mL−1), and high (250 ng mL−1) spike levels. Method detection levels ranged 0.4–13.0 ng mL−1. Following development, the method was applied to smallmouth bass (Micropterus dolomieu) plasma samples (n = 10) collected from adults in the Chesapeake Bay watershed. Individual plasma samples resulted in four to seven analytes detected with summed concentrations ranging 16.4–95.0 ng mL−1. Biological multiresidue pesticide methods help elucidate recent exposures of bioactive compounds to nontarget organisms.

Integrating spatial stream network models and environmentalDNAto estimate current and future distributions of nonnative Smallmouth Bass

AbstractObjectiveClimate change is fueling the rapid range expansion of invasive species in freshwater ecosystems. This has led to mounting calls from natural resource managers for more robust predictions of invasive species distributions to anticipate threats to species of concern and implement proactive conservation and restoration actions. Here, we applied recent advances in fish sampling and statistical modeling in river networks to estimate the current and future watershed‐scale spatial distribution of nonnative Smallmouth BassMicropterus dolomieu.MethodsWe integrated a spatial stream network (SSN) model of stream temperature, landscape environmental covariates, and Smallmouth Bass occurrence data based on environmental DNA (eDNA) detections to develop an SSN species distribution model (SDM) representing current Smallmouth Bass distributions in the Chehalis River, Washington State, a large coastal river basin of ongoing watershed‐scale restoration. The SDM was informed by spatially intensive eDNA sampling from 135 locations in the main stem and major tributaries. We then applied downscaled climate change projections to the SSN SDM to predict Smallmouth Bass range expansion in the basin by late century.ResultWe identified high levels of spatial autocorrelation at hydrological distances of ≤10 km in our eDNA data set, underscoring the importance of applying an SSN modeling framework. Stream temperature was identified as the most important environmental covariate explaining variability in Smallmouth Bass occurrence. Model predictions estimated that current suitable summer habitat for Smallmouth Bass habitat spans 681 km and is projected to nearly double by late century (1333 km) under a moderate climate change scenario. Current and future suitable habitat for Smallmouth Bass is prevalent in important tributaries for spring Chinook SalmonOncorhynchus tshawytscha, a species of major conservation concern in the Chehalis River and more broadly along the Pacific coast. In both the main stem and tributaries, the SSN SDM predictions of the upstream leading edges of Smallmouth Bass closely align with (within 4.8 km) edges identified by spatially intensive eDNA sampling.ConclusionOur study highlights the value of integrating SSN models with rapidly growing eDNA data sets for accurate and precise riverine fish distribution estimation. Our application provides crucial insights for anticipating the impacts of shifting invasive species on Pacific salmon Oncorhynchusspp. in a warming world.

Mark–recapture surveys affect nest site fidelity but not reproductive timing of male Smallmouth Bass

AbstractObjectiveFish population surveys in north‐temperate lakes are often conducted in the fall or spring when individuals are easy to capture with traditional fisheries techniques. Because some fishes are preparing to spawn or are spawning during these seasons, there is a critical need to better understand the potential influences of these surveys on decisions that are related to fish reproduction.MethodsWe tested whether spring mark–recapture surveys using fyke nets followed by electrofishing affect the reproductive behaviors of male Smallmouth Bass Micropterus dolomieu in a northern Wisconsin lake. Fyke netting, electrofishing, and whole‐lake nest snorkeling surveys were conducted during 2001–2008, and Floy‐tagged males were tracked across years to test whether capture in the fyke nets only or capture in the electrofishing survey influenced interyear nest site fidelity and reproductive timing.ResultThe mark–recapture surveys were conducted preceding the spawning of Smallmouth Bass, and returning males that were caught in the electrofishing survey nested ~50 m farther from their prior year's nest than both males that were captured only in fyke nets and males that were captured by neither method. Average interyear nest distances were ~200 m, and median interyear nest distances were ~90 m for males that were not captured in the electrofishing survey. Electrofishing and fyke netting did not influence the timing of reproduction.ConclusionSpring electrofishing surveys for Smallmouth Bass have the potential to displace breeding males from preferred nesting habitats. If displacement negatively influences fitness (i.e., age‐0 survivorship to maturation), spring electrofishing surveys would not be recommended for assessing Smallmouth Bass populations. However, spring population surveys often occur soon after ice off, and surveys that are conducted at these colder temperatures are typically less stressful and less likely to result in mortality. Future research should test for fitness implications of reduced nest site fidelity following electrofishing in Smallmouth Bass while considering potential fitness trade‐offs if surveys are moved later in the year.

Thermal tolerance and habitat preferences mediate how freshwater fish body sizes respond to warming

Recent studies have linked ecosystem warming to decreased mean body size in aquatic ectotherms but have often relied on experimental approaches. This study explores how climate change modifies adult body sizes in natural communities for five culturally, commercially, and recreationally important freshwater fish species that vary in thermal preferences (lake trout ( Salvelinus namaycush), lake whitefish ( Coregonus clupeaformis), walleye ( Sander vitreus), yellow perch ( Perca flavescens), and smallmouth bass ( Micropterus dolomieu)). Using data for >170 000 sampling records from >600 lakes spanning the entire province of Ontario, Canada, we employ a spatial analysis technique based on Integrated Nested Laplace Approximation to detect body size changes due to warming lake conditions. With warming conditions, cold-adapted species (lake whitefish) decreased in adult body size, while cool- and warm-adapted species (walleye and smallmouth bass) increased in adult body size. Our study, like others recently conducted in marine and freshwater systems, demonstrates that the responses of fish body sizes to warming are not a unidirectional shift and may be linked to the habitat and thermal preferences of individual fish species.

Male guarding behavior and brood predators of invasive Bluegill in a Japanese lake

AbstractObjectiveThe 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.MethodsBluegill spawning was studied in Lake Nojiri, Nagano, Japan, using underwater video recording and experimental removal of guarding males.ResultBluegill 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.ConclusionIn 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.

Gravel washing as a lacustrine spawning habitat restoration method for smallmouth bass

Smallmouth bass (Micropterus dolomieu) spawn on gravel and cobble in the littoral zone of lakes that may become degraded by the presence of fine sediments and decomposing organic matter. Substrate size and composition have been identified as important variables for nest site selection by male smallmouth bass. We tested whether ‘cleaning’ substrate by removing sediment with a pressure washer would increase the number of bass nests or the average total length (mm) of nesting smallmouth bass in selected areas of Big Rideau Lake, Ontario, Canada the following year using a before-after control-impact design. Treatment was not a significant predictor of nest abundance or average male length. Considering the strength of the experimental design it is reasonable to conclude that this intervention failed to enhance spawning substrate for smallmouth bass. Understanding the factors that maintain productive spawning sites for smallmouth bass is important to restoration effectiveness and determining where habitat enhancement will provide the greatest benefits.

Reservoir Stratification Modulates the Influence of Impoundments on Fish Mercury Concentrations along an Arid Land River System.

Impoundment is among the most common hydrologic alterations with impacts on aquatic ecosystems that can include effects on mercury (Hg) cycling. However, landscape-scale differences in Hg bioaccumulation between reservoirs and other habitats are not well characterized nor are the processes driving these differences. We examined total Hg (THg) concentrations of Smallmouth Bass (Micropterus dolomieu) collected from reservoir, tailrace, and free-flowing reaches along an 863 km segment of the Snake River, USA, a semiarid river with 22 impoundments along its course. Across three size-classes (putative 1-year-old, first reproductive, and harvestable sized fish), THg concentrations in reservoirs and tailraces averaged 76% higher than those in free-flowing segments. Among reservoirs, THg concentrations were highest in reservoirs with inconsistent stratification patterns, 47% higher than annually stratified, and 144% higher than unstratified reservoirs. Fish THg concentrations in tailraces immediately downstream of stratified reservoirs were higher than those below unstratified (38-130%) or inconsistently stratified (32-79%) reservoirs. Stratification regimes influenced the exceedance of fish and human health benchmarks, with 52-80% of fish from stratifying reservoirs and downstream tailraces exceeding a human consumption benchmark, compared to 6-17% where stratification did not occur. These findings suggest that impoundment and stratification play important roles in determining the patterns of Hg exposure risk across the landscape.

Expansion of smallmouth bass distribution and habitat overlap with juvenile Chinook salmon in the Willamette River, Oregon

AbstractSmallmouth bass populations have expanded far beyond their native range and these predatory fish present a pervasive threat to native aquatic species throughout North America. In the western United States, smallmouth bass are now present in river and reservoir habitats where Pacific salmon are found and are considered a potential threat to salmon recovery in many locations. We conducted a study to determine if smallmouth bass are expanding their range in the mainstem Willamette River, Oregon, and developed a model to assess habitat overlap between smallmouth bass and juvenile Chinook salmon. Sampling during 2011–2022 revealed that the distribution of smallmouth bass had expanded throughout that timeframe to encompass the entire mainstem Willamette River, including important rearing habitats for juvenile Chinook salmon. The model predicted that smallmouth bass and juvenile Chinook salmon habitat overlap was substantial, highlighting the need for additional research to evaluate for potential negative impacts to salmon recovery in the basin. The model was also used to evaluate the efficacy of using flow management to reduce interactions between these two species, but the scenarios we examined suggested that this was not a viable option. These results highlight the need for continued research to assess interactions between smallmouth bass and juvenile salmon, and other native species of concern, in the Willamette River Basin. The development of the model is useful for resource managers to understand interactions between these species to prioritize locations for sampling in the future.

Effects of Rapid Thermal Cycling (Cold Shock) on Fish Health: Evidence from Controlled Laboratory Experiments, Behavior, and Telemetry

Powerplants frequently use river water for cooling, subsequently discharging warm effluent. Some of these plants can cycle on and off rapidly based on electricity demand, resulting in dramatic temperature fluctuations in the receiving waters. To understand the impacts on resident fish populations in the Upper Mississippi River, we (i) assessed the effects of rapid water cooling on three native fish species; (ii) investigated whether smallmouth bass (Micropterus dolomieu) behavior favored movement into thermal plumes when given a choice of cooler or ambient water; and (iii) tracked native M. dolomieu with acoustic tags and recorded core body temperature during the thermal cycling process of a steam electric powerplant. In cold shock experiments, mortality was associated with rapid temperature declines and dependent on the final (cold) holding temperature. The species or developmental stage of the tested organism did not affect survival. When given a choice between warm and ambient waters, M. dolomieu exhibited little inclination to acclimate to the warmer water and instead “self-regulated” by moving in and out of the warm water plume. This finding was supported by telemetry data on M. dolomieu. The core temperature of the fish never increased more than 2 °C above the ambient (upstream) Mississippi River temperature, even during warm effluent discharge.

Long‐term patterns of fish community structure and decline in native species in a Colorado River reservoir, Arizona and Nevada

AbstractObjectiveThe Colorado River has undergone substantial anthropogenic modifications, and a suite of nonnative species have been introduced since the 1800s; consequently, native fish communities are severely imperiled. We examined temporal patterns in fish community structure in Lake Mohave (i.e., lower Colorado River basin) over 40 years from 1980 to 2020.MethodsWe examined long‐term abundance and richness trends and the trajectory of fish community structure in multivariate space to assess stability and turnover using results from biannual (spring and autumn) trammel‐net monitoring over 40 years from 1980 to 2020.ResultNonnative fishes were established prior to sampling, precluding the ability to determine historical fish community structure. Bonytail Gila elegans and Razorback Sucker Xyrauchen texanus were the only two remaining native fishes, and both declined precipitously in abundance through time. However, a repatriation program initiated in 1991 prevented Razorback Sucker from extirpation, while reintroduction efforts for Bonytail have failed. Both wild populations are gone. Total catch per unit effort showed a negative relationship from 1980 to 2020, whereas total species richness showed no relationship. Long‐term abundance trends at the species level indicated three nonnative species (i.e., Gizzard Shad Dorosoma cepedianum, Yellow Bullhead Ameiurus natalis, and Smallmouth Bass Micropterus dolomieu) increased, nine decreased, and three showed no relationship. Fish community composition exhibited low stability and moderate turnover and shifted directionally through time in multivariate space, with the formation of three clusters, possibly indicating alternative states.ConclusionThe contemporary fish community shows little resemblance to the endemic ichthyofauna that has historically occupied the Colorado River, and the Razorback Sucker is the only remaining native species due to recovery efforts. Continued adaptive management will be required to preserve the most genetically diverse Razorback Sucker population in the Colorado River system, especially while coexisting with an unstable nonnative fish community.

TRIM21 of Micropterus salmoides exerts antiviral roles against largemouth bass ulcer syndrome virus

Tripartite motif 21 (TRIM21), a member of the TRIM family, plays an important role in apoptosis, autophagy and ubiquitination in human, and has been proven to play antiviral roles in different organisms. In this study, the TRIM21 gene of Micropterus salmoides (MsTRIM21) was cloned, and it encoded 376 amino acids, which showed 89.3% similarity with Micropterus dolomieu and 38.3% with homo sapiens. Bioinformatics analysis revealed MsTRIM21 contained four domains: C4HC3-type RING-variant (RINGv), coiled coil, PRY and SPRY. The high expression level of MsTRIM21 could be detected in liver, stomach and muscle of healthy Micropterus salmoides, and it was significantly upregulated in head kidney, muscle, gill and brain and significantly down-regulated in the stomach of Micropterus salmoides infected with largemouth bass ulcer syndrome virus (LBUSV). The overexpression of MsTRIM21 could significantly inhibit the viral replication in vitro, evidenced by the reduction of CPE severity and the downregulation of the viral gene transcription. In addition, the overexpression of MsTRIM21 could significantly increase the expression level of interferon regulatory factor (IRF) 3, IRF7, myxovirus resistance 1 (Mx1), interferon stimulated gene 15 (ISG15), double-stranded RNA-activated protein kinase (PKR) and tumor necrosis factor α (TNF-α) in vitro, indicating the enhancement of innate immune response and inflammatory response, which may directly affect the replication of LBUSV. Thus, these results provide new lights on the roles of fish TRIM21 in innate immune response against iridovirus.

Predicting sport fish mercury contamination in heavily managed reservoirs: Implications for human and ecological health.

Mercury (Hg) is a concerning contaminant due to its widespread distribution and tendency to accumulate to harmful concentrations in biota. We used a machine learning approach called random forest (RF) to test for different predictors of Hg concentrations in three species of Colorado reservoir sport fish. The RF approach indicated that the best predictors of 864 mm northern pike (Esox lucius) Hg concentrations were covariates related to salmonid stocking in each study system, while system-specific metrics related to productivity and forage base were the best predictors of Hg concentrations of 381 mm smallmouth bass (Micropterus dolomieu), and walleye (Sander vitreus). Protecting human and ecological health from Hg contamination requires an understanding of fish Hg concentrations and variability across the landscape and through time. The RF approach could be applied to identify potential areas/systems of concern, and predict whether sport fish Hg concentrations may change as a result of a variety of factors to help prioritize, focus, and streamline monitoring efforts to effectively and efficiently inform human and ecological health.

Elements and omega-3 fatty acids in fishes along a large, dammed river

Damming of a river can trap and elevate levels of sediment-bound elements and alter food web dynamics in created reservoirs. It follows that dams may alter how elements and other nutrients, like the beneficial omega-3 fatty acids (n-3 FAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are accumulated in fish and thus the chemical composition of species above and below this barrier to migration. This study examined the spatial and species differences in contaminants and nutrients in fish from the Wolastoq | Saint John River (New Brunswick, Canada) in association with a large hydroelectric dam (Mactaquac Generating Station; MQGS), a river which supports both recreational fisheries and subsistence fishing by Indigenous communities. In 2020 and 2021, Smallmouth Bass, Yellow Perch, American Eel, and Striped Bass were collected from locations upstream (reservoir and river) and downstream of the MQGS and analyzed for mercury (Hg) and 30 other trace elements, n-3 FAs, δ15N, and δ13C. Fish from the reservoir were highest in the beneficial elements P, S, and K, while fish from upstream of the reservoir had lower levels of toxic elements, including Hg. The dam appeared to alter food web dynamics, as fish from the reservoir and immediately downstream of the dam had higher δ15N and reservoir fish were depleted in δ13C. DHA and Hg were positively corelated with δ15N, and EPA in Smallmouth Bass was higher in sites where fish had higher δ13C. Overall, this study suggests that the dam altered food web dynamics and the uptake of contaminants and nutrients by fish, and that location and species are important factors when examining the risks and benefits of consuming wild fish from a system impacted by a large dam.

Limited hybridisation and introgression despite stocking among endemic Interior Highlands black basses (Centrarchidae: Micropterus)

AbstractAimSmallmouth Bass (Micropterus dolomieu; SMB) are globally popular among anglers and have been widely introduced (i.e. stocked) for population management and sportfishing. Importantly, stocking was prevalent before cryptic diversity within the SMB complex was known, which now includes three newly elevated species: Neosho Bass (M. velox; NB), Little River Bass (M. sp. cf. dolomieu Little River; LRB) and Ouachita Bass (M. sp. cf. dolomieu Ouachita River; OB). We sought to quantify population structure and hybridisation and introgression in these three recently described species.LocationSpecies‐level diversity, particularly in the basin‐restricted LRB and OB in the Ouachita Mountains within the Central Interior Highlands (CIH), North America, suggests the presence of distinct genetic variation that could be eroded by introgression.MethodsWe estimated interspecific introgression and intraspecific population differentiation in the Smallmouth Bass species complex (SMB‐C) using 472 specimens comprising SMB, NB, LRB and OB, including the naturally sympatric Spotted Bass (M. punctulatus; SPB). Genomic samples were genotyped on a SNP panel of 192 loci designed to detect allele‐sharing on multiple hierarchical levels.ResultsWe found low range‐wide hybridisation between species in the SMB‐C and SPB (mostly SMB‐C backcrosses), and interspecific heterozygosity varied, indicating differential introgression. Range‐wide hybridisation between species in the CIH and SMB was similar overall (but mostly F2 and CIH backcrosses) and was observed in streams with known SMB stocking in connected reservoirs. Interspecific heterozygosity in SMB hybrids was also generally lower, indicating later‐generation backcrosses. We found strong population structure in the Ouachita Mountains (LRB and OB).Main ConclusionsDespite isolated incidences of natural (SPB) and human‐mediated (SMB) introgression, genomic identity appears intact in endemic LRB and OB, suggesting potential ecological or behavioural isolating mechanisms preventing cross‐species reproduction. Our findings reveal that genetic variation remains in cryptic, basin‐restricted species in the Ouachita Mountains ecoregion that may be managed for long‐term conservation.

Evaluating blood, gill, and muscle biopsy methods on the behaviour, reproductive success, and survival of a wild freshwater fish

Non-lethal biopsy methods (including blood, gill, and muscle biopsies) have been used to study the health and physiological status of wild fishes. Nonetheless, concerns exist regarding the impact of non-lethal sampling on relevant welfare measures such as behaviour and survival. Here, nesting Smallmouth Bass (Micropterus dolomieu) were used as a model species to study in situ how fish respond to non-lethal sampling. Male Smallmouth Bass provide sole parental care and guard well-defined nests for a period of several weeks, providing a unique opportunity to assess behaviour, reproductive success, and survival in the wild. Fish were captured from their nests by angling and subjected to a biopsy (either blood, gill, or muscle), or a combination of all three biopsy methods prior to release. A control group that was captured but not biopsied as well as a non-angled control were also included. Nests were monitored for a period of four weeks or until the parental males either abandoned offspring, died, or raised a brood to independence. Single biopsies, regardless of the biopsy type, were found to have no impact on parental care and survival, but fish that received the combined treatment took longer to return to their nest and displayed a 6.5 times greater likelihood of nest abandonment. Mortality was only observed in fish that received the combined biopsy treatment. As such, this study reveals that it is possible to maintain the welfare status of Smallmouth Bass in the wild by using individual biopsies, thus emphasizing the importance of making careful decisions about which tissues are needed to achieve desired study objectives. This is one of the few studies to assess the behavioural and fitness consequences of increasingly common non-lethal biopsy methods and provides useful information on the relative consequences of different biopsy methods on wild fish.

Endocrine and scavenging cell functions of a juvenile fish heart atrium: Fine structure aspects and translating conjectures

BackgroundThe atrium of the juvenile teleost, smallmouth bass, Micropterus dolomieu Lacépède showed a pigmented endocardium. Our goal was to use fine structure to survey this fish heart tissues and verify the content responsible for this shrouding and discuss mammalian, translational conjectures about this cardiac structure. MethodsUsing electron microscopy, heart pericardium, myocardium, and endocardium were analyzed, including atrial peptide immunolabeling. ResultsThe endocardium endothelial cells of the atrium revealed pinocytosis and endocytosis activities that resulted in accumulated electron-contrasted secondary lysosomes and lipofuscin bodies not found in the ventricle endocardium. This endothelium contacted subjacent atrial and ventricular myocardial cells producing immunolabeled atrial peptide-containing vesicles. Other migrating cells, including melano-macrophages, were noticed in the atrial sub endocardium. ConclusionsThe endocardium functioned as a potent blood-heart barrier where transcytosis and dispatching of numerous materials, including those atrial peptides, between myocardium and the circulation occur. Peculiarly, this juvenile endothelium revealed abundant lysosomal processing of scavenged circulation materials like in a reticuloendothelial tissue. These juvenile cell's accumulated ‘aging’ lipofuscin bodies as organized deposits into a network with other organelles, especially mitochondria without evident disposal. Additionally, other cells, including melano-macrophages roamed both sub endocardium and ventricle; those also can influence the viewed pigmentation. Some of these data comforted the endocardial mesodermal lineage, still sketchy for all vertebrates while fish heart development is still used. These observations could raise questions: Does turnover of lipofuscin and associated captures make endocardial cells to model other mammalian pathologies, including those associated with heart failure?

Life-history habitat suitability modelling of a potential invasive alien species, smallmouth bass (Micropterus dolomieu), in South Korea

The aim of this study was to predict the distribution of a potential invasive alien species, smallmouth bass (Micropterus dolomieu), in South Korea using a life-history-based habitat suitability model. Environmental data (air temperature, water temperature, and fish occurrence) at present (2011–2020) were collected from 160 representative sites across the five river basins (Han, Nakdong, Guem, Seomjin, and Yeongsan). Future predictions were conducted under the representative concentration pathway 8.5 scenario in the 2050s (2046–2055) and the 2080s (2076–2085). Two spawning scenarios were implemented in the future, where smallmouth bass will not change the spawning season in the non-adaptive scenario and change the season in the adaptive scenario. The life-history habitat suitability (LHS) of smallmouth bass was evaluated using the geometric mean of the annual habitat suitability indices (HSIs) for each life stage (adult, juvenile, fry, and spawner). The LHS model was validated using the occurrence data of largemouth bass (Micropterus salmoides), which shares most of its habitats with smallmouth bass. The average LHS of smallmouth bass in South Korea was predicted to be 0.519 at present and expected to be 0.491 and 0.541 in the 2080s under non-adaptive and adaptive scenarios, respectively. Considering that the period for spawner fish may change in the future under climate change, the adaptive scenario seems to be more reasonable. The potential presence rate of smallmouth bass in South Korea was 100% at present, except for the Han River Basin (66%) which was expected to increase to 86% in the 2080s under the adaptive scenarios. The LHS model predicted that smallmouth bass could inhabit South Korea, and its distribution may expand under global warming, requiring urgent preventive measures.