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At early life stages invasive fishes may have no innate or learned behavioral responses to native predators. However, social cues expressed by shoal mates is one strategy species use to assess risk. By shoaling and using social cues, fishes may identify and mimic others with anti-predator behaviors to increase their own survival. Ability of non-native fishes, such as bighead carp (Hypophthalmichthys nobilis), to mimic native species that have experienced predatory threats is not known. In this experimental study, we varied the number of experienced individuals and the species composition to contrast the responses of naive juvenile bighead carp exposed to predatory kairomones when grouped with differing numbers of either experienced conspecific or experienced heterospecific (golden shiner, Notemigonus crysoleucas) shoal mates. We found fully naive groups of bighead carp did not respond to largemouth bass kairomones, but that naive individuals could mimic anti-predatory behaviors of experienced individuals, even when those experienced individuals were heterospecifics. Diverse alarm responses of bighead carp to composition and experience suggest that responses of this species are plastic. Through changing responses based on shoal experience level and composition, plastic social learning highlights how naive individuals may adapt to novel predator threats, which could inform predictions of non-native persistence in novel waterways.

Predator-prey interactions exert significant influence over the survival of juvenile fish cohorts. Therefore, susceptibility of a habitat to invasion is influenced by the capacity of native predators to regulate invasive species through consumption. Closely related predators often share similar characteristics (e.g., odors or body morphometry), and prey species capable of expressing generalized behavioral responses to predators with similar characteristics may increase their chances for survival. Here, we examined how naive juvenile silver carp (Hypophthalmichthys molitrix), an invasive Asian carp, respond to three predator odors from predators commonly found in Midwestern lakes and rivers of the USA. We tested two congeneric species of bass (largemouth Micropterus salmoides and smallmouth M. dolomieu bass) and one outgroup, longnose gar (Lepisosteus osseus). Additionally, we tested how silver carp conditioned to recognize the odor of one group, largemouth bass, responded to the predator odors of the congeneric species and the outgroup. We found that juvenile silver carp showed no innate response to any of the three predator odors. Additionally, although they could be conditioned to recognize predator odors from largemouth bass, they were unable to generalize predator odors to smallmouth bass or longnose gar odor. These results suggest that invasive species could be less likely to persist in environments with diverse predator communities than environments of equal densities with uniform predator communities and that future studies should continue to explore this area as well as focus on understanding dynamics in predator-prey interactions of invasive species.

Predation is an important factor influencing the strength and success of a year class in many prey fishes. Many adaptations, including chemical cues, benefit shoaling groups by informing members of a possible impending predatory threat. Bighead (Hypophthalmichthys nobilis) and silver carps (Hypophthalmichthys molitrix) are widely dispersed invasive fishes that spend much of their first year at a size vulnerable to predation. The objective of this study was to evaluate the fright response of juvenile bighead and silver carps when exposed to alarm cues from conspecific and heterospecific fishes. Groups of carps were exposed to 5 mL of alarm cue from either bighead carp, silver carp, golden shiner (Notemigonus crysoleucas), or fathead minnow (Pimephales promelas). Behavior was recorded before and after the application of the treatment. Our results indicate that both species were unable to recognize chemical alarm cues from North American cypriniforms, yet both were able to recognize conspecific alarm cues. However, the two species of bigheaded carps respond to conspecific chemicals differently. Silver carp increase distance among individuals, whereas bighead carp reduce distance between individuals. Both show a reduction in activity after chemical application. Though both species recognize conspecific alarm cues, bighead carp exhibit similar fright patterns when exposed to alarm chemicals of silver carp, yet no behavioral responses were detected in silver carp when exposed to alarm chemicals of bighead carp. An understanding of fright response in bighead and silver carps aids understanding of predator interactions and ecological roles of these fishes, and can be utilized in population management applications.

Infochemical landscapes, also referred to as landscapes of fear, can strongly influence the distribution of organisms. Planktivore infochemicals alter zooplankton distribution; zooplankton avoid ma...

Predicting changes in reservoir conditions from climatic warming is hindered by the paucity of long-term data on temperature and thermal and oxygen structure replicated across a range of reservoir sizes. The present study characterizes seasonal patterns in temperature, thermal structure, and dissolved oxygen availability in reservoirs, and evaluates how critical periods for aquatic organisms (i.e., periods of maximum temperature and minimum oxygen) for these features are affected by atmospheric temperature anomalies at different time lags. Temperature and dissolved oxygen were measured from May through October at 1 m intervals from surface to bottom for 10 reservoirs sampled between 14 and 21 years during 1995–2016. For most temperature and oxygen metrics July was the period of thermal maxima and oxygen minima across reservoirs, exceptions were thermocline depth, which was static from May through October, and bottom water temperature which peaked in August. Surface water temperature of reservoirs increased 0.6 °C for every 1.0 °C increase in atmospheric temperature in July independent of reservoir area. Although the percentage of water that was oxic in July decreased with increasing July air temperatures, it increased with warming air temperatures from February to April. These long-term data derived patterns highlight the importance of reservoir size and lag periods in building a framework for predicting climate-induced changes in the thermal and oxygen environments of reservoirs, which have important implications for water quality and ecosystem processes and the associated dynamics of reservoir flora and fauna.

Variation in the distribution and abundance of nearshore fishes is critical to understand food web processes and fishery management issues in Lake Michigan. This study characterised patterns in abundance of three common nearshore species, yellow perch Perca flavescens (Mitchell), round goby Neogobius melanostomus (Pallas) and alewife Alosa pseudoharengus (Wilson), in relation to spatio‐temporal, abiotic and biotic factors using gillnet sampling conducted across 5 years at multiple locations representing different substrates. Significant variations were observed in alewife and round goby catches between locations. A negative relationship between round goby and age‐0 yellow perch catch was observed, indicating potential competition between the two species. This study demonstrates that variability in nearshore fish communities can be driven by factors including substrate and interspecific interactions. Given the prominent role these species play in Lake Michigan's food web and thus their importance to fishery production, a thorough understanding of these factors is warranted.

Although forested riparian buffers can improve stream habitat, there remains debate as to whether biotic integrity can be maintained by buffers in highly degraded watersheds. To determine if forest buffers can ameliorate cropland impacts, we examined macroinvertebrate and fish assemblages in headwater streams categorized into three land use groups (High Buffer-Low Agriculture, High Buffer-High Agriculture, Low Buffer-High Agriculture). Sampling was conducted seasonally over 3 years to explore temporal patterns in biotic assemblages related to land use, instream habitat, and water quality parameters. Macroinvertebrate and fish abundance were higher in low buffer streams due to large numbers of pollution tolerant taxa and herbivores that proliferated with increased periphyton. In contrast, High Buffer-Low Agriculture streams had the best biotic integrity likely due to increased depth and better habitat quality. Non-metric multidimensional scaling ordinations of macroinvertebrate taxa showed no separations, but fish communities were significantly different among all three land use groups. Findings suggest fish community structure is more sensitive than macroinvertebrates to agricultural influences at both the riparian and watershed scales. Our study provides information on the effects of riparian vegetation on agricultural stream communities and highlights the importance of managing riparian forests to conserve stream biotic integrity.

We contrasted near- and offshore zooplankton biomass and assemblage structure in 15 reservoirs in the central United States. In particular, we evaluated whether season and the dominant pela...

Early life stages of fishes are sensitive to ecological and environmental disturbances and experience very high mortality rates. During early ontogeny, the growth and survival of larval fish often depends on food availability. Because habitat and diet shifts are strongly tied to individual body size, factors that influence the growth rates of individuals (e.g. resource limitation, competition) also affect other aspects of ontogeny including the timing of habitat or diet shifts. In the context of biological invasions, non‐native species can potentially disrupt the interaction of larval fish with their food via competition for shared prey, reducing growth and survival during a vulnerable period of an organism's life history. We hypothesised that invasive planktivores negatively affect native species through the vulnerable larval life stage via competition for zooplankton resources. To test this hypothesis, we conducted a series of experiments to assess and contrast the effects of invasive (bighead carp, Hypophthalmichthys nobilis) and native (golden shiners, Notemigonus crysoleucas) planktivores on zooplankton densities, and their effects on the growth, survival, abundance, and habitat use of larval bluegill (Lepomis macrochirus). Overall, the effects of the invasive planktivore were consistently greater than the native planktivore in terms of reduced prey densities, reduced bluegill growth rates, and delays to the timing of ontogenetic habitat shifts. Growth rates of bluegill larvae were reduced by 58–87% in the presence of bighead carp and 37% in the presence of golden shiners (relative to controls), but such reductions did not consistently lead to reduced survival (in mesocosm experiment) or relative abundance (in pond experiment). However, we estimated that bighead carp and golden shiners delayed ontogenetic habitat shifts in bluegill by 9–24 and 1–3 days, respectively. Although we did not detect an effect of planktivores on the numbers of larval bluegill, our findings suggest that bighead carp may still affect bluegill ontogeny and freshwater food webs by disrupting the timing of ontogenetic habitat shifts. By affecting the coupling of habitats via organism movements during early ontogeny, bighead carp may indirectly disrupt predator–prey interactions of native taxa.

The early foraging ecology of alligator gar (Atractosteus spatula) is poorly documented, with little information available on young‐of‐year food habits or ontogenetic diet shifts. We conducted laboratory experiments to quantify prey selection and foraging behaviours of larval and early juvenile alligator gar (16–80 mm TL) simultaneously offered zooplankton, chironomid larvae and one of three densities of fish prey. The smallest size groups of alligator gar consumed zooplankton almost exclusively, but with increasing size, selection for zooplankton declined and selection for fish prey increased. At higher densities of fish prey, alligator gar exhibited lower selection for zooplankton and positively selected for fish at smaller sizes. Ingestion efficiencies for chironomids were considerably lower than for zooplankton or fish prey, resulting in low rates of consumption and negative selection for chironomids by all size groups of alligator gar. Fish prey elicited a different foraging response from alligator gar than zooplankton or chironomids, as alligator gar pursued and struck at fish over longer distances than for other prey types. With increasing size, alligator gar used a wider vertical range of the water column for foraging, changed their strike tactics and exhibited decreased handling times for zooplankton and fish. These observations indicate that alligator gar undergo several functional and behavioural changes during early ontogeny that facilitate a rapid transition to piscivory, but fish prey density strongly affects prey consumption patterns and the size at which alligator gar transition to piscivory.

Monitoring ichthyoplankton is useful for identifying reproductive fronts and spawning locations of bigheaded carps (Hypophthalmichthys spp.). Unfortunately, sorting and identifying ichthyoplankton to monitor for bigheaded carp reproduction is time consuming and expensive. Traditional methods require frequent egg-larvae sampling, sorting of all samples to obtain presumptively identified bigheaded carp, and genetic validation of presumptively identified eggs. Quantitative PCR (qPCR) has the potential to streamline this process by identifying samples that likely do or do not contain a target species. Our objective was to develop a genetic screening tool using qPCR with the duplex assays SCTM4/5 and BHTM1/2 to prioritize samples that have a higher likelihood of containing bigheaded carp eggs or larvae. We used tandem ichthyoplankton samples collected for monitoring bigheaded carps in the Upper Mississippi, Illinois, and St. Croix rivers to evaluate the effectiveness of qPCR as a screening tool. Samples with > 10,000 copies of DNA had 100% occurrence of bigheaded carp eggs or larvae in the traditionally sorted samples, whereas samples with

Fish herding (driving fish into nets) is used by commercial fishers to increase harvest of invasive bigheaded carp (Hypophthalmichthys spp.), yet has not been widely adopted for fisheries monitoring purposes. We conducted an experiment to assess whether fish herding using percussive sound or electrical stimuli can enhance catch rates and detection of bigheaded carp and other fishes in surface-to-bottom gill nets. Catch rates (fish net set−1) from traditional gill net sets where no herding method was applied were compared to sets combined with either sound stimuli (physical impacts to the boat hull and water surface to produce percussive sound) or electricity produced from a pulsed-DC electrofisher to manipulate fish movements. For most species, herding increased catch rates and detection probability compared to control sets. Sound stimuli increased catch rates of Silver Carp (Hypophthalmichthys molitrix) by over three times, whereas electrical stimuli increased catch rates by over six times. Catch of Bighead Carp (Hypophthalmichthys nobilis) was highest in nets paired with sound stimuli. Herding methods also reduced the number of samples required to attain target detection probabilities for bigheaded carp. Herding techniques combined with gill netting may be a valuable option for targeted bigheaded carp sampling, especially when electrofishing or netting alone is ineffective for these evasive fishes. Synergistic methods may provide a cost effective means of improving detection probabilities for bigheaded carp at their invasion front or other locations where densities are low and uncertainty of capture is high.

Identifying spawning grounds of Asian carp is important for determining the reproductive front of invasive populations. Ichthyoplankton monitoring along the Illinois Waterway (IWW) has provided information on abundances of Asian carp eggs in the IWW's navigation pools. Post-fertilization times derived from egg development stages and water temperatures can be used to estimate spawning times of Asian carp eggs, but estimating how far these eggs have drifted requires information on river hydraulics. A Fluvial Egg Drift Simulator (FluEgg) program was designed to predict the drift of Asian carp eggs in the riverine environment with egg growth considered. This paper presents a reverse-time particle tracking (RTPT) algorithm for back-casting the spawning location of eggs from their collection site. The RTPT algorithm was implemented as a module in FluEgg. The new version of FluEgg was coupled with an unsteady hydrodynamic model of the IWW to predict the spawning locations for 530 eggs that were collected in June 2015. The results indicate that tailwater sections below the Locks and Dams (L&Ds) in each navigation pool appear to be preferred spawning locations for Silver Carp (a species of Asian carp). From the data analyzed, the most upstream spawning location for the June 2015 spawning period was in the upper Marseilles navigation pool, downstream of the Dresden Island L&D. The RTPT algorithm can efficiently estimate spawning locations for multiple egg samples.

Ecosystem level effects of common (Cyprinus carpio) and bighead carp (Hypophthalmichthys nobilis) have generally focused on adult life stages. The objective of our mesocosm study was to investigate and contrast the roles of juvenile common and bighead carp in structuring planktonic invertebrate assemblages, with focus on rotifers. We examined whether predation by juvenile carp was indiscriminate or size-selective with respect to prey size. Furthermore, we examined how changes to large and small prey influenced the potential for compensatory increases of some taxa within prey assemblages. Both species of juvenile carp reduced large zooplankton taxa. However, rotifer responses were variable depending on the taxon and predator combination. Juvenile common carp enhanced abundance for Polyartha and Squatinella, but most taxa were unaffected. Juvenile bighead carp had a more varied effect on rotifer abundance, having no effect on most, reducing Keratella and enhancing Anuraeopsis. We also estimated net filtration volume of the zooplankton community for each of the treatments and found partial compensation in net filtration because of the increased abundance of a few rotifer taxa, but this reduction did not match the depletion of macrozooplankton. Rotifers that benefitted from the presence of fish predators likely responded positively because of reduced predation by mesopredators, because of their short generation times, and/or from reduced competition.

Aquatic organisms, especially fishes, exhibit exceptional diversity in mouth morphology and this variation has been shown to influence foraging patterns. We compared mouth morphology among muskellunge Esox masquinongy, northern pike Esox lucius and their hybrid, tiger muskellunge E. masquinongy x E. lucius. Head and mouth size among the three taxa were similar for juveniles (

The River Redhorse (Moxostoma carinatum) is a large riverine catostomid that has experienced substantial declines across much of its historic range. Conservation of this species is hindered by a lack of knowledge about many aspects of its life history. In order to better understand the seasonal movements and habitat associations of this species, adult River Redhorse were captured from the Kankakee River, Illinois, implanted with radiotransmitters, and tracked throughout an annual cycle. Habitat data were recorded at all locations where radio-tagged River Redhorse were located. Eight of ten individuals displayed fidelity to a relatively short length of river (total range ≤ 8.7 km), whereas two individuals exhibited substantially greater movements (total range ≥ 23.1 km). Movement patterns of River Redhorse varied across seasons, with the largest ranges and highest displacements occurring during spring, and the smallest ranges and lowest movement rates occurring during summer. River Redhorse predominately o...

Cortisol, the main glucocorticoid stress hormone in teleost fish, is of interest as a mediator of maternal stress on offspring characteristics because it plays an organizational role during early development. The present study tested the hypothesis that maternal exposure to cortisol treatment prior to spawn affects offspring phenotype using wild largemouth bass (Micropterus salmoides). Baseline and stress-induced cortisol concentrations, body size (i.e. length and mass), and behavior (i.e. anxiety, exploration, boldness, and aggression) were assessed at different offspring life-stages and compared between offspring of control and cortisol-treated females. Cortisol administration did not affect spawning success or timing, nor were whole-body cortisol concentrations different between embryos from cortisol-treated and control females. However, maternal cortisol treatment had significant effects on offspring stress responsiveness, mass, and behavior. Compared to offspring of control females, offspring of cortisol-treated females exhibited larger mass right after hatch, and young-of-the-year mounted an attenuated cortisol response to an acute stressor, and exhibited less thigmotaxic anxiety, exploratory behavior, boldness and aggression. Thus, offspring phenotype was affected by elevated maternal cortisol levels despite the absence of a significant increase in embryo cortisol concentrations, suggesting that a mechanism other than the direct deposition of cortisol into eggs mediates effects on offspring. The results of the present raise questions about the mechanisms through which maternal stress influences offspring behavior and physiology, as well as the impacts of such phenotypic changes on offspring fitness.

Understanding spatial and temporal fluctuations in animal populations remains a central theme in ecology. Here, we investigated the extent of common carp (Cyprinus carpio) recruitment synchrony across North America in relation to a suite of climatic conditions. Common carp were collected from 21 populations up to a linear distance of 2300 km between the most southern and northern locations. Age-frequency histograms were used to estimate year-class strength, and correlation coefficients were used to evaluate synchrony among populations and environmental variables. We then evaluated relationships between common carp recruitment and winter growing degree-days (GDD), summer GDD, precipitation, wind events, and the El Niño Southern Oscillation Index (ENSO). Common carp recruitment was synchronous up to 756 km but asynchronous at larger scales. Winter and summer GDD, precipitation, and wind were also synchronous among locations up to 1640 km apart. Summer GDD appeared most influential to common carp recruitment but varied across latitudes, with negative effects identified at low latitudes and positive effects identified at higher latitudes. Our results provide new insights into the spatial scale of recruitment synchrony of a non-native freshwater fish and indicate that climatic conditions at local to regional scales likely influence recruitment patterns.

Summer stratification often leads to large areas of hypolimnetic hypoxia in lakes and reservoirs. These areas of hypoxia alter fish behaviours and distributions as well as restrict access to valuable prey resources, yet few studies have examined foraging behaviour of fish in response to low dissolved oxygen (DO) concentrations. We observed foraging behaviour of juvenile largemouth bass, Micropterus salmoides, in response to varying DO concentrations in tanks that simulated a stratified lake water column during the summer: 28°C oxygenated epilimnion, 15°C deoxygenated hypolimnion. Compared with saturated concentrations (8.0–9.0 mg/L), hypolimnetic oxygen concentrations of 3.0 mg/L and 1.5 mg/L resulted in a drastic decrease in prey consumption, handling efficiency and time spent below the thermocline mainly due to avoidance behaviour of hypoxic conditions. However, we found at high hypolimnetic prey densities, individual fish were more willing to venture into reduced oxygen concentrations. Several unique behaviours including transporting prey above the oxycline for consumption, aquatic surface respiration and gill flaring were employed by largemouth bass foraging in low oxygen environments. Reduced hypolimnetic oxygen concentrations may influence and alter feeding strategies, especially for fish that rely on benthic prey resources.

Communities of organisms are shaped by a complex suite of positive and negative species interactions. Ecological phenomena like biological invasions typically evoke notions of negative effects on native communities. Yet, negative effects within specific food-web components can also have positive feedbacks that manifest elsewhere within the food web. We designed an experiment to evaluate the direct and indirect effects of invasive bighead carp (Hypophthalmichthys nobilis: Cyprinidae) on planktonic and benthic invertebrates and the growth and survival of juvenile bluegill sunfish (Lepomis macrochirus: Centrarchidae). Our experiment indicated that the presence of bighead carp indirectly facilitated bluegill growth and survival. The underlying processes driving predator–predator facilitation stemmed from a combination of indirect interactions occurring through invertebrates in planktonic and vegetated habitats. Individual bluegill consumed more cladocerans and predatory macroinvertebrates in the presence of bighead carp. The presence of bighead carp appears to have indirectly influenced interactions among cladocerans, invertebrate predators, and bluegill. Understanding the cumulative direct and indirect effects of bigheaded carp on aquatic ecosystems requires the documentation of both negative and positive effects. Although one taxon benefitted from the presence of an invader, our findings demonstrate that this response occurred because bigheaded carp caused imbalances within the food web. We urge that future studies consider a priori how positive and negative interspecific interactions shape the structure of food webs.

Summary Ecological theory has long recognized the importance of positive and negative species interactions as drivers of food web structure, yet many studies have only focused on competition. Because competitive and facilitative mechanisms operate simultaneously, but through different food web pathways, the balance of their combined effects can produce complex and variable responses. We used a response-surface experimental design to assess the roles of negative (e.g., intra-, interspecific competition) and positive (e.g., facilitation) interactions between native and invasive juvenile fishes. We tested whether these interactions alter the densities of planktonic and benthic invertebrates to evaluate the magnitude and mechanism(s) influencing the acceptance or resistance of biological invaders. Interactions between bighead carp (Hypophthalmichthys nobilis) and bluegill (Lepomis macrochirus) or common carp (Cyprinus carpio) were evaluated in mesocosms. Intraspecific interactions were 1.5 to 2.4 times stronger than interspecific interactions between carp species. The only instance of interspecific competition resulted in bighead carp reducing the daily growth of bluegill, whereas the reciprocal interaction resulted in facilitation. Facilitation occurred when bluegill increased the daily growth of low density bighead carp treatments, despite increased numbers of fishes. Bighead carp also increased densities of benthic Chironomidae larvae, which were subsequently consumed by bluegill, but did not result in enhanced bluegill growth. These suites of interactions were not observed between common and bighead carp. Our response-surface design proved useful for comparing the relative magnitude of intra- vs. interspecific competition, identifying facilitation among species, and tracing attendant effects on invertebrate communities. By accounting for the directionality of interactions within our experimental framework and tracking responses of prey at lower trophic levels, we provide a clearer understanding of how competitive effects and stressed consumers alter prey communities and influence facilitation. This article is protected by copyright. All rights reserved.

Muskellunge Esox masquinongy are broadly distributed across the northern United States and southern Canada. Intraspecific genetic variation suggests the existence of divergent stocks related to residence in major river drainages. Populations and stocks have likely adapted to specific environmental conditions associated with geographic location, especially latitude and the associated thermal regime. In this study, we examined differences in survival and growth among stocks of juvenile Muskellunge stocked into lakes throughout Illinois. Muskellunge from the Ohio River drainage stock, the upper Mississippi River drainage stock, and the current mixed Illinois broodstock were used for comparisons. Stocking mortality was related to temperature and was greatest for Illinois and Ohio River drainage fish that were stocked during the early fall. Mississippi River drainage fish experienced high mortality over the first summer after stocking, resulting in the lowest abundance during the second fall poststocki...

Many behaviours have differential fitness consequences across thermal and ecological contexts, indicating that both ecological shifts and warming temperatures induced by climatic change may alter how organisms behave. However, empirical evidence of temperature-driven behavioural selection in natural systems is lacking. We compared behaviours and behavioural syndromes related to activity, exploration, boldness and aggression in populations of largemouth bass (Micropterus salmoides) from ambient lakes to the those from artificially warmed, power plant cooling lakes to investigate changes in behaviours associated with warmer environments. Activity, exploration, boldness and aggression of juvenile largemouth bass were assessed in laboratory conditions using a novel environment assay and a risky situation assay. We found that activity and exploratory behaviours were higher and decreased through first year ontogeny in populations from heated lakes, whereas these behaviours were lower and showed no relationship through ontogeny in populations from ambient lakes. We attribute these differences to the changes in food source availability in heated lakes associated with temperature-driven ecological effects. Bold and aggressive behaviours tended to differ between populations, as did correlations between behaviours, but did not differ between ambient and heated lakes. The findings of this work identify that large ecological changes associated with warming environments, such as food availability, may drive changes in some aspects of behavioural expression in largemouth bass but that other aspects of behavioural expression may be driven by lake-specific factors not related to warming.

Ectotherms are susceptible to increasing environmental temperatures associated with anthropogenic warming. Supra-optimum temperatures lead to declining aerobic capacity and can increase exposure to lethal temperatures, resulting in reduced performance. Although the capacity of phenotypic plasticity to minimize the effects of temperature on physiological processes is well studied, evidence of generational changes (e.g. transgenerational plasticity and rapid adaptation) in response to environmental warming is limited in natural populations. We investigated metabolism, growth, and thermal tolerance of largemouth bass (Micropterus salmoides) populations inhabiting thermally altered lakes (i.e. power plant cooling lakes) which have year-round elevated temperature regimes and exhibit supra-optimum temperatures on a yearly basis, and compared these traits with those in largemouth bass populations from ambient lakes. Largemouth bass from ambient and heated groups (n = 3 populations per group) were spawned in an ambient, common garden pond environment, then acclimated to either a normal summertime temperature (24 °C) or a supra-optimum temperature (30 °C). Fish from heated populations had significant reductions in the resting metabolic rate at both temperatures and markedly increased growth rates at 30 °C. By comparing pond-raised fish to fish removed directly from heated lakes, we showed that developmental plasticity played little role in establishing the metabolic rate. A lower resting metabolic rate contributed to an increase in the conversion efficiency of food to biomass of largemouth bass from heated lakes, regardless of temperature. Despite inhabiting heated lakes for many decades, neither critical thermal maximum nor minimum were altered in heated populations when raised in a common garden environment. These results suggest that largemouth bass can lessen sub-lethal effects of warming by altering physiological processes to reduce the impact of warming on aerobic scope and that these changes are generationally transient, but changes in maximum thermal tolerance in response to warming is limited to phenotypic plasticity.

Little is known about the size-dependent consequences of stressors on wild animals, which is particularly relevant during winter where size-specific trends in survival are common. Here, exogenous cortisol manipulation was used to investigate the effect of a physiological challenge on overwinter mortality and spring condition of largemouth bass (Micropterus salmoides) across a range of body sizes. Fish were wild-caught in the fall, assigned into either control or cortisol manipulated treatments, and held in replicated experimental ponds. For bass that survived the winter, length, mass, and health metrics (e.g., gonadosomatic index [GSI], hepatosomatic index [HSI], and water content) were determined in the spring. Winter survival was marginally lower for cortisol treated bass; however, there was no influence of initial length, mass, or condition on overwinter survival. When bass were grouped by size, survival was significantly higher for bass 300-350 mm in length compared to those

Effective management and monitoring programs require confidence regarding basic biological sampling. Gear comparisons are often required to determine the most effective techniques. Such is the case for populations of invasive Asian carps Hypophthalmichthys spp., which have recently occurred in large numbers throughout sections of the Mississippi River basin. We tested five gears (mini-fyke nets, beach seine, purse seine, pulsed-DC electrofishing, and gill net) that targeted juvenile (age 0) Silver Carp H. molitrix at sites along the Illinois River during 2014 and 2015 to determine the most effective ones for age-0 Silver Carp. We considered the most cost-effective gear to be the one that provided the largest catch at a minimal expenditure of labor. Mini-fyke nets were the most effective at collecting large numbers of age-0 Silver Carp, followed in decreasing order by beach seines, pulsed-DC electrofishing, purse seines, and gill nets. The smallest Silver Carp were caught in beach seines and the la...

The study of fish diets is an integral part of many fisheries research and management programs. Several studies have evaluated the effectiveness of nonlethal stomach content collection methods but none have considered the effectiveness of lethal methods that may also be biased by continued prey digestion. We compared one nonlethal and two lethal methods of stomach content collection and preservation for juvenile Largemouth Bass Micropterus salmoides ranging in size from 51–68 mm TL. Macroinvertebrates and zooplankton from stomachs of juvenile Largemouth Bass were collected using three methods, including gastric lavage (stomach contents immediately preserved), removing and preserving stomachs from fresh fish (whole stomach preserved after 3 h on ice), and removing and preserving stomachs after the fish had been frozen whole (stomach preserved after whole fish was frozen for 3 weeks at −20°C in a freezer). There were significant differences in total biomass of zooplankton and the total number of ind...

We examined how different exploratory behavioral types of largemouth bass responded to differing prey communities by determining effects on growth, survival and diet in experimental ponds. We found evidence that non-explorer largemouth bass target young-of-year bluegill early on in life, but bluegill were not an important diet item by late summer. The presence of young-of-year bluegill as prey does appear to affect the foraging strategy of the two exploring types differently. In the absence of small bluegill, both behavioral types feed primarily on benthic invertebrates and zooplankton. When small bluegill were present, we saw a shift away from zooplankton as prey for largemouth bass. However, that shift was toward more benthic invertebrates for non-exploring behavioral types and toward terrestrial insects for exploring behavioral types. Thus, it appears that prey community composition can have important effects on the way in which different behavioral types interact with their environment.

Numerous simulation studies have considered the effects of impending climate change on lakes. Predictive models exist for the responses of a multitude of variables to a warmer climate, and potential effects on food webs and ecosystem functions. Although these predictions are numerous, there is a need for manipulative experiments testing for the effects of warming on actual lake systems. We used power plant lakes across the central Midwestern US as a substitute for future climate change effects. These treatment lakes receive heated effluent and are typically 2–6 °C warmer than other regional lakes. We collected data from 1997 to 2010 on a number of abiotic and biotic variables from three of these treatment lakes and six control lakes that were of similar size and location but did not have an artificial thermal regime. Phosphorus and phytoplankton concentrations were similar between treatment groups, although treatment lakes had greater phosphorus and less phytoplankton in September. No differences existed in turbidity (measured as Secchi depth transparency). Zooplankton were less abundant in treatment lakes than in control lakes throughout our sampling period (May–October), with differences in cladocerans driving this disparity. There was evidence of earlier spawning of gizzard shad (Dorosoma cepedianum) due to the warmer temperature regime, but not for bluegill (Lepomis macrochirus). Average sizes of juvenile bluegill were larger in warmed systems in July and August. Juvenile largemouth bass (Micropterus salmoides) were larger in heated systems in June, but no differences existed in July or August. Growth of adult largemouth bass was greater in systems with a warmer thermal regime. Our results provide insights into patterns that can be expected in the future, and may be used to further understand the wide-reaching implications of climate change.

We compared three entrapment gears to determine which method was the most effective for capturing invasive Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix in terms of numbers of fish captured and labor invested. Gears were deployed concurrently in two backwater lakes of the Illinois River during the summers of 2012–2014. Overall, the nightly catch rates of all fishes, Bighead Carp, and Silver Carp were one to three orders of magnitude greater in pound nets than in either fyke nets or hoop nets. Pound nets collected larger Bighead Carp than hoop nets and fyke nets. Hoop nets were ineffective at catching Asian carp in backwater lakes. Estimation of the effort required to deploy, maintain, and remove each gear type indicated that pound nets were the most cost-effective gear due to their high catch rates of Asian carp relative to the labor hours invested to collect the catch. Pound nets appear to be an effective means of removing Asian carp in backwater lake habitats of the Illinoi...

Over-winter mortality is an important selective force for warm-water fish (e.g., centrarchids) that live in temperate habitats. Inherent challenges faced by fish during winter may be compounded by additional stressors that activate the hypothalamic–pituitary–interrenal axis, either before or during winter, leading to negative sub-lethal impacts on fish health and condition, and possibly reducing chance of survival. We used experimental cortisol manipulation to test the hypothesis that juvenile largemouth bass ( Micropterus salmoides ) exposed to semi-chronic elevation in cortisol prior to winter would experience higher levels of over-winter mortality, physiological alterations and impaired immune status relative to control and sham-treated bass. Over-winter survival in experimental ponds was high, averaging 83%, and did not differ among treatment groups. Over the study period, bass exhibited an average increase in mass of 19.4%, as well as a slight increase in Fulton's condition factor, but neither measure differed among groups. Hepatosomatic index in cortisol-treated bass was 23% lower than in control fish, suggesting lower energy status, but white muscle lipid content was similar across all groups. Lastly, there was no difference in spleen somatic index or parasite load among treatment groups, indicating no long-term immune impairment related to our cortisol manipulation. The current study adds to a growing body of literature on glucocorticoid manipulations where field-based findings are not consistent with laboratory-based conceptual understanding of multiple stressors. This suggests that field conditions may provide fish with opportunities to mitigate negative effects of some stressors.

Waters in urban areas often experience hypoxic events due to combined sewer overflows, which have the potential to negatively affect aquatic biota. Despite these hypoxic events, many urban areas have diverse fish assemblages, suggesting hypoxia has a minimal impact. Data to quantify the impacts of aquatic hypoxia in urban systems are currently lacking. The current study sought to define how rain-induced hypoxia affected the movement, distribution, and physiology of individual Largemouth Bass Micropterus salmoides residing in the Chicago Area Waterway System (CAWS), an urban area prone to episodes of hypoxia. Following the onset of hypoxic events, the likelihood of Largemouth Bass remaining in hypoxic water was reduced, but fish did not completely avoid hypoxic areas. This suggests that hypoxia exerts only a moderate influence on the movement of Largemouth Bass. Field sampling showed that Largemouth Bass from the site prone to hypoxia were not in poor nutritional condition and were not suffering fr...

Largemouth Bass Micropterus salmoides undergo a diet shift to fish prey during the juvenile stage, but mechanisms influencing piscivorous behavior are largely unknown. In laboratory experiments, we examined ontogenetic effects of predator and prey size on piscivory of juvenile Largemouth Bass. Prey size preferences were determined in aquaria experiments by introducing multiple size ranges of either Bluegill Lepomis macrochirus, Gizzard Shad Dorosoma cepedianum, or Fathead Minnow Pimephales promelas with a Largemouth Bass from one of three length-classes (30, 50, and 75 mm TL). For Gizzard Shad, Largemouth Bass most often selected larger sizes (33–65% of Largemouth Bass length) than in experiments with either Fathead Minnow or Bluegill (25–48%). Although an optimal foraging model (handling time/prey dry mass) predicted most prey sizes chosen, Largemouth Bass, with their large gape, chose slightly larger prey than predicted for all three prey species. Using optimal-sized prey, we further investigate...

Recruitment of fishes is difficult to predict due to inter-annual and system variation. For example, the early life history of fishes inhabiting expansive freshwater systems such as the Great Lakes differs from other freshwater environments but has received less attention. Alewife Alosa pseudoharengus , an anadromous species adapted to living exclusively in freshwater, provides an opportunity to evaluate processes regulating growth and survival of a fish with marine origins inhabiting a large freshwater system. We collected age-0 alewives at three distinct locations (nearshore Chicago, nearshore Waukegan, offshore) in southwestern Lake Michigan during 2005 and 2006 to estimate density, growth, and survival. Larval alewife densities were up to three times greater and hatching peaks occurred earlier in 2005 compared to 2006. Back-calculated alewife hatch dates indicated that peak hatch occurred two weeks prior to peak catch rates, with similar hatching distributions of larvae collected between nearshore and offshore environments. Alewives up to approximately 16 d of age were collected in both nearshore locations before appearing in the offshore environment. Alewife growth rates were influenced by zooplankton density, water temperature, and hatching date whereas survival from the nearshore to offshore environment was influenced by wind events and hatching date. Prey availability and passive larval transport driven by offshore wind events are more commonly identified as factors influencing marine rather than freshwater larvae. Thus, factors affecting recruitment dynamics of fishes in large complex inland systems may be more similar to marine than freshwater systems.

Due to concerns of global climate change, additional research is needed to quantify the thermal tolerance of species, and how organisms are able to adapt to changes in thermal regime. We quantified the thermal tolerance and thermal stress response of a temperate sportfish from two different thermal envi- ronments. One group of largemouth bass (Micropterus salmoides) inhabited thermally enhanced reservoirs (used for power plant cooling), with water tem- peratures typically 2-5 C warmer than nearby reser- voirs. We tested fish for chronic thermal maxima and reaction to an 8 C heat shock using three common physiological indices of stress. We observed no evidence of differences between groups in thermal maxima. We observed no differences in thermal maxima between fish from artificially warmed and natural systems. Our results disagree with research, suggesting differences due to adaptation to different thermal environments. We speculate that behavioral modifications, lack of adequate time for genetic divergence, or the robust genetic plasticity of large- mouth bass explain the lack of difference between treatment groups.