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Morphology, size and physiological properties change markedly across fish ontogeny. This impacts locomotor performance and organismal fitness, although the effects are unpredictable due to the complexity of phenotype–function relationships. Morphological and behavioral changes with growth are often paralleled by changes in habitat use, diet and vulnerability to predators. Our goal was to quantify the changes in external morphology and escape performance throughout post-larval development in bluegill sunfish ( Lepomis macrochirus ), and place these changes in context with known changes in habitat use in the field. Development into adult ecomorphs is associated with phenotypic plasticity in response to habitat-specific differences in diet. On this basis, we hypothesized that variation in morphology and performance would increase during bluegill ontogeny as diversification of adult ecomorphs occurred. However, we found that variation in phenotype and escape performance decreased during early ontogeny. Phenotypic variation expanded later in development, after fish gained access to the variety of habitats and food types that may favor phenotypic plasticity. Performance is predicted to decline with growth due to the differential scaling of inertia and cross-sectional area, a major determinant of muscle force. In contrast, acceleration increased with size, and velocity and acceleration increased more rapidly with size than predicted. Post-larval maturation in bluegill featured a shift to a deeper body shape, and an increase in the relative size of the anal and caudal fins. This was a likely factor in the deviation of escape performance scaling relationships from predictions based on geometric similarity. [ABSTRACT FROM AUTHOR]

Bluegill sunfish (Lepomis macrochirus) are one of the classic systems for studying male alternative reproductive tactics (ARTs) in teleost fishes. In this species, there are two distinct life histories: parental and cuckolder, encompassing three reproductive tactics, parental, satellite, and sneaker. The parental life history is fixed, whereas individuals who enter the cuckolder life history transition from sneaker to satellite tactic as they grow. For this study, we used RNAseq to characterize the brain transcriptome of the three male tactics and females during spawning to identify gene ontology (GO) categories and potential candidate genes associated with each tactic. We found that sneaker males had higher levels of gene expression differentiation compared to the other two male tactics. Sneaker males also had higher expression in ionotropic glutamate receptor genes, specifically AMPA receptors, compared to other males, which may be important for increased spatial working memory while attempting to cuckold parental males at their nests. Larger differences in gene expression also occurred among male tactics than between males and females. We found significant expression differences in several candidate genes that were previously identified in other species with ARTs and suggest a previously undescribed role for cAMP-responsive element modulator (crem) in influencing parental male behaviors during spawning. [ABSTRACT FROM AUTHOR]

Background. The wide availability of specimen-based museum collections allows scientists to address a variety of ecological and systematic hypotheses from a broad timeframe and extensive spatial scale. However, techniques employed to preserve and maintain these collections affect morphology, potentially altering or skewing any morphological comparisons inherent in research study questions. The purpose of this study was to better understand and describe the effects that preservation techniques may have on fish specimens. Materials and methods. Bluegill, Lepomis macrochirus Rafinesque, 1819, and green sunfish, Lepomis cyanellus Rafinesque, 1819, were initially preserved for six weeks in a 10% formalin solution and then transferred to 70% ethyl alcohol for 46 additional weeks to determine how the commonly used preservation methods influence morphology. Fish were photographed at 0, 3, 6, 12, 24, 39, and 52 weeks of preservation to assess changes in shape. Standard length and maximum depth were measured on all fish images using Sigma Scan Pro. These measurements were then used to generate aspect ratios (maximum depth vs. standard length) for each fish. Additionally, geometric morphometric techniques (relative warp analysis) using 10 digital landmarks, were also used to evaluate overall morphological change. Results. During the 52-week period of preservation, fish standard length was reduced, but this dimension shrank proportionally with body depth. This finding was confirmed along the major gradients elicited from relative warp axis scores tested using repeated measures ANOVA. However, with both species, morphological contortions were observed immediately after the fish were placed in formalin and again when this fixative was replaced with ethyl alcohol. Conclusion. Ultimately, shape stabilized after a period of acclimatization of up to 39 weeks. This stabilization phenomenon provides evidence that long term museum collections do plateau in shape change and may be compared to address a variety of ecological and evolutionary hypotheses.

The drag coefficient bluegill sunfish Lepomis macrochirus was estimated from coasting deceleration as (mean ± SD) 0.0154 ± 0.0070 at a Reynolds number of 41,000 ± 14,000. This was within the coasting range in other species and lower than values obtained from dead drag measurements in this species and others. Low momentum losses during coasting may allow its use during intermittent propulsion to modulate power output or maximize energy economy. [ABSTRACT FROM AUTHOR]

Information is lacking on preserving fish carcasses to minimize postmortem autolysis artifacts when a necropsy cannot be performed immediately. The purpose of this study was to qualitatively identify and score histologic postmortem changes in two species of freshwater fish (bluegill—Lepomis macrochirus; crappie—Pomoxis annularis), at varied time intervals and storage temperatures, to assess the histologic quality of collected samples. A pooled sample of 36 mix sex individuals of healthy bluegill and crappie were euthanized, stored either at room temperature, refrigerated at 4 °C, or frozen at −20 °C, and then necropsied at 0, 4, 24, and 48 h intervals. Histologic specimens were evaluated by light microscopy. Data showed that immediate harvesting of fresh samples provides the best quality and refrigeration would be the preferred method of storage if sample collection had to be delayed for up to 24 h. When sample collection must be delayed more than 24 h, the preferred method of storage to minimize autolysis artifacts is freezing if evaluation of the gastrointestinal tract is most important, or refrigeration if gill histology is most important. The gill arch, intestinal tract, followed by the liver and kidney were the most sensitive organs to autolysis.

The emergent contaminant family, per- and poly-fluorinated alkyl substances (PFAS) has gained research attention due to their widespread detection and stability within the environment. Despite the growing amount of research on perfluorooctanesulfonic acid (PFOS) and perfluoro- n -octanoic acid (PFOA) in aquatic organisms, investigations detailing behavioral and physiological effects of aquatic organisms exposed to a mixture of PFAS analytes in the wild have been limited. The objective of this study was to evaluate the potential behavioral and histological effects of environmental exposure to PFAS compounds within multiple trophic levels of aquatic ecosystems. The current study investigates effects of environmentally relevant PFAS concentration exposures in crayfish (Faxonius immunis, F. rusticus, F. virilis) and bluegill (Lepomis macrochirus) sourced from four water bodies in Northern Michigan. Antipredator response and foraging behavioral assays were used to investigate potential effects on crayfish; a swimming speed behavioral assay and liver and gill histology analysis were used to investigate potential effects on fish. Linear mixed model and multiple regression analyses resulted in significant relationships between tissue accumulation levels of long chain PFAS compounds and crayfish foraging and fish critical swimming speed responses. Crayfish foraging decreased and fish critical swim speeds increased with PFAS exposure which may lead to energetic and population concerns. Antipredator response in crayfish and liver and gill histology in fish were not significantly related to PFAS tissue or water concentrations. The sensitivity of crayfish and bluegill behavior contributes to the growing body of research regarding the differential toxicity of short-chain and long-chain PFAS compounds. The sensitivity of some aquatic organism behaviors to PFAS accumulated in tissue may have implications for PFAS transfer and alterations to ecosystem functioning; based on the results of this field study, further laboratory research is recommended to further evaluate these relationships. • Behavior and histology were analyzed in relation to environmental PFAS exposure. • Crayfish foraging decreased and fish swimming speed increased with PFAS exposure. • Behaviors were more strongly related to long chain PFAS relative to short chain PFAS concentrations. [ABSTRACT FROM AUTHOR]

Science-based decision making in fisheries management requires the collection of sampling data with the acknowledgment that all gears have inherent sampling biases. Fyke nets are a common tool for sampling panfish. However, recent evaluations suggest hoop nets are more effective for evaluating these populations. We compared panfish relative abundance, size structure, condition, sampling effort to capture 100 individuals, and sampling precision for small (61 × 122-cm frames) and large (91 × 183-cm frames) fyke nets soaked for 24 h and tandem hoop nets soaked for 72 h during spring and fall. Hoop nets and large fyke nets captured more Bluegills Lepomis macrochirus, Black Crappies Pomoxis nigromaculatus, and White Crappies P. annularis than did small fyke nets, but catch rates for Redear Sunfish L. microlophus were similar among gear types. Bluegills captured in hoop nets were generally longer than those captured in small or large fyke nets, but the length of other panfish was similar among gears. Bluegill size structure was generally largest and Black Crappie size structure was generally smallest in hoop nets compared with that in fyke nets. Relative weight was greater for Bluegills captured in small fyke nets and was higher in the spring than fall. Hoop nets generally captured more panfish with fewer net sets and with greater precision than did small or large fyke nets, providing an additional tool for fisheries biologists for population assessments. [ABSTRACT FROM AUTHOR]

Most teleost fishes, like the bluegill sunfish Lepomis macrochirus , have multiple flexible fins that are used as modifiable control surfaces. This helps to make fish highly maneuverable, permitting behaviors like reversing direction of motion and swimming backwards without having to rotate body position. To answer the question of how fish swim backwards we used high–speed videography and electromyography to determine the kinematics and muscle activity necessary to produce reverse-direction propulsion in four bluegill sunfish. We found that, in contrast to slow forward swimming, low-speed backward swimming is a multi-fin behavior, utilizing the pectoral, dorsal, anal, and caudal fins. The pectoral fins alternate beats, each fin broadly flaring on the outstroke and feathered on the instroke. The dorsal fin and dorsal portion of the caudal fin move out of phase as do the anal fin and ventral portion of the caudal fin. Electromyography of muscles in the pectoral, dorsal, anal, and caudal fins demonstrated bilateral activation when these fins changed direction, suggesting that fins are stiffened at this time. In addition to backward propulsion by the pectoral fins, particle image velocimetry revealed that the dorsal and anal fins are capable of producing reverse momentum jets to propel the fish backward. Because teleost fishes are statically unstable, locomotion at slow speeds requires precise fin control to adequately balance torques produced about the center of mass. Therefore, the kinematics of backward swimming may be the result of compensation for rolling, pitching, and yawning instability. We suggest that asymmetric pectoral fin activity with feathering during adduction balances rolling instability. The ventral to dorsal undulatory wave on the caudal fin controls pitch instability and yaw instability encountered from pectoral-driven backward locomotion. Thrust generation from the dorsal and anal fins decreases the destabilizing effect of the long moment arm of the tail in backward swimming. Thus, backward locomotion at slow speed is not simply the reverse of slow forward swimming. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Food chain efficiency ( FCE), the proportion of primary production converted to production of the top trophic level, can influence several ecosystem services as well as the biodiversity and productivity of each trophic level. Aquatic FCE is affected by light and nutrient supply, largely via effects on primary producer stoichiometry that propagate to herbivores and then carnivores. Here, we test the hypothesis that the identity of the top carnivore mediates FCE responses to changes in light and nutrient supply., We conducted a large-scale, 6-week mesocosm experiment in which we manipulated light and nutrient (nitrogen and phosphorus) supply and the identity of the carnivore in a 2 × 2 × 2 factorial design. We quantified the response of FCE and the biomass and productivity of each trophic level (phytoplankton, zooplankton, and carnivore). We used an invertebrate, Chaoborus americanus, and a vertebrate, bluegill sunfish ( Lepomis macrochirus), as the two carnivores in this study because of the large difference in phosphorus requirements between these taxa., We predicted that bluegill would be more likely to experience P-limitation due to higher P requirements, and hence that FCE would be lower in the bluegill treatments than in the Chaoborus treatments. We also expected the interactive effect of light and nutrients to be stronger in the bluegill treatments. Within a carnivore treatment, we predicted highest FCE under low light and high nutrient supply, as these conditions would produce high-quality (low C:nutrient) algal resources. In contrast, if food quantity had a stronger effect on carnivore production than food quality, carnivore production would increase proportionally with primary production, thus FCE would be similar across light and nutrient treatments., Carnivore identity mediated the effects of light and nutrients on FCE, and as predicted FCE was higher in food chains with Chaoborus than with bluegill. Also as predicted, FCE in Chaoborus treatments was higher under low light. However, FCE in bluegill treatments was higher at high light supply, opposite to our predictions. In addition, bluegill production increased proportionally with primary production, while Chaoborus production was not correlated with primary production, suggesting that bluegill responded more strongly to food quantity than to food quality. These carnivore taxa differ in traits other than body stoichiometry, for example, feeding selectivity, which may have contributed to the observed differences in FCE between carnivores., Comparison of our results with those from previous experiments showed that FCE responds similarly to light and nutrients in food chains with Chaoborus and larval fish (gizzard shad: Clupeidae), but very differently in food chains with bluegill. These findings warrant further investigation into the mechanisms related to carnivore identity (e.g., developmental stage, feeding selectivity) underlying these responses, and highlight the importance of considering both top-down and bottom-up effects when evaluating food chain responses to changing light and nutrient conditions. [ABSTRACT FROM AUTHOR]

Classification approaches have been used to understand the habitat suitability of key species. Partial dependence function is an especially useful concept despite of a lack of studies that compare the results of the function against observations. Furthermore, there has been scant research investigating the relative performance of classification approaches for describing habitat suitability. Thus, we aim to assess the applicability of partial dependence function combined with classification approaches to describe habitat suitability of the bluegill Lepomis macrochirus , a riverine fish in the Kanto region of Japan. A total of 425 samples, along with eight environmental variables, were surveyed by the National Censuses on River Environments and were used throughout this research. Five classification approaches were combined with a partial dependence function to assess the habitat suitability of bluegill. The areas under the curves based on the training and test data were calculated 100 times using each of the five classification approaches. Additionally, partial dependence on individual and paired environmental variables was estimated using each combination of a five-classification approach and partial dependence function, and this dependence was plotted to determine the habitat suitability of bluegill. As a result, random forest approach demonstrated high predictive accuracy compared to other classification approaches. The combination of the partial dependence function and random forest described the peaks of habitat suitability observed in the field, both using individual and paired environmental variables. Moreover, habitat suitability based on pairs of environmental variables also indicated that bluegill changes their habitat throughout the year. [ABSTRACT FROM AUTHOR]

Amphibians can be partitioned among ponds based on their ability to tolerate fish predation. However, even among fish-tolerant species susceptibility to fish predators varies, with consequences for both prey and predator. We examined the effects of Bluegill ( Lepomis macrochirus) and tadpole density on two fish-tolerant species of tadpoles (American Toad, Anaxyrus americanus; American Bullfrog, Lithobates catesbeianus). For A. americanus, Bluegill presence decreased survivorship, whereas in L. catesbeianus, survivorship was higher with Bluegill. Growth of neither species was affected by Bluegill. In A. americanus, development increased with initial tadpole density with Bluegill, but decreased with initial tadpole density in the absence of Bluegill. Anaxyrus americanus were less active with Bluegill. Bluegill grew faster with initial A. americanus tadpole density, but showed no change in growth with initial L. catesbeianus tadpole density. There was more periphyton present at the end of both experiments in mesocosms with Bluegill, and periphyton decreased with increasing tadpole density at a faster rate in the presence of A. americanus tadpoles compared to L. catesbeianus tadpoles. Our results show that not all fish-tolerant species of anurans are affected in the same way by fish predators, with potential consequences for the anurans, fish predator, and the broader aquatic community. [ABSTRACT FROM AUTHOR]

Five semi-purified diets were formulated with varying crude protein (CP) level (ranging from 20.77 to 45.69%) to assess the dietary protein requirement of juvenile bluegill sunfish ( Lepomis macrochirus ). Each diet was given to triplicate groups (20 fish per group, 1.20 g per fish) for 10 weeks. In this study, the weight gain (WG) values showed a general increasing trend with increasing dietary CP level up to 40.23%, and then no further improvement of growth was observed with further increase in dietary CP level. In addition, feed efficiency (FE) also improved with increase in dietary CP level; the maximum value was observed in fish fed diet with 40.23% CP. Besides, fish fed diets with 20.77 and 28.16% CP had significant higher daily feed intake (DFI) and lower energy retention (ER), lipid retention (LR) and nitrogen retention (NR) values than other treatments ( P < 0.05). Moreover, fish fed 20.77% CP diet with the highest starch content showed the highest hepatosomatic index (HSI) and relatively higher liver glycogen content than other groups. However, no significant difference in liver lipid content was observed among all dietary treatments. Fish fed diets with 20.77 and 28.16% CP had a relatively lower whole body protein and dorsal muscle protein content than other treatments. Based on broken-line regression analysis, the optimal dietary protein content for sunfish is about 41.51 to 42.37%. Statement of Relevance The main aim of this study is to quantify the optimum amount of dietary protein for juvenile bluegill sunfish ( L. macrochirus ). The research outcomes will develop formulated diets for L. macrochirus and will have good potential of being commercialized. [ABSTRACT FROM AUTHOR]

Fish scales are morphologically diverse among species, within species, and on individuals. Scales of bony fishes are often categorized into three main types: cycloid scales have smooth edges; spinoid scales have spines protruding from the body of the scale; ctenoid scales have interdigitating spines protruding from the posterior margin of the scale. For this study, we used two- and three-dimensional (2D and 3D) visualization techniques to investigate scale morphology of bluegill sunfish ( Lepomis macrochirus ) on different regions of the body. Micro-CT scanning was used to visualize individual scales taken from different regions, and a new technique called GelSight was used to rapidly measure the 3D surface structure and elevation profiles of in situ scale patches from different regions. We used these data to compare the surface morphology of scales from different regions, using morphological measurements and surface metrology metrics to develop a set of shape variables. We performed a discriminant function analysis to show that bluegill scales differ across the body − scales are cycloid on the opercle but ctenoid on the rest of the body, and the proportion of ctenii coverage increases ventrally on the fish. Scales on the opercle and just below the anterior spinous dorsal fin were smaller in height, length, and thickness than scales elsewhere on the body. Surface roughness did not appear to differ over the body of the fish, although scales at the start of the caudal peduncle had higher skew values than other scales, indicating they have a surface that contains more peaks than valleys. Scale shape also differs along the body, with scales near the base of the tail having a more elongated shape. This study adds to our knowledge of scale structure and diversity in fishes, and the 3D measurement of scale surface structure provides the basis for future testing of functional hypotheses relating scale morphology to locomotor performance. [ABSTRACT FROM AUTHOR]

There is increasing evidence that temperature effects on sex ratio in fish species are ubiquitous. Temperature effects on sex ratio could be influenced by parent, strain, and population, whether in fish species with temperature-dependent sex determination or genetic sex determination plus temperature effects. In the present study, effects of genotype-temperature interactions on sex determination in bluegill sunfish were further investigated, based on our previous results, using four geographic strains: Hebron, Jones, Hocking, and Missouri. In the Hebron strain, the two higher-temperature treatment groups (24 °C and 32 °C) produced more males than the low-temperature treatment group (17 °C) from 6 days post-hatching (dph) to 90 dph. In contrast, the low-temperature treatment produced more males than the other two higher-temperature treatments in the Jones strain. No significant effects of temperature on sex ratio were detected in the other two strains. Our results from sex ratio variance in different treatment times suggest that the thermosensitive period of sex differentiation occurs prior to 40 dph. Our results further confirmed that genotype-temperature interactions influence sex determination in bluegill. Therefore, to significantly increase the proportion of males, which grow faster and larger than females, a consumer- and environment-friendly approach may be achieved through selection of temperature sensitivity in bluegill. [ABSTRACT FROM AUTHOR]

Many species undergo substantial ontogenetic changes in elemental content that often accompany significant shifts in diet. However, it is unclear how elemental imbalance varies across ontogeny and whether these changes are caused by ontogenetic diet shifts., Because elemental imbalance can affect individual growth rates, behaviour and nutrient cycling, understanding the role of ecological stoichiometry in consumers with ontogenetic diet shifts will enhance our ability to predict how individuals and populations influence broader ecological processes., In a field survey, we examined ontogenetic changes in stoichiometry of the bluegill sunfish ( Lepomis macrochirus), which undergoes an ontogenetic diet shift from zooplankton to benthic invertebrates. Specifically, we quantified the elemental composition of diets, bodies and excreta of bluegill ranging in size from larvae to small adults (10-110 mm total length). We compared imbalance between diet elemental content and individual needs before and after the diet shift., At around 25 mm total length, bluegill diet shifted from zooplankton to benthic invertebrates. Benthic invertebrates had lower nitrogen (N) and phosphorus (P) contents than zooplankton. Elemental imbalance estimates indicated potential carbon (C) limitation in all sizes of bluegill, and the diet shift tended to reduce C imbalance relative to P. However, N:P imbalance was exacerbated by the diet shift, resulting in high ratios of N:P in excreta. Changes in per cent N and C:N ratios in bluegill were generally associated with the diet shift and can be explained by the levels of these elements in the diet. In contrast, bluegill P and calcium contents increased dramatically prior to the diet shift and are more likely a result of ontogenetic constraints, specifically skeletal development in larval fish., Our results indicate that ontogenetic diet shifts can produce trade-offs in imbalance between different elemental ratios, and provide stoichiometrically explicit support for previous findings that energetics (including C limitation and food availability) is an important driver of bluegill diet shifts. The patterns in elemental imbalance associated with diet shifts may alter a consumer's role in ecosystem-level processes like nutrient cycling. [ABSTRACT FROM AUTHOR]

In the face of a changing climate, questions regarding sub-lethal effects of elevated habitat temperature on the physiology of ectotherms remain unanswered. In particular, long-term responses of ectotherms to the warming trend in tropical regions are unknown, and understudied due to the difficulties in specimen and community traceability. In freshwater lakes employed as cooling reservoirs for power plants, increased physiological stress from high water temperature can potentially alter the community structure of fishes. We employ this highly tractable system to assess how thermal regimes can alter the physiology and ecology of aquatic species. We documented a significantly reduced lifespan, growth performance, and a shift in the age structure towards younger individuals in the thermally- impacted Coffeen Lake population of bluegill ( Lepomis macrochirus ), compared to a non-impacted control group (Lake Mattoon). Average age calculated for the Lake Mattoon population was 2.42 years, whereas the average age of bluegill from Coffeen Lake was only 0.96 years, and average specimen mass in Lake Mattoon was more than six times that of Coffeen Lake. During laboratory cross-acclimation studies of bluegill from Lake Mattoon at 17.5 and 35.0 °C, citrate synthase (CS) activity obtained from white muscle was regulated through acclimation, whereas cold-acclimated specimens exhibited twice the activity at 25 °C, if compared to CS activity values from warm-acclimated specimens. This study raises the questions about the causal relationships between physiological performance and habitat temperature, in particular how thresholds in an organism's physiology may modulate their community structure, and consequently their ecological success. [ABSTRACT FROM AUTHOR]

[Display omitted] • Climate change is expected to alter the composition of stream fish communities. • Summer and dry season temperatures are closely linked to fish distributions. • Cool- and cold-water communities are expected to experience the greatest losses. • Portions of Iowa, Illinois, and Wisconsin were most at risk within our study area. • Coupling climate risk with threat data can help identify management opportunities. Climate change is expected to alter stream fish habitat potentially leading to changes in the composition and distribution of fish communities. In the Northeastern and Midwestern United States we identified the distribution and characteristics of those fish communities most and least at risk of experiencing changes in climate which deviate from the climate they are associated with. We classified stream fish communities based on a suite of climate and environmental variables with multivariate regression trees under both recent and future conditions based on eight climate models. Our findings showed that some areas, such as the majority of the Illinois, Wisconsin, and Iowa), have high levels of risk of change in stream class, while much of Kentucky, West Virginia, Virginia, Pennsylvania, Eastern Ohio, Southern Michigan, and the Atlantic Coast are at relatively low risk. Stream class shifts ranged from over 75% of segments lost (associated with cooler temperatures) to gains of over 40% (associated with warmer temperatures). Common warmwater species such as green sunfish (Lepomis cyanellus), bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides) are expected to have the largest net gains in associated stream classes, while species associated with cooler streams such as Southern redbelly dace (Chrosomus erythrogaster), slimy sculpin (Cottus cognatus), and Eastern blacknose dace (Rhinichthys atratulus) were expected to experience the largest proportional losses. By pairing our climate risk predictions with other stressors such anthropogenic land use, habitat fragmentation, and water quality impairment, we identified opportunities for preservation (low risk due to all threats), restoration (low risk due to climate, high risk due to other stressors), and adaptation (high climate risk with low risk from other stressors). Understanding which communities are at risk due to climate change will aid in developing adaptation strategies to help sustain them in the future. [ABSTRACT FROM AUTHOR]

• QSAR was built for toxicity data of pesticides to various fish species. • Random forest was used to establish the classification model of LC 50. • Only 8 descriptors were used in the models for 1106 organic pesticides. • The total data set has prediction accuracy above 96%. Aquatic toxicity of pesticides can result in poisoning of many non-target organisms, of which various fishes are the most prominent one. It is a challenge to predict the toxicity (LC 50) classes of organic pesticides to various fish species from global QSAR models with a larger applicability domain. In this paper, by applying the random forest (RF) algorithm for a two-class problem, only eight molecular descriptors were used to develop a quantitative structure–activity relationship (QSAR) model for 1106 toxicity data (96 h , LC 50) of organic pesticides to various fish species including Oncorhynchus mykiss, Lepomis macrochirus, Pimephales promelas, Brachydanio rerio, Cyprinodon, Cyprinus carpio , etc. By the prediction of the optimal RF Model I (ntree =280, mtry = 3 and nodesize = 5), the training set (885 organic pesticides) has the prediction accuracies of 99.6% for Class 1 (LC 50 ≤ 10) and 96.7% for Class 2 (LC 50 > 10); the test set (221 organic pesticides) has the accuracies being 90.8% for Class 1 and 91.2% for Class 2. The optimal RF Model I is satisfactory compared with other QSAR model reported in the literature, although its descriptor subset is small. [ABSTRACT FROM AUTHOR]

• Cyanotoxins can accumulate in fish tissues through trophic transfer. • Microcystin concentrations in bluegill were higher than in largemouth bass. • Microcystin was highest in fish livers, followed by kidneys, and then muscles. • Time of year was the greatest predictor of microcystin in fish tissues. • Low but frequent water microcystin occurrences can result in accumulation in fish. Cyanobacterial blooms sometimes create secondary metabolites that can be transferred between trophic levels and accumulate in fish, but little is known about what time of year fish are most susceptible. Here, we examine microcystin in the muscle, liver, and kidney of bluegill and largemouth bass from an agricultural reservoir over 12 months. We identify which fish characteristics and water parameters best explain microcystin accumulation in fish tissues. Microcystin in bluegill was significantly higher than largemouth bass. In both species, microcystin was highest in livers (bluegill mean = 57.6 ng g −1, largemouth bass mean = 71.8 ng g −1 wet weight [ww]), then kidneys (bluegill mean = 27.1, largemouth bass mean = 22.7 ng g −1 ww), followed by muscles (bluegill mean = 7.6, largemouth bass mean = 5.7 ng g −1 ww). Adult bluegill feed on benthic macroinvertebrates and zooplankton, which may explain their higher microcystin concentrations compared to largemouth bass, which are primarily piscivorous. Harvest date emerged as the best predictor of microcystin in muscles and kidneys, with the highest concentrations occurring in April. Microcystin in water also emerged as a significant predictor, albeit much lower than harvest date, suggesting that low but persistent microcystin concentrations in water may result in accumulation of this cyanotoxin in fish. This study is the first to examine microcystin in fish from the North American Great Plains and one of only 5 studies that investigate microcystin in bluegill and largemouth bass. Additional investigation into the relationship between cyanobacteria and fish health is warranted, especially during spring when fish microcystin concentrations were highest. [ABSTRACT FROM AUTHOR]

Reservoirs exhibit gradients in conditions and resources along the transition from lotic to lentic habitat that may be important to bluegill ecology. The lotic–lentic gradient can be partitioned into three functional zones: the riverine, transitional, and lacustrine zones. We measured catch frequency and length of bluegills (Lepomis macrochirus) captured along the periphery of these areas (i.e., in the littoral zone of each functional zone) for four small reservoirs in Southeastern Ohio during the summer months of three years. Catch frequency differed between zones for two reservoirs, but these differences were not observed in other years. There was no relationship between reservoir zone and either standard length or catch frequency when the data for all reservoirs were pooled, but we did observe a bimodal length distribution in all reservoirs. A combination of ecological factors including inter and intraspecific competition, predation intensity, management practices, limnology, and assemblage complexity may be mitigating bluegill distribution and abundance in reservoirs. Therefore, a functional zone (categorical) approach to understanding bluegill ecology in reservoirs may not be appropriate.

Morphological responses to flowing water have been documented in many fishes, but rarely reported in species with gibbose body types, despite their use of riffles in rivers and streams. In this study, we compared morphological responses to water flow in three gibbose centrarchids: bluegill ( Lepomis macrochirus Rafinesque, 1819), pumpkinseed ( Lepomis gibbosus (L., 1758)), and rock bass ( Ambloplites rupestris (Rafinesque, 1817)). Flow-through plexiglass units, set to either a sustained flow or static conditions, were used to rear juveniles from each species for an 80-day period. All three species developed more streamlined body forms, longer and thinner caudal peduncles, and longer pectoral fins when reared in sustained current. Pumpkinseed exhibited the highest level of phenotypic plasticity in response to water flow, followed closely by bluegill; rock bass was the least plastic species. Rock bass developed longer predorsal and prepectoral lengths, which differ from the morphological changes observed in bluegill and pumpkinseed. The findings not only suggest that some gibbose fishes are capable of exhibiting strong phenotypic responses to water flow, but that many morphological changes are species specific, even within the same taxonomic family. Lastly, all three species developed shorter dorsal fin base lengths when reared under flowing condition, which differs from some previously documented work on fusiform fishes. The results of this study provide a better understanding of how morphology in three closely related species varies in response to environmental conditions. [ABSTRACT FROM AUTHOR]

For many fish species, the pectoral fins serve as important propulsors and stabilizers and are precisely controlled. Although it has been shown that mechanosensory feedback from the fin ray afferent nerves provides information on ray bending and position, the effects of this feedback on fin movement are not known. In other taxa, including insects and mammals, sensory feedback from the limbs has been shown to be important for control of limb-based behaviors and we hypothesized that this is also the case for the fishes. In this study, we examined the impact of the loss of sensory feedback from the pectoral fins on movement kinematics during hover behavior. Research was performed with bluegill sunfish (Lepomis macrochirus), a model for understanding the biomechanics of swimming and for bio-inspired design of engineered fins. The bluegill beats its pectoral fins rhythmically, and in coordination with pelvic and median fin movement, to maintain a stationary position while hovering. Bilateral deafferentation of the fin rays results in a splay-finned posture where fins beat regularly but at a higher frequency and without adducting fully against the side of the body. For unilateral transections, more irregular changes in fin movements were recorded. These data indicate that sensory feedback from the fin rays and membrane is important for generating normal hover movements but is not necessary for generating rhythmic fin movement. [ABSTRACT FROM AUTHOR]

One of the most-studied unsteady locomotor behaviors exhibited by fishes is the c-start escape response. Although the kinematics of these responses have been studied extensively and two well-defined kinematic stages have been documented, only a few studies have focused on hydrodynamic patterns generated by fishes executing escape behaviors. Previous work has shown that escape responses by bluegill sunfish generate three distinct vortex rings, each with central orthogonal jet flows, and here we extend this conclusion to two other species: stickleback and mosquitofish. Jet #1 is formed by the tail during Stage 1, and moves in the same direction as Stage-2 movement of the fish, thereby reducing final escape-velocity but also rotating the fish. Jet #2, in contrast, moves approximately opposite to the final direction of the fish's motion and contains the bulk of the total fluid-momentum powering the escape response. Jet #3 forms during Stage 2 in the mid-body region and moves in a direction approximately perpendicular to jets 1 and 2, across the direction of movement of the body. In this study, we used a mechanical controller to impulsively move passively flexible plastic panels of three different stiffnesses in heave, pitch, and heave+pitch motions to study the effects of stiffness on unsteady hydrodynamics of escape. We were able to produce kinematics very similar to those of fish c-starts and also to reproduce the 3-jet hydrodynamic pattern of the c-start using a panel of medium flexural stiffness and the combined heave+pitch motion. This medium-stiffness panel matched the measured stiffness of the near-tail region of fish bodies. This motion also produced positive power when the panel straightened during stage 2 of the escape response. More flexible and stiffer panels resulted in non-biological kinematics and patterns of flow for all motions. The use of simple flexible models with a mechanical controller and program of fish-like motion is a promising approach for studying unsteady behaviors of fish which can be difficult to manipulate experimentally in live animals. [ABSTRACT FROM AUTHOR]

Nitrogen often is omitted in fertilization of sportfish ponds in the southeastern United States that have been fertilized for several years with both nitrogen and phosphorus. This practice was tested in 40-yr-old research ponds at the Auburn University E. W. Shell Fisheries Center from which sediment had been removed 2 to 9 yr earlier to restore bottoms nearly to their original soil composition. In ponds from which sediment had been removed 8 yr before, there was no difference ( P > 0.05) in harvest weight of bluegill ( Lepomis macrochirus ) between ponds receiving nitrogen plus phosphorus fertilization (6 kg N and 3 kg P 2 O 5 ha − 1 application − 1 ) and those fertilized only with phosphorus (3 kg P 2 O 5 ha − 1 application − 1 ). Grass carp controlled aquatic macrophytes effectively in most ponds and did not interfere with bluegill yield. No correlation (R 2 = 0.040, P > 0.05) was found between time since sediment removal and bluegill yield in 13 ponds treated only with phosphate fertilizer at 3 kg P 2 O 5 ha − 1 application − 1 . Concentrations of soluble reactive phosphorus and total ammonia nitrogen in the water column were correlated (R 2 = 0.312 and R 2 = 0.514, respectively, P < 0.05) with time since sediment removal. An earlier study showed that nitrogen fertilization was necessary in sportfish ponds the year following sediment removal. In the present study, there was much variation in production among ponds treated with nitrogen plus phosphorus as well as those treated only with phosphorus as typically encountered in pond fertilization trials. Nevertheless, results suggest that nitrogen fertilization of sportfish ponds possibly can be ceased after only 2 years of fertilization with nitrogen and phosphorus. Statement of relevance This research work provides useful information for pond managers when developing a fertilization schedule. The results of the present study do suggest that after 2 yr of nitrogen plus phosphorus fertilization, pond manager might cease nitrogen fertilization and assess the response of the phytoplankton bloom. Omitting nitrogen fertilization from ponds lessens fertilizer cost and reduces possible nitrogen pollution of nearby natural waters. [ABSTRACT FROM AUTHOR]

We compared the environmental and biotic characteristics of farm ponds with and without the invasive fish, largemouth bass ( Micropterus salmoides), and bluegill ( Lepomis macrochirus), with varying degrees of aquatic vegetation cover in western Japan. Redundancy analysis (RDA) revealed that aquatic vegetation cover and pond area were significant environmental variables in explaining the variance in aquatic organisms. Aquatic vegetation cover predominantly affected Odonata and Hemiptera larvae, and the native cyprinid, Hemigrammocypris rasborella, while the pond area mainly affected the two exotic fishes (largemouth bass and bluegill), Viviparidae, Oligocheata, Ephemeroptera, and chironomid larvae. In the RDA biplot for aquatic organisms, the RDA1 axis appeared to separate the exotic fish group (bluegill, largemouth bass, Gammaridae, Oligochaeta, Viviparidae, Ephemeroptera, Trichoptera, and chironomid larvae) from the native fish group ( H. rasborella, Oryzias latipes, Rhinogobius sp., Odonata, shrimps, and Hemiptera larvae). The best path model results indicated that the presence of piscivorous largemouth bass had a significantly negative effect on native fish numbers; largemouth bass also had a positive indirect effect on benthic organism numbers. Our data suggest that the depletion of native fishes via top-down effects by exotic largemouth bass may indirectly increase the number of benthic organisms as a result of trophic-cascading effects. [ABSTRACT FROM AUTHOR]

In teleosts, the area of peak ganglion cell density in the retina (area centralis, AC) is thought to reflect the primary visual axis for feeding. The bluegill Lepomis macrochirus are known to undergo ontogenetic shifts in diet preference, but because their diet is affected by population density, interspecific competition, and seasonal changes in prey availability, they are considered generalist predators. We investigated whether the diet shifts of the bluegill were associated with a change in the location of the AC (total length of fish specimens, range 44-243 mm). The AC was located temporally in the retina of smaller fish (40-100 mm), and the area of increased density included the ventral and central regions of the retina. Conversely, the AC was located in the dorso-temporal region of the retina in larger (100-200 mm) fish. Lastly, in the largest bluegill (> 200 mm), the AC was located in the temporal region of the retina. In all cases, the orientation of the visual axis was consistent with the known diet preferences of the different size classes. [ABSTRACT FROM AUTHOR]

In the traditional osmorespiratory compromise, as seen in the hypoxia-intolerant freshwater rainbow trout (Oncorhynchus mykiss), the branchial modifications that occur to improve O2 uptake during hypoxia result in unfavorable increases in the fluxes of ions and water.However, at least one hypoxia-tolerant freshwater species, the Amazonian oscar (Astronotus ocellatus), shows exactly the opposite: decreased branchial flux rates of ions, water, and nitrogenous wastes during acute hypoxia. In order to find out whether the two strategies were widespread, we used a standard 2-h normoxia, 2-h hypoxia (20%-30% saturation), 2-h normoxic recovery protocol to survey 10 other phylogenetically diverse tropical and temperate species. Unidirectional influx and efflux rates of Na+ and net flux rates of K+, ammonia, and urea-N weremeasured. The flux reduction strategy was seen only in one additional species, the Amazonian tambaqui (Colossoma macropomum), which is similarly hypoxia tolerant and lives in the same ion-poor waters as the oscar. However, five other species exhibited evidence of the increased flux rates typical of the traditional osmorespiratory compromise in the trout: the rosaceu tetra (Hyphessobrycon bentosi rosaceus), the moenkhausia tetra (Moenkhausia diktyota), the bluegill sunfish (Lepomis macrochirus), the zebra fish (Danio rerio), and the goldfish (Carassius auratus). Four other species exhibited no marked flux changes during hypoxia: the cardinal tetra (Paracheirodon axelrodi), the hemigrammus tetra (Hemigrammus rhodostomus), the pumpkinseed sunfish (Lepomis gibbosus), and the Atlantic killifish (Fundulus heteroclitus). Overall, a diversity of strategies exist; we speculate that these may be linked to differences in habitat and/or lifestyle. [ABSTRACT FROM AUTHOR]

In modern days, to enrich e-business, the websites are personalized for each user by understanding their interests and behavior. The main challenges of online usage data are information overload and their dynamic nature. In this paper, to address these issues, a WebBluegillRecom-annealing dynamic recommender system that uses web usage mining techniques in tandem with software agents developed for providing dynamic recommendations to users that can be used for customizing a website is proposed. The proposed WebBluegillRecom-annealing dynamic recommender uses swarm intelligence from the foraging behavior of a bluegill fish. It overcomes the information overload by handling dynamic behaviors of users. Our dynamic recommender system was compared against traditional collaborative filtering systems. The results show that the proposed system has higher precision, coverage, F1 measure, and scalability than the traditional collaborative filtering systems. Moreover, the recommendations given by our system overcome the overspecialization problem by including variety in recommendations. [ABSTRACT FROM AUTHOR]

Species sensitivity distribution (SSD) method has been widely used to derive water quality criteria (WQC). However, the toxicity data of some environmental pollutants are not easily accessible, especially for endangered and threatened species. Thus, it would be very desirable and economical to predict the toxicity of those species not subjected to toxicity test with the aid of a mathematical model. The interspecies correlation estimation (ICE) model (developed by the US Environmental Protection Agency (USEPA)) uses the initial toxicity estimate for one species to produce correlated toxicity values for multiple species, and it can be utilized to develop SSD and HC (hazardous concentration, 5th percentile). In this study, we explored the applicability of ICE to predict toxicity of phenanthrene to various species. ICE-based SSDs were generated using three surrogate species ( Oncorhynchus mykiss, Lepomis macrochirus, and Daphnia magna) and compared with the metrical-based SSD. The corresponding HC of both models were also compared. The results showed there were no significant differences between HC derived from measured acute and ICE-based predicted values. The ICE model was verified as a valid approach for generating SSDs with limited toxicity data and deriving WQC for phenanthrene. [ABSTRACT FROM AUTHOR]

Many bluegill (Lepomis macrochirus) populations are characterized by a stunted adult size structure and consist primarily of individuals that mature at a relatively young age and small size. Little is known about maternal effects in bluegill populations and whether they may explain the occurrence of stunted growth. We spawned bluegill from both stunted and non-stunted populations in experimental tanks and collected eggs and larvae from each clutch. We determined whether differences in egg and oil globule diameter and larval growth existed between eggs collected from females from each population. Egg and oil globule diameter were not related to female length and did not differ between stunted and non-stunted populations. Larvae length after 21 d was positively related to egg diameter but was not related to either female length or oil globule diameter. Consequently, egg diameter had a greater influence on larval growth than female source population or size. No differences were observed between source populations indicating that some aspects of early life history are more heavily influenced by egg properties than adult life history differences between parental source populations. [ABSTRACT FROM AUTHOR]

The mode of toxic action (MOA) has been recognized as a key determinant of chemical toxicity and as an alternative to chemical class-based predictive toxicity modeling. However, the development of quantitative structure activity relationship (QSAR) and other models has been limited by the availability of comprehensive high quality MOA and toxicity databases. The current study developed a dataset of MOA assignments for 1213 chemicals that included a diversity of metals, pesticides, and other organic compounds that encompassed six broad and 31 specific MOAs. MOA assignments were made using a combination of high confidence approaches that included international consensus classifications, QSAR predictions, and weight of evidence professional judgment based on an assessment of structure and literature information. A toxicity database of 674 acute values linked to chemical MOA was developed for fish and invertebrates. Additionally, species-specific measured or high confidence estimated acute values were developed for the four aquatic species with the most reported toxicity values: rainbow trout ( Oncorhynchus mykiss ), fathead minnow ( Pimephales promelas ), bluegill ( Lepomis macrochirus ), and the cladoceran ( Daphnia magna ). Measured acute toxicity values met strict standardization and quality assurance requirements. Toxicity values for chemicals with missing species-specific data were estimated using established interspecies correlation models and procedures (Web-ICE; http://epa.gov/ceampubl/fchain/webice/ ), with the highest confidence values selected. The resulting dataset of MOA assignments and paired toxicity values are provided in spreadsheet format as a comprehensive standardized dataset available for predictive aquatic toxicology model development. [ABSTRACT FROM AUTHOR]

One of the primary factors associated with mortality in catch-and-release recreational fisheries is depth of hook position relative to the snout, with deeper hooking locations (i.e., gullet) increasing risk of injury to vital tissues. As a result, there have been attempts to develop angling methods and gear that are less likely to result in deep hooking. Circle hooks represent an alternative to conventional “J” style hooks (J-hooks), and in general circle hooks have been shown to reduce the tendency for deep hooking in a variety of species, which can significantly improve post-release survival. Relative to fishing with J-hooks, circle hook manufacturers typically recommend that anglers use a rod movement (i.e., hook-set) of reduced intensity and force (i.e., a light hook-set), thereby maximizing the benefit of circle hooks by reducing the tendency for deep hooking and injury. To evaluate whether hook-set technique can affect hooking and injury in fish, we tested different combinations of hooks (circle hooks and J-hooks) and hook-set techniques (e.g., light, moderate, or heavy force, or with a bobber) in an angling study for bluegill ( Lepomis macrochirus ) in Lake Opinicon, Ontario, Canada. Binary responses of capture success and deep hooking were analysed with logistic regression. There was no significant interaction between hook type and hook-set, but overall, J-hooks increased the odds of successfully capturing a bluegill and also the odds of deep hooking a bluegill relative to circle hooks. The bobber hook-set technique increased the odds of deep hooking a bluegill relative to the active hook-setting techniques. This study suggests both deep hooking and capture of bluegill are significantly affected by both hook types and hook-set techniques. [ABSTRACT FROM AUTHOR]

We provide a checklist of the common parasites of bluegill (Lepomis macrochirus) and redbreast sunfish (Lepomis auritus) collected from eight creeks within an urban watershed located in Columbus, Georgia. A total of 12 parasite species were observed from 427 fish dissected. Bluegill (n = 222) were infected with 11 species, which included five species of larval helminths (Proteocephalus sp., Bothriocephalus sp., Posthodiplostomum minimum, Diplostomulum sp. and Clinostomum complanatum), one adult trematode (Pisciamphistoma stunkardi), four adult nematodes (Philometra sp., Philometra intraoculus, Spinetectus carolini and Camallanus oxycephalus) and one adult acanthocephalan (Neochinorhynchus cylindratus). Redbreast sunfish (n = 205) were infected with the same parasite species, except for the absence of larval Bothriocephalus sp. and the presence of an adult trematode (Crepidostomum cooperi). Metacercariae of the trematode P. minimum were the most common parasite in both fish species. Similar parasite communities in these sunfishes suggest that these species share similar microhabitats within the watershed, food resources and foraging sites. Seasonal comparison between the number of summer and winter parasites indicate a greater mean number of parasites per host in summer. We discuss the utility of such baseline parasite data in the potential environmental monitoring of the Bull and Upatoi Creeks watershed. [ABSTRACT FROM AUTHOR]

This study evaluated the effect of reduced aggregate panfish bag limits (from 25 to 10) on the size structure of BluegillLepomis macrochiruspopulations in seven natural lakes in Wisconsin. For assessing the overall significance of treatments, each treatment lake was paired with a control lake in which the regulation was not implemented. Across all lakes, mean total length (TL) of sampled Bluegills was significantly greater in treatment lakes than in control lakes after the regulation was implemented: on average, mean TL increased by 20.3 mm. However, efficacy of reduced bag limits varied substantially across lakes as mean TL improvements ranged from −5.1 to 63.5 mm in individual lakes. This variation could be strongly explained (R2= 0.81) by lake Secchi depth (lakes with reduced water clarity showed larger improvements in mean TL,R= −0.62) and regulation duration (size structure improved continuously with time after the reduced daily bag limit was implemented,R= 0.75). Reduced bag limits are a useful tool for providing improvements to Bluegill size structure in Wisconsin lakes, but would be most effective in more productive waterbodies and will require substantial time investments after implementation. Received September 18, 2014; accepted December 18, 2014 [ABSTRACT FROM AUTHOR]

In their natural environment, fish must swim stably through unsteady flows and vortices, including vertical vortices, typically shed by posts in a flow, horizontal cross-flow vortices, often produced by a step or a waterfall in a stream, and streamwise vortices, where the axis of rotation is aligned with the direction of the flow. Streamwise vortices are commonly shed by bluff bodies in streams and by ships' propellers and axial turbines, but we know little about their effects on fish. Here, we describe how bluegill sunfish use more energy and are destabilized more often in flow with strong streamwise vorticity. The vortices were created inside a sealed flow tank by an array of four turbines with similar diameter to the experimental fish. We measured oxygen consumption for seven sunfish swimming at 1.5 body lengths (BL) s~1 with the turbines rotating at 2 Hz and with the turbines off (control). Simultaneously, we filmed the fish ventrally and recorded the fraction of time spent maneuvering side-to-side and accelerating forward. Separately, we also recorded lateral and ventral video for a combination of swimming speeds (0.5, 1.5 and 2.5 BL s-1) and turbine speeds (0, 1, 2 and 3 Hz), immediately after turning the turbines on and 10 min later to test for accommodation. Bluegill sunfish are negatively affected by streamwise vorticity. Spills (loss of heading), maneuvers and accelerations were more frequent when the turbines were on than in the control treatment. These unsteady behaviors, particularly acceleration, correlated with an increase in oxygen consumption in the vortex flow. Bluegill sunfish are generally fast to recover from roll perturbations and do so by moving their pectoral fins. The frequency of spills decreased after the turbines had run for 10 min, but was still markedly higher than in the control, showing that fish partially adapt to streamwise vorticity, but not completely. Coping with streamwise vorticity may be an important energetic cost for stream fishes or migratory fishes. [ABSTRACT FROM AUTHOR]

Stable isotope analysis is frequently used to examine resource use in wild populations, but it often involves invasive or lethal methods of collecting tissue samples. The development of less invasive or nonlethal sampling techniques will expand the possible uses of stable isotopes. We examined whether fish eggs meet three basic requirements for inferring female resource use from them: (1) the isotope composition of the eggs is correlated with that of other maternal tissues for which isotope composition is known to be related to diet; (2) the isotope composition remains constant over the egg development period; and (3) dietary inferences using eggs are similar to those for other maternal tissues. Using artificial crosses, we tested the relationship between eggs and two commonly sampled maternal tissues (white muscle and liver) in wild-caught BluegillsLepomis macrochirus. We found that egg isotope composition was strongly correlated with that of other maternal tissues, particularly liver, and remained constant from prefertilization to the day of hatch, with no change in13C and an increase of only 0.3‰ in15N. Furthermore, the results of SIAR (Stable Isotope Analysis in R) mixing models indicated a large degree of overlap in diet estimates between eggs and the other maternal tissues. Overall, eggs can be reliably used to infer the prebreeding foraging ecology of female Bluegills throughout the egg development period. Received July 10, 2014; accepted October 28, 2014 [ABSTRACT FROM AUTHOR]

The crucian carp ( Carassius spp.) fishery in Lake Biwa, Shiga Prefecture, Japan, is economically and culturally important. Annual fishery catch, however, has been decimated allegedly due to predation by largemouth bass ( Micropterus salmoides) and bluegill ( Lepomis macrochirus). This prompted the local government to restore natural stocks by rearing juvenile crucian carps in rice fields, but to little avail. Little is known about the post-release fate of aquacultured fish in this system. Hence, we conducted the present study to address the following questions: 1) How quickly do carp juveniles disperse from rice fields into Lake Biwa?, 2) Are carp juveniles preyed upon by largemouth bass and bluegill en route to Lake Biwa?, 3) Are there any differences in dispersal patterns or predation loss among different species or different size classes of crucian carps? Results showed that the approximately 1 km movement from rice fields into Lake Biwa via the Ezura River was completed within about 2 weeks of release. Largemouth bass consume carp juveniles, whereas bluegill consume few juveniles. Largemouth bass selected to consume larger juveniles, and C. grandoculis over C. cuvieri. These results suggest that: 1) carp juveniles should be released at smaller sizes (<30 mm), 2) C. cuvieri may withstand predation pressure better than C. grandoculis, and 3) the presence of larger alternative prey may help reduce predation on juveniles. Rice fields are ideal nursery grounds for growing larval fish at low cost and effort. Increasing the post-release survival will effectively restore fishery resources in inland waters. [ABSTRACT FROM AUTHOR]

Bluegill Lepomis macrochirus and green sunfish Lepomis cyanellus were examined using geometric morphometrics to evaluate the variation in morphology between fishes that reside in lentic ( e.g. lakes) and lotic ( e.g. streams) ecosystems. Live fishes were collected from reservoirs and rivers in central Indiana, while additional fishes were sampled from museum collections at Ball State University and the Illinois Natural History Survey. Male and female L. macrochirus and female L. cyanellus from lentic systems display a deeper body than those from lotic systems, while no differences were found in male L. cyanellus morphometry. A deeper body promotes greater manoeuverability, typically desirable in lentic systems. In contrast, the more streamlined body of the fishes found in lotic systems reduces drag as it contends with flowing water, ultimately maximizing energy efficiency. The absence of morphological differences, such as those found in male L. cyanellus, may be caused by fish occupying both lentic and lotic systems, from the population not having been present in the body of water long enough to display any adaptations, or from a lack of statistical power caused by the small sample size. [ABSTRACT FROM AUTHOR]

Florida apple snails (Pomacea paludosa) are critical to Florida wetland food webs. Past studies emphasized that large predators consumed relatively large specimens (> 20 mm shells) of these snails. Past studies also identified crayfish, fish, and turtles as predators of hatchling (≈3- 6 mm) and juvenile-sized apple snails, but quantitative relationships between these predators and a range of sizes of apple snails are scant. We identified predators not yet reported in the literature: the Seminole killifish (Fundulus seminolis), bluegill (Lepomis macrochirus), greater siren (Siren lacertina), and non-indigenous Mayan cichlid (Cichlasoma urophthalmus). We quantified the relationship between predator size and maximum snail size consumed for the following predators: crayfish (Procambarus alieni), turtles (Kinostemon bauri and Sternotherus odoratus), and redear sunfish (Lepomis microlophus). Predator size explained 60% to 78% of the variation in prey size eaten (which ranged from 4 to 22 mm shell length). When offered multiple sizes of prey simultaneously, crayfish and turtles ate snails smaller than the maximum size they were capable of consuming. All size classes of apple snails could fall prey to a variety of predators common to Florida wetlands. Understanding apple snail population ecology requires additional studies to quantify predation impacts on juvenile snails from aquatic predators. [ABSTRACT FROM AUTHOR]

The environmental DNA (eDNA) technique is expected to become a powerful, non-invasive tool for estimating the distribution and biomass of organisms. This technique was recently shown to be applicable to aquatic vertebrates by collecting extraorganismal DNA floating in the water or absorbed onto suspended particles. However, basic information on eDNA release rate is lacking, despite it being essential for practical applications. In this series of experiments with bluegill sunfish (Lepomis macrochirus), we examined the effect of fish developmental stage on eDNA release rate. eDNA concentration reached equilibrium 3 days after the individual fish were introduced into the separate containers, enabling calculation of the eDNA release rate (copies h−1) from individual fish on the assumption that the number of eDNA released from the fish per unit time equals total degradation in the container (copies h−1). The eDNA release rate was 3–4 times higher in the adult (body weight: 30–75 g) than in the juvenile group (0.5–2.0 g). Such positive relationship between fish size and eDNA release rate support the possibility of biomass rather than density estimation using eDNA techniques. However, the eDNA release rate per fish body weight (copies h−1 g−1) was slightly higher in the juvenile than the adult group, which is likely because of the ontogenetic reduction in metabolic activity. Therefore, quantitative eDNA data should be carefully interpreted to avoid overestimating biomass when the population is dominated by juveniles, because the age structure of the focal population is often variable and unseen in the field. eDNA degradation rates (copies l−1 h−1), calculated by curve fitting of time-dependent changes in eDNA concentrations after fish removal, were 5.1–15.9% per hour (half-life: 6.3 h). This suggests that quantitative eDNA data should be corrected using a degradation curve attained in the target field. [ABSTRACT FROM AUTHOR]

Electrofishing is widely used to monitor fish species composition and relative abundance in streams and lakes. According to standard protocols, multiple segments are selected in a body of water to monitor population relative abundance as the ratio of total catch to total sampling effort. The standard protocol provides an assessment of fish distribution at a macrohabitat scale among segments, but not within segments. An ancillary protocol was developed for assessing fish distribution at a finer scale within electrofishing segments. The ancillary protocol was used to estimate spacing, dispersion, and association of two species along shore segments in two local reservoirs. The added information provided by the ancillary protocol may be useful for assessing fish distribution relative to fish of the same species, to fish of different species, and to environmental or habitat characteristics. [ABSTRACT FROM AUTHOR]

Contaminants of emerging concern, particularly endocrine active compounds (EACs), have been identified as a threat to aquatic wildlife. However, little is known about the impact of EACs on lakes through groundwater from onsite wastewater treatment systems (OWTS). This study aims to identify specific contributions of OWTS to Sullivan Lake, Minnesota, USA. Lake hydrology, water chemistry, caged bluegill sunfish ( Lepomis macrochirus), and larval fathead minnow ( Pimephales promelas) exposures were used to assess whether EACs entered the lake through OWTS inflow and the resultant biological impact on fish. Study areas included two OWTS-influenced near-shore sites with native bluegill spawning habitats and two in-lake control sites without nearby EAC sources. Caged bluegill sunfish were analyzed for plasma vitellogenin concentrations, organosomatic indices, and histological pathologies. Surface and porewater was collected from each site and analyzed for EACs. Porewater was also collected for laboratory exposure of larval fathead minnow, before analysis of predator escape performance and gene expression profiles. Chemical analysis showed EACs present at low concentrations at each study site, whereas discrete variations were reported between sites and between summer and fall samplings. Body condition index and liver vacuolization of sunfish were found to differ among study sites as did gene expression in exposed larval fathead minnows. Interestingly, biological exposure data and water chemistry did not match. Therefore, although results highlight the potential impacts of seepage from OWTS, further investigation of mixture effects and life history factor as well as chemical fate is warranted. [ABSTRACT FROM AUTHOR]