Redear Sunfish Research Articles

PARASITISM IN HYBRID SUNFISH (LEPOMIS SPP.): PATTERNS OF INFECTION AT THE INDIVIDUAL AND COMMUNITY LEVEL.

Sunfish (Lepomis spp.) are among the most common piscine inhabitants of freshwater lakes and ponds in North America. Lepomis spp. breed at the same time creating hybrid zones, where genetically distinct populations mate and produce mixed offspring that are sexually viable hybrids. One aspect of hybridization that may have important consequences is parasitism and its patterns of recruitment in the hybrid sunfish. This study investigated these patterns both at the level of the individual parasite species as well as in the parasite communities infecting the fish. Two sample sites possessing hybrid sunfish populations were investigated: 1 system had bluegill sunfish (Lepomis macrochirus), redear sunfish (Lepomis microlophus), and their hybrids, while the other system had bluegill sunfish (L. macrochirus), green sunfish (Lepomis cyanellus), and their hybrids. The hybrids were infected by mostly generalist parasites that commonly infect all Lepomis spp. Most of the individual parasite species followed a dominance pattern (59.1%) of infection, where parasite abundance in hybrids resembled at least one of the parental species, with the remainder exhibiting intermediate levels of parasitism, supporting an additive pattern of parasite recruitment (40.1%). At the community level, the patterns of parasite recruitment differed in L. macrochirus × L. microlophus hybrids, which showed a dominance pattern, and L. macrochirus × L. cyanellus hybrids, which showed an additive pattern of parasite recruitment. These differences in parasite recruitment between hybrid groups may be attributed to varying degrees of dietary and niche overlap between the parental species in the 2 study systems.

Redear Sunfish Occurrence, Abundance, Growth, and Size Structure as Related to Abiotic and Biotic Factors in Florida Lakes

AbstractPanfish support popular, socioeconomically valuable fisheries across the United States. Whereas Bluegill Lepomis macrochirus and Black Crappie Pomoxis nigromaculatus receive considerable research attention, Redear Sunfish L. microlophus are seldom studied despite their wide distribution, large size, socioeconomic contributions, and invasion potential in parts of their introduced range. We evaluated Redear Sunfish occurrence, density, relative abundance, growth, and size structure in 60 Florida lakes with varied surface area (2–12,412 ha), trophic state (oligotrophic to hypereutrophic), and macrophyte abundance (0.3–100% of lake volume inhabited), a range of environmental conditions over which Redear Sunfish populations have scarcely been investigated. Lake surface area, chlorophyll‐a concentration, and macrophyte abundance explained 98% of variation in Redear Sunfish occurrence. Redear Sunfish density increased asymptotically with calcium concentration, whereas relative abundance (electrofishing fish/h) peaked at intermediate surface area (50–100 ha) and chlorophyll a (20 μg/L). Mean length at age 3 declined with increasing macrophyte abundance and was parabolically related to Redear Sunfish density, peaking at approximately 450 fish/ha. The proportional size distribution (PSD) and PSD of preferred‐length fish were also negatively related to macrophyte abundance, and PSD declined with increasing Redear Sunfish density. Our results suggest that Redear Sunfish fisheries with abundant individuals of quality size (≥180 mm) require large (>100 ha), fertile (>20 μg/L chlorophyll a) lakes with calcium concentrations >5 mg/L, moderate macrophyte abundance (0–25% of lake volume inhabited), and Redear Sunfish densities between 200 and 700 fish/ha. Our modeling approach can help managers predict Redear Sunfish occurrence, density, relative abundance, growth, and size structure based on a suite of abiotic and biotic variables.

Stress response gene family expansions correlate with invasive potential in teleost fish.

The bluegill sunfish Lepomis macrochirus and the closely related redear sunfish Lepomis microlophus have important ecological and recreational value and are widely used for research and aquaculture. While both species have been introduced outside of their native ranges, only the bluegill is considered invasive. Here, we report de novo transcriptome assemblies for these fish as a resource for sunfish biology. Comparative analyses of the transcriptomes revealed an unexpected, bluegill-specific expansion in the HSP70 and HSP90 molecular chaperone gene families. These expansions were not unique to the bluegill as expansions in HSP70s and HSP90s were identified in the genomes of other teleost fish using the NCBI RefSeq database. To determine whether gene family expansions are specific for thermal stress responses, GST and SOD gene families that are associated with oxidative stress responses were also analyzed. Species-specific expansions were also observed for these gene families in distinct fish species. Validating our approach, previously described expansions in the MHC gene family were also identified. Intriguingly, the number of HSP70 paralogs was positively correlated with thermotolerance range for each species, suggesting that these expansions can impact organismal physiology. Furthermore, fish that are considered invasive contained a higher average number of HSP70 paralogs than non-invasive fish. Invasive fish also had higher average numbers of HSP90, MHC and GST paralogs, but not SOD paralogs. Taken together, we propose that expansions in key cellular stress response gene families represent novel genetic signatures that correlate with invasive potential.

Effects of Acute Temperature Change Associated with Handling Practices on Metabolic Rate Stabilization in Two Centrarchids

AbstractSportfishing and hatchery practices routinely subject fish to acute temperature changes through placement of fish in live wells and normal handling and transportation procedures. Acute temperature changes alter metabolic rate in ectotherms; however, the rapidity of the response to reach a new homeostatic state is not well known. Therefore, the response duration in metabolic rate after acute temperature change was measured in two centrarchid species, the Largemouth Bass Micropterus salmoides and Redear Sunfish Lepomis microlophus, which are representative of two different body shapes and are both commonly pursued in recreational fishing and reared in hatcheries. Largemouth Bass were acclimated to either 20°C or 30°C, and Redear Sunfish were acclimated to 24°C. Aerobic metabolic rate was measured immediately after acute temperature change (−4, +0, or +4°C) and was measured repeatedly in cycles of 5.5 or 10.0 min, respectively, until the metabolic rate stabilized. In Largemouth Bass, the metabolic rate stabilized similarly or more slowly following a moderate high‐temperature shock (+4°C; 44 min) compared to transfer to conditions with no temperature change (+0°C) or a moderate low‐temperature shock (−4°C; 16–48 min). In contrast, the metabolic rate in Redear Sunfish stabilized faster after transfer to +4°C (15 min) than after transfer to −4°C or +0°C (both 31 min), possibly because the elevated metabolic rate after transfer was sustained. Notably, for both species, metabolic rates stabilized at a generally lower level after transfer to −4°C than after transfer to +0°C or +4°C. Therefore, the duration until stabilization of metabolic rate after acute temperature change may depend upon species and acclimation temperature, although for both species examined, the energy savings in reduced metabolic rates after moderate cold shock may be beneficial for recovery from sportfishing or hatchery practices.

A needle in the haystack? Applying species co-occurrence frameworks with fish assemblage data to identify species associations and sharpen ecological hypotheses.

Different species can associate or interact in many ways, and methods exist for inferring associations and underlying mechanisms from incidence data (e.g., co-occurrence frameworks). These methods have received criticism despite their recent resurgence in the literature. However, co-occurrence frameworks for identifying nonrandomly associated species pairs (e.g., aggregated or segregated pairs) have value as heuristic tools for sharpening hypotheses concerning fish ecology. This paper provides a case study examining species co-occurrence across 33 stream fish assemblages in southeastern Oklahoma, USA, which were sampled twice (1974 and 2014). This study sought to determine (a) which species were nonrandomly associated, (b) what processes might have driven these associations and (c) how consistent patterns were across time. Associations among most pairs of species (24 species, 276 unique pairs) were not significantly different from random (>80%). Among all significant, nonrandomly associated species pairs (54 unique pairs), 78% (42 pairs) were aggregated and 22% (12 pairs) segregated. Most of these (28 pairs, 52%) were hypothesized to be driven by nonbiotic mechanisms: habitat filtering (20 pairs, 37%), dispersal limitation (two pairs, 0.4%) or both (six pairs, 11%). The remaining 26 nonrandomly associated pairs (48%) had no detectable signal of spatial or environmental factors involved with the association, therefore the potential for biotic interaction was not refuted. Only five species pairs were consistently associated across both sampling periods: stonerollers Campostoma spp. and orangebelly darter Etheostoma radiosum; red shiner Cyprinella lutrensis and bullhead minnow Pimephales vigilax; bluegill sunfish Lepomis macrochirus and redear sunfish Lepomis microlophus; redfin shiner Lythrurus umbratilis and bluntnose minnow Pimephales notatus; and bigeye shiner Notropis boops and golden shiner Notemigonus crysoleucas. Frameworks for identifying nonrandomly associated species pairs can provide insight into broader mechanisms of species assembly and point to potentially interesting species interactions (out of many possible pairs). However, this approach is best applied as a tool for sharpening hypotheses to be investigated further. Rather than a weakness, the heuristic nature is the strength of such methods, and can help guide biologists toward better questions by employing relatively cheap diversity survey data, which are often already in hand, to reduce complex interaction networks down to their nonstochastic parts which warrant further investigation.

A Comparison of Two Methods for Sampling Bluegill and Redear Sunfish in Small Impoundments

AbstractBluegill Lepomis macrochirus and Redear Sunfish L. microlophus are highly regarded recreational species throughout North America. Management of these species relies on sampling methods that accurately and efficiently describe population characteristics of the target population. Largemouth Bass Micropterus salmoides and crappies Pomoxis spp. are commonly sampled with spring electrofishing and fall fyke netting, respectively. If lepomids can be effectively sampled concurrently with Largemouth Bass or crappies with one of these sampling methods, it would improve sampling efficiency in small impoundments. Our objective was to compare two sampling methods (North American standard fyke netting and electrofishing) for sampling Bluegill and Redear Sunfish populations in small impoundments by comparing size structure, sampling precision (relative standard error), and sampling efficiency (effort needed to collect 125 stock‐length fish). Typically, spring electrofishing caught a wider size range of Bluegill and Redear Sunfish than fyke nets, but proportional size distribution was similar between gears. However, length frequencies differed between gears in all impoundments for Bluegill and in three of five impoundments for Redear Sunfish. Electrofishing typically caught a greater proportion of large lepomids than fyke nets in those cases, though the differences were subtle and management decisions would likely be similar using data from either gear. With the exception of Pawhuska Lake (which had low catch rates leading to poor precision for both species and both gears), catch rates were typically high enough to collect sufficient numbers (125 stock‐length fish) of Bluegill to adequately describe size structure with 5–20 net‐nights for fyke nets or 4–28 transects for electrofishing, but Redear Sunfish sampling would require considerably more sampling effort to produce sufficient amounts of fish in most cases (24–79 net‐nights for fyke nets or 12–57 transects for electrofishing). Spring electrofishing is the more precise (lower relative standard error) of the two sampling methods for collecting lepomids.

An Integrated Pest Management Tactic for Quagga Mussels: Site‐Specific Application of Fish Biological Control Agents

AbstractThe quagga mussel Dreissena bugensis is a harmful aquatic pest that invaded the southwestern USA in 2007. Challenges with managing this pest have been encountered because the invaded systems are primarily open‐water sources used for human consumption and/or are connected to freshwater habitats containing threatened and endangered species. Existing chemical and physical control methods are undesirable, and the use of some methods is restricted or prohibited because they pose risks to humans and ecosystems more broadly. To address this problem, we investigated the efficacy of using resident fishes as biocontrol agents for managing different life stages of quagga mussels on different spatial scales in a site‐specific manner. We conducted field experiments to test whether planktivorous Bluegill Lepomis macrochirus reduced mussel infestations on substrates of varying orientations in small and large pens through predation on larval mussels. We also performed an experiment to evaluate whether carnivorous Redear Sunfish L. microlophus reduced mussel infestations established on substrates of varying orientations in small pens through predation on juvenile and adult mussels. Bluegill significantly reduced mussel infestations on all substrates in the pens through predation on larvae and small juvenile mussels. Redear Sunfish reduced existing juvenile and adult mussel populations in some cases, with consumption varying among individuals and substrate orientations. Our results indicate that fishes, specifically Bluegill, may represent effective site‐specific biocontrol agents for quagga mussels, reducing impacts on targeted infrastructure (e.g., water towers, docks, and pipes) and habitats having different surface orientations by controlling more than one life stage of the pest. Development of an integrated pest management strategy that considers application of this tactic in combination with others would undoubtedly improve the management of quagga mussels—and potentially that of congeneric zebra mussels D. polymorpha—within lake and reservoir ecosystems.

First record of pughead deformity in redear sunfish Lepomis microlophus (Günther, 1859)

The first record of pughead deformity in redear sunfish Lepomis microlophus is presented based on a single specimen captured from a wild population in a small Oklahoma reservoir. The pugheaded specimen was compared to normal fish from the same population. The pugheaded fish had slightly poorer body condition, although total length was comparable to normal individuals of the same age. Poorer condition may have resulted from difficulty feeding due to incomplete mouth closure and restricted gape caused by severe deformity of the anterior neurocranium and upper jaw. Extreme drought conditions leading to deteriorated water quality during early development may have resulted in the deformity of the redear sunfish. The incidence rate of pugheadedness in this redear sunfish population was below 1%, comparable to rates reported in other wild freshwater fish populations.

Feeding Regime Has Little Impact on Weight Loss of Hybrid Crappies Pomoxis spp. and Redear Sunfish at a Low (Winter) Water Temperature when Fed a Noncommercial Diet of Blood Worms

AbstractWinter mortality is a problem for fish producers in temperate regions of the USA, including Arkansas. Hybrid crappies (Black Crappie Pomoxis nigromaculatus × White Crappie P. annularis) and Redear Sunfish Lepomis microlophus are popular among recreational anglers. Methods of winter feeding vary widely among existing commercial farms. The impact of different winter feeding regimes on performance of hybrid crappies and Redear Sunfish was evaluated in temperature‐controlled aquarium systems. Juvenile hybrid crappies and Redear Sunfish were cultured at approximately 9°C to mimic winter conditions. Three feeding regimes were implemented (3 tanks/regime) in which an ad libitum ration of blood worms was administered twice per week, once per week, or once per month. After 13 weeks of culture, there were no observed differences in weight loss, survival, specific growth rate, or final individual weight for either hybrid crappies or Redear Sunfish. Hybrid crappies lost 27–29% of their initial body weight, while Redear Sunfish lost more than 30% of their initial body weight. Fatty acid composition of both species differed significantly among feeding treatments, showing a decline in saturated fatty acids from initial levels and increases in or static levels of highly unsaturated fatty acids. Results suggest that feeding regime has little effect on weight gain in hybrid crappies and Redear Sunfish when fed at a colder water temperature.

A question of scale: Weak evidence for broad regional synchrony in fish year-class strength within or among species in inland lakes

Spatially-correlated abiotic and biotic conditions can potentially induce synchrony in the dynamics of disparate populations or species. However, such potential synchrony among species or populations may be tempered by dynamics operating at finer temporal and spatial scales, as well as species-specific responses to environmental conditions. We examined within- and among-species synchrony in year-class strength across 130 lakes in northern Indiana over 30 years to evaluate the relative scale of potential synchrony and its possible ecological mechanisms in five recreationally important fish species: black crappie (Pomoxis nigromaculatus), bluegill (Lepomis macrochirus), largemouth bass (Micropterus salmoides), redear sunfish (L. microlophus), and yellow perch (Perca flavescens). Bluegill and black crappie recruitment was significantly positively correlated when the species coexisted, and relative year-class strength of both species was positively related to mean annual wind speed. However, there were few other instances of recruitment synchrony between or within species, regardless of whether synchrony was assessed within or among lake systems. In addition, habitat similarity and regional weather patterns also played a limited and inconsistent role in shaping recruitment strength or synchrony in these small inland systems. These results suggest that fish recruitment dynamics in small, inland systems are most often a function of system-specific biotic interactions that mask limited input from broader climatological influences, and that understanding recruitment in small lakes will require examinations on appropriately fine spatial and temporal scales.

Many head designs, one super slurp

![Graphic][1] Fish have a remarkably diverse array of head designs, from snail-crushing redear sunfish to dainty zebrafish that feed on plankton and wide-mouthed bewhiskered catfish, but they all have one thing in common: they all suck. Corrine Jacobs and Roi Holzman, from the University of

Comparison of Three Methods for Sampling Panfish in Iowa Impoundments

AbstractScience‐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.Received March 4, 2016; accepted July 13, 2016 Published online October 28, 2016

Relating fish health and reproductive metrics to contaminant bioaccumulation at the Tennessee Valley Authority Kingston coal ash spill site.

A 4.1 million m(3) coal ash release into the Emory and Clinch rivers in December 2008 at the Tennessee Valley Authority's Kingston Fossil Plant in east Tennessee, USA, prompted a long-term, large-scale biological monitoring effort to determine if there are chronic effects of this spill on resident biota. Because of the magnitude of the ash spill and the potential for exposure to coal ash-associated contaminants [e.g., selenium (Se), arsenic (As), and mercury (Hg)] which are bioaccumulative and may present human and ecological risks, an integrative, bioindicator approach was used. Three species of fish were monitored-bluegill (Lepomis macrochirus), redear sunfish (L. microlophus), and largemouth bass (Micropterus salmoides)-at ash-affected and reference sites annually for 5years following the spill. On the same individual fish, contaminant burdens were measured in various tissues, blood chemistry parameters as metrics of fish health, and various condition and reproduction indices. A multivariate statistical approach was then used to evaluate relationships between contaminant bioaccumulation and fish metrics to assess the chronic, sub-lethal effects of exposure to the complex mixture of coal ash-associated contaminants at and around the ash spill site. This study suggests that while fish tissue concentrations of some ash-associated contaminants are elevated at the spill site, there was no consistent evidence of compromised fish health linked with the spill. Further, although relationships between elevated fillet burdens of ash-associated contaminants and some fish metrics were found, these relationships were not indicative of exposure to coal ash or spill sites. The present study adds to the weight of evidence from prior studies suggesting that fish populations have not incurred significant biological effects from spilled ash at this site: findings that are relevant to the current national discussions on the safe disposal of coal ash waste.

Influence of metal(loid) bioaccumulation and maternal transfer on embryo-larval development in fish exposed to a major coal ash spill

In December 2008, an earthen retaining wall at the Tennessee Valley Authority (TVA) Kingston Fossil Fuel Plant failed and released 4.1 millionm3 of coal ash to rivers flowing into Watts Bar Reservoir in east Tennessee, United States (U.S.). As part of a comprehensive effort to evaluate the risks to aquatic resources from this spill – the largest in U.S. history – we compared bioaccumulation and maternal transfer of selenium (Se), arsenic (As), and mercury (Hg) in adult redear sunfish (Lepomis macrolophus), collected two years after the spill from both coal-ash exposed and non-exposed areas of the Emory and Clinch Rivers, with the success of embryo-larval development in their offspring. Whole body and ovary concentrations of Se in female sunfish at three study sites downstream of the spill were significantly elevated (site means=4.9–5.3 and 6.7–9.0mg/kg d.w. whole body and ovary concentrations, respectively) compared with concentrations in fish from reference sites upstream of the spill site (2.2–3.2mg/kg d.w. for whole bodies and 3.6–4.8mg/kg d.w. for ovaries). However, Se concentrations in coal ash-exposed areas remain below proposed U.S. Environmental Protection Agency (USEPA) criteria for the protection of aquatic life. Site-to-site variation in fish concentrations of As and Hg were not well-correlated with ash-exposure, reflecting the multiple sources of these metal(loid)s in the affected watersheds. In 7-day laboratory tests of embryos and larvae derived from in vitro crosses of eggs and sperm from these field-collected sunfish, fertilization success, hatching success, embryo-larval survival, and incidences of developmental abnormalities did not differ significantly between ash-exposed and non-exposed fish. Furthermore, these developmental endpoints were not correlated with whole body or ovary concentrations of Se, As, or Hg in the maternal fish, or with fish size, ovary weight, or gonadal-somatic indices. Results from this and related studies associated with the Kingston coal ash spill are consistent with proposed USEPA fish-based water quality criteria for Se, and to date continue to suggest that long-term exposures to sediment containing residual ash may not present a significant chronic risk to fish populations exposed to this major coal ash release.

A Pilot Study Testing a Natural and a Synthetic Molluscicide for Controlling Invasive Apple Snails (Pomacea maculata).

Pomacea maculata (formerly P. insularum), an apple snail native to South America, was discovered in Louisiana in 2008. These snails strip vegetation, reproduce at tremendous rates, and have reduced rice production and caused ecosystem changes in Asia. In this pilot study snails were exposed to two molluscicides, a tea (Camellia sinensis) seed derivative (TSD) or niclosamide monohydrate (Pestanal(®), 2',5-dichloro-4'-nitrosalicylanilide, CAS #73360-56-2). Mortality was recorded after exposure to high or low concentrations (0.03 and 0.015g/L for TSD, 1.3 and 0.13mg/L for niclosamide). The TSD induced 100% mortality at both concentrations. Niclosamide caused 100% and 17% mortality at high and low concentrations respectively. These molluscicides were also tested on potential biocontrol agents, the red swamp crayfish (Procambarus clarkii) and redear sunfish (Lepomis microlophus). No crayfish mortalities occurred at either concentration for either chemical, but sunfish experienced 100% mortality with TSD (0.03g/L), and 21% mortality with niclosamide (0.13mg/L).

Morphological Confirmation ofHomalometron(Trematoda: Apocreadiidae) Species in Freshwater Fishes in Southeastern Texas, U.S.A., with Description of Two Species

ABSTRACT: Recent work using DNA sequence data considered Homalometron armatum (McCallum, 1895) Manter, 1947 (Trematoda: Apocreadiidae) to consist of 3 species. The goal of the present investigation was to test, using new collections, whether these 3 putative species could be recognized and differentiated morphometrically. Newly collected worms from freshwater drum (Aplodinotus grunniens) and redear sunfish (Lepomis microlophus) in Texas, U.S.A., were combined with existing museum collections in multivariate analyses of morphometric characteristics. Principal components analysis on new collections suggested that worms did group by morphometric characteristics relativized by worm length. Discriminant function analyses demonstrated a high degree of fidelity between a priori classification of worms and the ability to discriminate among populations using morphometric data. Based on these results, the 2 as-yet undescribed species of Homalometron are named herein.

Diet Partitioning in a Diverse Centrarchid Assemblage in the Atchafalaya River Basin, Louisiana

AbstractWe examined trophic and habitat resource partitioning among seven centrarchid species inhabiting four macrohabitat types in the Atchafalaya River basin (ARB), a 900‐km2 bottomland hardwood swamp in south‐central Louisiana. Fish (n = 2,036) were collected at 24 sites by boat electrofishing, and trophic position was determined from stomach contents and tissue analysis of 15N and 13C stable isotope signatures (n = 140). Stomach content analysis (index of relative importance), Morisita's index of dietary overlap, and canonical correspondence analysis revealed little effect of ARB macrohabitat type on centrarchid trophic relationships despite significant habitat alterations in dredged canals. Analyses revealed substantial diet overlap among three predominately insectivorous species (Bluegill Lepomis macrochirus, Redspotted Sunfish L. miniatus, and Longear Sunfish L. megalotis), whereas much more distinctive trophic positions were occupied by Largemouth Bass Micropterus salmoides (dominant prey = fish), Black Crappies Pomoxis nigromaculatus (palaemonid shrimp), Redear Sunfish L. microlophus (mollusks), and Warmouths L. gulosus (crayfish). Stable isotope signatures reflected dietary differences among species and complemented stomach content analyses in assessing the feeding ecology of these centrarchids, although isotopic similarities were sometimes higher than actual similarities in diet composition. Results suggest that centrarchid functional morphology and prey selection, combined with the diversity and productivity of ARB littoral habitats, effectively reduce the potential for competition among the seven cohabiting centrarchids.

Behavioral Responses of Representative Freshwater Fish Species to Electromagnetic Fields

AbstractHydrokinetic energy is proposed as an environmentally preferred means of generating electricity from river and tidal currents. To resolve environmental concerns, it is important to investigate potential effects on aquatic organisms from the electromagnetic fields (EMFs) that are created by underwater generators and transmission cables. We evaluated the behavioral responses of some representative freshwater fishes to static and variable EMFs in a series of laboratory experiments. Fish were exposed for 46 h to a static (DC) EMF with a permanent bar magnet or to a variable (AC) EMF with an electromagnet. Fish locations were recorded with a digital imaging system, and changes in activity level and distribution relative to the magnet position were quantified at 5‐min intervals. Experiments with Fathead Minnow Pimephales promelas, Redear Sunfish Lepomis microlophus, Striped Bass Morone saxatilis, Lake Sturgeon Acipenser fulvescens, and Channel Catfish Ictalurus punctatus produced mixed results. Except for Fathead Minnow, there was no effect on fish activity level. Only Redear Sunfish and Channel Catfish exhibited a change in distribution relative to the position of the magnet, with both species showing an apparent attraction to the EMF source. In a separate experiment, rapid behavioral responses of Paddlefish Polyodon spathula and Lake Sturgeon to the onset of an AC field were recorded with high‐speed video. Paddlefish did not react to a variable, 60‐Hz magnetic field (i.e., like that emitted by an AC generator or cable), but Lake Sturgeon consistently responded with a variety of altered swimming behaviors. These results will be useful for positioning cables or generators to minimize interactions with EMF‐sensitive species.

Invasive quagga mussels can be attenuated by redear sunfish (Lepomis microlophus) in the Southwestern United States

The degree to which invasive quagga mussels have spread across the Southwestern United States is unprecedented, and until now, none of the controls currently available is risk-free to the environment or human health. Here we demonstrate that stocking high-density (0.42fish/m3 or 1.90fish/m2) redear sunfish (Lepomis microlophus) in an infested lake enclosure removed adult quagga mussels efficiently and appeared to suppress their growth and recruitment. However, mussels were not eradicated during the short term experimental course. Long-term study needs to be conducted to determine whether mussels can be completely eliminated by redear sunfish and what optimum density would be required for balancing high efficacy mussel control with cost-effectiveness. Redear sunfish is a species native to the Southeastern United States that has become a popular, stocked sportfish in the Southwest. Targeted stocking of redear sunfish may be an efficient and environmentally friendly approach to mitigate the colonization of invasive quagga mussels in suitable open water ecosystems, especially those with new dreissenid infestations or those threatened by invasion.

Influence of Environmental Variables and Species Interactions on Sport Fish Communities in Small Missouri Impoundments

AbstractSmall impoundments (<400 ha) are numerous and provide close‐to‐home fishing opportunities for anglers but may not support optimal sport fisheries. Most of these fisheries are managed by harvest regulations, but watershed and impoundment characteristics, poor water quality, or detrimental species interactions can also influence the desirability of fisheries. We examined the relative importance of watershed characteristics, impoundment morphology, water quality, and species interactions in explaining differences in relative abundance, growth, and size structure of five sport fish species (largemouth bass Micropterus salmoides, bluegill Lepomis macrochirus, redear sunfish L. microlophus, white crappie Pomoxis annularis, and black crappie P. nigromaculatus) among 89 small Missouri impoundments spanning a large fertility gradient. Using regression analysis, we found that variables associated with predation, competition, and lake fertility were most important in explaining variation in sport fish demographics, whereas watershed and impoundment morphology variables were typically less important. Lakes with dense largemouth bass populations commonly contained sunfish and crappie populations with desirable size structure and growth, implying that predation was a strong structuring force. Density‐dependent growth was common among all sport fish species. White crappies and black crappies had better growth or size structure in lakes with fewer bluegills, suggesting competition among these species. Lakes containing common carp Cyprinus carpio had fewer largemouth bass and slower‐growing black crappies than lakes without common carp. The presence of gizzard shad Dorosoma cepedianum benefited largemouth bass populations but negatively affected bluegill and black crappie populations. Growth and size structure of sport fishes usually improved with increasing lake fertility. Predation and competition seemed to be most important in structuring sport fish communities in these impoundments provided that lake fertility was adequate to sustain acceptable abundances and growth rates of these fishes.Received February 10, 2012; accepted August 17, 2012