Adult Bluegills Research Articles

Microcystin accumulation in Sportfish from an agricultural reservoir differs among feeding guild, tissue type, and time of sampling.

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=57.6ng g-1, largemouth bass mean=71.8ng g-1 wet weight [ww]), then kidneys (bluegill mean=27.1, largemouth bass mean=22.7ng g-1 ww), followed by muscles (bluegill mean=7.6, largemouth bass mean=5.7ng 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.

Bluegill Picornavirus isolated from a mortality event involving Bluegill (Lepomis macrochirus) in the upper Mississippi River.

A mortality event involving an estimated 1,000 adult bluegills (Lepomis macrochirus) was observed in an ice-covered backwater lake of the upper Mississippi River near Alma, Wisconsin, in December of 2017. Macroscopic signs of disease included abdominal distension due to fluid accumulation within the internal organs as well as external and internal haemorrhaging. Histological evaluation revealed chronic peritonitis with peritoneal adhesions in all fish examined. Kidney, spleen and ascites fluid samples were collected from diseased bluegills and examined for the presence of pathogens. Bluegill picornavirus (BGPV) was isolated using tissue cell culture methods utilizing a recently developed, uncharacterized bluegill fry cell line (BF-4), and the presence of this virus was confirmed through molecular identification. The current geographic range, known susceptible hosts as well as historical epizootics associated with BPGV is discussed. The ability of BGPV to cause significant mortality in wild fish further emphasizes the importance of monitoring both wild and hatchery populations for this pathogen.

Effects of Common Carp on Trophic Dynamics of Sport Fishes in Shallow South Dakota Water Bodies

AbstractThe Common Carp Cyprinus carpio is one of the most common freshwater fish invaders worldwide, creating adverse effects on water quality and impacting ecosystem structure and function. To assess how Common Carp impact food web dynamics, we compared the trophic dynamics of Bluegills Lepomis macrochirus and Largemouth Bass Micropterus salmoides in three lakes containing Common Carp populations with the trophic dynamics in three lakes without Common Carp. All six lakes were located in eastern South Dakota. Stable isotope analysis was used to estimate trophic positions and indicate energy sources utilized by adult and age‐0 fish. Additionally, diets of age‐0 Bluegills were analyzed to assess whether Common Carp were inhibiting ontogenetic diet shifts, and bomb calorimetry was used to evaluate differences in energy density of age‐0 fish prior to winter. Age‐0 fish and adult Bluegills derived significantly more energy from pelagic sources in the systems populated with Common Carp. Adult Bluegills in Common Carp systems remained at a relatively constant trophic position across their entire size range, whereas in non–Common Carp systems, the trophic positions of adult Bluegills tended to increase with size. Even though age‐0 fish relied more heavily on pelagic‐derived energy in the systems with Common Carp, significant differences were not observed in the autumn energy densities of age‐0 fish or in the age‐0 Bluegills’ diet. Given our results, Common Carp are unlikely to impact overwinter survival of age‐0 fish in these shallow systems. The present study illustrates the value of using stable isotopes for food web investigations and demonstrates that Common Carp do alter trophic dynamics of other fishes in the systems they invade, but responses differ depending upon the species and life stage.Received February 11, 2016; accepted November 28, 2016 Published online February 21, 2017

Collapse of a reproducing population of non-native African jewelfish (Hemichromis letourneuxi) in a Florida lake

Established populations of non-natives may collapse without a clear causal mechanism. Hypothetically, fluctuations in habitat structural complexity may influence dynamics of invaders and the biotic resistance offered by predators. Herein I report observations of the collapse of a reproducing population of the nonnative African jewelfish ( Hemichromis letourneuxi) in a Florida lake concurrent with an unusual low-water period. I test the hypothesis that predation may have played a key role in the collapse using a combination of field surveys of habitat and fish abundance and predator-prey experiments. Habitat complexity was high before and after the low water period but virtually nonexistent during low water. The abundance of African jewelfish and native juvenile bluegill ( Lepomis macrochirus) and eastern mosquitofish ( Gambusia holbrooki) declined concurrently with decreasing complexity but the native species rebounded when lake levels increased. Large-bodied natives such as largemouth bass (Micropterus salmoides) and adult bluegill showed no pattern of fluctuation related to habitat complexity. African jewelfish survival was 1.6 times greater at high versus low complexity and over 7 times higher versus no complexity in the presence of largemouth bass. Conversely, eastern mosquitofish, a species that exerts strong effects on small-bodied fishes in structurally complex habitats had no effect on African jewelfish survival. Predation effects on suscep tible non-natives should be considered as a potential control action. Population collapse is understudied but may provide insights into long-term dynamics of invaders and information useful for management of problematic species.

Mercury Concentrations of Bluegill (Lepomis macrochirus) Vary by Sex

Patterns in relative differences in contaminant concentrations between the sexes across many species of fish may reveal clues for important behavioral and physiological differences between the sexes, and may also be useful in developing fish consumption advisories and efficient designs for programs meant to monitor contaminant levels in fish. We determined skin-off fillet and whole-fish total mercury (Hg) concentrations of 28 adult female and 26 adult male bluegills (Lepomis macrochirus) from Squaw Lake, Oakland County, Michigan (MI), USA. Bioenergetics modeling was used to quantify the effect of growth dilution on the difference in Hg concentrations between the sexes. On average, skin-off fillet and whole-fish Hg concentrations were 25.4% higher and 26.6% higher, respectively, in females compared with males. Thus, the relative difference in Hg concentrations between the sexes for skin-off fillets was nearly identical to that for whole fish. However, mean skin-off fillet Hg concentration (363 ng/g) was 2.3 times greater than mean whole-fish Hg concentration (155 ng/g). Males grew substantially faster than females, and bioenergetics modeling results indicated that the growth dilution effect could account for females having 14.4% higher Hg concentrations than males. Our findings should be useful in revising fish consumption advisories.

Differences between main-channel and off-channel food webs in the upper Mississippi River revealed by fatty acid profiles of consumers

Large river systems are often thought to contain a mosaic of patches with different habitat characteristics driven by differences in flow and mixing environments. Off-channel habitats (e.g., backwater areas, secondary channels) can become semi-isolated from main-channel water inputs, leading to the development of distinct biogeochemical environments. Observations of adult bluegill (Lepomis macrochirus) in the main channel of the Mississippi River led to speculation that the main channel offered superior food resources relative to off-channel areas. One important aspect of food quality is the quantity and composition of polyunsaturated fatty acids (PUFA). We sampled consumers from main-channel and backwater habitats to determine whether they differed in PUFA content. Main-channel individuals for relatively immobile species (young-of-year bluegill, zebra mussels [Dreissena polymorpha], and plain pocketbook mussels [Lampsilis cardium]) had significantly greater PUFA content than off-channel individuals. No difference in PUFA was observed for the more mobile gizzard shad (Dorsoma cepedianum), which may move between main-channel and off-channel habitats even at early life-history stages. As off-channel habitats become isolated from main-channel waters, flow and water column nitrogen decrease, potentially improving conditions for nitrogen-fixing cyanobacteria and vascular plants that, in turn, have low PUFA content. We conclude that main-channel food webs of the upper Mississippi River provide higher quality food resources for some riverine consumers as compared to food webs in off-channel habitats.

Growth and Survival of Largemouth Bass following Supplemental Feeding of Bluegills in Small Impoundments

AbstractWe investigated whether providing supplemental pellet feed to Bluegills Lepomis macrochirus in small impoundments increased their growth and reproductive rates after stocking and whether the supplemental feeding of Bluegills had positive indirect effects on Largemouth Bass Micropterus salmoides during the initial stocking year. In 2010, we stocked adult Bluegills and Largemouth Bass into nine 0.1‐ha ponds; three replicate ponds were each provided with no pelleted food (control), a low ration (1.52 kg·ha−1·d−1), or a high ration (2.68 kg·ha−1·d−1). Supplemental feeding yielded increases in the growth of newly stocked Bluegills, the gonadosomatic index of female Bluegills, and the density of larval Bluegills within 4 months of stocking. In contrast, the sizes of adult and age‐0 Largemouth Bass and the density and biomass of age‐0 Bluegills during fall were not affected by feeding within the time frame of our study. The results demonstrate that supplemental pellet feeding is useful when the management goal is to increase Bluegill size and reproductive output and that these effects develop soon after stocking. We conclude that supplemental feeding is a beneficial enhancement technique for application to Bluegills in recently stocked impoundments.Received May 13, 2012; accepted November 20, 2012

A robotic fish caudal fin: effects of stiffness and motor program on locomotor performance

We designed a robotic fish caudal fin with six individually moveable fin rays based on the tail of the bluegill sunfish, Lepomis macrochirus. Previous fish robotic tail designs have loosely resembled the caudal fin of fishes, but have not incorporated key biomechanical components such as fin rays that can be controlled to generate complex tail conformations and motion programs similar to those seen in the locomotor repertoire of live fishes. We used this robotic caudal fin to test for the effects of fin ray stiffness, frequency and motion program on the generation of thrust and lift forces. Five different sets of fin rays were constructed to be from 150 to 2000 times the stiffness of biological fin rays, appropriately scaled for the robotic caudal fin, which had linear dimensions approximately four times larger than those of adult bluegill sunfish. Five caudal fin motion programs were identified as kinematic features of swimming behaviors in live bluegill sunfish, and were used to program the kinematic repertoire: flat movement of the entire fin, cupping of the fin, W-shaped fin motion, fin undulation and rolling movements. The robotic fin was flapped at frequencies ranging from 0.5 to 2.4 Hz. All fin motions produced force in the thrust direction, and the cupping motion produced the most thrust in almost all cases. Only the undulatory motion produced lift force of similar magnitude to the thrust force. More compliant fin rays produced lower peak magnitude forces than the stiffer fin rays at the same frequency. Thrust and lift forces increased with increasing flapping frequency; thrust was maximized by the 500× stiffness fin rays and lift was maximized by the 1000× stiffness fin rays.

Effects of Common Carp on Reproduction, Growth, and Survival of Largemouth Bass and Bluegills

AbstractThe common carp Cyprinus carpio was introduced to North America more than a century ago, but little research has focused on interactions between this invasive species and native fishes. We used large mesocosms (600 m2) within drainable 0.4‐ha ponds to examine the effects of adult common carp on (1) reproduction of largemouth bass Micropterus salmoides and bluegills Lepomis macrochirus and (2) growth and survival of the larvae and juveniles of these centrarchid species. In separate enclosures, adult bluegills or largemouth bass were stocked with or without common carp. In enclosures with common carp, turbidity was substantially higher, but both centrarchid species spawned and the densities and sizes of larval largemouth bass and bluegills were similar to those of larvae in enclosures without common carp. As juveniles grew, largemouth bass survived at a higher rate but were smaller in enclosures containing common carp compared with largemouth bass in enclosures without common carp. In a second experiment, we stocked known numbers of older juvenile centrarchids into enclosures and found decreased growth for both largemouth bass and bluegills. However, survival of largemouth bass was again higher in enclosures with common carp. Although centrarchid spawning was successful and larval growth and survival did not decrease in the presence of common carp, centrarchid growth slowed at the juvenile stage, probably due to food resource limitation resulting from direct competition with common carp for invertebrate forage, high turbidity caused by common carp, or both of these factors.

Lateral distribution of fishes in the main‐channel trough of a large floodplain river: Implications for restoration

AbstractMajor river channels have been extensively altered worldwide. The development of restoration strategies for those alterations requires fundamental information, including the use of large deep channels by fishes. We trawled within parallel paths distributed across the width of the main‐channel trough of the Mississippi River to identify how the lateral distribution of fishes responds to variations in flow ranging from 50% to 200% of the annual median, water temperature ranging from 9 to 29°C and commercial shipping traffic ranging from 0 to 9 vessels per day. Among the species we encountered, only shovelnose sturgeon (Scaphirhynchus platorynchus) were persistent channel residents that remained concentrated along the main‐channel centreline regardless of flow, temperature and traffic. Other persistent residents showed no distinct pattern in lateral distribution, concentrated along the deep channel margins or varied in lateral distribution with flow. Surprisingly, large adult bluegill (Lepomis macrochirus), which are conventionally viewed as limnophils, were the second‐most abundant species in our samples and became increasingly abundant within the deep channel trough as flow decreased below the annual median. Clearly, those fishes exploit resources contained in the main channel and are, therefore, better viewed as opportunistic limno‐rheophils. Our results imply the existence of poorly understood food resources in the main channel. We conjecture that re‐creation of free‐flowing secondary channels and features that increase the production and transport of invertebrates in channels can help mitigate adverse effects of channel alteration and commercial shipping. Published in 2009 by John Wiley & Sons, Ltd.

Bluegill Recruitment, Growth, Population Size Structure, and Associated Factors in Minnesota Lakes

AbstractTo better understand the differences among populations of bluegill Lepomis macrochirus, we analyzed the relationships between bluegill recruitment, growth, population size structure, and associated factors from approximately 2,600 Minnesota lakes. Potential explanatory variables for our models included bluegill year‐class strength, growth, population size structure, the relative abundance and mean weight of predator species, physical and chemical characteristics of lakes, summer air temperature, and season. Bluegill year‐class strength, growth, and population size structure were more strongly related to each other than to predator and lake characteristics, temperature, or season. Growth of age‐6 bluegills was positively associated with population size structure and inversely related to year‐class strength, suggesting density‐dependent growth effects for adult bluegills. Growth of age‐3 bluegills was inversely related to Secchi depth, so early growth and productivity may be linked. Bluegill population size structure was positively associated with length at age 5, as expected from the analysis of growth, and was inversely associated with mean year‐class strength. Bluegill year‐class strength was negatively associated with population size structure, length at ages 4 and 5, and lake area. Although predator variables were not included in one‐ or two‐variable regression models, bluegill growth was positively related to the relative abundance of yellow perch Perca flavescens, walleye Sander vitreus (formerly Stizostedion vitreum), black bullhead Ameiurus melas, and brown bullhead A. nebulosus and negatively related to that of largemouth bass Micropterus salmoides and yellow bullhead A. natalis. The results suggest that management strategies for improving bluegill growth and population size structure should focus on bluegill recruitment and growth rather than on external environmental factors.

Age‐0 Gizzard Shad Abundance is Reduced in the Presence of Macrophytes: Implications for Interactions with Bluegills

AbstractThe abundance of gizzard shad Dorosoma cepedianum may be reduced in the presence of macrophytes, which may lessen the frequently observed negative interactions with coinhabiting bluegills Lepomis macrochirus. We used a series of experimental pond studies and a small‐lake data set to examine relationships among gizzard shad, bluegills, and macrophytes. Fall age‐0 gizzard shad abundance was lower in vegetated experimental ponds than in unvegetated ponds, but mean total length (TL) did not differ. Larval gizzard shad abundance did not differ between vegetated and unvegetated ponds, but the relative survival of age‐0 gizzard shad (ratio of fall juveniles to the total number of larvae collected) was higher in unvegetated ponds. In ponds with macrophyte coverage ranging from 0% to 100%, age‐0 gizzard shad abundance declined with increasing macrophyte coverage; however, age‐0 bluegill abundance was unrelated to macrophyte coverage. The abundance and size of age‐0 gizzard shad and age‐0 bluegills were unrelated in these ponds. By examining the small‐lake data, we found that the proportion of lakes containing gizzard shad decreased with increasing macrophyte coverage. The proportion of bluegill populations containing large adults (>203 mm TL) increased with macrophyte coverage for lakes with gizzard shad but not for lakes without gizzard shad. Although the actual mechanisms are not clear, we suggest that competitive interactions between gizzard shad and adult bluegills are density dependent and lessen with increasing macrophyte coverage because of decreasing gizzard shad abundance.

Interactions between adult and larval bluegill sunfish: positive and negative effects.

Adult fish may affect the growth and survival of conspecific larvae through a variety of pathways, including negative interactions via competition for shared limiting resources or via predation (i.e., cannibalism), and positive interactions due to the consumption of larval predators and via resource enhancement (i.e., presence of adults increases availability of larval prey). To examine the overall effect of adult bluegill sunfish (Lepomis macrochirus) on larval bluegill, we conducted a field experiment in which we manipulated adult densities and quantified larval growth and survival, prey abundance, invertebrate predator abundance, and cannibalism. The presence of adult bluegill had a negative effect on final larval mass. This response was consistent with competition for zooplankton prey. Adult bluegill reduced the abundance of large zooplankton (e.g., Chaoborus and Daphnia), which were the dominant prey of bluegill larvae in the absence of adults. Larvae in the no-adult treatment also had significantly more prey in their stomachs compared to larvae in the presence of adults. Larval survival was maximized at intermediate adult densities and the overall production of larvae peaked at intermediate adult densities. The higher larval survival at intermediate adult densities is attributed to a reduction in invertebrate predators in treatments with adult bluegill; invertebrate predators experienced an 80% reduction in the presence of adult fish. Decreased larval survival at the highest adult density was not due to resource limitation and may be due to cannibalism, which was not directly observed in our study, but has been observed in other studies.

Adult Fish Predation on Freshwater Limnetic Fish Larvae: A Mesocosm Experiment

Abstract We demonstrated that predation by adult bluegills Lepomis macrochirus and white crappies Pomoxis annularis may be a major source of mortality for freshwater larval fish. In 5.3-m3 mesocosms, we compared the survival of larval bluegill prey (19 larvae/m3; mean standard length (SL), 8.6 mm; range, 3–22 mm) in the presence of adult bluegills, adult white crappies, or adult gizzard shad Dorosoma cepedianum with the survival of predator-free controls. The duration of the experiments was 3.7 h for bluegills, 3.2 h for white crappies, 5.5 h for gizzard shad, and 4.3 h for the predator-free controls. Larval fish survival in both the bluegill and white crappie predator treatments was lower than that of the predator-free controls, whereas larval fish survival in the gizzard shad treatments did not differ from that of the controls. The instantaneous hourly mortality rate attributable to predation was 0.11 for bluegill (9.8 larvae consumed/predator each hour) and 0.05 for white crappie (4.8 larvae consumed/p...

The effects of fish on assemblages of amphibians in ponds: a field experiment

1. Bluegill sunfish (Lepomis macrochirus) dominate fish assemblages of small lakes and ponds throughout the eastern United States and may play a major role in structuring aquatic communities. We examined the impact of adult bluegill on amphibian density by stocking bluegill at a range of densities into partitions of an experimental pond in which amphibians were free to colonize.2. Adult bluegill had a major impact on the amphibian assemblage. By the end of the experiment, gray treefrog (Hyla versicolor) tadpoles were nine times less abundant, and red‐spotted newt (Notophthalmus viridescens) adults were three times less abundant in the presence of adult bluegill than in their absence. In contrast, bullfrog (Rana catesbeiana) tadpoles tended to increase in the presence of adult bluegill. Adult bluegill also had a negative effect on the abundance of predaceous aquatic insects.3. There was no indication that interactions among amphibians were significant in determining the above patterns. We suggest that the strong impact of adult bluegill resulted from a combination of direct and indirect effects on amphibian larvae and predaceous aquatic insects.

Ecological restructuring in experimental aquatic mesocosms due to the application of diflubenzuron

AbstractDiflubenzuron is a chitin‐inhibiting insecticide that is registered for use in controlling a multitude of invertebrate pests. The selective mode of action of diflubenzuron provided us with a unique tool for examining the indirect responses of an experimental aquatic ecosystem following direct impacts at the primary consumer (invertebrate) trophic level. Twelve outdoor aquatic mesocosms (0.1 ha each) were randomly assigned to three treatments of diflubenzuron (four mesocosms/treatment): control, monthly (five total 10‐μg/L applications), or biweekly (twice monthly; nine total 10‐μg/L applications). Direct impacts on invertebrates (numbers and species composition of insects and zooplankton) and indirect impacts on fish (mortality, growth, and reproduction of bluegill sunfish and largemouth bass), phytoplankton (biomass and productivity), and water quality were measured over 16 weeks posttreatment. Both monthly and biweekly treatments of diflubenzuron decreased total numbers (fivefold reduction) and species richness (twofold reduction) and increased dominance (twofold increase) of zooplankton within 4 weeks posttreatment; Cladocerans, Copepods, and Rotifers were all sensitive. Diflubenzuron reduced species richness of emergent insects, which resulted in increased dominance by a few species; however, impacts on emergent insects were confounded by a treatment × time interaction. Direct reductions in invertebrate grazers caused indirect increases in algal biomass. Indirect effects on biomass (50% reduction) and individual weight (50% reduction) of juvenile bluegill occurred because of apparent decreases in invertebrate food resources. No statistically significant impacts were observed on adult bluegill or largemouth bass for the duration of the experiment. Results indicated that diflubenzuron had both direct and indirect impacts on the experimental aquatic ecosystems under the conditions tested.

Effects of esfenvalerate on the reproductive success of the bluegill sunfish, Lepomis macrochirus in littoral enclosures.

Adult bluegills were exposed to the synthetic pyrethroid esfenvalerate, during a reproduction study conducted in six littoral enclosures located in a 2-ha pond near Duluth, Minnesota. Bluegill reproductive success was determined after two applications of esfenvalerate at nominal concentrations of 0.0, 0.01, 0.08, 0.20, 1. 0, and 5.0 microg/L. Responses measured were adult behavior and spawning, embryo hatchability, larval survival until swim-up, young-of-the-year (Y-O-Y) growth, and total biomass. All adult bluegills died within one day following the first application at 5.0 microg/L. Successful spawning and resulting hatching of offspring were observed at all esfenvalerate concentrations except 5.0 microg/L. Following exposure at 1.0 microg/L, spawning was delayed for 15 days and few or no larvae survived. Bluegill Y-O-Y growth was reduced by 62, 57, and 86% in the 0.08, 0.20, and 1.0 microg/L esfenvalerate treated enclosures. Delayed adult spawning and reduced Y-O-Y growth may result in poor Y-O-Y overwinter survival which would result in a diminished or extirpated year class.

Effects of Implanted Transmitters on Adult Bluegills at Two Temperatures

Abstract Laterally compressed panfishes are small and have limited intraperitoneal space; thus, they may suffer adversely from surgically implanted transmitters even if the transmitter meets the generally recommended ratio of transmitter weight to fish weight of 2%. We studied the effects of intraperitoneal transmitters (2.81 g) on survival, growth, healing, and health of bluegills Lepomis macrochirus (mean weight 133 g) held for 8 weeks at 6°C and 20°C. Radio-tagged bluegills at 20°C had a mortality rate of 10% and tag loss rate of 15%. At 6°C, bluegills had no mortality or tag loss. Radio-tagged and reference fish fed in both 20°C raceways; however, a few reference fish appeared dominant at feeding time. This dominance by a few reference fish was also indicated by a large weight gain for three reference fish in each 20°C raceway. At 6°C, neither reference fish nor radio-tagged fish fed activity. Radio-tagged fish held at 20°C exhibited pelvic fin erosion, erythema and necrosis at the antenna exit and at...

Effects of Azinphos-methyl on the Reproductive Success of the Bluegill Sunfish, Lepomis macrochirus, in Littoral Enclosures

Adult bluegills were exposed to a single application of azinphos-methyl in 12 littoral enclosures in a northern Minnesota pond. Responses measured were adult behavior and spawning, embryo hatchability, larval survival until swim-up, young-of-year (Y-O-Y) growth, and total biomass. Four enclosures each were treated at 1.0 and 4.0 μg/liter and four remained untreated. The half-life of azinphos-methyl was 2.3 and 2.4 days at each of the two treatment levels, respectively. Quantifiable residues remained in the water for 8 days. Concentrations of 4.0 or 1.0 μg/liter did not cause any significant long-term (63 day) effects on bluegill reproduction, embryo hatchability, larval survival, growth, or biomass. Although important bluegill prey such as copepod nauplii and cladocerans were significantly or greatly reduced by Day 7 following treatment, they recovered to levels equal to or greater than some of the control enclosures by Day 35. The apparent lack of significant long-term effects on reproductive success can be partially explained by the relatively short half-life of azinphos-methyl in littoral enclosures.

Effects of diflubenzuron on the reproductive success of the bluegill sunfish, Lepomis macrochirus

AbstractExposure to diflubenzuron concentrations of 2.5 μg/L reduced growth of young‐of‐the‐year (Y‐O‐Y) bluegill by 56 and 86% in replicate enclosures and by 88 and 97% at 30 μg/L. An adult bluegill reproduction study was conducted in six littoral enclosures located in a 2‐ha pond near Duluth, Minnesota. Decreased growth of Y‐O‐Y bluegill resulted from the reduction or elimination of preferred invertebrate prey items by diflubenzuron that led to different and/or less Y‐O‐Y food consumption. Adult bluegill behavior and spawning, embryo hatching, larval survival until swim‐up, and Y‐O‐Y biomass were also studied. Before the first two diflubenzuron applications, spawning occurred in all enclosures; following the first application, spawning occurred in both control enclosures and one 30‐μg/L enclosure. Successful embryo hatching and larval swim‐up occurred in all enclosures prior to the first application, and in one control and one 30‐μg/L enclosure following application. The Y‐O‐Y growth was the most sensitive end point, and Y‐O‐Y biomass was among the least sensitive end points for bluegill reproductive success. The Y‐O‐Y bluegills (and potentially other fish species) that are exposed to diflubenzuron concentrations of ≥2.5 μg/L may experience reduced growth, which can result in greater starvation, increased predation, reductions in over‐winter survival, and diminished to poor recruitment.