Male Bluegill Research Articles

Angling of hybrid sunfish from a hatchery pond with potential implications for community fisheries

Hatcheries are frequently called upon to produce catchable-sized fish for stocking community fishing ponds. Desirable attributes of fish selected for stocking into community ponds are that they are easy to produce in a hatchery system to sizes anglers are interested in catching and they provide anglers with high catch rates once stocked. Hybrid sunfish [male Bluegill (Lepomis macrochirus) × female Green Sunfish (L. cyanellus)] have attributes that potentially make them attractive for use in community fishing ponds. We assessed initial angler catch rates of 100 stocked hybrid sunfish in a 0.12-ha hatchery pond and after being subjected to angling (four, 1-hr catch-and-release fishing events with five anglers). We also investigated whether catch rates would change following a supplemental stocking of an additional 100 hybrid sunfish (four, 1-hr catch-and-release fishing events with five anglers). The anal fin of each fish in the second stocking was hole punched to differentiate them from those of the first stocking and fish caught by anglers were hole punched in the caudal fin each time they were caught before being released back into the pond. Angler catch rates were highest during initial fishing events that followed stocking (9.2 fish/angler hr and 18.0 fish/angler hr) and substantially declined in subsequent events (≤3.4 fish/angler hr). Catches of the newly stocked fish and previously stocked fish contributed to the high catch following the supplemental stocking. Most (80 %) of the fish were caught in the first 30 min of each event and 45 % were caught during the first 10 min. Anglers were able to catch 88 % of the fish from the first stocking and 67 % from the second stocking at least once. No mortality occurred during the study as all fish were recovered when the pond was drained. Our results suggest that hybrid sunfish will potentially provide high initial catch rates following stocking into community ponds, but managers should expect reduced catch rates following initial fishing even without harvest. Additional stocking will be needed to provide periodic increases in angler catch rates even without harvest.

Similarity at the major histocompatibility complex class II does not influence mating patterns in bluegill (Lepomis macrochirus)

In many species, individuals prefer mates that are genetically dissimilar at the major histocompatibility complex (MHC), likely because it improves offspring resistance to pathogens. Here, we provide the first characterization of the MHC class II peptide binding region in bluegill (Lepomis macrochirus) and examine its effect on mating patterns. We captured female and male bluegill during spawning and sequenced these fish at the MHC. We found strong evidence that positive selection promotes genetic diversity at the MHC in bluegill, with a 5:2 ratio of non-synonymous to synonymous mutations. However, we found no evidence that the MHC led to disassortative mating between females and parental males. Extra-pair mating and the presence of specialized cuckolder males may have an important, albeit still unresolved, role in shaping mating patterns at the MHC in bluegill. The immune genes of the MHC allow individuals to recognize and respond to pathogens. High sequence diversity at the MHC is thought to enable individuals to recognize a wider range of pathogens. In many animals, individuals select mates that have dissimilar MHC sequences, which can improve the immune function of their offspring. We provide the first characterization of the MHC class II gene in bluegill sunfish and show that selection appears to be increasing sequence diversity at this gene. However, we found no evidence that the MHC shapes mating patterns in this 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.

Contaminants reduce male contribution to reproduction at the population scale

In many populations, males compete for mates and contribute to genetic diversity, but are assumed to have little impact on population growth rates and density, because one father is all that is necessary to fertilize a large number of eggs and sire a potential cohort. A factor affecting male reproductive output is exposure to contaminants that either disrupt endocrine function or mimic hormones. Polychlorinated biphenyls (PCBs) persist in aquatic ecosystems and may interfere with the reproductive contribution of male fish to populations. We quantified 28 PCB congeners in adult male bluegills across eight Illinois lakes. In spring 2011 and 2012, mature male bluegills from lakes with conspecifics with PCB whole‐body residues ranging from undetectable to high (2,000 ng/g dry mass total PCBs) were placed in experimental ponds with mature females containing no detectable PCB body residues and allowed to reproduce in spring under natural conditions. The presence of PCBs in fish had no effect on the presence of intersex or other gonadal deformities in adult males nor was gonad size, lipid concentration, and survival affected. Males with high PCBs were heavier than those from lakes with low PCB concentrations. The relative density of juvenile bluegills produced in ponds by fall, a fitness endpoint in this species, was negatively related to contaminant concentration in fathers. Contaminant exposure and other factors that affect male reproduction may not only suppress the relative contribution of males to genetic diversity, but also the overall density of cohorts within populations.

Androgen effects on immune gene expression during parental care in bluegill sunfish (Lepomis macrochirus)

Reproductive efforts are energetically costly and often result in significant trade-offs with other metabolic processes. In many animals, androgens influence how this energy is allocated during the breeding period. In this study, androgen levels of parental bluegill sunfish (Lepomis macrochirus Rafinesque, 1819) were manipulated by implanting males with either 11-ketotestosterone (11-KT) or flutamide (an androgen receptor antagonist) shortly after spawning. Parental behaviours were assessed for 3 days after implantation. Differential brain gene expression between the two groups was examined using a 44 000 microarray gene chip. We found that 11-KT-implanted males exhibited lower levels of expression of genes related to immune function compared with flutamide-implanted males, suggesting that high androgen levels negatively affect the male immune system. These data thus indicate that a significant trade-off may exist between maintaining high levels of androgens and decreased immune function in parental male bluegill.

Alternative male reproductive tactics drive asymmetrical hybridization between sunfishes ( Lepomis spp.)

The potential role of alternative reproductive tactics in circumventing premating isolating mechanisms and driving hybridization between species has long been recognized, but to date there is little empirical support from natural systems. Hybridization occurs between bluegill (Lepomis macrochirus) and pumpkinseed sunfish (Lepomis gibbosus) and it is known to be asymmetrical (male bluegill × female pumpkinseed). Here, we test whether this pattern is driven by a recognition failure by pumpkinseed females or by an alternative cuckolder reproductive tactic in bluegill males. Using genetic parentage data, we found that bluegill cuckolders fathered 24.9% of the larvae in bluegill nests, but no evidence that pumpkinseed females spawned in bluegill nests. Pumpkinseed cuckolders fathered 8.7% of the larvae in pumpkinseed nests, whereas bluegill cuckolders fathered 13.6% of the larvae in those nests. Bluegill cuckolders thus frequently spawn in pumpkinseed nests and are responsible for the asymmetrical hybridization between the species. We discuss the evolutionary consequences of interactions between bluegill and pumpkinseed and the role of alternative reproductive tactics in adaptation and introgression.

Hybridization in Sunfish Influences the Muscle Metabolic Phenotype

Hybridization has the potential to exert pleiotropic effects on metabolism. Effects on mitochondrial enzymes may arise through incompatibilities in nuclear- and mitochondrial-encoded subunits of the enzyme complexes of oxidative phosphorylation. We explored the metabolic phenotype of bluegill (Lepomis macrochirus), pumpkinseed (Lepomis gibbosus), and their unidirectional F(1) hybrids (male bluegill × female pumpkinseed). In hybrids, glycolytic enzyme activities were indistinguishable from (aldolase, pyruvate kinase) or intermediate to (lactate dehydrogenase, phosphoglucoisomerase) parentals, but complex IV activities aligned with pumpkinseed, both 30% lower than bluegill. In isolated mitochondria, the specific activities of complexes I, II, and V were indistinguishable between groups. However, both complex III and IV showed indications of depressed activities in hybrid mitochondria, though no effects on mitochondrial state 3 or state 4 respiration were apparent. The patterns in complex IV activities were due to differences in enzyme content rather than enzyme V(max); immunoblots comparing complex IV content with catalytic activity were indistinguishable between groups. The sequence differences in complex IV catalytic subunits (CO1, CO2, CO3) were minor in nature; however, the mtDNA-encoded subunit of complex III (cytochrome b) showed eight differences between bluegill and pumpkinseed, several of which could have structural consequences to the multimeric enzyme, contributing to the depressed complex III catalytic activity in hybrids.

Nest‐site fidelity in parental male bluegill Lepomis macrochirus: spatial patterns and the influence of prior mating success

A 4 year mark-recapture study examined the pattern of nesting site fidelity of parental-type male bluegill Lepomis macrochirus. The study results indicated that iteroparous male L. macrochirus choose new nest sites near their own previously used sites. The scale of site fidelity varied, but generally males choose to renest within shoreline areas rather than specific or exact nest locations (94% within-year, 86% among-years). Iteroparous males also displayed no preference to nest in proximity to neighbouring males from previous colonies to suggest social fidelity. Contrary to expectation, manipulating males' reproductive success had no significant effect on the pattern or scale of male reproductive site fidelity.

Establishment of Mostly Male Groups of Bluegills by Grading Selection and Evaluation of their Growth Performance

AbstractConcerns over the economic feasibility of commercial aquaculture production of bluegills Lepomis macrochirus have heightened the need for strategies to enhance growth. Recent studies have shown that individually reared bluegill males can grow twice as fast as females; such studies have generated increased interest in development of mostly male or all‐male populations. In this study, we developed a practical procedure to establish mostly male bluegill groups through grading selection and we tested their growth against that of a normal population. A single cohort of bluegill juveniles was cultured in a pond for 1 year; when the fish reached a mean weight of 30.1 g, the cohort was graded and divided into two mostly male groups (top 25% and top 50% of fish by total length) and a mixed‐sex control group. The percentage of males in each group was as follows: 50.0% in the mixed control group, 75.4% in the top 25% group, and 69.7% in the top 50% group. Weight gain per fish in the top 25% group was significantly greater (P < 0.05) than that in the mixed group throughout most of the experiment. There were no significant differences detected in survival among the three groups, although the top 25% group had survival of 96.0% compared with 90.6% and 90.5% for the top 50% group and the mixed control group, respectively. The top 25% group had the highest percentage (46.3%) of fish reaching 150 g at the end of the experiment, followed by the top 50% group (28.3%), and the mixed control group (12.7%). The coefficient of variation (CV) for weight decreased in all three groups over time; the mostly male groups maintained lower initial and final CV values than did the mixed control group. Results indicate that mostly male bluegill groups are able to grow faster than typical mixed‐sex populations, and social interaction costs among communally reared males did not significantly decrease growth of mostly male populations in the aquaculture settings.

Paternity, parental behavior and circulating steroid hormone concentrations in nest-tending male bluegill

Like many teleost fishes, bluegill ( Lepomis macrochirus) are characterized by sole male parental care of offspring. In addition, bluegill parental males experience cuckoldry by specialized parasitic male morphs. This cuckoldry has previously been shown to influence the expression of parental care behavior. To better understand some of the proximate mechanisms mediating parental behavior, we examined the relationships between circulating steroid hormones, paternity, and parental behavior during the egg and fry stages of care in parentals that spawned during the first third of the breeding season. During the egg stage of care, we found that males with higher paternity had lower levels of testosterone, but there was no relationship between paternity and either 11-ketotestosterone or cortisol. There also was no relationship between the hormones and care behavior comprising fanning of the eggs, nest rim circles, chases of brood predators, or pecking at the eggs (indicative of egg cannibalism), except for a negative relationship between cortisol and pecking behavior. During the fry stage of care, we conversely found that males with higher paternity had higher levels of testosterone and 11-ketotestosterone. There also was a negative relationship between the concentrations of these two androgens and the defensive behavior of males when exposed to a potential brood predator (a pumpkinseed, Lepomis gibbosus). We discuss these results in relation to previous work in fishes and other vertebrate taxa. Overall, our data suggest a complex relationship between circulating steroid hormone levels, paternity and parental behavior.

Examining Interpopulation Variation in Bluegill Growth Rates and Size Structure: Effects of Harvest, Maturation, and Environmental Variables

AbstractUnderstanding how life history variation and the environment affect growth and population size structure is an important theme of fisheries ecology. However, the interactions among important biotic and abiotic factors and their relative importance in the context of population‐specific variation are seldom considered. We used an information theoretic approach to investigate how environmental variables interact with important life history parameters to influence population size structure of bluegills Lepomis macrochirus. We sampled bluegill populations in 23 Illinois reservoirs to examine the effects of temperature, water transparency, and prey availability and bluegill density, harvest, and size at maturation on bluegill growth and population size structure. Good growth and large body size were associated with warm, clear lakes containing abundant prey resources. An exception to this pattern was early growth (length at age 2): Larger body size at age 2 was associated with relatively low Secchi depth (i.e., turbid water). In addition, size at maturation was positively related to size of adult male bluegills. Interestingly, bluegill density and harvest mortality—factors that are often considered important within populations—did not contribute much explanatory power to our among‐system models. Whereas harvest and density‐dependent growth have been shown to influence individual bluegill populations, their effects across a range of populations appear to be mitigated by temperature, water transparency, and prey availability. Although growth of individuals can be influenced by a variety of factors, our investigation suggests that fairly straightforward mechanisms at broader spatial scales are responsible for explaining variation among populations.

Temporal variation in cuckoldry and paternity in two sunfish species (Lepomis spp.) with alternative reproductive tactics

Male alternative reproductive tactics have been described in many mating systems. In fishes, these tactics typically involve a territorial male that defends a spawning site or nest and a parasitic male that uses sneaking or female mimicry to steal fertilizations from the territorial male. In this paper, we use molecular genetic markers to examine the success of males that adopt alternative reproductive tactics in two sunfishes, comprising the bluegill ( Lepomis macrochirus Rafinesque, 1819) and the pumpkinseed ( Lepomis gibbosus (L., 1758)). In sunfishes, the tactics are referred to as parental (territorial male) and cuckolder (parasitic male). We show that cuckoldry rates peak in the second trimester of the breeding season in bluegill, whereas cuckoldry rates are lowest during this period in pumpkinseed. We also show that paternity of parental male bluegill is positively correlated with body condition, but not body length or mass. No relationship between these phenotypic variables and paternity in pumpkinseed was found. We discuss the patterns of cuckoldry in relation to differences between the species in mating opportunities, parental male defence ability, and cuckolder density. Finally, we discuss how the paternity data can be used to differentiate between two mechanisms underlying the expression of alternative reproductive tactics, comprising the condition strategy and alternative strategies.

Rearing Male Bluegills Indoors May Be Advantageous for Producing Food‐size Sunfish

Abstract.— An indicated demand for sunfish (Lepomis spp.) as a food fish remains untested because of continuing inability to efficiently rear these fishes to required large sizes (≥227 g; 0.5 lbs). A recent study involving parallel, indoor rearing of two sunfishes under favorable conditions showed that bluegills Lepomis macrochirus possessed markedly higher growth capacity than B × G hybrids (F1: male bluegill × female green sunfish, Lepomis cyanellus). B × G hybrids had been thought to possess superior growth capacity and so have received more attention than bluegills as a food‐fish candidate in many areas of the USA. Reanalysis of data from the recent study with emphasis on gender differences revealed that the male bluegills possessed much higher growth capacity than male B × G hybrids, at least from May to March as Age 1 and then early Age 2 fish. Male bluegills reached 67% of food‐market weight within the 10‐mo period from a starting weight of 7 g; male B × G hybrids reached only 24% of this weight. Male bluegills’ more rapid growth versus male B × G hybrids’ apparently involved less growth energy allocation to gonad development. Female bluegills grew slower than male bluegills but also outgrew male and female B × G hybrids whose growth trajectories declined in midsummer (June) and remained largely flat through March. The previous view that B × G hybrids possess higher growth capacity than bluegills was fostered by studies in ponds where bluegill growth can be impeded by high reproduction rates and, as this study reveals, by high densities and exposure to suboptimal temperatures when their growth potential is high. Indoor rearing of male bluegills should ameliorate most pond‐related growth impediments and take fuller advantage of their rapid growth capacity.

Effects of Increased Feeding Frequency on Growth of Hybrid Bluegill in Ponds

AbstractIncreased feeding frequency has been used in aquaculture to increase growth and food conversion efficiency, and recent laboratory studies have indicated that feeding frequency could be used to reduce the size variation within groups of hybrid bluegills (F1: Male bluegill Lepomis macrochirus × female green sunfish L. cyanellus). Our experiment evaluated the growth of pond‐reared hybrid bluegills fed equal amounts of food either once or four times per day. We were particularly interested in reducing the size variation and increasing the percentage of harvestable‐size fish (≥110 g). After 194 d, there was no significant effect of feeding frequency on growth, food conversion efficiency, size variation, or percentage of harvestable‐size fish.

Relationships among steroid hormones, body size, paternity, and parental care behaviors in male bluegill sunfish

Relationships among steroid hormones, body size, paternity, and parental care behaviors in male bluegill sunfish

Condition‐dependent nesting in bluegill sunfish Lepomis macrochirus

1. There are two prominent, nonmutually exclusive hypotheses to explain the timing of reproduction in animals: energetic constraint and adaptive behaviour. 2. We tested these hypotheses by quantifying the costs and benefits of nesting at different times in the season for male bluegill sunfish Lepomis macrochirus, a species with paternal care, in Lake Opinicon (Ontario, Canada). 3. The value of nesting at different times during the breeding season (RSb) was determined from spawning individuals as RSb = Pb x Cb x Sb x Ob, where Pb is the probability of spawning during each bout b, Cb is the expected brood size, Sb is the expected brood survivorship to 'swim-up', and Ob is the survivorship of free-swimming fry to age 1 year. 4. The results show that the value of nesting peaks during the middle of the season. However, nesting patterns varied with male condition and not all males nested at the peak. 5. Larger males, which were able to nest multiple times, first nested early in the season when overwinter survivorship of offspring and renesting opportunities later in the season were maximized. These males had the highest seasonal reproductive success. 6. Smaller males, which nested a single time, delayed nesting until the middle of the season when spawning opportunities and brood sizes were greatest. 7. These data suggest that both energetics and adaptive behaviour play roles in determining the timing of reproduction.

Plasma levels of androgens and cortisol in relation to breeding behavior in parental male bluegill sunfish, Lepomis macrochirus

Like many teleosts, male bluegill sunfish ( Lepomis macrochirus) provide sole parental care. To understand some of the proximate costs of parental care, we measured body condition and plasma levels of testosterone (T), 11-ketotestosterone (11KT) and cortisol in nesting bluegill males during pre-spawning, spawning and parental care stages. T and 11KT were at their highest mean levels during the pre-spawning period and decreased to lower levels early during the parental care period before rising again when the eggs hatched. Cortisol levels fluctuated across the breeding stages, but there was a noticeable increase from low levels on the day of spawning during the first 2 days of parental care when egg fanning is most intense. Levels of all hormones varied considerably among males, with androgen levels often correlating positively with a male's body condition. We also demonstrate, using a brood reduction experiment and repeated sampling of known individuals, that the presence of eggs affects hormone levels shortly after eggs hatch. Parental males in better body condition had higher levels of androgens during parental care. Males that were known to renest later in the season also had higher androgen levels and were in better body condition during the first nesting bout than males only known to have nested once. However, circulating levels of cortisol did not differ significantly between these groups. We discuss our findings in the context of proximate and ultimate costs of parental care and propose several reasons why elevated androgen levels may not be as incompatible with the expression of paternal care in male teleosts, as compared with avian and mammalian fathers.

Improvement of Bioenergetics Model Predictions for Fish Undergoing Compensatory Growth

AbstractA previous evaluation of a bioenergetics model applied to juvenile hybrid sunfish (F1 hybrid of female green sunfish Lepomis cyanellus × male bluegill L. macrochirus) undergoing compensatory growth (CG) indicated that the model substantially overestimated growth and underestimated cumulative consumption. This result suggested that fish bioenergetics models might not adequately account for physiological shifts that occur during CG. However, we demonstrate that application of a recently developed procedure for correcting consumption‐ and growth‐rate‐dependent systematic errors common among bioenergetics models negates much of the predictive error that had been attributed to the physiological complexities of CG. Correction equations for estimating the model‐relative growth rate error (predicted less observed; g · g−1 · d−1) from the observed mean daily consumption rate (g · g−1 · d−1) and the consumption rate error (predicted less observed; g · g−1 · d−1) from the observed relative growth rate (g · g−1 · d−1) were derived by applying linear regression analysis to data from individual hybrid sunfish not undergoing CG. These independently generated correction equations significantly improved model predictions of growth and cumulative consumption for three groups of fish undergoing CG at one temperature near their growth optimum. The findings indicate that the high consumption and growth rates characteristic of fish undergoing CG merely amplify the consumption‐ and growth‐rate‐dependent errors inherent in bioenergetics models and that model predictions for fish undergoing CG can be significantly improved through application of the correction procedure.

Fertilization dynamics of sperm from different male mating tactics in bluegill (Lepomis macrochirus)

Sperm competition results in the evolution of ejaculate characteristics such as high sperm density, high motility, and fast sperm swimming speed. A fundamental assumption of sperm competition theory is that ejaculates with high motility and fast-swimming sperm have an advantage with respect to fertilization success. We tested this assumption by studying the fertilization dynamics of alternative mating tactics (cuckolders and parentals) of male bluegill (Lepomis macrochirus Rafinesque, 1819). Sneakers (cuckolders) have faster swimming sperm and a higher proportion of motile sperm immediately following sperm activation than do parentals; however, these variables decline more quickly over time in sneaker sperm than in the sperm of parental males. We used a controlled fertilization experiment to test the prediction that parental males will have higher fertilization success than sneakers late in the sperm activation cycle because of the reduced rate of decline in ejaculate quality over time. We found that as the time from sperm activation increases parental sperm fertilizes more eggs than the sperm of sneakers. Our results support the idea that fertilization success is higher when ejaculates contain a higher proportion of either motile sperm or faster swimming sperm, all else being equal. In addition, after controlling for time from sperm activation, we found a significant bias in fertilization success toward parental males, suggesting that cryptic female choice might play a role in fertilization dynamics.

Motility, ATP levels and metabolic enzyme activity of sperm from bluegill ( Lepomis macrochirus)

Male bluegill displays one of two life history tactics. Some males (termed “parentals”) delay reproduction until ca. 7 years of age, at which time they build nests and actively courts females. Others mature precociously (sneakers) and obtain fertilizations by cuckolding parental males. In the current study, we studied the relations among sperm motility, ATP levels, and metabolic enzyme activity in parental and sneaker bluegill. In both reproductive tactics, sperm swimming speed and ATP levels declined in parallel over the first 60 s of motility. Although sneaker sperm initially had higher ATP levels than parental sperm, by ∼30 s postactivation, no differences existed between tactics. No differences were noted between tactics in swimming speed, percent motility, or the activities of key metabolic enzymes, although sperm from parentals had a higher ratio of creatine phosphokinase (CPK) to citrate synthase (CS). In both tactics, with increasing CPK and CS activity, sperm ATP levels increased at 20 s postactivation, suggesting that capacities for phosphocreatine hydrolysis and aerobic metabolism may influence interindividual variation in rates of ATP depletion. Nonetheless, there was no relation between sperm ATP levels and either swimming speed or percent of sperm that were motile. This suggests that interindividual variation in ATP levels may not be the primary determinant of variation in sperm swimming performance in bluegill.