Size-specific growth of bluegill, largemouth bass and channel catfish in relation to prey availability and limnological variables

Growth of sympatric populations of three important sport fish species: bluegill Lepomis macrochirus , largemouth bass Micropterus salmoides and channel catfish Ictalurus punctatus , in 14 Illinois reservoirs was assessed in an attempt to relate size-specific growth to environmental conditions. Multiple regression relationships for most species and size classes explained a large percentage of the variation in growth. Growth of small bluegill (50 mm total length, L _T) showed a strong negative relationship with bluegill catch per unit effort (cpue), per cent littoral area and pH. Large bluegill (150 mm L _T) growth was negatively related to Daphnia spp. and benthic macroinvertebrate abundance and lake volume, and positively related to bluegill cpue. Growth of small (100 mm L _T) and large (250 mm L _T) largemouth bass was not well explained by any of the measured variables. Growth of both small (300 mm L _T) and large (450 mm L _T) channel catfish was strongly positively related to forage fishes and ichthyoplankton abundance, and per cent littoral area while negatively related to benthic macroinvertebrates. By identifying environmental conditions associated with increased growth rates, these models provide direction for managing fish populations and suggest testable hypotheses for future study of the complex interactions between environmental conditions and growth.     

Patterns of Fish Growth along a Residential Development Gradient in North Temperate Lakes

Residential development of lakeshores is expected to change a variety of key lake features that include increased nutrient loading, increased invasion rate of nonnative species, increased exploitation rates of fishes by anglers, and alteration of littoral habitats. All of these factors may alter the capacity of lakes to support productive native fish populations. Fourteen north temperate lakes were surveyed to examine how growth rates of two common fish species (bluegill sunfish, Lepomis macrochirus; largemouth bass, Micropterus salmoides) varied along a residential development gradient. Size-specific growth rates for both species were negatively correlated with the degree of lakeshore residential development, although this trend was not statistically significant for largemouth bass. On average, annual growth rates for bluegill sunfish were 2.6 times lower in heavily developed lakes than in undeveloped lakes. This effect of lakeshore development on fish growth was not size specific for bluegills between 60 and 140 mm in total length. An index of population production rate that accounted for both the size-specific growth rate and the size distribution of fishes showed that bluegill populations were approximately 2.3 times less productive in highly developed lakes than in undeveloped lakes. Our results suggest that extensive residential development of lakeshores may reduce the fish production capacity of aquatic ecosystems. Received 29 April 1999; Accepted 26 October 1999.     

Predator-prey interactions in size-structured fish communities: implications of prey growth

Predator-prey interactions among size-structured populations may be strongly influenced by factors which affect growth rates of prey. I examined the importance of prey growth in the interaction between large-mouth bass (Micropterus salmoides) and their prey, bluegill (Lepomis macrochirus), by analyzing diets and growth rates of bass in a set of seven lakes in south-central Wisconsin. Sizes of bluegill consumed by bass changed dramatically across a gradient of bluegill growth, which resulted in differing patterns of bass growth. In lakes with slow bluegill growth, small bass fed on the youngest bluegill cohort, but large bass were capable of feeding on several age classes. Consequently, bass growth rates were strongly size-dependent; small bass ate small prey and had low growth, but growth rates increased substantially with size as bass ate progressively larger prey. When bluegill had high growth rates, they quickly reached a size refuge from predation and bass of all sizes were restricted to feeding on the youngest/smallest prey. In these lakes, bass growth rates were more uniform across bass sizes. Because growth rates influence population size-distributions, variation in bluegill growth can have strong effects on the structure of bass populations. These effects could potentially feed back to further influence the interaction between predator and prey.     

Variation in growth and age at maturity in bluegill sunfish: genetic or environmental effects?

Populations of bluegill sunfish Lepomis macrochirus , experiencing heavy juvenile predation, showed increased growth rates and increased age and size at maturity relative to populations experiencing decreased predation on juveniles but increased predation on adults. This study examined bluegills experimentally from both types of populations and a cross between them in a common environment to determine if variation in growth and age at maturity is genetically or environmentally induced. Two factorial experiments, varying strain of bluegills and resource availability, were used to evaluate differences in growth rate. One experiment, varying strain of bluegills, was used to assess differences in age at maturity. Growth was strongly influenced by resource level, but growth rate did not vary among populations. Nearly all bluegills in each population matured at 1 year of age in a common environment. Thus, variation observed in source populations must be mostly attributable to differences in the environment between populations. At least three factors could potentially cause differences in growth and age at maturity: (1) variation in resource availability; (2) variation in demographic structure; and (3) variation in size-specific mortality rates caused by differences in predator abundance between populations. Observed patterns of variation between populations are best explained by effects of differences in predator populations.     

Intra- and inter-specific variation in metabolic gene expression in relationship to environmental hypoxia

In this study, we explored how environmental oxygen levels affect the metabolic phenotype of sympatric sunfish known to differ in their hypoxia tolerance. We examined bluegill (Lepomis macrochirus) and pumpkinseed (Lepomis gibbosus), two species commonly found in the same water bodies, though pumpkinseed are considered more hypoxia tolerant, and survive in hypoxic lakes that exclude bluegill. Freshly caught Lake Opinicon pumpkinseed possessed significantly higher glycolytic enzyme activities (PGI, ALD, GAPDH, ENO, and LDH) than bluegill, but after holding the fish in an oxygenated environment for 7days, pumpkinseed glycolytic enzymes (PGI, ALD, and LDH) and mRNA (LDHA and HIF1α) declined to bluegill's levels. When glycolytic enzymes and mRNA were compared in pumpkinseed populations from seven lakes, only Penyck Lake pumpkinseed had significantly elevated glycolytic enzyme activity that did not diminish with normoxic holding. The levels of mRNA for LDHA and HIF1α did not differ between lakes and did not change in response to normoxic holding in the Penyck Lake fish. Collectively, these studies on sunfish show that hypoxia tolerance contributes to ecological niche specialization between species, and provides an example of a population that has adapted chronically elevated glycolytic enzyme activity independent of current dissolved oxygen in the water.     

Influence of intra‐ and interspecific variation in predator–prey body size ratios on trophic interaction strengths

1. Predation is a pervasive force that structures food webs and directly influences ecosystem functioning. The relative body sizes of predators and prey may be an important determinant of interaction strengths. However, studies quantifying the combined influence of intra‐ and interspecific variation in predator–prey body size ratios are lacking.
2. We use a comparative functional response approach to examine interaction strengths between three size classes of invasive bluegill and largemouth bass toward three scaled size classes of their tilapia prey. We then quantify the influence of intra‐ and interspecific predator–prey body mass ratios on the scaling of attack rates and handling times.
3. Type II functional responses were displayed by both predators across all predator and prey size classes. Largemouth bass consumed more than bluegill at small and intermediate predator size classes, while large predators of both species were more similar. Small prey were most vulnerable overall; however, differential attack rates among prey were emergent across predator sizes. For both bluegill and largemouth bass, small predators exhibited higher attack rates toward small and intermediate prey sizes, while larger predators exhibited greater attack rates toward large prey. Conversely, handling times increased with prey size, with small bluegill exhibiting particularly low feeding rates toward medium–large prey types. Attack rates for both predators peaked unimodally at intermediate predator–prey body mass ratios, while handling times generally shortened across increasing body mass ratios.
4. We thus demonstrate effects of body size ratios on predator–prey interaction strengths between key fish species, with attack rates and handling times dependent on the relative sizes of predator–prey participants.
5. Considerations for intra‐ and interspecific body size ratio effects are critical for predicting the strengths of interactions within ecosystems and may drive differential ecological impacts among invasive species as size ratios shift.

     

Mitochondrial and Nuclear Gene Dynamics of Introduced Populations of Lepomis Macrochirus

A population of bluegill sunfish, Lepomis macrochirus, was introduced into three man-made ponds in 1966. Analyses of these ponds in 1984 and 1985 found significant mtDNA divergence without nuclear gene differentiation. The difference between nuclear gene and mtDNA measures of interpopulational divergence was very large and suggests that sexual asymmetries in life histories may be important considerations in mtDNA and nuclear gene rates of divergence. The rapid divergence of mtDNA haplotype frequencies suggests that sorting of previously existing variation may accelerate mtDNA divergence among recently isolated populations.     

Examination of the effects of largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus) on the ecosystem attributes of lake Kawahara-oike,Nagasaki, Japan

The introduction of largemouth bass (Micropterus salmoides) and bluegill sunfish (Lepomis macrochirus) into the freshwater ecosystems of Japan has resulted in the suppression and/or replacement of native species, generating considerable concerns among resource managers. The impacts of largemouth bass and bluegill on native fauna have been examined in aquaria and isolated farm ponds, but there is limited work examining the likelihood to fundamentally modifying Japan's lakes. The objective of the present study is to examine the direct and synergistic ecological effects of largemouth bass and bluegill on the biotic communities of Lake Kawahara-oike, Nagasaki, Japan, using an ecosystem (Ecopath) modeling approach. Specifically, we examine whether the two fish species have played a critical role in shaping the trophodynamics of the lake. We attempt to shed light on the trophic interactions between largemouth bass and bluegill and subsequently evaluate to what extent these interactions facilitate their establishment at the expense of native species. We also examine how these changes propagate through the Lake Kawahara-oike food web. Our study suggests that the introduction of bluegill has induced a range of changes at multiple trophic levels. The present analysis also provides evidence that largemouth bass was unable to exert significant top-down control on the growth rates of the bluegill population. Largemouth bass and bluegill appear to prevail over the native fish species populations and can apparently coexist in large numbers in invaded lakes. Future management strategies controlling invasive species are urgently required, if the integrity of native Japanese fish communities is to be protected.     

Contrasting growth strategies of pond versus marine populations of nine-spined stickleback (Pungitius pungitius): a combined effect of predation and competition?

Gigantism in isolated ponds in the absence of sympatric fish species has previously been observed in nine-spined sticklebacks (Pungitius pungitius). Patterns in sexual size dimorphism suggested that fecundity selection acting on females might be responsible for the phenomenon. However, the growth strategy behind gigantism in pond sticklebacks has not been studied yet. Here, we compared von Bertalanffy growth parameters of four independent nine-spined stickleback populations reared in a common laboratory environment: two coastal marine (typical size) and two pond (giant size) populations. We found that both pond populations had larger estimated final size than marine populations, which in turn exhibited higher intrinsic growth rates than the pond populations. Female growth strategies were more divergent among marine and pond populations than those of males. Asymptotic body size and intrinsic growth rate were strongly negatively correlated. Hence, pond versus marine populations exhibited different growth strategies along a continuum. Our data suggest that quick maturation—even with the cost of being small (low fecundity)—is favoured in marine environments. On the contrary, growth to a giant final size (high fecundity)—even if it entails extended growth period—is favoured in ponds. We suggest that the absence (ponds) versus presence (marine environment) of sympatric predatory fish species, and the consequent change in the importance of intraspecific competition are responsible for the divergence in growth strategies. The sex-dependence of the patterns further emphasizes the role of females in the body size divergence in the species. Possible alternative hypotheses are also discussed.     

Predator-induced delayed maturity in bluegill sunfish (Lepomis macrochirus): variation among populations

Previous studies suggested that differences in age at maturity among populations of bluegill sunfish (Lepomis macrochirus) were not genetically based, but rather were a phenotypic response to the presence of predators. I conducted two experiments to determine if the presence of largemouth bass affected age at maturity in bluegill sunfish. Bluegills from three populations were tested to see if the response to the threat of predation varied among source populations. Juvenile bluegills were maintained in the presence of predators or in controls with no contact with predators. Refuge use and growth were monitored during the experiments and reproductive activity was evaluated when bluegills reached age 1. Bluegills from one population exhibited delayed maturity in the presence of predators. Individuals from the other two populations showed no significant differences between predator and control treatments. The population that responded to the presence of predators had a history of high predation levels over the past 30–40 years. The other populations had a history of low levels of predation. This study suggests that presence of predators can induce phenotypic shifts in age at maturity of bluegills, but that the magnitude of response varies among populations in a manner consistent with historical patterns of coexistence. Received: 7 August 1996 / Accepted: 8 August 1997     

Scale strength as a cost of rapid growth in sunfish

Comparisons among populations have revealed adaptive variation in growth rate within several species. However, theoretical models suggest that a cost to rapid growth must exist in order to explain why some populations grow slowly. Based on previous work with development of the cranial skeleton in pumpkinseed sunfish, we proposed that rapid growth may compromise the strength of all skeletal elements in vertebrates. Using pumpkinseed from six populations known to differ in their intrinsic growth rates, we correlated strength of scales, in terms of resistance to penetration, with individual growth rate. We found a negative correlation that was consistent both within and among populations. This trade-off between growth rate and scale strength may have fitness consequences in terms of likelihood of surviving predation attempts or swimming efficiency.     

Reproductive investment and somatic growth rates in longear sunfish

Synopsis Allocation of energy to current reproduction at the expense of other functions, such as growth, can limit future reproductive potential. This cost of reproduction is a central concept of life history theory but has been difficult to verify in comparative field studies. Three levels of comparison of growth rates and reproductive investments were evaluated within and among populations of longear sunfish,Lepomis megalotis. All three demonstrated high levels of reproductive investment associated with reduced somatic growth. Within populations of central longear sunfish there are precociously mature sneaker makes and later maturing parental makes; sneakers have greater gonadosomatic index (GSI) values and slower somatic growth rates than parental makes. Between subspecies of longear sunfish grown under common conditions, there are differences in age at maturity and in the level of physiological reproductive investment that are associated with distinct differences in growth rates. Between populations of central longear sunfish inhabiting different sites, there are differences in the level of reproductive investment that are also associated with differences in somatic growth. Each comparison produced evidence that trade-offs occur between these life history traits, supporting the hypothesis that there is a cost of reproduction among male sunfish and suggesting that differences in strategies of reproductive investment contribute to variation in somatic growth.     

Analyzing nested variation in the body form of Lepomid sunfishes

Phylogenetic hierarchies are often composed of younger diverging lineages nested within older diverging lineages. Comparing phenotypic variation among several hierarchical levels can be used to test hypotheses about selection, phenotypic evolution and speciation. Such hierarchical comparisons have only been performed in threespine stickleback, and so here we use a hierarchical pattern of divergences between near-shore littoral and off-shore pelagic habitats to test for selection on the evolution of body form in Lepomis sunfish in lakes. We compare variation in external body form between fish from littoral and pelagic habitats at three levels: among ecomorphs within individual lake populations (intrapopulation), among populations of the same species in different lakes (interpopulation), and between bluegill and pumpkinseed sunfish species (interspecifically). Using geometric morphometric methods, we first demonstrate that interpopulation variation in mean body form of pumpkinseed sunfish varies with the presence of pelagic habitat. We then incorporate these results with existing data in order to test the similarity of phenotypic divergence between littoral and pelagic habitats at different hierarchical levels. Parallel relationships between certain body form traits (head length, caudal length and pectoral length) and habitat occur at all three levels suggesting that selection persistently acts at all levels to diversify these traits and so may contribute to species formation. For other traits (caudal depth and pectoral altitude), divergence between habitats is inconsistent at different hierarchical levels. Thus, nested biological variation in Lepomid body form reflects a history of deterministic selection and historical contingency, and also identifies traits that likely have likely influenced fitness and so serve important functions.     

Ontogenetic diet shifts produce trade‐offs in elemental imbalance in bluegill sunfish

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Sympatric Divergence and Performance Trade-Offs of Bluegill Ecomorphs

Phenotypic plasticity in response to environmental cues can create distinct morphological types within populations. This variation in form, and potentially function, may be a factor in initiating population divergence and the formation of new species. Here we show the translation of sympatric, habitat-specific morphological divergence into performance differences in energy economy, maneuverability and steady-state locomotion. Littoral and pelagic bluegill sunfish ecomorphs show differences in performance that appear adaptive within their respective habitats: greater maneuverability in the heavily vegetated littoral; greater steady-state swimming speed and economy in the open-water pelagic. This represents a trade-off in unsteady versus steady swimming performance, likely because morphological features associated with maximizing maneuverability are incompatible with enhancing steady-swimming performance. This may constrain the direction of adaptive change, maintaining the divergence created by phenotypic plasticity. The combination of habitat specific sympatric adaptation and constraints imposed by performance trade-offs may be an important factor underlying the high rate of speciation in freshwater fishes from post-glacial lakes.     

Orientation behaviour of Lepomis macrochirus Rafinesque to salinity fluctuations

The impact of the rate of salinity change has never been studied in primary freshwater fish occupying oligohaline marshes, where they are near their upper physiological limits. We conducted experiments on the bluegill sunfish, Lepomis macrochirus Rafinesque, to examine their orientation to salinity changes under winter temperature and photoperiod. We found significant difference in behavioural responses to rates of salinity change. The responses to the two flow rate changes indicate orthokinesis for ± 1.0‰ and −12.0‰ change h ⁻¹ treatments; however, a 'closure' type of response is apparent during +12.0‰ change h ⁻¹ treatment. These results indicate that bluegill sunfish respond behaviourally to salinity change, but reduce all overt activity when rate changes are unnatural and potentially lethal. It is apparent that behavioural and physiological responses are synergistic when the salinity exceeds a critical rate of change, which presumably is based upon the species' recent acclimatization history. Moreover, an orthokinetic response to the rate of salinity change may allow bluegill sunfish to move into and out of oligohaline marshes.     

Life history constraints explain negative relationship between fish productivity and dissolved organic carbon in lakes

Resource availability constrains the life history strategies available to organisms and may thereby limit population growth rates and productivity. We used this conceptual framework to explore the mechanisms driving recently reported negative relationships between fish productivity and dissolved organic carbon (DOC) concentrations in lakes. We studied populations of bluegill (Lepomis macrochirus) in a set of lakes with DOC concentrations ranging from 3 to 24 mg/L; previous work has demonstrated that primary and secondary productivity of food webs is negatively related to DOC concentration across this gradient. For each population, we quantified individual growth rate, age at maturity, age‐specific fecundity, maximum age, length‐weight and length‐egg size relationships, and other life history characteristics. We observed a strong negative relationship between maximum size and DOC concentration; for instance, fish reached masses of 150 to 260 g in low‐DOC lakes but <120 g in high‐DOC lakes. Relationships between fecundity and length, and between egg size and length, were constant across the DOC gradient. Because fish in high‐DOC lakes reached smaller sizes but had similar fecundity and egg size at a given size, their total lifetime fecundity was as much as two orders of magnitude lower than fish in low‐DOC lakes. High DOC concentrations appeared to constrain the range of bluegill life history strategies available; populations in high‐DOC lakes always had low initial growth rates and high ages at maturity, whereas populations in low‐DOC showed higher variability in these traits. This was also the case for the intrinsic rates of natural increase of these populations, which were always low at the high end of the DOC gradient. The potentially lower capacity for fish populations in high‐DOC lakes to recover from exploitation has clear implications for the sustainable management of recreational fisheries in the face of considerable spatial heterogeneity and ongoing temporal change in lake DOC concentrations.     

The effects of intraspecific competition on the prey capture behavior and kinematics of the bluegill sunfish, Lepomis macrochirus

Competition has broad effects on fish and specifically the effects of competition on the prey capture kinematics and behavior are important for the assessment of future prey capture studies in bony fishes. Prey capture kinematics and behavior in bony fishes have been shown to be affected by temperature and satiation. The densities at which bony fish are kept have also been shown to affect their growth, behavior, prey selection, feeding and physiology. We investigated how density induced intraspecific competition for food affects the prey capture kinematics of juvenile bluegill sunfish, Lepomis macrochirus. High speed video was utilized to film five bold individuals feeding at three different densities representing different levels of intraspecific competition. We hypothesized that: (1) the feeding kinematics will be faster at higher levels of competition compared to lower levels of competition, and (2) bluegill should shift from more suction-based feeding towards more ram-based feeding with increasing levels of competition in order to outcompete conspecifics for a prey item. We found that, with increased intraspecific competition, prey capture became faster, involving more rapid jaw opening and therefore greater inertial suction, shorter mouth closing times, and shorter gape cycles. Furthermore, the attack velocity of the fish increased with increasing competition, however a shift towards primarily ram based feeding was not confirmed. Our study demonstrates that prey capture kinematics are affected by the presence of conspecifics and future studies need to consider the effects of competition on prey capture kinematics.     

Failure to induce over-compensation of growth in maturing yellow perch

Unlike juvenile F1 male bluegill Lepomis macrochrus × female green sunfish L. cyanellus , maximized episodes of compensatory growth (CG) in 2 year yellow perch Perca flavescens did not surpass control masses because internal regulation caused abrupt appetite reduction upon catch-up. Together, the hybrid sunfish study and present work indicate that CG-maximizing feeding schedules and absence of an internal growth limiting mechanism are both required to produce substantial growth overcompensation (GOC). The less vigorous and less resilient CG responses of the yellow perch relative to those of the similarly fed hybrid sunfish appear indicative of the lack of GOC capacity in the former. This contrast, and results of previous studies are interpreted to suggest that GOC capacity may be limited to early life stages of fishes which have a substantial reproductive potential but are at high risk of mortality due to their small size. The possibility that GOC capacity is time-of-year-dependent and species-specific is considered also. Food deprivation periods that produced the strongest CG responses differed for male (2 days) and female (12 days) yellow perch. Among controls fed without restriction, growth rate and growth efficiency of female yellow perch exceeded those of males two-fold, however, males showed a greater capacity to catch-up to same-sex controls when undergoing CG. A feeding schedule using maintenance feeding v. food deprivation to elicit CG yielded the most rapid catch-up to control masses in the yellow perch. Such feeding schedules may produce even greater GOC than was achieved previously in hybrid sunfish, where feeding schedules involving food deprivation were employed.     

Prey life-history and bioenergetic responses across a predation gradient

To evaluate the importance of non-consumptive effects of predators on prey life histories under natural conditions, an index of predator abundance was developed for naturally occurring populations of a common prey fish, the yellow perch Perca flavescens, and compared to life-history variables and rates of prey energy acquisition and allocation as estimated from mass balance models. The predation index was positively related to maximum size and size at maturity in both male and female P. flavescens, but not with life span or reproductive investment. The predation index was positively related to size-adjusted specific growth rates and growth efficiencies but negatively related to model estimates of size-adjusted specific consumption and activity rates in both vulnerable (small) and invulnerable (large) size classes of P. flavescens. These observations suggest a trade-off between growth and activity rates, mediated by reduced activity in response to increasing predator densities. Lower growth rates and growth efficiencies in populations with fewer predators, despite increased consumption suggests either 1) a reduction in prey resources at lower predator densities or 2) an intrinsic cost of rapid prey growth that makes it unfavourable unless offset by a perceived threat of predation. This study provides evidence of trade-offs between growth and activity rates induced by predation risk in natural prey fish populations and illustrates how behavioural modification induced through predation can shape the life histories of prey fish species.