Foraging in Non-Native Environments: Comparison of Nile Tilapia and Three Co-Occurring Native Centrarchids in Invaded Coastal Mississippi Watersheds

We examined the diet of the alien Nile tilapia and bluegill, redear sunfish, and largemouth bass over a two-year period in coastal Mississippi. Nile tilapia diet was visually separated from the three natives based on group-average linkage cluster analysis. Sequential two-way nested analysis of similarities indicted there was no season effect (Global R = 0.026, P = 24.3%), but there was a moderate size class effect (Global R = 0.457, P = 0.1%) and a strong species effect (Global R = 0.876, P = 0.1%). Pairwise tests indicated species fed on different components of and locations within the environment, with bluegill, redear sunfish and largemouth bass (all R ≤ 0.683, P = 0.1%) having the most similar dietary components and Nile tilapia (all R ≥ 0.953, P = 0.1%) having the most distinct. Multivariate dispersion indicated that largemouth bass (1.425) and bluegill (1.394) had the most diverse diets compared to redear sunfish (0.906) and Nile tilapia (0.918). Similarities of percentages indicated that diets were separated based on prey: bluegill and redear sunfish consumed chironomids and insects; largemouth bass consumed fish and insects; and Nile tilapia fed most often on sediment resources such as nematodes, rotifers, bryozoans and hydrozoans. Nile tilapia had the highest frequency of mud, sand and detritus in their stomachs, suggesting they fed directly on bottom sediments. These data and the fact that Nile tilapia has a 1.3–7.6 times longer intestine on average than its body length, support our contention that this alien species feeds at the base of the food web and is well adapted to survive and proliferate in non-native environments.     

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.     

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.     

Host specificity among Ancyrocephalinae (Monogenoidea) of Nebraska sunfish

This study addressed the problem of local patterns of host specificity among Ancyrocephalinae (Monogenoidea) on bass and sunfish species, when the hosts occur in different species combinations in separate ponds. One hundred fifty-three fish of the Centrarchidae, from 4 study sites in Nebraska, were collected. Host species included bluegill (Lepomis macrochirus), green sunfish (L. cyanellus), largemouth bass (Micropterus salmoides), black crappie (Pomoxis nigromaculatus), white crappie (P. annularis), and rock bass (Ambloplites rupestris). These fish occurred in different species combinations, depending on the pond sampled. Results indicated that several centrarchid species could inhabit the same pond and yet support distinct monogene communities. Clavunculus bursatus, Onchocleidus helicis, O. principalis, and Syncleithrum fusiformis were found only on largemouth bass, regardless of what other centrarchids were present in a particular pond. Haplocleidus dispar occurred on green sunfish, bluegill, largemouth bass, and black crappie, and H. furcatus occurred on both bluegill and largemouth bass. Onchocleidus cyanellus and O. ferox were found on both bluegill and green sunfish. Rock bass were present in only 1 of the 4 ponds, but were not infected with any monogenes, even though co-occurring centrarchids were often heavily infected. Largemouth bass had the most diverse ancyrocephaline communities. The degree of parasite host specificity among these monogenes was inversely related to the diversity of host species present in a particular pond. In general, the parasites were more host specific than might be inferred from the literature; parasite species did not necessarily colonize supposedly receptive host species even when the latter were present, and host relatedness was the major factor in determining whether host species shared a common parasite species.     

Gape Limitation, Prey Size Refuges and the Top–down Impacts of Piscivorous Largemouth Bass in Shallow Pond Ecosystems

Top–down control of phytoplankton biomass through piscivorous fish manipulation has been explored in numerous ecological and biomanipulation experiments. Piscivores are gape-limited predators and it is hypothesized that the distribution of gape sizes relative to distribution of body depths of prey fish may restrict piscivore effects cascading to plankton. We examined the top–down effects of piscivorous largemouth bass on nutrients, turbidity, phytoplankton, zooplankton and fish in ponds containing fish assemblages with species representing a range of body sizes and feeding habits (western mosquitofish, bluegill, channel catfish, gizzard shad and common carp). The experimental design consisted of three replicated treatments: fishless ponds (NF), fish community without largemouth bass (FC), and fish community with largemouth bass (FCB). Turbidity, chlorophyll a, cyclopoid copepodid and copepod nauplii densities were significantly greater in FC and FCB ponds than in NF ponds. However, these response variables were not significantly different in FC and FCB ponds. The biomass and density of shallow-bodied western mosquitofish were reduced and bluegill body depths shifted toward larger size classes in the presence of largemouth bass, but the biomass and density of all other fish species and of the total fish community were unaffected by the presence of largemouth bass. Our results show that top–down impacts of largemouth bass in ecosystems containing small- and deep-bodied fish species may be most intense at the top of the food web and alter the size distribution and species composition of the fish community. However, these top–down effects may not cascade to the level of the plankton when large-bodied benthivorous fish species are abundant.     

Performance as a fish predator of largemouth bass [<Emphasis Type="Italic">Micropterus salmoides</Emphasis> (Lacepède)] invading Japanese freshwaters: a review

This review focuses on how predator performance of the invasive largemouth bass [Micropterus salmoides (Lacepède)] has been, or will be, formed in Japanese freshwaters. Predation impacts of largemouth bass on fish communities appear pervasive in both Japanese as well as North American freshwaters. Factors affecting performance as a piscivorous predator are (1) light intensity and water clarity, (2) oxygen depletion, (3) prey size and gape size, (4) behavioral refuge of prey, (5) weed beds as refuge for prey fish, (6) interaction with bluegill. Size and behavioral refuges requirements are so rigorous that they may have evolved only in some North American prey fish species like bluegill; therefore, most Japanese native fish species are unlikely to be equipped with such refuges. However, refuge habitats like aquatic weed beds could develop in Japanese freshwaters, allowing prey fish species to survive under predation pressure. The density, architecture, and species composition of aquatic plants may affect their suitability as refuges. Studies in Japanese waters have suggested that the presence of rich aquatic vegetation or invasive bluegill in bass-introduced waters have suppressed the predation impact of largemouth bass on fish communities. In addition to these environmental factors, original genotypic and phenotypic traits of the introduced largemouth bass, and hybridization between different lineages of largemouth bass or with Florida bass [Micropterus floridanus (Lesueur)] may be involved in further adaptation of invasive largemouth bass to Japanese freshwaters.     

First record of Neoergasilus japonicus (Poecilostomatoida: Ergasilidae), a parasitic copepod new to the Laurentian Great Lakes

The parasitic copepod Neoergasilus japonicus, native to eastern Asia, was first collected from 4 species of fish (fathead minnow, Pimephales promelas; largemouth bass, Micropterus salmoides; pumpkinseed sunfish, Lepomis gibbosus; and yellow perch, Perca flavescens) in July 1994 in Saginaw Bay, Lake Huron, Michigan. Further sampling in the bay in 2001 revealed infections on 7 additional species (bluegill, Lepomis macrochirus; carp, Cyprinus carpio; channel catfish, Ictalurus punctatus; goldfish, Carassius auratus; green sunfish, Lepomis cyanellus; rock bass, Ambloplites rupestris; and smallmouth bass, Micropterus dolomieu). An additional 21 species examined in 2001 were devoid of the parasite. A limited collection of fish from Lake Superior (n = 8) and Lake Michigan (n = 46) in 1994 showed no infection. Neoergasilus japonicus is most frequently found attached to the dorsal fin and, in decreasing frequency, on the anal, tail, pelvic, and pectoral fins. Prevalence generally ranged from 15 to 70 and intensity from 1 to 10. The greatest number of copepods on a single host was 44. The copepod Neoergasilus japonicus appears to disperse over long distances rather quickly, spreading across Europe in 20 yr and then moving on to North America over a span of 10 yr. Its main vehicle of transport and introduction into the Great Lakes is probably exotic fish hosts associated with the fish-culture industry.     

Invasive carp and prey community composition disrupt trophic cascades in eutrophic ponds

The role of trophic cascades in structuring freshwater communities has been extensively studied. Most of this work, however, has been conducted in oligotrophic northern lakes that contain highly vulnerable cyprinid prey: aquatic communities where trophic interactions are likely to be stronger than in many other systems. Fewer studies have been conducted in eutrophic systems or have examined the bottom-up effects of benthivorous fishes, and none have directly compared these effects to those of piscivores on ecosystem structure and function. We conducted enclosure experiments in eutrophic ponds to examine trophic effects of invasive benthivores (common carp—Cyprinus carpio L.), native piscivores (largemouth bass—Micropterus salmoides [Lacepède]), and their interactions with common centrarchid prey with well-developed anti-predatory behaviors (age-1 bluegill—Lepomis macrochirus Rafinesque and young-of-year largemouth bass). At the end of the 60-day experiment, common carp had strong bottom-up effects that increased total phosphorus and turbidity while decreasing chlorophyll a biomass and macrophyte cover that resulted in decreased macroinvertebrate biomass and also decreased growth in both juvenile largemouth bass and bluegill. Piscivorous largemouth bass, however, did not affect the survival of either planktivorous juvenile largemouth bass or bluegill. Growth of juvenile largemouth bass was also not affected, but juvenile bluegill growth was significantly diminished, possibly due to nonconsumptive effects of predation. Our results suggest that, in a centrarchid-dominated eutrophic system, top-down effects of predators are overwhelmed by common carp-mediated bottom-up effects. These bottom-up effects strongly affected multiple trophic levels, thus altering aquatic community structure and function.     

The facilitation of the native bluegill sunfish by the invasive bighead carp

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Using Environmental DNA to Estimate the Distribution of an Invasive Fish Species in Ponds

Knowledge of the presence of an invasive species is critical to monitoring the sustainability of communities and ecosystems. Environmental DNA (eDNA), DNA fragments that are likely to be bound to organic matters in the water or in shed cells, has been used to monitor the presence of aquatic animals. Using an eDNA-based method, we estimated the presence of the invasive bluegill sunfish, Lepomis macrochirus, in 70 ponds located in seven locales on the Japanese mainland and on surrounding islands. We quantified the concentration of DNA copies in a 1 L water sample using quantitative real-time polymerase chain reaction (qPCR) with a primer/probe set. In addition, we visually observed the bluegill presence in the ponds from the shoreline. We detected bluegill eDNA in all the ponds where bluegills were observed visually and some where bluegills were not observed. Bluegills were also less prevalent on the islands than the mainland, likely owing to limited dispersal and introduction by humans. Our eDNA method simply and rapidly detects the presence of this invasive fish species with less disturbance to the environment during field surveys than traditional methods.     

Hunting behavior of Florida largemouth bass, Micropterus salmoides floridanus, in a channelized river

The distribution and behavior of Florida largemouth bass, Micropterus salmoides floridanus, and their main prey (sunfish, genus Lepomis, and the cichlid Tilapia mariae) were studied in southern Florida to determine how fish behave in the simplified habitats found in channelized rivers. Time budgets were constructed from focal animal observations on 69 bass. Patterns of behavior associated with hunting were performed during a significantly higher proportion of the time when bass were in vegetated habitats. Scan samples of the behavior of 236 observed bass revealed that hunting was more common in areas of high structural complexity. Only 38% of observed bass were solitary, with the majority occurring in groups with either conspecifics or in mixed-species groups with similar sized bluegill sunfish, Lepomis macrochirus. Largemouth bass (n=1014) and sunfish (n=1372) were significantly more abundant in areas with vegetation and were almost entirely absent from the water column in the center of the canal. All species of fish avoided the water column, where currents were swift and no cover was available. The structure of the habitat appears to be important in the way largemouth bass organize their activity patterns. This suggests that habitat availability in channelized rivers significantly influences important behaviors such as hunting, thus potentially altering energy budgets and population dynamics of both predator and prey.     

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.

     

Phenotypic variation and vulnerability to predation in juvenile bluegill sunfish (<Emphasis Type="Italic">Lepomis macrochirus</Emphasis>)

Bluegill sunfish (Lepomis macrochirus) are known to diversify into two forms specialized for foraging on either limnetic or littoral prey. Because juvenile bluegills seek vegetative cover in the presence of largemouth bass (Micropterus salmoides) predators, natural selection should favor the littoral body design at size ranges most vulnerable to predation. Yet within bluegill populations, both limnetic and littoral forms occur where vegetation and predators are present. While adaptive for foraging in different environments, does habitat-linked phenotypic variation also influence predator evasiveness for juvenile bluegills? We evaluate this question by quantifying susceptibility to predation for two groups of morphologically distinct bluegills; a limnetic form characteristic of bluegills inhabiting open water areas (limnetic bluegill) and a littoral form characteristic of bluegills inhabiting dense vegetation (littoral bluegill). In a series of predation trials, we found that bluegill behaviors differed in open water habitat but not in simulated vegetation. In open water habitat, limnetic bluegills formed more dense shoaling aggregations, maintained a larger distance from the predator, and required longer amounts of time to capture than littoral bluegill. When provided with simulated vegetation, largemouth bass spent longer amounts of time pursuing littoral bluegill and captured significantly fewer littoral bluegills than limnetic fish. Hence, morphological and behavioral variation in bluegills was linked to differential susceptibility to predation in open water and vegetated environments. Combined with previous studies, these findings show that morphological and behavioral adaptations enhance both foraging performance and predator evasiveness in different lake habitats.     

Food habits and relative abundances of native piscivores: implications for controlling common carp

Common carp (Cyprinus carpio, carp) are a widespread and ecologically destructive invasive fish species. Carp management is critical for maintaining healthy aquatic ecosystems, and many control options are available, but most have proven to be ineffective. Carp abundances have increased at The Nature Conservancy’s Emiquon Preserve, Illinois, since its restoration in 2007 despite management efforts to suppress this species. We conducted a comparative diet study in Illinois, Tennessee, and Wisconsin to test whether bowfin (Amia calva), spotted gar (Lepisosteus oculatus, gar), and largemouth bass (Micropterus salmoides) commonly preyed upon carp. We focused on bowfin and gar because they are hypoxia-tolerant, similar to carp. We also assessed whether specific fish community characteristics were correlated with carp relative abundances. We found no evidence that bowfin, gar, and bass consumed large numbers of carp. However, carp may be limited in some ecosystems (e.g., Reelfoot Lake, Tennessee) through alternative mechanisms associated with bowfin, gar, bass, and bluegill (Lepomis macrochirus) included in a diverse native fish community.     

Changes in Diet and Food Consumption of Largemouth Bass Following Large-scale Hydrilla Reduction in Lake Seminole, Georgia

Largemouth bass Micropterus salmoides Lacepède growth (in length) increased an average of 14% and bioenergetics modeling predicted a 38% increase in total annual food consumption following a large-scale reduction of hydrilla Hydrilla verticillata L.f. Royle in Spring Creek, a 2,343-ha embayment of Lake Seminole, Georgia. Coverage of submersed aquatic vegetation (SAV) declined from 76% to 22% in 1 year due to a drip-delivery fluridone treatment. In contrast, largemouth bass growth only increased an average of 4% and bioenegetics modeling predicted a 13% increase in total food consumption over the same time period in the Chattahoochee River embyament, where SAV coverage naturally declined from 26% to 15%. Diets were collected from a total of 4,409 largemouth bass over a 2.5-year period in the two embayments; the primary diet item (by weight) for largemouth bass in both embayments was sunfish (mostly Lepomis spp.). Diets before and after SAV reduction were generally similar for fish greater than stock-size (≥203 mm) in the Spring Creek arm; however, fewer invertebrates were consumed after SAV reduction. Low diet similarity was observed in smaller fish, caused by a decline in consumption of grass shrimp and sunfishes and an increase in use of damselflies, shiners Notropis spp., and topminnows Fundulus spp. after SAV reduction. Diets were similar between the same time periods for all sizes of fish in the Chattahoochee River arm. These results agreed with many laboratory results describing the effects of aquatic plant density on largemouth bass food consumption and growth, and demonstrated that increased predation efficiency resulting from decreased plant abundance was likely a stronger factor determining growth rates than any potential diet shift that may occur as a result in vegetation decline.     

Evidence for leptin expression in fishes

Tissues from bony fish were screened with anti-mouse leptin antibodies to detect the presence of the fat-regulating hormone in fishes. Low molecular-weight (16 kDa) immunoreactive bands were detected in blood, brain, heart and liver of green sunfish (Lepomis cyanellus), bluegill sunfish (Lepomis macrochirus), largemouth bass (Micropterus salmoides), white crappie (Pomonix annularis), channel catfish (Ictalurus punctatus), and rainbow trout (Oncorhynchus mykiss). To further verify that we had identified leptin, the response of fish "leptin" was measured in fed and fasted green sunfish. Fed sunfish had approximately threefold higher concentration of leptin in blood than did fasted sunfish (fed vs. fasted; 0.599 +/- 0.03 microg/microl vs. 0.196 +/- 0.04 microg/microl; P > F = 0.0001), which is consistent with mammalian models of leptin function. Brain leptin concentration is also positively correlated with percent body fat in white crappie and bluegill. Based upon electrophoretic mobility, immunoreactivity, response to fasting, and correlation with adiposity, we believe we have the first evidence for leptin expression in an ectotherm.     

Competition during early ontogeny: Effects of native and invasive planktivores on the growth,survival, and habitat use of bluegill

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Development and application of environmental DNA surveillance for the threatened crucian carp (Carassius carassius)

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The energetic impact of overwinter prey assemblages on age-0 largemouth bass, <Emphasis Type="Italic">Micropterus salmoides</Emphasis>

Synopsis We compared survival, growth, and swimming performance of two size classes of age-0 largemouth bass, Micropterus salmoides, in the spring after being fed diets of bluegill, Lepomis macrochirus, fathead minnows, Pimephales promelas, or invertebrate prey during the winter. Regardless of prey assemblage, survival was uniformly high and independent of size. Length, wet- and dry-mass, and condition was also similar among treatments for both size classes. However, variation in individual performance differed, with the lowest variability in growth occurring among small age-0 largemouth bass in the invertebrate only treatment. Absolute and length corrected swimming speeds of largemouth bass were highest for invertebrate prey assemblages, intermediate for fathead minnow prey, and lowest for bluegill prey. The patterns in growth and spring swimming performance likely reflect the varied nutritive quality of different prey, the ability of largemouth bass to capture different prey, and competition with the piscine prey.     

Difference in the hypoxia tolerance of the round crucian carp and largemouth bass: implications for physiological refugia in the macrophyte zone

The hypoxia tolerance of larval and juvenile round crucian carp, Carassius auratus grandoculis, and largemouth bass, Micropterus salmoides, was determined using respirometry to examine the potential of hypoxic areas in the macrophyte zone as physiological refugia for round crucian carp. The tolerance, which was measured as the critical oxygen concentration (Pc), was 1.32 mg O₂/l in the round crucian carp and 1.93 mg O₂/l in the largemouth bass. As the round crucian carp tolerated hypoxia better than the largemouth bass, hypoxic areas in the macrophyte zone might function as physiological refugia for round crucian carp.