Laboratory constraints on feeding behaviours in polymorphic bluegill sunfish (Lepomis macrochirus)

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Sperm investment and alternative mating tactics in bluegill sunfish (Lepomis macrochirus)

Although alternative mating tactics are found in males of manyspecies, little is known about tactic-specific adaptations tosperm competition and the mechanism by which fertilization successis obtained. We now report on the sperm investment patternsof males that use alternative mating tactics in bluegill sunfish(Lepomis macrochirus). Bluegill males are characterized by threealternative mating tactics: parentals, sneakers, and satellites.Parentals delay maturation and adopt a courting and guardingtactic, whereas sneakers and satellites mature precociouslyand, respectively, use sneaking and female mimicry to stealfertilizations from parentals. We found differences among thetactics in testes weight, sperm longevity, and ejaculate spermdensity and competitiveness. Parentals had the largest testes,but the smallest relative to their body weight. Satellites hadintermediate-sized testes, and sneakers had the smallest testes,but the largest relative to their body weight. Within each tactic,there was a positive relationship between testes weight andbody weight, but the exact relationship differed among the tacticsand could not be attributed solely to allometry. Parentals hadlonger-lived sperm compared with that of both sneakers and satellites.Ejaculate sperm density was greatest in sneakers, satelliteswere intermediate, and parentals had the lowest. Competitionexperiments involving equal volumes of ejaculate showed thatfertilization success increased linearly with sperm number,consistent with a rafflelike process. However, independent ofsperm number, parental sperm were superior at fertilizing eggs.We interpret these sperm investment patterns in relation todifferences in sperm competition risk, number of mating opportunities,and alternative investment options.     

Planktivory by bluegill (Lepomis macrochirus) on Leptodora kindti in a small North American lake

Leptodora kindti (Crustacea: Cladocera) is a large species of zooplankton (2–18 mm length) that is exceptionally transparent. This transparency is believed to be a means by which it successfully coexists in lakes with planktivorous fishes. We investigated the gut remains of bluegill (Lepomis macrochirus) that had been feeding on L. kindti and Daphnia (D. galeata and D. retrocurva) in the wild (Lake Zurich, Illinois) and found that bluegill readily preyed on L. kindti as small as 3–5 mm length, and strongly selected L. kindti over Daphnia galeata and Daphnia retrocurva. The large compound eye of L. kindti is one half to one complete order of magnitude larger than Daphnia's eye, consistent with the hypothesis that eye area is an important visual cue for fishes. Moreover, the slope of the relationship between eye area and body length is an order of magnitude shallower in L. kindti than Daphnia, suggesting that eye area has been under stronger negative selection in L. kindti. Results suggest that L. kindti's large and dark eye compromises the transparent nature of its body.     

Diet of bluegill Lepomis macrochirus in a South African reservoir during winter and summer

Alien fishes are considered a major threat to aquatic biodiversity in South Africa, yet relatively little regional information on their biology and ecology is available for many of these species. Seasonal changes in the diet of the bluegill Lepomis macrochirus in Howieson’s Poort Dam, Grahamstown, were assessed during summer and winter in 2014–2015, using stomach content analysis. In winter, juvenile and adult fish diets were dominated by crustacean zooplankton and insects, respectively. In summer, juvenile fish fed on crustaceans and insects, whereas adults consumed mostly fish eggs, indicating a potential impact by these invasive fish on native fish through oophagy.     

Potential importance of lagoons as breeding grounds for bluegill Lepomis macrochirus in Lake Biwa, Japan

Exotic bluegill Lepomis macrochirus have been propagating in the littoral region of Lake Biwa and its tributary lagoons. To investigate the reproductive activity of bluegill in the prespawning season, fish samples were collected from three sites at the littoral region of the lake and their nearby lagoons. The number of females relative to the total number of specimens tended to be higher in lagoons than in the adjacent littoral sites in the lake. The females collected from lagoons had significantly larger ovaries than those from the lake. The means of gonadal somatic index of females in the lake ranged from 1.77 to 3.44, whereas those in lagoons ranged from 4.35 to 12.2. The higher temperature conditions of lagoons appeared to be responsible for the higher maturation of ovaries of the fish in lagoons. The environmental condition of lagoons is potentially suitable for the active growth of larvae, subsequently increasing their overwintering success. Therefore, earlier spawning of bluegill in lagoons might have contributed to the propagation of bluegill in Lake Biwa to some extent.     

Pharmacology of the retractor lentis muscle of the bluegill (Lepomis macrochirus)

We studied accommodative nerve-muscle transmission in a teleost fish, the bluegill (Lepomis macrochirus). The muscle contracted with electrical stimulation to move the spherical lens along the pupil plane in the eye ball so that the distance between the lens and retina changes. The dose-dependent effect on the lens muscle of acethylcholine and its related substances (nicotine, muscarine, curare and atropine), glutamate, gamma-aminobutyric acid, serotonin, glycine, dopamine and noradrenaline was observed with a binocular microscope. Its video image was processed by a computer to measure the shortening of the muscle. Among the transmitter candidates applied only acethylcholine caused a contraction and elicited the lens movement. Muscarine caused strong contraction of the muscle even in a low concentration (1 nM) while nicotine did not. The contraction was antagonized by atropine but not curare. Previous studies based on intraperitoneally injected reagents suggested a cholinergic innervation on the lens muscle. Our pharmacologic results verified by direct anatomical measurements on the isolated lens-muscle-nerve preparation unambiguously establish the dose-dependent muscarinic-cholinergic innervation to the lens muscle by parasympathetic postganglionic fibers.Abbreviations Ach Acetylcholine - GABA gamma-aminobutyric acid - TTX tetrodotoxin - RML Resting muscle length     

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     

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 approximately 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.     

Aggressive habituation and rim circling in the social organization of bluegill sunfish (Lepomis macrochirus)

Synopsis The rim circling (RC), and aggressive habituation of nesting bluegills were studied in natural colonies during the six days of the reproductive period following spawning. To examine the stimulus specificity of aggressive habituation, selected test individuals and four neighbors were observed on four occasions during one day. After the first observation period established baseline data on aggressive interactions, the appearances of three of the neighbors were manipulated and further observations were made. Two more observation periods followed, separated by a sham manipulation to allow for possible disturbance effects. Fish lengths, inter-nest distances, and positions in the colony were also recorded.An analysis of the data demonstrated that aggressive interaction increased for the three manipulated neighbors. There were no significant differences among the data for the fourth (control) neighbors. The enhanced aggressive interactions between the test and manipulated males were initiated by the males at least partially in response to the changed appearance of the neighbor. Further, the level of aggressive interaction returned to normal after about 2 hours, indicating that the test male had habituated to the new appearances of his neighbors. Thus visual appearance plays an important role in the habituation of aggression between neighboring bluegills. It was not possible to determine if the behavior of the neighbor was also an important cue used in aggressive habituation, but this seems likely. Advantages of aggressive habituation are discussed. It is noteworthy that aggression decreased as internest distance increased.Levels of RC varied significantly over the six days, in a time course dissimilar from aggression. The RC rate is dependent on size of male, nest locality, and circling activity of neighbors. Observations on the synchrony of rim circling indicated social facilitation. It is argued that RC probably fulfills an advertisement function important in defending the brood. The motivation for RC is likely complex, and its performance reflects a mixed aggressive and reproductive strategy in the nesting population. Aggressive habituation functions in the social organization of bluegills to facilitate the occurrence of group displays such as RC.     

Utilizing stomach content and faecal DNA analysis techniques to assess the feeding behaviour of largemouth bass Micropterus salmoides and bluegill Lepomis macrochirus

In this study, the feeding behaviour of the non‐native invasive predatory fishes largemouth bass Micropterus salmoides and bluegill Lepomis macrochirus was studied in the Ezura River, a northern tributary of Lake Biwa, Japan. Prey composition was estimated based on visual examination of stomach contents and faecal DNA analysis to determine feeding habits of these predatory fishes. Stomach content analysis showed that native fishes (e.g. ayu Plecoglossus altivelis and gobies Rhinogobius spp.) and shrimps (e.g. Palaemon paucidens) were the major prey items for M. salmoides, while snails, larval Chironomidae and submerged macrophytes were the dominant prey items of L. macrochirus. Micropterus salmoides tended to select larger fish in the case of crucian carp Carassius spp., but smaller fishes in the case of P. altivelis and Rhinogobius spp. Faecal DNA analyses revealed prey compositions similar to those identified in predator stomach contents, and identified additional prey species not detected in stomach content inspection. This study demonstrated that both stomach content inspection and DNA‐based analysis bear several inherent shortcomings and advantages. The former method is straightforward, although identification of species can be inaccurate or impossible, whereas the latter method allows for accurate species identification, but cannot distinguish prey size or stage. Hence, integration of morphology‐based and DNA‐based methods can provide more reliable estimates of foraging habits of predatory fishes.     

Decomposition of Blue-Green Algal (Cyanobacterial) Blooms in Lake Mendota, Wisconsin

Decomposition of natural populations of Lake Mendota phytoplankton dominated by blue-green algae (cyanobacteria) was monitored by using oxygen uptake and disappearance of chlorophyll, algal volume (fluorescence microscopy), particulate protein, particulate organic carbon, and photosynthetic ability (¹⁴CO₂ up-take). In some experiments, decomposition of ¹⁴C-labeled axenic cultures of Anabaena sp. was also measured. In addition to decomposition, mineralization of inorganic nitrogen and phosphorus were followed in some experiments. Decomposition could be described as a first-order process, and the rate of decomposition was similar to that found by others using pure cultures of eucaryotic algae. Nitrogen and phosphorus never limited the decomposition process, even when the lake water was severely limited in soluble forms of these nutrients. This suggests that the bacteria responsible for decomposition can obtain all of their key nutrients for growth from the blue-green algal cells. Filtration of lake water through plankton netting that removed up to 90% of the algal biomass usually did not cause a similar decrease in oxygen demand, suggesting that most of the particulate organic matter used for respiration of the decomposing bacteria was in a small-particle fraction. Short-term oxygen demand correlated well with the particulate chlorophyll concentration of the sample, and a relationship was derived that could be used to predict community respiration of the lake from chlorophyll concentration. Kinetic analysis showed that not all analyzed components disappeared at the same rate during the decomposition process. The relative rates of decrease of the measured parameters were as follows: photosynthetic ability > algal volume > particulate chlorophyll > particulate protein. Decomposition of ¹⁴C-labeled Anabaena occurred at similar rates with aerobic epilimnetic water and with anaerobic sediment, but was considerably slower with anaerobic hypolimnetic water. Of the various genera present in the lake, Aphanizomenon and Anabaena were more sensitive to decomposition than was Microcystis. In addition to providing a general picture of the decomposition process, the present work relates to other work on sedimentation to provide a detailed picture of the fate of blue-green algal biomass in a eutrophic lake ecosystem.     

Behavioral changes in bluegill (Lepomis macrochirus) as indicators of sublethal effects of metals

Synopsis The development of rapid, yet sensitive toxicity testing methods is needed for the establishment of water quality standards to protect aquatic life. A technique using changes in the behavior of bluegill (Lepomis macrochirus) was utilized to evaluate the impact of five sublethal levels of a cadmium (Cd) and zinc (Zn) mixture. The technique proved very sensitive and various changes in behavior occurred at the lowest metal levels used; 21 ug Cd per liter and 99 ug Zn per liter. Coughs, yawns, partial jerks and jerk swimming were especially sensitive indicators of elevated metal levels. The frequency, but not the form, of eight of the nine behaviors quantified changed significantly with increasing metal levels.     

Origin and dispersal of bluegill sunfish, Lepomis macrochirus, in Japan and Korea

The bluegill sunfish, Lepomis macrochirus, is a notorious exotic species in many freshwater ecosystems, currently expanding its distribution worldwide. In 1960, a small group of bluegills captured in the Mississippi River at Guttenberg in Iowa were imported to Japan as a gift from the mayor of Chicago to the Japanese government. The offspring of these fish were released into the wild in Japan and also in Korea. Over 40 years after this first introduction, L. macrochirus now occupies all the freshwater ecosystems of both countries. We compared invading populations of L. macrochirus in Japan and Korea with native populations in the USA, using PCR-RFLP (polymerase chain reaction-restricted fragment length polymorphism) analyses of mitochondrial DNA, to estimate the origin and dispersal of L. macrochirus in Japan and Korea. Five haplotypes of mitochondrial DNA detected in Japanese and Korean populations completely coincided with the haplotypes of the Guttenberg population. Haplotype diversity of invading populations was shown to be highest in populations established in the 1960s, while genetic variability was lower in more recently established populations. Our results suggest that all L. macrochirus in Japan and Korea have originated from the 15 fish first introduced in 1960. Low haplotype diversity in newly established populations is probably due to genetic drift arising from repeated population bottlenecks, while the high similarity of haplotypes among neighbouring populations is considered to reflect the history of transplantation by humans.     

Maintenance of female mimicry as a reproductive strategy in bluegill sunfish (Lepomis macrochirus)

Synopsis In species where male reproductive success is dependent on male competition and aggression, alternative reproductive patterns, thought to represent a reduction in male reproductive effort, sometimes occur. Female mimicry in bluegill sunfish (Lepomis macrochirus) is an example of an obligate alternative male strategy. Female mimics are small, sexually mature males which mimic the details of female behavior, and gain access to functional females attracted to the nests of large, aggressive territorial males. The costs of female mimicry relative to nesting male behavior are discussed and two hypotheses, deception and mutual gain, are presented to explain the tolerance and courtship of female mimics by nesting males.     

Aspects of color vision in bluegill sunfish (Lepomis macrochirus): ecological and evolutionary relevance

Summary Spectral sensitivity curves were measured for bluegills using a heart-rate conditioning technique. A mean spectral sensitivity curve (n=3) determined using a white background exhibited two main peaks, indicating the possible presence of two cone photoreceptors mechanisms. Chromatic adaptation was used to separate the contribution of the cone mechanisms to sensitivity. Peak sensitivities were located at 540 and 640 nm against red and blue-green backgrounds, respectively.Light adaptation curves were measured for each cone mechanism indicating that these cone mechanisms have their greatest contrast sensitivity at higher background intensities. Spatial summation properties were also measured for each cone mechanism revealing a critical diameter (summation area) of 5° for both mechanisms.Microspectrophotometric (MSP) measurements were made on individuals from the same group of bluegills used in the above experiments. The results showed the presence of two cone types: single green-sensitive cones with an average _max of 536 nm (SD±1.8nm,n=11) and twin redsensitive cones with an average _max of 620 nm (SD ±1.9 nm,n=11).The correlation between the visual pigment absorption spectra and action spectra of the two cone mechanisms indicate a sound physiological basis for sensitivity. The functional properties of the two cone mechanisms, will be discussed in relation to the ecological and behavioral aspects of bluegills.Abbreviation TVI threshold vs intensity     

The effects of feeding history and environment on condition,body composition and growth of bluegills Lepomis macrochirus

Initial relative mass (W_R, low v. high) and energetic trajectory in time (starved v. fed) were experimentally manipulated in bluegill Lepomis macrochirus. Fed fish starting at low W_R grew more and gained more W_R than fed fish starting at high W_R. Similarly, starved fish starting at high W_R lost more mass and W_R than did starved fish starting at low W_R. Temporal changes in other variables did not consistently match that of W_R, but, by the end of the experiment, proximate composition showed a high correlation to W_R. Regression slopes of W_R on proximate composition increased with time in the laboratory. Differences between wild and laboratory fish appeared to result from relaxation of environmental stress. When excess resources are available such that L. macrochirus grow, condition indices will increase, but individual response will depend on initial values and thus past environmental experience.     

Daily ration of juvenile Coregonus lavaretus (L.) fed on living zooplankton

Juvenile whitefish, Coregonus lavaretus (L.), wet weight 0.04 to 5.2 g, from Lake Constance were kept at 10, 12 and 16° C water temperature, respectively and fed with living zooplankton. The experimental duration lasted 72 to 120 h. Daily rations were defined as the amount of zooplankton remaining subtracted from the amount of zooplankton added after a 24 h interval. The mortality of the zooplankton was determined in parallel experiments without fish. Relative daily ration (zooplankton weight/fish weight) v. fish weight increased up to a fish dry weight of approximately 0.12 g and then decreased steadily. The maximum daily ration was about 270% of fish body wet weight (wet/wet) corresponding to 75% of body dry weight (dry/dry), respectively. In fishes of a dry weight higher than 0.12 g (wet weight 0.65 g) a significant difference in food intake was found between 12 and 16° C. The specific growth rate ranged from nearly 0 up to 33% per day. No correlation was found between daily ration and specific growth rate.     

Musculoskeletal morphology and regionalization within the dorsal and anal fins of bluegill sunfish (Lepomis macrochirus)

Ray‐finned fishes actively control the shape and orientation of their fins to either generate or resist hydrodynamic forces. Because of the emergent mechanical properties of their segmented, bilaminar fin rays (lepidotrichia), and actuation by multiple muscles, fish can control the rigidity and curvature of individual rays independently, thereby varying the resultant forces across the fin surfaces. Expecting that differences in fin‐ray morphology should reflect variation in their mechanical properties, we measured several musculoskeletal features of individual spines and rays of the dorsal and anal fins of bluegill sunfish, Lepomis macrochirus, and assessed their mobility and flexibility. We separated the fin‐rays into four groups based on the fin (dorsal or anal) or fin‐ray type (spine or ray) and measured the length of the spines/rays and the mass of the three median fin‐ray muscles: the inclinators, erectors and depressors. Within the two ray groups, we measured the portion of the rays that were segmented vs. unsegmented and branched vs. unbranched. For the majority of variables tested, we found that variations between fin‐rays within each group were significantly related to position within the fin and these patterns were conserved between the dorsal and anal rays. Based on positional variations in fin‐ray and muscle parameters, we suggest that anterior and posterior regions of each fin perform different functions when interacting with the surrounding fluid. Specifically, we suggest that the stiffer anterior rays of the soft dorsal and anal fins maintain stability and keep the flow across the fins steady. The posterior rays, which are more flexible with a greater range of motion, fine‐tune their stiffness and orientation, directing the resultant flow to generate lateral and some thrust forces, thus acting as an accessory caudal fin. J. Morphol., 2012. © 2011 Wiley Periodicals, Inc.