Calcium-induced quiescence of sperm motility in the bluegill (Lepomis macrochirus)

Before dilution in hypoosmotic media sperm of freshwater fish are maintained quiescent by a range of factors including osmolality, K+ and pH, and the onset of motility is generally associated with an increase in cytoplasmic Ca2+. In contrast, Ca2+ in conjunction with osmolality was found to inhibit motility of intact bluegill sperm. Consistent with seminal plasma composition, 0.16 mmol/L Ca2+ and greater, in conjunction with an osmotic concentration of 290 mOsm/kg, inhibited the onset of bluegill sperm motility; sperm diluted in saline at 290 mOsm/kg without Ca2+ became motile. Cations Mn2+ and Sr2+, in conjunction with osmolality, had an inhibitory effect on initiation of sperm motility similar to that of Ca2+. Sperm motility was inhibited by Ca2+ channel blockers nimodipine and nifedipine, the mitochondrial Ca2+ uniporter inhibitor ruthenium red and the calmodulin inhibitors W-7 and trifluoperazine dihydrochloride. These results provide evidence that elevated cytoplasmic Ca2+ inhibits sperm motility and yet low levels permit or promote motility. This study demonstrates a unique inhibitory action of Ca2+ on the motility of intact fish sperm at physiologically relevant levels.     

Choice in the bluegill (Lepomis macrochirus)

To study matching in a species distantly related to mammals and birds, seven bluegill were trained to break a photobeam using a nose-poke response for access to pelleted food in their home aquaria during one-h sessions. Reinforcer ratios available from the two response alternatives varied among the following: 16:1, 8:1, 4:1, 1:1, 1:4, 1:8, and 1:16. The overall reinforcement rate was held at 0.8/min. All experiments were conducted in a closed economy, i.e., the fish's daily food ration was available only during experimental sessions. Matching functions are reported for each fish using all combinations of scheduled and obtained reinforcer ratios as the independent variables and response and time ratios as the dependent variables. All matching functions had slopes less than 1.0 and r² values above 0.70. Overall response rates were unrelated to the reinforcer ratios but, as with other species studied, changeover rates were highest for the 1:1 condition and lowest for the 16:1 conditions. These results are consistent with data obtained from more traditionally studied taxa (e.g., birds, mammals, and primates), and similar previous studies with fish, suggesting that matching has been conserved since fish, birds, and mammals evolved from a common ancestor over 400 million years ago.     

Intestinal coccidiosis in bluegill, Lepomis macrochirus

Developmental stages of a coccidial parasite were observed in young-of-year bluegill (Lepomis macrochirus) from an impoundment lake in Norfolk County, Virginia. The fish were anorexic and lethargic. Necropsy examination revealed emaciated bluegill with little or no abdominal fat and no food in the stomach or intestines. Coccidia were present in the posterior intestine in moderately large numbers. Few sporulated oocysts were present, and identification to genus was not possible. Epithelial cell destruction, sloughing of the intestinal mucosa, and hemorrhage were associated with the developing coccidial parasites. Coccidia were not observed within other organ systems. No pathogenic bacteria were isolated from the fish tissues. Our findings indicate that intestinal coccidiosis may pose a significant health problem in young bluegill.     

Mitochondrial genome sequence of the bluegill sunfish (Lepomis macrochirus)

The bluegill sunfish (Lepomis macrochirus) belongs to Lepomis genera of the family Centrarchidae, which is an economically important freshwater species in China. This study presents the complete mitochondrial genome of L. macrochirus, which is the first complete sequence from sunfish species. L. macrochirus mitochondrial DNA is 16,489 bp long, with the genome organization and gene order being identical to that of the typical vertebrate.     

Epitheliocystis,a new infectious disease of the bluegill (Lepomis macrochirus)

A new infectious, benign and chronic disease, histopathologically distinct from the viral disease lymphocystis, has been found in the bluegill. The symptoms are much enlarged cells in skin and gill epithelium, filled with basophilic granules. By electron microscopy these granules were shown to be organisms with the morphological characteristics ofBedsonia (Miyagawanella). During an attempt to isolate the agent in the bluegill fibroblast cell line BF-2, a cytopathic effect somewhat resembling the lesionsin vivo was found in the first passage. In later passages the agent was lost, but a true virus eliciting a distinctive fusiform cytopathic effect was recovered from these passages. The virus was found to be cytopathogenic also for the rainbow trout cell line RTG-2, but no recognizable disease could be evoked in young bluegills by inoculation of infected cell culture material. While the larger sized, non-viral organism is almost certainly the etiological agent of epitheliocystis, the role of the virus is, therefore, conjectural. Electron microscopy of thin sections has shown the virus to resemble influenza virus in morphology.     

Drag coefficient estimates from coasting bluegill sunfish Lepomis macrochirus

The drag coefficient bluegill sunfish Lepomis macrochirus was estimated from coasting deceleration as (mean ± SD) 0.0154 ± 0.0070 at a Reynolds number of 41,000 ± 14,000. This was within the coasting range in other species and lower than values obtained from dead drag measurements in this species and others. Low momentum losses during coasting may allow its use during intermittent propulsion to modulate power output or maximize energy economy.     

The intestinal loops of bluegill fish, Lepomis macrochirus

The structural configurations of the intestinal loops of bluegill fish (Lepomis macrochirus) and a correlation of their probable functional significance have been investigated. The bluegill fish accommodates its relatively large intestine in its smaller body cavity by developing two intestinal loops. Regional variations in the intestinal wall exist due to the presence of the intestinal loops. The structural complexity of the intestine by loop formation has apparently created a problem by posing an obstruction as well as deviation to the smooth flow of food. In order to solve this problem structural modifications in the walls of the intestinal loops are needed, as is observed by the variation in muscle thickness of greater and lesser curvature of both the intestinal loops.     

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.     

Genetic paternity analysis and breeding success in bluegill sunfish (Lepomis macrochirus)

Fish have some of the most complex mating systems known in the animal kingdom. With the advent of powerful genetic markers and an emerging mathematical framework to calculate parentage, it is now possible to analyze genetic relatedness and gene flow in these systems. An important example is the bluegill sunfish (Lepomis macrochirus) which consists of parental males that provide sole care for the young, cuckolder males that parasitize the parentals, and females that actively choose among males within dense breeding colonies. In this article genetic markers for bluegill are characterized and their utility in parentage studies is demonstrated by calculating the genetic relatedness of parental males to their broods for an entire natural breeding colony. A novel Monte Carlo simulation is developed to calculate the confidence in the relatedness estimates and these data are used to provide an estimate of the mean breeding success of parental and cuckolder males. Finally, the applications of genetic analyses to understanding mating systems, parental care, and life-history evolution in bluegill are discussed.     

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

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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     

Growth energy partitioning by juvenile bluegill sunfish, Lepomis macrochirus Rafinesque

Growth energy build-up and partitioning by immature bluegill sunfish were studied over the summer months from May to September 1984. Fish sampled in May showed low condition and low lipid reserves. Condition was restored to summer levels within the following month. Fat reserves were built up from 7% to 14% of body weight over the entire summer. Most (80%) of the annual length increase occurred from 1 June to 15 August. Over the winter period (October-April) condition dropped and lipids were depleted. Calculations showed that energy liberated through lipid depletion over this period could supply the energy requirements of inactive wintering fish. It is concluded that the sequencing of growth energy diversion into changes in body length, condition, and lipid build-up enhances mid-summer growth and overwinter survival.     

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     

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.     

Effects of different acids on the bluegill sunfish, Lepomis macrochirus Rafinesque

The concentration of hydrogen ions which caused 50% mortality of bluegill in 96 h (96 h LC50) was between pH 3.5 and 3.0 for four acids; sulphuric, nitric, phosphoric and hydrochloric. Therefore, it appears that any contribution by the anions of these acids to fish toxicity is similar. This suggests that the quantity rather than the quality of acids is the primary factor in fish toxicity brought about by acid precipitation.
At sublethal concentrations of acids, bluegill became hypoactive with respect to their swimming behaviour.     

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.