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

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The Effects of Satiation on Strike Mode and Prey Capture Kinematics in the Largemouth bass, Micropterus salmoides

The feeding mechanism and kinematics of prey capture have been studied in many fishes. However, the effects of satiation on the strike mode and prey capture kinematics have never been directly measured. We analyze 12 kinematic variables to determine the effects of satiation on prey capture in five largemouth bass, Micropterus salmoides, by using high speed videography. We also present the first experimental test for modulatory capabilities in response to satiation, by using the ram-suction index. Significant changes in the kinematic variables of maximum lower jaw depression, maximum gape distance, maximum hyoid depression, time to maximum hyoid depression, and time from maximum hyoid depression to recovery were seen with the effects of satiation. Change in the kinematic variables imply a decrease in jaw opening velocity and the magnitude of suction velocity created during repetitive strikes by M. salmoides with increasing satiation. The bass primarily uses a ram strike mode, with some suction bites occasionally. Ram-suction index analyses suggests that M. salmoides does not modulate strike mode in response to satiation. However, the bass modulate prey capture kinematics without altering strike mode with the effects of satiation. Prey capture success decreases in each bass, as the probability of a successful prey capture event becomes lower, with increasing satiation. These findings demonstrate that satiation can have major effects on prey capture kinematics and future studies of feeding kinematics should account for satiation in their analyses.     

Young whale sharks, Rhincodon typus, feeding on a copepod bloom near La Paz, Mexico

Seven small (3.2 to 5.2 m total length) whale sharks were observed suction feeding on patches of surface plankton in the Bay of La Paz within 1 km of shore and 2 km N of the phosphate dock at San Juan de la Costa, on 1–2 November 1993. The sharks were photographed and videotaped from the boat and by snorkelers in the water. When actively feeding the shark turned its head from side to side, part of the head was lifted out of the water, and the mouth opened and closed 7 to 28 times per minute (x=17, N=13). These suction gulps were synchronized with the opening and closing of the gill slits. This feeding behavior occurred only in the patchy areas of densely cloudy water, a layer 10 to 30 cm thick at the surface containing an immense concentration of copepods, 95% of which were identified as Acartia clausi. Remoras accompanying the whale sharks also fed on the plankton bloom. This revised version was published online in July 2006 with corrections to the Cover Date.     

Experimental study of the impacts of planktivorous fishes on plankton community and eutrophication of a tropical Brazilian reservoir

We examined the impacts of three facultative planktivorous fishes, Congo tilapia (Tilapia rendalli), bluegill (Lepomis macrochirus) and tambaqui (Colossoma macropomum), and an obligate planktivorous fish, silver carp (Hypophthalmichthys molitrix) on plankton community and water quality of a tropical eutrophic reservoir, Paranoá Reservoir, Brasília, Brazil, conducting both laboratory selective grazing experiments and an enclosure experiment. The first two species inhabit this reservoir and the remaining two are recommended for introduction. The field experiment was performed in ten limnocorrals (2 m³ each) and lasted five weeks. During the enclosure experiment, silver carp suppressed copepod nauplii, cladocerans and rotifers while the presence of tilapia and bluegill were associated with increased rotifers density. The dominant blue-green algae,Cylindrospermopsis raciborskii (98% of phytoplankton biomass) was enhanced in the presence of bluegill, tilapia and tambaqui, but reduced in the presence of silver carp. This impact on plankton is in agreement with the results of the laboratory feeding trials. The observed alterations in water quality parameters in fish limnocorrals are discussed in relation to plankton community and eutrophication of this ecosystem. It is suggested that the control of the undesirable algaeC. raciborskii directly by silver carp grazing is a promising management tool.     

A review of planktivorous fishes: Their evolution,feeding behaviours,selectivities, and impacts

The classical approach of limnologists has been to consider the interactions between lake ecosystem components as an unidirectional flow of influence from nutrients to the phytoplankton, to the zooplankton, and finally to the fish, through successive controls by physical, chemical, and biological processes (Strakraba, 1967). The effect of planktivorous fishes on zooplankton and phytoplankton communities was not recognized until the studies of Hrbáek et al. (1961), Hrbáek (1962), Brooks & Dodson (1965) and Strakraba (1965). They showed that (1) in ponds and lakes in the presence of planktivorous fishes the zooplankton communities were composed of smaller bodied species than in those lacking planktivores, and (2) the resulting small-bodied zooplankton communities affected the phytoplankton communities. Although the variability of the phytoplankton response to fish predation showed the importance of other factors (such as nutrient limitation and interspecific competition of algae), these studies emphasized that zooplankton and phytoplankton communities can be affected by the feeding selectivity of planktivorous fishes. During the last two decades, many limnological studies have focused on this dramatic impact of fish on plankton communities. The direct response of zooplankton communities to visual fish predation (i.e. particulate feeding) has been of major interest, whereas the multilevel effects of filter-feeding fish (predation on zooplankton plus grazing on phytoplankton) have been neglected. The objectives of this review are to document fish-plankton interrelationships in order to (1) provide insights into the impact of fish on plankton communities, and (2) outline mechanistic models of planktivory according to the feeding repertory and the selectivity of the fish, the adaptive responses of the plankton, and the environmental conditions.The approach adopted here is based on field and laboratory experimental results derived from the literature on tropical and temperate freshwater (occasionally marine) systems. Four types of planktivorous fish are distinguished: the gape-limited larvae and small fish species, the particulate feeders, the pump filter feeders, and the tow-net filter feeders. For each type of planktivore, the mechanisms of prey selection are analyzed from the point of view of both the predator and the prey. To investigate the main determinants of the predator feeding selectivity, and to discuss its potential effects on prey communities, the predation-act is divided into a sequence of successive events (Holling, 1966): detection, pursuit, capture, retention, and digestion for particulate feeders; and capture, retention, and digestion for filter feeders. The strengths and weaknesses of various measures of selectivity (i.e. electivity indices), as well as their appropriate usages are considered. Available prey selection models and optimal foraging theories are analyzed for the different planktivore feeding modes. Mechanistic models based on Holling's (loc. cit.) approach are proposed for each feeding mode to determine differential prey vulnerabilities and optimal diet breadth.This review has application to several fields, including general ecology, limnology, fisheries management (for example, utilization of planktonic resources, stocking, introduction, or maintenance of natural fish populations), and biological control of the eutrophication processes (biomanipulation approaches). It emphasizes the real need for more knowledge of the feeding selectivity and food utilization of planktivores. It concludes that predator and prey are mutually adapted. Thus, in most cases, study of plankton dynamics and water quality should include the assessment of fish predation and grazing pressures.     

Just keep swimming? Observations of resting behavior in gray reef sharks Carcharhinus amblyrhynchos (Bleeker, 1856)

Understanding the respiratory modes of sharks has important implications for studying the metabolism, energetics, and behavioral strategies of different species. Here we provide the first reported observations of resting behavior in the gray reef shark Carcharhinus amblyrhynchos, a species typically considered an obligate ram ventilator. Observations were made at several locations in the Republic of Seychelles, where sharks were found resting under reef ledges and were unresponsive to the presence of divers. These findings update our understanding of the respiratory mode of this species and have implications for future research.     

Some 20th century fish discoveries

Of the approximately 1.5 million species described to date, about 48 170 (3.2%) are vertebrates. Of these 24 618 (51%) are fishes. Amazingly, 41% of fishes are found in fresh water which makes up a negligible percentage of the water on earth. The sea accounts for 97% of all water on the planet and contains 58% of the fish species, mostly from shallow, warm-coastal areas. The families Cichlidae, Cyprinidae, Characidae, Loricariidae, and Cyprinodontidae constitute about half of all the recently described new freshwater fish species named in the period 1978–1993. The Gobiidae and Serranidae are the marine families with the largest number of recently described new species. The most new freshwater teleost names came from South America (39%), Africa (32%) and Asia (17%). New fish species continue to be described at the rate of roughly 130–160 each year. An estimated 13 775 new fish names have been proposed in this century, representing about 56% of all currently known fish species. Three species are discussed in detail to represent remarkable examples of 20th century fish discoveries: the coelacanth Latimeria chalumnae, the salamanderfish Lepidogalaxias salamandroides of Western Australia, and the megamouth shark Megachasma pelagios. This revised version was published online in July 2006 with corrections to the Cover Date.     

Angular roughshark Oxynotus centrina (Squaliformes: Oxynotidae) in captivity feeding exclusively on elasmobranch eggs: an overlooked feeding niche or a matter of individual taste?

A specimen of angular roughshark Oxynotus centrina has been kept successfully in captivity for the first time. Over a period of 24 months, the specimen preyed exclusively on the contents of elasmobranch egg cases, suggesting a specialized trophic niche.     

Modulation in Feeding Kinematics and Motor Pattern of the Nurse Shark <Emphasis Type="Italic">Ginglymostoma cirratum</Emphasis>

Synopsis Studies of feeding in bony fishes have almost universally demonstrated the ability of individuals to modulate their method of capture in response to differing stimuli. Preliminary evidence indicates that morphologically specialized inertial suction feeding sharks are the most likely fishes to lack inherent modulatory ability. We examined the ability of the nurse shark, Ginglymostoma cirratum, to modulate its feeding behavior based on different food types and sizes. G. cirratum is an inertial suction feeding fish that is apparently stereotyped in its food capture behavior. Electromyography showed no statistical difference between feeding motor patterns based on food type (squid or fish) or size (gape width or twice gape width), although there were slight inter-individual differences in the onset of muscle firing for some muscles. Kinematic analysis showed a statistical difference in variables associated with durations for different food types, with the durations for all variables being faster for squid bites than fish bites, but no difference based on the size of the food item. This apparent lack of modulation may be associated with specialization of the morphology and behavior of G. cirratum for obligate suction prey capture. This functional specialization constrains the method in which G. cirratum captures prey but does not appear to result in dietary specialization. An unusual post capture spit-suck manipulation allows this shark to handle and ingest large prey.     

Prey capture behavior and kinematics of the Atlantic cownose ray, Rhinoptera bonasus

The structurally reinforced jaws of the cownose ray, Rhinoptera bonasus testify to this species' durophagous diet of mollusks, but seem ill-suited to the behaviors necessary for excavating such prey. This study explores this discordance by investigating the prey excavation and capture kinematics of R. bonasus. Based on the basal suction feeding mechanism in this group of fishes, we hypothesized a hydraulic method of excavation. As expected, prey capture kinematics of R. bonasus show marked differences relative to other elasmobranchs, relating to prey excavation and use of the cephalic lobes (modified anterior pectoral fin extensions unique to derived myliobatiform rays). Prey are excavated by repeated opening and closing of the jaws to fluidize surrounding sand. The food item is then enclosed laterally by the depressed cephalic lobes, which transport it toward the mouth for ingestion by inertial suction. Unlike in most sharks, upper jaw protrusion and mandibular depression are simultaneous. During food capture, the ray's spiracle, mouth, and gill slit movements are timed such that water enters only the mouth (e.g., the spiracle closes prior to prey capture and reopens immediately following). Indigestible parts are then hydraulically winnowed from edible prey portions, by mouth movements similar to those used in excavation, and ejected through the mouth. The unique sensory/manipulatory capabilities of the cephalic lobes, as well as the cownose ray's hydraulic excavation/winnowing behaviors and suction feeding, make this species an effective benthic predator, despite its epibenthic lifestyle.     

Biomechanical trade-offs bias rates of evolution in the feeding apparatus of fishes

Morphological diversification does not proceed evenly across the organism. Some body parts tend to evolve at higher rates than others, and these rate biases are often attributed to sexual and natural selection or to genetic constraints. We hypothesized that variation in the rates of morphological evolution among body parts could also be related to the performance consequences of the functional systems that make up the body. Specifically, we tested the widely held expectation that the rate of evolution for a trait is negatively correlated with the strength of biomechanical trade-offs to which it is exposed. We quantified the magnitude of trade-offs acting on the morphological components of three feeding-related functional systems in four radiations of teleost fishes. After accounting for differences in the rates of morphological evolution between radiations, we found that traits that contribute more to performance trade-offs tend to evolve more rapidly, contrary to the prediction. While ecological and genetic factors are known to have strong effects on rates of phenotypic evolution, this study highlights the role of the biomechanical architecture of functional systems in biasing the rates and direction of trait evolution.     

Stereotypic behavior in wild marine carnivores?

Stereotypic behavior is observed in many species within zoological institutions. Attempts to reduce such behavior typically involve some form of environmental enrichment that provides opportunities for species appropriate behavior or some degree of control within the environment. However, environmental enrichment has never been completely successful in eliminating stereotypic behavior for an entire group of animals within a zoological facility. In the wild, stereotypic behavior is rarely observed. Documenting the occurrence of stereotypic behavior in the wild, and circumstances in which it occurs, could help provide insight into the causes of such behavior within zoological institutions. The following commentary details the observations of wild lemon sharks (Negaprion brevirostris) engaging in a stereotyped swimming pattern behind a research vessel north of Grand Bahama Island, Bahamas. We consider a possible explanation for the sharks' behavior and hope to stimulate conversation as well as increase examination of animal management routines in zoological facilities. Zoo Biol 30:365–370, 2011. © 2010 Wiley‐Liss, Inc.     

应用脂肪酸组成研究热带东太平洋同域中上层鲨鱼营养生态位分化

物种对食物资源利用方式的差异,即营养生态位分化是物种共存的先决条件之一,对种间营养生态位的比较研究有助于了解同域分布物种的共存机制。脂肪酸组成可反映生物较长时间尺度的摄食信息,对探讨物种间营养生态位分化具有重要指示作用。热带东太平洋主要栖息有8种大型中上层鲨鱼,大青鲨(Prionace glauca)、大眼长尾鲨(Alopias superciliosus)、镰状真鲨(Carcharhinus falciformis)、长鳍真鲨(Carcharhinus longimanus)、浅海长尾鲨(Alopias pelagicus)、尖吻鲭鲨(Isurus oxyrinchus)、路氏双髻鲨(Sphyrna lewini)和锤头双髻鲨(Sphyrna zygaena),通过比较其肌肉脂肪酸组成,分析种间食性差异,营养关系及营养生态位分化。结果表明,尖吻鲭鲨营养级相对较高,大青鲨相对较低。3种鼠鲨与5种真鲨存在食性差异或栖息地隔离。浅海长尾鲨与大眼长尾鲨营养生态位重叠程度较高,存在激烈的资源竞争。大青鲨与镰状真鲨生态位宽度较大,表征其对环境的可塑性较强;尖吻鲭鲨和路氏双髻鲨生态位宽度较小,表现为其食性的特化。本研究解释了脂肪酸组成分析在鲨鱼摄食研究中的潜在应用,对分析大洋性鲨鱼的营养生态位分化,资源分配方式及同域共存机制有一定的应用价值。