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In their natural habitat, fish rarely swim steadily. Instead they frequently accelerate and decelerate. Relatively little is known about how fish produce extra force for acceleration in routine swimming behavior. In this study, we examined the flow around bluegill sunfish Lepomis macrochirus during steady swimming and during forward acceleration, starting at a range of initial swimming speeds. We found that bluegill produce vortices with higher circulation during acceleration, indicating a higher force per tail beat, but they do not substantially redirect the force. We quantified the flow patterns using high speed video and particle image velocimetry and measured acceleration with small inertial measurement units attached to each fish. Even in steady tail beats, the fish accelerates slightly during each tail beat, and the magnitude of the acceleration varies. In steady tail beats, however, a high acceleration is followed by a lower acceleration or a deceleration, so that the swimming speed is maintained; in unsteady tail beats, the fish maintains the acceleration over several tail beats, so that the swimming speed increases. We can thus compare the wake and kinematics during single steady and unsteady tail beats that have the same peak acceleration. During unsteady tail beats when the fish accelerates forward for several tail beats, the wake vortex forces are much higher than those at the same acceleration during single tail beats in steady swimming. The fish also undulates its body at higher amplitude and frequency during unsteady tail beats. These kinematic changes likely increase the fluid dynamic added mass of the body, increasing the forces required to sustain acceleration over several tail beats. The high amplitude and high frequency movements are also likely required to generate the higher forces needed for acceleration. Thus, it appears that bluegill sunfish face a trade-off during acceleration: the body movements required for acceleration also make it harder to accelerate. [ABSTRACT FROM AUTHOR]

Suction-feeding fish rapidly expand the mouth cavity to generate high-velocity fluid flows that accelerate food into the mouth. Such fast and forceful suction expansion poses a challenge, as muscle power is limited by muscle mass and the muscles in fish heads are relatively small. The largemouth bass powers expansion with its large body muscles, with negligible power produced by the head muscles (including the sternohyoideus). However, bluegill sunfish -- with powerful strikes but different morphology and feeding behavior -- may use a different balance of cranial and axial musculature to power feeding and different power outputs from these muscles. We estimated the power required for suction expansion in sunfish from measurements of intraoral pressure and rate of volume change, and measured muscle length and velocity. Unlike largemouth bass, the sternohyoideus did shorten to generate power, but it and other head muscles were too small to contribute more than 5-10% of peak expansion power in sunfish. We found no evidence of catapult-style power amplification. Instead, sunfish powered suction feeding by generating high power outputs (up to 438 W kg-1) from their axial muscles. These muscles shortened across the cranial half of the body as in bass, but at faster speeds that may be nearer the optimum for power production. Sunfish were able to generate strikes of the same absolute power as bass, but with 30-40% of the axial muscle mass. Thus, species may use the body and head muscles differently to meet the requirements of suction feeding, depending on their morphology and behavior. [ABSTRACT FROM AUTHOR]

For many fish species, the pectoral fins serve as important propulsors and stabilizers and are precisely controlled. Although it has been shown that mechanosensory feedback from the fin ray afferent nerves provides information on ray bending and position, the effects of this feedback on fin movement are not known. In other taxa, including insects and mammals, sensory feedback from the limbs has been shown to be important for control of limb-based behaviors and we hypothesized that this is also the case for the fishes. In this study, we examined the impact of the loss of sensory feedback from the pectoral fins on movement kinematics during hover behavior. Research was performed with bluegill sunfish (Lepomis macrochirus), a model for understanding the biomechanics of swimming and for bio-inspired design of engineered fins. The bluegill beats its pectoral fins rhythmically, and in coordination with pelvic and median fin movement, to maintain a stationary position while hovering. Bilateral deafferentation of the fin rays results in a splay-finned posture where fins beat regularly but at a higher frequency and without adducting fully against the side of the body. For unilateral transections, more irregular changes in fin movements were recorded. These data indicate that sensory feedback from the fin rays and membrane is important for generating normal hover movements but is not necessary for generating rhythmic fin movement. [ABSTRACT FROM AUTHOR]

In their natural environment, fish must swim stably through unsteady flows and vortices, including vertical vortices, typically shed by posts in a flow, horizontal cross-flow vortices, often produced by a step or a waterfall in a stream, and streamwise vortices, where the axis of rotation is aligned with the direction of the flow. Streamwise vortices are commonly shed by bluff bodies in streams and by ships' propellers and axial turbines, but we know little about their effects on fish. Here, we describe how bluegill sunfish use more energy and are destabilized more often in flow with strong streamwise vorticity. The vortices were created inside a sealed flow tank by an array of four turbines with similar diameter to the experimental fish. We measured oxygen consumption for seven sunfish swimming at 1.5 body lengths (BL) s~1 with the turbines rotating at 2 Hz and with the turbines off (control). Simultaneously, we filmed the fish ventrally and recorded the fraction of time spent maneuvering side-to-side and accelerating forward. Separately, we also recorded lateral and ventral video for a combination of swimming speeds (0.5, 1.5 and 2.5 BL s-1) and turbine speeds (0, 1, 2 and 3 Hz), immediately after turning the turbines on and 10 min later to test for accommodation. Bluegill sunfish are negatively affected by streamwise vorticity. Spills (loss of heading), maneuvers and accelerations were more frequent when the turbines were on than in the control treatment. These unsteady behaviors, particularly acceleration, correlated with an increase in oxygen consumption in the vortex flow. Bluegill sunfish are generally fast to recover from roll perturbations and do so by moving their pectoral fins. The frequency of spills decreased after the turbines had run for 10 min, but was still markedly higher than in the control, showing that fish partially adapt to streamwise vorticity, but not completely. Coping with streamwise vorticity may be an important energetic cost for stream fishes or migratory fishes. [ABSTRACT FROM AUTHOR]

An undulatory pattern of body bending in which waves pass along the body from head to tail is a major mechanism of creating thrust in many fish species during steady locomotion. Analyses of live fish swimming have provided the foundation of our current understanding of undulatory locomotion, but our inability to experimentally manipulate key variables such as body length, flexural stiffness and tailbeat frequency in freely swimming fish has limited our ability to investigate a number of important features of undulatory propulsion. In this paper we use a mechanical flapping apparatus to create an undulatory wave in swimming flexible foils driven with a heave motion at their leading edge, and compare this motion with body bending patterns of bluegill sunfish (Lepomis macrochirus) and clown knifefish (Notopterus chitala). We found similar swimming speeds, Reynolds and Strouhal numbers, and patterns of curvature and shape between these fish and foils, suggesting that flexible foils provide a useful model for understanding fish undulatory locomotion. We swam foils with different lengths, stiffnesses and heave frequencies while measuring forces, torques and hydrodynamics. From measured forces and torques we calculated thrust and power coefficients, work and cost of transport for each foil. We found that increasing frequency and stiffness produced faster swimming speeds and more thrust. Increasing length had minimal impact on swimming speed, but had a large impact on Strouhal number, thrust coefficient and cost of transport. Foils that were both stiff and long had the lowest cost of transport (in mJ m−1 g−1) at low cycle frequencies, and the ability to reach the highest speed at high cycle frequencies. [ABSTRACT FROM AUTHOR]

Fast starts are crucial in the survival of aquatic swimmers to capture prey or avoid predators. Currently, it is widely accepted that during C-starts: (1) the caudal fin generates a considerable hydrodynamic force; and (2) anal/dorsal fins are erected to significantly increase the hydrodynamic force. In this work, the above hypotheses on the role of fins during C-starts are studied using experimentally guided numerical simulations of four bluegill sunfish, whose fins are removed or erected. The amount of force created by the body and fins at each time instant was not constant and varied during the C-start. Nevertheless, in agreement with hypothesis (1), up to 70% of the instantaneous hydrodynamic force was generated by the tail during Stage 2 of the C-start, when the sunfish rapidly bends out of the C-shape. Additionally, the contribution in Stage 1, when the sunfish bends into a C-shape, is less than 20% at each instant. Most of the force in Stage 1 was produced by the body of the sunfish. In contrast to hypothesis (2), the effect of erection/removal of the fins was less than 5% of the instantaneous force in both Stages 1 and 2, except for a short period of time (2 ms) just before Stage 2. However, it is known that the anal/dorsal fins are actively controlled during the C-start from muscle activity measurements. Based on the results presented here, it is suggested that the active control of the anal/dorsal fins can be related to retaining the stability of the sunfish against roll and pitch movements during the C-start. Furthermore, the erection of the fins increases the moment of inertia to make the roll and pitch movements more difficult. [ABSTRACT FROM AUTHOR]

Although kinematic analysis of individual fin rays provides valuable insight into the contribution of median fins to C-start performance, it paints an incomplete picture of the complex movements and deformation of the flexible fin surface. To expand our analysis of median fin function during the escape response of bluegill sunfish (Lepomis macrochirus), patterns of spanwise and chordwise curvature of the soft dorsal and anal fin surfaces were examined from the same video sequences previously used in analysis of fin-ray movement and orientation. We found that both the span and chord undergo undulation, starting in the anterior region of either fin. Initiated early in Stage 1 of the C-start, the undulation travels in a postero-distal direction, reaching the trailing edge of the fins during early Stage 2. Maximum spanwise curvature typically occurred among the more flexible posterior fin rays, though there was no consistent correlation between maximum curvature and fin-ray position. Undulatory patterns suggest different mechanisms of action for the fin regions. In the anterior fin region, where the fin rays are oriented dorsoventrally, undulation is directed primarily chordwise, initiating a transfer of momentum into the water to overcome the inertia of the flow and direct the water posteriorly. Within the posterior region, where the fin rays are oriented caudally, undulation is predominantly directed spanwise; thus, the posterior fin region acts to ultimately accelerate this water towards the tail to increase thrust forces. Treatment of median fins as appendages with uniform properties does not do justice to their complexity and effectiveness as control surfaces. [ABSTRACT FROM AUTHOR]

The fast-start escape response is critically important to avoid predation, and axial movements driving it have been studied intensively. Large median dorsal and anal fins located near the tail have been hypothesized to increase acceleration away from the threat, yet the contribution of flexible median fins remains undescribed. To investigate the role of median fins, C-start escape responses of bluegill sunfish (Lepomis macrochirus) were recorded by three high-speed, high-resolution cameras at 500framess"1 and the 3-D kinematics of individual dorsal and anal fin rays were analyzed. Movement and orientation of the fin rays relative to the body axis were calculated throughout the duration of the C-start. We found that: (1) timing and magnitude of angular displacement varied among fin rays based on position within the fin and (2) kinematic patterns support the prediction that fin rays are actively resisting hydrodynamlc forces and transmitting momentum into the water. We suggest that regions within the fins have different roles. Anterior regions of the fins are rapidly elevated to increase the volume of water that the fish may interact with and transmit force into, thus generating greater total momentum. The movement pattern of all the fin rays creates traveling waves that move posteriorly along the length of the fin, moving water as they do so. Flexible posterior regions ultimately act to accelerate this water towards the tail, potentially interacting with vortices generated by the caudal fin during the C-start. Despite their simple appearance, median fins are highly complex and versatile control surfaces that modulate locomotor performance. [ABSTRACT FROM AUTHOR]

A protrusible upper jaw has independently evolved multiple times within teleosts and has been implicated in the success of two groups in particular: Acanthomorpha and Cypriniformes. We use digital particle image velocimetry (DPIV) to compare suction feeding flow dynamics in a representative of each of these clades: goldfish and bluegill. Using DPIV, we contrast the spatial pattern of flow, the temporal relationship between flow and head kinematics, and the contribution of jaw protrusion to the forces exerted on prey. As expected, the spatial patterns of flow were similar in the two species. However, goldfish were slower to reach maximal kinematic excursions, and were more flexible in the relative timing of jaw protrusion, other jaw movements and suction flows. Goldfish were also able to sustain flow speeds for a prolonged period of time as compared with bluegill, in part because goldfish generate lower peak flow speeds. In both species, jaw protrusion increased the force exerted on the prey. However, slower jaw protrusion in goldfish resulted in less augmentation of suction forces. This difference in force exerted on prey corresponds with differences in trophic niches and feeding behavior of the two species. The bluegill uses powerful suction to capture insect larvae whereas the goldfish uses winnowing to sort through detritus and sediment. The kinethmoid of goldfish may permit jaw protrusion that is independent of lower jaw movement, which could explain the ability of goldfish to decouple suction flows (due to buccal expansion) from upper jaw protrusion. Nevertheless, our results show that jaw protrusion allows both species to augment the force exerted on prey, suggesting that this is a fundamental benefit of jaw protrusion to suction feeders. [ABSTRACT FROM AUTHOR]

In this work we study the hydrodynamics of a bluegill sunfish performing a C-start maneuver in unprecedented detail using 3-D numerical simulations guided by previous laboratory experiments with live fish. The 3-D fish body geometry and kinematics are reconstructed from the experiments using high-speed video and prescribed as input to the numerical simulation. The calculated instantaneous flow fields at various stages of the C-start maneuver are compared with the two-dimensional particle image velocimetry measurements, and are shown to capture essentially all flow features observed in the measurements with good quantitative accuracy; the simulations reveal the experimentally observed three primary jet flow patterns whose momentum time series are in very good agreement with the measured flow field. The simulations elucidate for the first time the complex 3-D structure of the wake during C-starts, revealing an intricate vortical structure consisting of multiple connected vortex loops at the end of the C-start. We also find that the force calculated based on the 3-D flow field has higher magnitudes than that implied by the jet momentum on the midplane, and it exhibits large and rapid fluctuations during the two stages of the C-start. These fluctuations are physical and are related to the change in the direction of the acceleration of the fish body, which changes the location of the high and low pressure pockets around the fish. [ABSTRACT FROM AUTHOR]

We designed a robotic fish caudal fin with six individually moveable fin rays based on the tail of the bluegill sunfish, Lepomis macrochirus. Previous fish robotic tail designs have loosely resembled the caudal fin of fishes, but have not incorporated key biomechanical components such as fin rays that can be controlled to generate complex tail conformations and motion programs similar to those seen in the locomotor repertoire of live fishes. We used this robotic caudal fin to test for the effects of fin ray stiffness, frequency and motion program on the generation of thrust and lift forces. Five different sets of fin rays were constructed to be from 150 to 2000 times the stiffness of biological fin rays, appropriately scaled for the robotic caudal fin, which had linear dimensions approximately four times larger than those of adult bluegill sunfish. Five caudal fin motion programs were identified as kinematic features of swimming behaviors in live bluegill sunfish, and were used to program the kinematic repertoire: flat movement of the entire fin, cupping of the fin, W-shaped fin motion, fin undulation and rolling movements. The robotic fin was flapped at frequencies ranging from 0.5 to 2.4 Hz. All fin motions produced force in the thrust direction, and the cupping motion produced the most thrust in almost all cases. Only the undulatory motion produced lift force of similar magnitude to the thrust force. More compliant fin rays produced lower peak magnitude forces than the stiffer fin rays at the same frequency. Thrust and lift forces increased with increasing flapping frequency; thrust was maximized by the 500× stiffness fin rays and lift was maximized by the 1000× stiffness fin rays. [ABSTRACT FROM AUTHOR]

A biorobotic pectoral fin was developed and used to study how the flexural rigidities of fin rays within a highly deformable fish fin affect the fin's propulsive forces. The design of the biorobotic fin was based on a detailed analysis of the pectoral fin of the bluegill sunfish (Lepomis macrochirus). The biorobotic fin was made to execute the kinematics used by the biological fin during steady swimming, and to have structural properties that modeled those of the biological fin. This resulted in an engineered fin that had a similar interaction with the water as the biological fin and that created close approximations of the three-dimensional motions, flows, and forces produced by the sunfish during low speed, steady swimming. Experimental trials were conducted during which biorobotic fins of seven different stiffness configurations were flapped at frequencies from 0.5 to 2.0 Hz in flows with velocities that ranged from 0 to 270 mm s1. During these trials, thrust and lift forces were measured, kinematics were recorded in three dimensions, and digital particle image velocimetry was used to evaluate flow hydrodynamics. The results of the trials revealed that slight changes to the fin's mechanical properties or to the operating conditions can have significant impact on the direction, magnitude and time course of the propulsive forces. In general, the magnitude of the 2-D (thrust and lift) propulsive force scaled with fin ray stiffness, and increased as the fin's flapping speed increased or as the velocity of the flow decreased. [ABSTRACT FROM AUTHOR]

Energetic analysis of ecologically relevant behaviors can be useful because animals are energetically limited by available muscle mass. In this study we hypothesized that two major determinants of suction feeding performance, the magnitudes of buccal volumetric expansion and subambient buccal pressure, would be correlated with, and limited by, available muscle mass. At least four individuals of three centrarchid species were studied: largemouth bass (Micropterus salmoides), bluegill (Lepomis macrochirus) and green sunfish (Lepomis cyanellus). Buccal pressure was measured directly via cannulation of the buccal cavity with a catheter-tipped pressure transducer. Buccal expansion was estimated from lateral high-speed video (500 or 1000Hz) sequences and published data on internal kinematics of largemouth bass. These estimates were calibrated from silicone casts made of the buccal cavity post-mortem. Estimated work and power were found to be significantly correlated with muscle mass over all individuals. The slopes of these relationships, estimates of mass-specific muscle work and power, were found to be 11±2 J kg-1 and 300±75W kg-1, respectively. These estimates are consistent with observations made of in vivo and in vitro muscle use and with digital particle image velocimetry measurements of water flow in feeding centrarchids. A direct trade-off between mean pressure and change in volume was observed, when the latter was normalized to muscle mass. We conclude that available muscle mass may be a useful metric of suction feeding performance, and that the ratio of muscle mass to buccal volume may be a useful predictor of subambient buccal pressure magnitude. [ABSTRACT FROM AUTHOR]

Evolutionary patterns of intrinsic caudal musculature in ray-finned fishes show that fine control of the dorsal lobe of the tall evolved first, followed by the ability to control the ventral lobe. This progression of increasing differentiation of musculature suggests specialization of caudal muscle roles. Fine control of fin elements is probably responsible for the range of fin conformations observed during different maneuvering behaviors. Here, we examine the kinematics of the caudal fin and the motor activity of the intrinsic caudal musculature during kick-and-glide, braking and backing maneuvers, and compare these data with our previous work on the function of the caudal fin during steady swimming. Kick-and-glide maneuvers consisted of large- amplitude, rapid lateral excursion of the tail fin, followed by forward movement of the fish with the caudal fin rays adducted to reduce surface area and with the tail held in line with the body. Just before the kick, the flexors dorsalis and ventralis, hypochordal longitudinalis, infracarinalis and supracarinalis showed strong activity. During braking, the dorsal and ventral lobes of the tail moved in opposite directions, forming an 'S'-shape, accompanied by strong activity in the interradialis muscles. During backing up, the ventral lobe initiated a dorsally directed wave along the distal edge of the caudal fin. The relative timing of the intrinsic caudal muscles varied between maneuvers, and their activation was independent of the activity of the red muscle of the axial myomeres in the caudal region. There was no coupling of muscle activity duration and electromyographic burst intensity in the intrinsic caudal muscles during maneuvers, as was observed in previous work on steady swimming. Principal-component analysis produced four components that cumulatively explained 73.6% of the variance and segregated kick-and-glide, braking and backing maneuvers from each other and from steady swimming. The activity patterns of the intrinsic caudal muscles during maneuvering suggest motor control independent from myotomal musculature, and specialization of individual muscles for specific kinematic roles. [ABSTRACT FROM AUTHOR]

Escape responses of fishes are one of the best characterized vertebrate behaviors, with extensive previous research on both the neural control and biomechanics of startle response performance. However, very little is known about the hydrodynamics of escape responses, despite the fact that understanding fluid flow patterns during the escape is critical for evaluating how body movement transfers power to the fluid, for defining the time course of power generation, and for characterizing the wake signature left by escaping fishes, which may provide information to predators. In this paper, we present an experimental hydrodynamic analysis of the C-start escape response in bluegill sunfish (Lepomis macrochirus). We used time-resolved digital particle image velocimetry at l000framess-1 (fps) to image flow patterns during the escape response. We analyzed flow patterns generated by the body separately from those generated by the dorsal and anal fins to assess the contribution of these median fins to escape momentum. Each escape response produced three distinct jets of fluid. Summing the components of fluid momentum in the jets provided an estimate of fish momentum that did not differ significantly from momentum measured from the escaping fish body. In contrast to conclusions drawn from previous kinematic analyses and theoretical models, the caudal fin generated momentum that opposes the escape during stage one, whereas the body bending during stage one contributed substantial propulsive momentum. Additionally, the dorsal and anal fins each contributed substantial momentum. The results underscore the importance of the dorsal and anal fins as propulsors and suggest that the size and placement of these fins may be a key determinant of fast start performance. [ABSTRACT FROM AUTHOR]

Many fish change gait within their aerobically supported range of swimming speeds. The effects of acute temperature change on this type of locomotor behavior are poorly understood. Bluegill sunfish swim in the labriform mode at low speeds and switch to undulatory swimming as their swimming speed increases. Maximum aerobic swimming speed (Umax), labriform-undulatory gait transition speed (Utrans) and the relationships between fin beat frequency and speed were measured at 14, 18, 22, 26 and 30°C in bluegill acclimated to 22°C. At temperatures below the acclimation temperature (Ta), Umax, Utrans and the caudal and pectoral fin beat frequencies at these speeds were reduced relative to the acclimation level. At temperatures above Ta there was no change in these variables relative to the acclimation level. Supplementation of oxygen levels at 30°C had no effect on swimming performance. The mechanical power output of the abductor superficialis, a pectoral fin abductor muscle, was measured in vitro at the same temperatures used for the swimming experiments. At and below Ta, maximal power output was produced at a cycle frequency approximately matching the in vivo pectoral fin beat frequency. At temperatures above Ta muscle power output and cycle frequency could be increased above the in vivo levels at Utrans. Our data suggest that the factors triggering the labriform-undulatory gait transition change with temperature. Muscle mechanical performance limited labriform swimming speed at Ta and below, but other mechanical or energetic factors limited labriform swimming speed at temperatures above Ta. [ABSTRACT FROM AUTHOR]

There are approximately 50 muscles that control tail fin shape in most teleost fishes, and although myotomal muscle function has been extensively studied, little work has been done on the intrinsic musculature that controls and shapes the tail. In this study we measured electrical activity in intrinsic tail musculature to determine if these muscles are active during steady rectilinear locomotion, and to compare intrinsic muscle recruitment patterns to previous data on myotomal muscle fibers. Five bluegill sunfish (Lepomis macrochlrus) were anaesthetized and electrode wires surgically placed into a total of 24 intrinsic caudal muscles, up to 13 at a time, and activity was correlated with synchronous recordings from myotomal fibers In the caudal peduncle. After recovery, fish swam steadily at speeds of 0.5, 1.2 and 2.0 L s-1, while filmed from lateral, posterior and ventral views simultaneously at 250 frames s-1. Comparison among speeds confirmed that muscle recruitment varies significantly with speed. At 0.5 L s-1, the caudal fin was generally not used for propulsion, and swimming was accomplished primarily through body undulations. Intrinsic caudal muscle activity at this speed was intermittent and variable. At 1.2 and 2.0 L s-1, the supracarinalis and infracarinalis muscles acted on the dorsal- and ventral-most fin rays, respectively, to expand the surface area of the caudal fin. The interradialis muscles adducted individual fin rays, dorsally to ventrally, following activation of the hypochordal longitudinalis. Contralateral muscle activity of interradialis muscles occurred as the caudal fin crossed the mean direction of travel and fin height was greatest, whereas ipsilateral activity of carinalis muscles occurred near points of maximum excursion of the fin, at speeds of 1.2 and 2.0 L s-1, after fin height was lowest. Burst intensity increased with swimming speed, suggesting stiffening of the tail fin against imposed hydrodynamic loads. Activity patterns of intrinsic caudal muscles suggest that these most posterior muscles in fishes, located within the tail, are among the very first recruited as swimming speed increases, and that slow undulatory swimming is powered by muscle fibers located posteriorly in the caudal peduncle and tail. [ABSTRACT FROM AUTHOR]

As their swimming speed increased, bluegill sunfish (Lepomis macrochirus) switched from pectoral-fin-powered labriform swimming to undulations of the body axis. This gait transition occurred at a mean swimming speed of 0.24±0.01 m s-1 and a pectoral fin beat frequency of 2.79±0.11 Hz (mean ± s.e.m., N=6). The power output available from the main upstroke (adductor profundus) and downstroke (abductor superficialis) muscles, measured using the work-loop technique was maximal at the gait transition point. The cost of transport, measured by respirometry, increased as the fish switched from labriform to undulatory swimming. Our data show that bluegill changed gait as swimming speed increased to recruit additional muscle mass, rather than to maximize economy, as is the case for many terrestrial animals. [ABSTRACT FROM AUTHOR]

Bluegill sunfish (Lepomis macrochirus) swim in the labriform mode at low speeds, generating lift and thrust by beating their pectoral fins. The maximal power output available from the two largest pectoral fin adductor and abductor muscles, constituting half of the total pectoral girdle muscle mass, was measured in vitro and used to estimate the muscle mechanical power output during maximal labriform swimming (Pmech; 0.15–0.21 W kg-1 body mass). Respirometry was used to estimate the total metabolic power input (Ptotal; 0.95 W kg-1 body mass) and the metabolic power available to the active muscle mass (Pmuscle; Ptotal minus standard metabolic rate, 0.57 W kg-1 body mass) at this swimming speed. Drag measurements made on towed, dead fish were used to estimate the mechanical power required to overcome body drag (Pdrag; 0.028 W kg-1 body mass). Efficiency estimates based on these data fell into the following ranges: overall swimming efficiency (ηgross=Pmech/PtotaI), 0.16–0.22; muscle efficiency (ηmuscle=Pmech/Pmuscle), 0.26–0.37; and propeller efficiency (ηprop=Pdrag/Pmech), 0.15–0.20. Comparison with other studies suggests that labriform swimming may be more efficient than swimming powered by undulations of the body axis. [ABSTRACT FROM AUTHOR]

During aquatic suction feeding, the predator opens its mouth and rapidly expands its buccal cavity, generating a flow field external to the mouth. The rapid expansion of the buccal cavity produces high fluid velocities and accelerations that extend only a short distance from the mouth (about half of one mouth diameter), and only persist for several milliseconds. Therefore, the predator must precisely time its strike to locate the prey within the narrow region of high flow, during the brief period when flow is at its peak. With flow being the agent for transferring force to the prey, the predator may enhance these forces by producing higher water velocities and faster acceleration at the mouth, but also through increasing the strike's accuracy, i.e. locating the prey closer to the mouth at the instant of peak flow speed. The objectives of this study were to directly measure forces exerted by bluegill Lepomis macrochirus on their prey and to determine how bluegill modify force output. Bluegill were offered ghost shrimp tethered to a load cell that recorded force at 5000 Hz, and feeding sequences were synchronously recorded using 500 Hz video. Peak forces exerted on attached 20 mm shrimp ranged from 0.005 N to 0.506 N. In accordance with the short duration of the strikes (average time to peak gape of ∼13 ms), the forces recorded were brief (∼12 ms from initiation to peak force), and force magnitude declined rapidly after peak force. Statistical analysis indicated that rate of buccal expansion, and prey size, but not strike initiation distance, significantly affected peak force. These observed variables were used with results from flow visualization studies to estimate the flow at the prey's location, which allowed the calculation of drag, pressure gradient force and acceleration reaction force. The relationship between these calculated forces and the measured forces was strong, indicating that the model can be used to estimate forces from strike kinematics. This model was then used to study the effects of strike initiation distance on peak force and on the rate of increasing force. Comparisons of model output to empirical results indicated that bluegill time their strike so as to exert an average of ∼70% of the peak possible force on the prey, and that the observed strike initiation distance corresponded to the distance that maximized modeled force on an attached prey. Our results highlight the ability of bluegill to produce high forces on their prey, and indicate that precision and visual acuity play important roles in prey acquisition, beyond their recognized role in prey detection. [ABSTRACT FROM AUTHOR]

Swimming and flying animals generate unsteady locomotive forces by delivering net momentum into the fluid wake. Hence, swimming and flying forces can be quantified by measuring the momentum of animal wakes. A recently developed model provides an approach to empirically deduce swimming and flying forces based on the measurement of velocity and vortex added-mass in the animal wake. The model is contingent on the identification of the vortex boundary in the wake. This paper demonstrates the application of that method to a case study quantifying the instantaneous locomotive forces generated by the pectoral fins of the bluegill sunfish (Lepomis macrochirus Rafinesque), measured using digital particle image velocimetry (DPIV). The finite-time Lyapunov exponent (FTLE) field calculated from the DPIV data was used to determine the wake vortex boundary, according to recently developed fluid dynamics theory. Momentum of the vortex wake and its added-mass were determined and the corresponding instantaneous locomotive forces were quantified at discrete time points during the fin stroke. The instantaneous forces estimated in this study agree in magnitude with the time-averaged forces quantified for the pectoral fin of the same species swimming in similar conditions and are consistent with the observed global motion of the animals. A key result of this study is its suggestion that the dynamical effect of the vortex wake on locomotion is to replace the real animal fin with an ‘effective appendage’, whose geometry is dictated by the FTLE field and whose interaction with the surrounding fluid is wholly dictated by inviscid concepts from potential flow theory. Benefits and limitations of this new framework for non-invasive instantaneous force measurement are discussed, and its application to comparative biomechanics and engineering studies is suggested. [ABSTRACT FROM AUTHOR]

Suction feeding fish draw prey into the mouth using a flow field that they generate external to the head. In this paper we present a multidimensional perspective on suction feeding performance that we illustrate in a comparative analysis of suction feeding ability in two members of Centrarchidae, the largemouth bass (Micropterus salmoides) and bluegill sunfish (Lepomis macrochirus). We present the first direct measurements of maximum fluid speed capacity, and we use this to calculate local fluid acceleration and volumetric flow rate. We also calculated the ingested volume and a novel metric of strike accuracy. In addition, we quantified for each species the effects of gape magnitude, time to peak gape, and swimming speed on features of the ingested volume of water. Digital particle image velocimetry (DPIV) and high-speed video were used to measure the flow in front of the mouths of three fish from each species in conjunction with a vertical laser sheet positioned on the mid-sagittal plane of the fish. From this we quantified the maximum fluid speed (in the earthbound and fish's frame of reference), acceleration and ingested volume. Our method for determining strike accuracy involved quantifying the location of the prey relative to the center of the parcel of ingested water. Bluegill sunfish generated higher fluid speeds in the earthbound frame of reference, accelerated the fluid faster, and were more accurate than largemouth bass. However, largemouth bass ingested a larger volume of water and generated a higher volumetric flow rate than bluegill sunfish. In addition, because largemouth bass swam faster during prey capture, they generated higher fluid speeds in the fish's frame of reference. Thus, while bluegill can exert higher drag forces on stationary prey items, largemouth bass more quickly close the distance between themselves and prey. The ingested volume and volumetric flow rate significantly increased as gape increased for both species, while time to peak gape had little effect on the volume. However, peak gape distance did not affect the maximum fluid speed entering the mouth for either species. We suggest that species that generate high fluid speeds in the earthbound frame of reference will commonly exhibit small mouths and a high capacity to deliver force to buccal expansion, while species that ingest a large volume of water and generate high volumetric flow rates will have larger buccal cavities and cranial expansion linkage systems that favor displacement over force delivery. [ABSTRACT FROM AUTHOR]

Fishes have an enormous diversity of body shapes and fin morphologies. From a hydrodynamic standpoint, the functional significance of this diversity is poorly understood, largely because the three-dimensional flow around swimming fish is almost completely unknown. Fully three-dimensional volumetric flow measurements are not currently feasible, but measurements in multiple transverse planes along the body can illuminate many of the important flow features. In this study, I analyze flow in the transverse plane at a range of positions around bluegill sunfish Lepomis macrochirus, from the trailing edges of the dorsal and anal fins to the near wake. Simultaneous particle image velocimetry and kinematic measurements were performed during swimming at 1.2 body lengths s-1 to describe the streamwise vortex structure, to quantify the contributions of each fin to the vortex wake, and to assess the importance of three-dimensional flow effects in swimming. Sunfish produce streamwise vortices from at least eight distinct places, including both the dorsal and ventral margins of the soft dorsal and anal fins, and the tips and central notched region of the caudal fin. I propose a three-dimensional structure of the vortex wake in which these vortices from the caudal notch are elongated by the dorso-ventral cupping motion of the tail, producing a structure like a hairpin vortex in the caudal fin vortex ring. Vortices from the dorsal and anal fin persist into the wake, probably linking up with the caudal fin vortices. These dorsal and anal fin vortices do not differ significantly in circulation from the two caudal fin tip vortices. Because the circulations are equal and the length of the trailing edge of the caudal fin is approximately equal to the combined trailing edge length of the dorsal and anal fins, I argue that the two anterior median fins produce a total force that is comparable to that of the caudal fin. To provide additional detail on how different positions contribute to total force along the posterior body, the change in vortex circulation as flow passes down the body is also analyzed. The posterior half of the caudal fin and the dorsal and anal fins add vortex circulation to the flow, but circulation appears to decrease around the peduncle and anterior caudal fin. Kinematic measurements indicate that the tail is angled correctly to enhance thrust through this interaction. Finally, the degree to which the caudal fin acts like a idealized two-dimensional plate is examined: approximately 25% of the flow near the tail is accelerated up and down, rather than laterally, producing wasted momentum, a loss not present in ideal two-dimensional theories. [ABSTRACT FROM AUTHOR]

Many natural animal movements involve accelerating from a standstill and then stopping. Obstacles in natural environments often limit the straight-line distance available for movement, and decreased braking ability theoretically can limit speed for short distances. Consequently, braking ability can be important for avoiding collisions with obstacles and exploiting resources effectively in complex environments. A presumed morphological correlate of improved braking performance in fish is increased pectoral fin area, because most fish protract these structures as they decelerate. However, the kinematics and modulation of velocity during starting and stopping are poorly understood for most species of fish as well as most species of animals. Thus, for bluegill sunfish Lepomis macrochirus with complete and partially ablated pectoral fins (35% original fin area), we analyzed high speed video recordings (200 images s-1) of predatory attacks with a start and stop in a short, standardized distance (40 cm). We quantified body displacement, velocity, acceleration, deceleration and several fin angle variables during each feeding. Unexpectedly, several variables including maximum velocity and maximum deceleration (grand means 72 cm s-1 and -512 cm s-2, respectively) did not change significantly with reduced pectoral fin area. The average values of braking movements of the median and caudal fins did increase with decreased pectoral fin area but lacked statistically significant differences. The primary mechanism of attaining similar braking performance with decreased area of the pectoral fins was that they were protracted significantly more (mean difference=42°) and with a significantly faster average velocity of protraction. Thus, pectoral fin area appears unlikely to be the primary constraint on braking performance for this particular task. [ABSTRACT FROM AUTHOR]

Dorsal and anal fins are median fins located above and below the centre of mass of fishes, each having a moment arm relative to the longitudinal axis. Understanding the kinematics of dorsal and anal fins may elucidate how these fins are used in concert to maintain and change fish body position and yet little is known about the functions of these fins. Using three synchronized high-speed cameras (500 frames s-1) we studied the three-dimensional kinematics of dorsal and anal fins during steady swimming (0.5-2.5 TL s-1, where TL=total length) and during slow speed maneuvers (0.5 TL s-1). By digitizing points along every other fin ray in the soft-rayed portion of the fins we were able to determine not only the movement of the fin surface but also the curvature of individual fin rays and the resulting fin surface shape. We found that dorsal and anal fins begin oscillating, in phase, at steady swimming speeds above 1.0 TL s-1 and that maximum lateral displacement of the trailing edge of the fins as well as fin area increase with increasing steady swimming speed. Differences in area, lateral displacement and moment arm between the dorsal and anal fin suggest that dorsal and anal fins produce balancing torques during steady swimming. During maneuvers, fin area is maximized and mean lateral excursion of both fins is greater than during steady swimming, with large variation among maneuvers. Fin surface shape changes dramatically during maneuvers. At any given point in time the spanwise (base to tip) curvature along fin rays can differ between adjacent rays, suggesting that fish have a high level of control over fin surface shape. Also, during maneuvers the whole surface of both dorsal and anal fins can be bent without individual fin rays exhibiting significant curvature. [ABSTRACT FROM AUTHOR]

It is well established that suction feeding fish use a variable amount of swimming (ram) during prey capture. However, the fluid mechanical effects of ram on suction feeding are not well established. In this study we quantified the effects of ram on the maximum fluid speed of the water entering the mouth during feeding as well as the spatial patterns of flow entering the mouth of suction-feeding bluegill sunfish Lepomis macrochirus. Using Digital Particle Image Velocimetry (DPIV) and high-speed video, we observed the flow in front of the mouth of three fish using a vertical laser sheet positioned on the midsagittal plane of the fish. From this we quantified the maximum fluid speed (measured at a distance in front of the mouth equal to one half of the maximum mouth diameter), the degree of focusing of water flow entering the mouth, and the shape of the ingested volume of water. Ram speed in 41 feeding sequences, measured at the time of maximum gape, ranged between 0 and 25 cm s-1, and the ratio of ram speed to fluid speed ranged from 0.1% to 19.1%. In a regression ram speed did not significantly affect peak fluid speed, but with an increase in ram speed the degree of focusing of water entering the mouth increased significantly, and the shape of the ingested volume of water became more elongate and narrow. The implications of these findings are that (1) suction feeders that employ ram of between 0% and 20% of fluid speed sacrifice little in terms of the fluid speeds they generate and (2) ram speed enhances the total body closing speed of the predator. [ABSTRACT FROM AUTHOR]

The suction-feeding fish generates a flow field external to its head in order to draw prey into the mouth. To date there are very few empirical measurements that characterize the fluid mechanics of suction feeding, particularly the temporal and spatial patterns of water velocity in front of the fish. To characterize the flow in front of suction-feeding bluegill sunfish Lepomis macrochirus, measurements with high spatial (<1 mm) and temporal (500 Hz) resolution were taken using Particle Image Velocimetry (PIV). In an analysis separate from the PIV, high-speed video sequences were used for a novel method of visually tracking every seed particle for the duration of each feeding in order to determine directly the total parcel of water that the fish ingests. PIV measurements and particle tracking show that water is drawn from all around the mouth. Fluid velocity decreases rapidly with distance from the mouth and is only significant (>5% of speed at the mouth) within roughly 1 mouth diameter of the fish. Suction feeders gain little in terms of extending this flow field by even substantial increases in the fluid speed at the mouth opening. Instead, the chief advantage of increased flow speed at the mouth may be the increased magnitude of generated forces within the space very close to the mouth. After scaling of the velocity field based on size of the mouth opening and the measured fluid speed at a fixed position, the measured velocity profiles for all feedings are very similar to one another, so that a functional relationship for the magnitude of fluid speed as a function of distance from the predator mouth is presented and shown to be accurate over the range of kinematic variables tested. This relationship describes the velocity field both along the centerline of the fish and along transects lying at an angle to the centerline within both the mid-sagittal and frontal planes. Comparison of the time-resolved fluid velocity measurements to gape kinematics demonstrate that peak fluid speed occurs simultaneously with 95% of peak gape, showing that the bluegill maximizes nearly simultaneously both the generated forces and size of the region over which these forces act. The magnitude of peak fluid speed during each strike decreases as a function of increasing time to peak gape (r²=0.87), demonstrating a strong relationship between the rate of buccal cavity expansion and maximum generated flow speed. [ABSTRACT FROM AUTHOR]

Flow in aquatic systems is characterized by unsteadiness that creates destabilizing perturbations. Appropriate correction responses depend on response latency. The time between a disturbance induced by either removal of a flow refuge or striking various parts of the body with a narrow water jet was measured for three species, chosen as examples of modes in teleostean body/fin organization that are expected to affect stability. Creek chub Semotilus atromaculatus is representative of fusiform-bodied soft-rayed teleosts, smallmouth bass Micropterus dolomieu of fnsiform-bodied spiny-rayed forms and bluegill Lepomis macrochirus of deep-bodied spiny-rayed forms. Observations were made at 23°C. Loss of refuge resulted in a surge that fish corrected by starting to swim within 129±29 ms (mean ± 2 S.E.M.) for chub, which was significantly shorter than minimal times of approximately 200 ms for bluegill and bass. Slips and heaves induced by water jets initially resulted in extension of the median and paired fins that would damp growth of the disturbance, but otherwise these disturbances were ignored. Yaws and pitches were more likely to cause fish to swim away from the stimulus, making corrections as they did so. There were no differences in latencies for slip, heave, yaw and pitch disturbances within each species, but !atencies varied among species. For these disturbances, responses averaged 123±19 ms for chub, again significantly smaller than those of 201±24 ms for bass and 208±52 ms for bluegill. Values for the two centrarchids were not significantly different (P>0.08). The response latency for rolling disturbances did not differ among species but was significantly smaller than that for other disturbances, with an overall latency of 70±15 ms. The greater responsiveness to hydrostatic rolling instability is attributed to functions requiring an upright posture and differences among species in habitat preferences. [ABSTRACT FROM AUTHOR]

Measures the fluid forces exerted by the left and right pectoral fins of the bluegill sunfish Lepomis macrochirus during turning using digital image particle velocimetry. Symmetrical motion of left and right fins; Patterns of water movement; Vortex ring momentum; Fin stroke timing.

Investigates the kinematics of feeding in the fish Lepomis macrochirus. Difference between aquatic prey transport from capture behavior of L. machrochirus; Comparison with capture and transport kinematics in species belonging to the amniote taxa; Comparison with feeding behavior in reptiles.

Examines the movements of different portions of pectoral fins of bluegill sunfish, Lepomis macrochirus. Examination of the effects of changes in speed on fin kinematics; Examination of the movements of the fin with respect to fluid flow; Determination whether fin movements conformed to hydrodynamis expectations for locomotor moves.

The article reports on a robotic fin, or robofin, developed by James Tangorra of Drexel University and colleagues. The robofin, based on the pectoral fin of the bluegill sunfish, was built in an attempt to replicate the sunfish's fluid dynamics and thrust characteristics. The scientists found that the most flexible fins produced thrust even when they were being swept forward, while more rigid fins produced drag.

The article presents research by researchers from the University of California Davis, Texas A&M University and Towson University on the production of kinematics of inferior feeding performance in a classic case of natural hybridization. They focus on a common cross between the bluegill sunfish, Leopomis macrochirus, and the green sunfish, L. cyanellus. They found out that the relationship between performance and morphology of the feeding hybrids is non-linear.