Pectoral Fin Locomotion Research Articles

A numerical investigation on thrust and torque production of a batoid fish with asymmetric pectoral fins flapping

Batoid fishes have agile maneuverability by flapping pectoral fins with complex undulatory waves. To reveal the effect of fin motion kinematics on torque production, we numerically study a cownose ray-like swimmer with asymmetrical left and right pectoral fin locomotion in the tethered mode. Our simulation results show that the flow patterns behind the left and right fin differ much due to different motion kinematics. A small flapping amplitude can change the orientation and size of the trailing edge vortices compared to a large flapping amplitude. Flapping frequency is essential to the form of trailing edge vortices which are missing at a low flapping frequency. A too-large wavenumber, thus chordwise deformation of the fin decreases the size and strength of wake vortices. In comparison, the phase difference between the two flapping fins has little effect on the wake structures, and thus, its torque production is limited. Under the parameters studied, a large difference in flapping frequency between the two fins produces the maximum turning torque attributed to the distinctive trailing edge vortices formation. This work may provide insight into the maneuverability control design of fin undulation-based bio-inspired underwater robots/vehicles.

Whole-body lift and ground effect during pectoral fin locomotion in the northern spearnose poacher ( Agonopsis vulsa)

The northern spearnose poacher, Agonopsis vulsa, is a benthic, heavily armored fish that swims primarily using pectoral fins. High-speed kinematics, whole-body lift measurements, and flow visualization were used to study how A. vulsa overcomes substantial negative buoyancy while generating forward thrust. Kinematics for five freely swimming poachers indicate that individuals tend to swim near the bottom (within 1 cm) with a consistently small (less than 1°) pitch angle of the body. When the poachers swam more than 1 cm above the bottom, however, body pitch angles were higher and varied inversely with speed, suggesting that lift may help overcome negative buoyancy. To determine the contribution of the body to total lift, fins were removed from euthanized fish ( n=3) and the lift and drag from the body were measured in a flume. Lift and drag were found to increase with increasing flow velocity and angle of attack (ANCOVA, p<0.0001 for both effects). Lift force from the body was found to supply approximately half of the force necessary to overcome negative buoyancy when the fish were swimming more than 1 cm above the bottom. Lastly, flow visualization experiments were performed to examine the mechanism of lift generation for near-bottom swimming. A vortex in the wake of the pectoral fins was observed to interact strongly with the substratum when the animals approached the bottom. These flow patterns suggest that, when swimming within 1 cm of the bottom, poachers may use hydrodynamic ground effect to augment lift, thereby counteracting negative buoyancy.

A potential-flow, deformable-body model for fluid–structure interactions with compact vorticity: application to animal swimming measurements

This paper presents an approach to quantify the unsteady fluid forces, moments and mass transport generated by swimming animals, based on measurements of the surrounding flow field. These goals are accomplished within a framework that is independent of the vorticity field, making it unnecessary to directly resolve boundary layers on the animal, body–vortex interactions, or interactions among vortex lines in the wake. Instead, the method identifies Lagrangian coherent structures in the flow, whose dynamics in flows with compact vorticity are shown to be well approximated by potential flow concepts, especially the Kirchhoff and deformation potentials from deformable body theory. Examples of the application of these methods are given for pectoral fin locomotion of the bluegill sunfish and undulatory swimming of jellyfish, and the methods are validated by analysis of a canonical starting vortex ring flow. The transition to a Lagrangian approach toward animal swimming measurements suggests the possibility of implementing recently developed particle tracking (vis-a-vis DPIV) techniques for fully three-dimensional measurements of animal swimming.

Locomotion with flexible propulsors: I. Experimental analysis of pectoral fin swimming in sunfish

A full understanding of the mechanics of locomotion can be achieved by incorporating descriptions of (1) three-dimensional kinematics of propulsor movement, (2) material properties of the propulsor, (3) power input and control and (4) the fluid dynamics effects of propulsor motion into (5) a three-dimensional computational framework that models the complexity of propulsors that deform and change area. In addition, robotic models would allow for further experimental investigation of changes to propulsor design and for testing of hypothesized relationships between movement and force production. Such a comprehensive suite of data is not yet available for any flexible propulsor. In this paper, we summarize our research program with the goal of producing a comprehensive data set for each of the five components noted above through a study of pectoral fin locomotion in one species of fish: the bluegill sunfish Lepomis macrochirus. Many fish use pectoral fins exclusively for locomotion, and pectoral fins in most fish are integral to generating force during maneuvering. Pectoral fins are complex structures composed of jointed bony supports that are under active control via pectoral fin musculature. During propulsion in sunfish, the fin deforms considerably, has two leading edges, and sunfish can rotate the whole fin or just control individual sections to vector thrust. Fin material properties vary along the length of fin rays and among rays. Experimental fluid dynamic analysis of sunfish pectoral fin locomotion reveals that the fin generates thrust throughout the fin beat cycle, and that the upper and lower edges each produce distinct simultaneous leading edge vortices. The following companion paper provides data on the computational approach taken to understand locomotion using flexible pectoral fins.

Gait transition and oxygen consumption in swimming striped surfperch Embiotoca lateralis Agassiz

A flow‐through respirometer and swim tunnel was used to estimate the gait transition speed (Up‐c) of striped surfperch Embiotoca lateralis, a labriform swimmer, and to investigate metabolic costs associated with gait transition. The Up‐c was defined as the lowest speed at which fish decrease the use of pectoral fins significantly. While the tail was first recruited for manoeuvring at relatively low swimming speeds, the use of the tail at these low speeds [as low as 0·75 body (fork) lengths s−1, LF s−1) was rare (&lt;10% of the total time). Tail movements at these low speeds appeared to be associated with occasional slow manoeuvres rather than providing power. As speed was increased beyond Up‐c, pectoral fin (PF) frequencies kept increasing when the tail was not used, while they did not when PF locomotion was aided by the tail. At these high speeds, the tail was employed for 40–50% of the time, either in addition to pectoral fins or during burst‐and‐coast mode. Oxygen consumption increased exponentially with swimming speeds up to gait transition, and then levelled off. Similarly, cost of transport (CT) decreased with increasing speed, and then levelled off near Up‐c. When speeds ≥Up‐c are considered, CT is higher than the theoretical curve extrapolated for PF swimming, suggesting that PF swimming appears to be higher energetically less costly than undulatory swimming using the tail.

Pectoral fin coordination and gait transitions in steadily swimming juvenile reef fishes

A common feature of animal locomotion is its organization into gaits with distinct patterns of movement and propulsor use for specific speeds. In terrestrial vertebrates, limb gaits have been extensively studied in diverse taxa and gait transitions have been shown to provide efficient locomotion across a wide range of speeds. In contrast, examination of gaits in fishes has focused on axial gaits and the transition between synchronous paired fin locomotion and axial propulsion. Because many fishes use their pectoral fins as their primary propulsors, we aimed to examine more broadly the use of pectoral fin gaits in locomotion. We used juvenile reef fishes in these experiments because their swimming could be recorded readily across a wide range of Reynolds numbers, which we thought would promote gait diversity. Based on previous work in larval fishes, we hypothesized that juveniles have alternating pectoral fin movements rather than the synchronous, or in-phase, coordination pattern of adults. In flow tank swim studies, we found that juvenile sapphire damselfish Pomacentrus pavo used two fin gaits during steady swimming. Below approximately 3 BL s(-1), P. pavo primarily swam with alternating fin strokes 180 degrees out of phase with one another. At speeds in the range of 3-4 BL s(-1), they performed a gait transition to synchronous fin coordination. Between approximately 4 and 8 BL s(-1), P. pavo primarily beat their fins synchronously. At around 8 BL s(-1) there was another gait transition to body-caudal fin swimming, in which the pectoral fins were tucked against the body. We suggest that the transition from alternating to synchronous fin coordination occurs due to mechanical limits of gait performance rather than to energy efficiency, stability or transitions in hydrodynamic regime. To determine whether this gait transition was species-specific, we surveyed pectoral fin locomotion in juveniles from 11 species in three reef fish families (Pomacentridae, Labridae and Scaridae). We found that this gait transition occurred in every species examined, suggesting that it may be a common behavior of juvenile reef fishes. Greater inclusion of early life history stages in the study of fin-based locomotion should significantly enhance and inform the growing body of work on these behaviors.

Motor patterns of labriform locomotion: kinematic and electromyographic analysis of pectoral fin swimming in the labrid fish Gomphosus varius

Labriform locomotion is a widespread swimming mechanism in fishes during which propulsive forces are generated by oscillating the pectoral fins. We examined the activity of the six major muscles that power the pectoral fin of the bird wrasse Gomphosus varius (Labridae: Perciformes). The muscles studied included the fin abductors (arrector ventralis, abductor superficialis and abductor profundus) and the fin adductors (arrector dorsalis, adductor superficialis and adductor profundus). Our goals were to determine the pattern of muscle activity that drives the fins in abduction and adduction cycles during pectoral fin locomotion, to examine changes in the timing and amplitude of electromyographic (EMG) patterns with increases in swimming speed and to correlate EMG patterns with the kinematics of pectoral fin propulsion. EMG data were recorded from three individuals over a range of swimming speeds from 15 to 70 cm s-1 (1&shy;4.8 TL s-1, where TL is total body length). The basic motor pattern of pectoral propulsion is alternating activity of the antagonist abductor and adductor groups. The downstroke is characterized by activity of the arrector ventralis muscle before the other abductors, whereas the upstroke involves nearly synchronous activity of the three adductors. Most EMG variables (duration, onset time, amplitude and integrated area) showed significant correlations with swimming speeds. However, the timing and duration of muscle activity are relatively constant across speeds when expressed as a fraction of the stride period, which decreases with increased velocity. Synchronous recordings of kinematic data (maximal abduction and adduction) with EMG data revealed that activity in the abductors began after maximal adduction and that activity in the adductors began nearly synchronously with maximal abduction. Thus, the pectoral fin mechanism of G. varius is activated by positive work from both abductor and adductor muscle groups over most of the range of swimming speeds. The adductors produce some negative work only at the highest swimming velocities. We combine information from pectoral fin morphology, swimming kinematics and motor patterns to interpret the musculoskeletal mechanism of pectoral propulsion in labrid fishes.

Labriform propulsion in fishes: kinematics of flapping aquatic flight in the bird wrasse Gomphosus varius (Labridae)

Labriform, or pectoral fin, propulsion is the primary swimming mode for many fishes, even at high relative speeds. Although kinematic data are critical for evaluating hydrodynamic models of propulsion, these data are largely lacking for labriform swimmers, especially for species that employ an exclusively labriform mode across a broad range of speeds. We present data on pectoral fin locomotion in Gomphosus varius (Labridae), a tropical coral reef fish that uses a lift-based mechanism to fly under water at sustained speeds of 1&shy;6 total body lengths s-1 (TL s-1). Lateral- and dorsal-view video images of three fish swimming in a flow tank at 1&shy;4 TL s-1 were recorded at 60 Hz. From the two views, we reconstructed the three-dimensional motion of the center of mass, the fin tip and two fin chords for multiple fin beats of each fish at each of four speeds. In G. varius, the fin oscillates largely up and down: the stroke plane is tilted by approximately 20 &deg; from the vertical. Both frequency and the area swept by the pectoral fins increase with swimming speed. Interestingly, there are individual differences in how this area increases. Relative to the fish, the fin tip in lateral view moves along the path of a thin, inclined figure-of-eight. Relative to a stationary observer, the fin tip traces a sawtooth pattern, but the teeth are recumbent (indicating net backwards movement) only at the slowest speeds. Distal fin chords pitch nose downward during the downstroke and nose upward during the upstroke. Hydrodynamic angles of attack are largely positive during the downstroke and negative during the upstroke. The geometry of the fin and incident flow suggests that the fin is generating lift with large upward and small forward components during the downstroke. The negative incident angles during the upstroke suggest that the fin is generating largely thrust during the upstroke. In general, the large thrust is combined with a downward force during the upstroke, but the net backwards motion of the fin at slow speeds generates a small upward component during slow swimming. Both the alternating sign of the hydrodynamic angle of attack and the observed reduced frequencies suggest that unsteady effects are important in G. varius aquatic flight, especially at low speeds. This study provides a framework for the comparison of aquatic flight by fishes with aerial flight by birds, bats and insects.

Pectoral Fin Locomotion in Fishes: Testing Drag-based Models Using Three-dimensional Kinematics

Paired fin propulsion in fishes has classically been divided into two categories which represent biomechanical extremes in the use of appendages for propulsion: lift-based and drag-based mechanisms of thrust production. Theoretical models predict that fishes using drag-based propulsion should have wedge-shaped fins with relatively blunt distal edges, a fin beat cycle that is oriented along the anteroposterior (x) axis, feathering of the fin to reduce drag during the protraction phase, and maximal fin area during the retraction phase as the fin sweeps posteriorly perpendicular to the body. In this paper we use a three-dimensional analysis of pectoral fin propulsion in the largemouth bass, Micropterus salmoides , to (1) evaluate the extent to which bass pectoral fin kinematics fit predictions of drag-based propulsion, and (2)demonstrate the complexity of fin movement when the traditional two-dimensional analysis is extended into three dimensions. We attached small markers to visualize the diaphanous distal fin edge, and we videotaped lateral and ventral views from which we could measure x, y, and z coordinates from the fin and body. We divided the fin into two triangular elements for which we calculated planar (three-dimensional) angles relative to each of three reference planes (XY, YZ and XZ) during the fin beat cycle. We show how angles of attack based only on two-dimensional data may result in gross errors that severely compromise understanding of the mechanics and hydrodynamics of pectoral propulsion. Furthermore, three-dimensional analysis revealed that bass fin kinematics are much more complex than expected on a rowing model of drag-based propulsion, and that the pectoral fins may produce drag-based thrust even during protraction. Three dimensional kinematic data are critical to understanding the hydrodynamics of aquatic animal propulsion. Such data are a necessary foundation for reconstructing patterns of movement, modeling (both theoretical and empirical), and for assessing the extent to which motion is under active control or a passive consequence of fluid resistance.

Functional Morphology of Aquatic Flight in Fishes: Kinematics, Electromyography, and Mechanical Modeling of Labriform Locomotion

Synopsis. Labriform locomotion is the primary swimming mode for many fishes that use the pectoral fins to generate thrust across a broad range of speeds. A review of the literature on hydrodynamics, kinematics, and morphology of pectoral fin mechanisms in fishes reveals that we lack several kinds of morphological and kinematic data that are critical for understanding thrust generation in this mode, particularly at higher velocities. Several needs include detailed three-dimensional kinematic data on species that are pectoral fin swimmers across a broad range of speeds, data on the motor patterns of pectoral fin muscles, and the development of a mechanical model of pectoral fin functional morphology. New data are presented here on pectoral fin locomotion in Gomphosus varius, a labrid fish that uses the pectoral fins at speeds of 1-6 total body lengths per second. Three-dimensional kinematic data for the pectoral fins of G. varius show that a typical drag-based mechanism is not used in this species. Instead, the thrust mechanics of this fish are dominated by lift forces and acceleration reaction forces. The fin is twisted like a propeller during the fin stroke, so that angles of attack are variable along the fin length. Electromyographic data on six fin muscles indicate the sequence of muscle activity that produces antagonistic fin abduction and adduction and controls the leading edge of the fin. EMG activity in abductors and adductors is synchronous with the start of abduction and adduction, re? spectively, so that muscle mechanics actuate the fin with positive work. A mechanical model of the pectoral fin is proposed in which fin morphometrics and computer simulations allow predictions of fin kinematics in three dimensions. The transmission of force and motion to the leading edge of the fin depends on the mechanical advantage of fin ray levers. An integrative program of research is suggested that will synthesize data on morphology, physiology, kinematics, and hydrodynamics to under? stand the mechanics of pectoral fin swimming.

Pectoral fin locomotion in the striped surfperch. I. Kinematic effects of swimming speed and body size

Swimming trials at increasing velocity were used to determine the effects of steady swimming speed on pectoral fin kinematics for an ontogenetic series of striped surfperch Embiotoca lateralis, ranging from 6 to 23 cm in standard length (SL). The fin stroke cycle consisted of a propulsive period, the duration of fin abduction and adduction, and a 'refractory' period, during which the fin remained adducted against the body. Pectoral fin-beat frequency (fp) measured as the inverse of the entire stride period, as in past studies, increased curvilinearly with speed. Frequency, calculated as the reciprocal of the propulsive period alone, increased linearly with speed, as shown previously for tail-beat frequency of fishes employing axial undulation. Fin-beat amplitude, measured as the vertical excursion of the pectoral fin tip during abduction, increased over a limited range of low speeds before reaching a plateau at 0.35&shy;0.40 SL. Pectoral fin locomotion was supplemented by intermittent caudal fin undulation as swimming speed increased. At the pectoral&shy;caudal gait transition speed (Up-c), frequency and amplitude attained maxima, suggesting that the fin musculature reached a physiological limit. The effects of body size on swimming kinematics differed according to the method used for expressing speed. At a given absolute speed, small fish used higher stride frequencies and increased frequency at a faster rate than large fish. In contrast, the relationship between fp and length-specific speed (SL s-1) had a greater slope for large fish and crossed that for small fish at high speeds. We recommend that comparisons across size be made using speeds expressed as a percentage of Up-c, at which kinematic variables influencing thrust are size-independent.

Pectoral fin locomotion in the striped surfperch. II. Scaling swimming kinematics and performance at a gait transition

In this study, we report the first allometric equations relating gait parameters and swimming speed to body size for fish employing pectoral fin locomotion. Comparisons of locomotor kinematics and performance among striped surfperch (Teleostei: Embiotocidae) are made at the pectoral&shy;caudal gait transition speed (Up-c). Up-c is considered to elicit physiologically equivalent levels of exercise in animals varying over 100-fold in body mass (Mb) by virtue of dynamically similar pectoral fin movements (constant duty factor, length-specific stride length and fin-beat amplitude) and size-independent propulsive efficiency. At Up-c, pectoral fin-beat frequency scales in proportion to Mb-0.12&plusmn;0.03, a size-dependence consistent with that observed for stride frequency in fishes swimming by axial undulatory propulsion and in many running tetrapods. It is proposed that the similarity in the scaling of frequency in these vertebrate groups reflects an underlying similarity in the allometry of the maximal velocity of muscle shortening. Absolute Up-c (m s-1) generally increases with body size, but the fastest speeds are not exhibited by the largest animals. A pattern of declining performance in fish 23 cm in standard length and longer may be related to their disproportionately small fin areas and aspect ratios. The pronounced negative allometry of Up-c expressed as standard body lengths per second indicates that a given length-specific speed does not induce comparable levels of activity in large and small fish. Thus, normalization of swimming speed to body length may not be a sufficient correction for kinematic comparisons across size.

KINEMATICS OF PECTORAL FIN LOCOMOTION IN THE BLUEGILL SUNFISH LEPOMIS MACROCHIRUS

The pectoral fins of ray-finned fishes are flexible and capable of complex movements, and yet little is known about the pattern of fin deformation during locomotion. For the most part, pectoral fins have been modeled as rigid plates. In order to examine the movements of different portions of pectoral fins, we quantified the kinematics of pectoral fin locomotion in the bluegill sunfish Lepomis macrochirus using several points on the distal fin edge and examined the effects of swimming speed on fin movements. We simultaneously videotaped the ventral and lateral views of pectoral fins of four fish swimming in a flow tank at five speeds ranging from 0.3 to 1.1 total lengths s-1. Four markers, placed on the distal edge of the fin, facilitated field-by-field analysis of kinematics. We used analyses of variance to test for significant variation with speed and among the different marker positions. Fin beat frequency increased significantly from 1.2 to 2.1 Hz as swimming speed increased from 0.3 to 1.0 total lengths s-1. Maximal velocities of movement for the tip of the fin during abduction and adduction generally increased significantly with increased swimming speed. The ratio of maximal speed of fin retraction to swimming speed declined steadily from 2.75 to 1.00 as swimming speed increased. Rather than the entire distal edge of the fin always moving synchronously, markers had phase lags as large as 32 with respect to the dorsal edge of the fin. The more ventral and proximal portions of the fin edge usually had smaller amplitudes of movement than did the more dorsal and distal locations. With increased swimming speed, the amplitudes of the lateral and longitudinal fin movements generally decreased. We used two distal markers and one basal reference point to determine the orientation of various planar fin elements. During early adduction and most of abduction, these planar fin elements usually had positive angles of attack. Because of fin rotation, angles of attack calculated from three-dimensional data differed considerably from those estimated from a simple lateral projection. As swimming speed increased, the angles of attack of the planar fin elements with respect to the overall direction of swimming approached zero. The oscillatory movements of the pectoral fins of bluegill suggest that both lift- and drag-based propulsive mechanisms are used to generate forward thrust. In addition, the reduced frequency parameter calculated for the pectoral fin of Lepomis (sigma=0.85) and the Reynolds number of 5x10(3) indicate that acceleration reaction forces may contribute significantly to thrust production and to the total force balance on the fin.

The swimming endurance of threespine sticklebacks, Gasterosteus aculeatus L., from the Afon Rheidol, Wales

The endurance of threespine sticklebacks, Gasterosteus aculeatus, swimming with pectoral fin locomotion at 20° C in a laboratory flume was measured. Each trial lasted a maximum of 480 min. At a speed of 4 body lengths per sec (L s−1) all fish were still swimming at the end of the trial, but endurance decreased at higher speeds. At speeds of 5 or 6 L s−1 (20–30 cm s−1) a few fish still maintained labriform locomotion for the 480 min. However, at a speed of 7 L s−1 all fish furled their pectoral fins and used body and caudal fin propulsion but fatigued rapidly. During sustained swimming, fish could cover distances of 6 km or more. No significant differences between males and females were found.