The musculotendinous system of an anguilliform swimmer: Muscles, myosepta, dermis, and their interconnections in Anguilla rostrata

Eel locomotion is considered typical of the anguilliform swimming mode of elongate fishes and has received substantial attention from various perspectives such as swimming kinematics, hydrodynamics, muscle physiology, and computational modeling. In contrast to the extensive knowledge of swimming mechanics, there is limited knowledge of the internal body morphology, including the body components that contribute to this function. In this study, we conduct a morphological analysis of the collagenous connective tissue system, i.e., the myosepta and skin, and of the red muscle fibers that sustain steady swimming, focusing on the interconnections between these systems, such as the muscle-tendon and myosepta-skin connections. Our aim is twofold: (1) to identify the morphological features that distinguish this anguilliform swimmer from subcarangiform and carangiform swimmers, and (2) to reveal possible pathways of muscular force transmission by the connective tissue in eels. To detect gradual morphological changes along the trunk we investigated anterior (0.4L), midbody (0.6L), and posterior body positions (0.75L) using microdissections, histology, and three-dimensional reconstructions. We find that eel myosepta have a mediolaterally oriented tendon in each the epaxial and hypaxial regions (epineural or epipleural tendon) and two longitudinally oriented tendons (myorhabdoid and lateral). The latter two are relatively short (4.5-5% of body length) and remain uniform along a rostrocaudal gradient. The skin and its connections were additionally analyzed using scanning electron microscopy (SEM). The stratum compactum of the dermis consists of approximately 30 layers of highly ordered collagen fibers of alternating caudodorsal and caudoventral direction, with fiber angles of 60.51 +/- 7.05 degrees (n = 30) and 57.58 +/- 6.92 degrees (n = 30), respectively. Myosepta insert into the collagenous dermis via fiber bundles that pass through the loose connective tissue of the stratum spongiosum of the dermis and either weave into the layers of the stratum compactum (weaving fiber bundles) or traverse the stratum compactum (transverse fiber bundles). These fiber bundles are evenly distributed along the insertion line of the myoseptum. Red muscles insert into lateral and myorhabdoid myoseptal tendons but not into the horizontal septum or dermis. Thus, red muscle forces might be distributed along these tendons but will only be delivered indirectly into the dermis and horizontal septum. The myosepta-dermis connections, however, appear to be too slack for efficient force transmission and collagenous connections between the myosepta and the horizontal septum are at obtuse angles, a morphology that appears inadequate for efficient force transmission. Though the main modes of undulatory locomotion (anguilliform, subcarangiform, and carangiform) have recently been shown to be very similar with respect to their midline kinematics, we are able to distinguish two morphological classes with respect to the shape and tendon architecture of myosepta. Eels are similar to subcarangiform swimmers (e.g., trout) but are substantially different from carangiform swimmers (e.g., mackerel). This information, in addition to data from kinematic and hydrodynamic studies of swimming, shows that features other than midline kinematics (e.g., wake patterns, muscle activation patterns, and morphology) might be better for describing the different swimming modes of fishes.     

Center of mass motion in swimming fish: effects of speed and locomotor mode during undulatory propulsion

Studies of center of mass (COM) motion are fundamental to understanding the dynamics of animal movement, and have been carried out extensively for terrestrial and aerial locomotion. But despite a large amount of literature describing different body movement patterns in fishes, analyses of how the center of mass moves during undulatory propulsion are not available. These data would be valuable for understanding the dynamics of different body movement patterns and the effect of differing body shapes on locomotor force production. In the present study, we analyzed the magnitude and frequency components of COM motion in three dimensions (x: surge, y: sway, z: heave) in three fish species (eel, bluegill sunfish, and clown knifefish) swimming with four locomotor modes at three speeds using high-speed video, and used an image cross-correlation technique to estimate COM motion, thus enabling untethered and unrestrained locomotion. Anguilliform swimming by eels shows reduced COM surge oscillation magnitude relative to carangiform swimming, but not compared to knifefish using a gymnotiform locomotor style. Labriform swimming (bluegill at 0.5 body lengths/s) displays reduced COM sway oscillation relative to swimming in a carangiform style at higher speeds. Oscillation frequency of the COM in the surge direction occurs at twice the tail beat frequency for carangiform and anguilliform swimming, but at the same frequency as the tail beat for gymnotiform locomotion in clown knifefish. Scaling analysis of COM heave oscillation for terrestrial locomotion suggests that COM heave motion scales with positive allometry, and that fish have relatively low COM oscillations for their body size.     

The role of mechanical resonance in the neural control of swimming in fishes

The bodies of many fishes are flexible, elastic structures; if you bend them, they spring back. Therefore, they should have a resonant frequency: a bending frequency at which the output amplitude is maximized for a particular input. Previous groups have hypothesized that swimming at this resonant frequency could maximize efficiency, and that a neural circuit called the central pattern generator might be able to entrain to a mechanical resonance. However, fishes swim in water, which may potentially damp out many resonant effects. Additionally, their bodies are elongated, which means that bending can occur in complicated ways along the length of the body. We review previous studies of the mechanical properties of fish bodies, and then present new data that demonstrate complex bending properties of elongated fish bodies. Resonant peaks in amplitude exist, but there may be many of them depending on the body wavelength. Additionally, they may not correspond to the maximum swimming speed. Next, we describe experiments using a closed-loop preparation of the lamprey, in which a preparation of the spinal cord is linked to a real-time simulation of the muscle and body properties, allowing us to examine resonance entrainment as we vary the simulated resonant frequency. We find that resonance entrainment does occur, but is rare. Gain had a significant, though weak, effect, and a nonlinear muscle model produced resonance entrainment more often than a linear filter. We speculate that resonance may not be a critical effect for efficient swimming in elongate, anguilliform swimmers, though it may be more important for stiffer carangiform and thunniform fishes.     

Volumetric imaging of fish locomotion

Fishes use multiple flexible fins in order to move and maintain stability in a complex fluid environment. We used a new approach, a volumetric velocimetry imaging system, to provide the first instantaneous three-dimensional views of wake structures as they are produced by freely swimming fishes. This new technology allowed us to demonstrate conclusively the linked ring vortex wake pattern that is produced by the symmetrical (homocercal) tail of fishes, and to visualize for the first time the three-dimensional vortex wake interaction between the dorsal and anal fins and the tail. We found that the dorsal and anal fin wakes were rapidly (within one tail beat) assimilated into the caudal fin vortex wake. These results show that volumetric imaging of biologically generated flow patterns can reveal new features of locomotor dynamics, and provides an avenue for future investigations of the diversity of fish swimming patterns and their hydrodynamic consequences.     

Experimental Hydrodynamics and Evolution: Function of Median Fins in Ray-finned Fishes

The median fins of fishes consist of the dorsal, anal, and caudal fins and have long been thought to play an important role in generating locomotor force during both steady swimming and maneuvering. But the orientations and magnitudes of these forces, the mechanisms by which they are generated, and how fish modulate median fin forces have remained largely unknown until the recent advent of Digital Particle Image Velocimetry (DPIV) which allows empirical analysis of force magnitude and direction. Experimental hydrodynamic studies of median fin function in fishes are of special utility when conducted in a comparative phylogenetic context, and we have examined fin function in four ray-finned fish clades (sturgeon, trout, sunfish, and mackerel) with the goal of testing classical hypotheses of fin function and evolution. In this paper we summarize two recent technical developments in DPIV methodology, and discuss key recent findings relevant to median fin function. High-resolution DPIV using a recursive local-correlation algorithm allows quantification of small vortices, while stereo-DPIV permits simultaneous measurement of x, y, and z flow velocity components within a single planar light sheet. Analyses of median fin wakes reveal that lateral forces are high relative to thrust force, and that mechanical performance of median fins (i.e., thrust as a proportion of total force) averages 0.35, a surprisingly low value. Large lateral forces which could arise as an unavoidable consequence of thrust generation using an undulatory propulsor may also enhance stability and maneuverability. Analysis of hydrodynamic function of the soft dorsal fin in bluegill sunfish shows that a thrust wake is generated that accounts for 12% of total thrust and that the thrust generation by the caudal fin may be enhanced by interception of the dorsal fin wake. Integration of experimental studies of fin wakes, computational approaches, and mechanical models of fin function promise understanding of instantaneous forces on fish fins during the propulsive cycle as well as exploration of a broader locomotor design space and its hydrodynamic consequences.     

Ecomorphology of Locomotion in Labrid Fishes

The Labridae is an ecologically diverse group of mostly reef associated marine fishes that swim primarily by oscillating their pectoral fins. To generate locomotor thrust, labrids employ the paired pectoral fins in motions that range from a fore-aft rowing stroke to a dorso-ventral flapping stroke. Species that emphasize one or the other behavior are expected to benefit from alternative fin shapes that maximize performance of their primary swimming behavior. We document the diversity of pectoral fin shape in 143 species of labrids from the Great Barrier Reef and the Caribbean. Pectoral fin aspect ratio ranged among species from 1.12 to 4.48 and showed a distribution with two peaks at about 2.0 and 3.0. Higher aspect ratio fins typically had a relatively long leading edge and were narrower distally. Body mass only explained 3% of the variation in fin aspect ratio in spite of four orders of magnitude range and an expectation that the advantages of high aspect ratio fins and flapping motion are greatest at large body sizes. Aspect ratio was correlated with the angle of attachment of the fin on the body (r = 0.65), indicating that the orientation of the pectoral girdle is rotated in high aspect ratio species to enable them to move their fin in a flapping motion. Field measures of routine swimming speed were made in 43 species from the Great Barrier Reef. Multiple regression revealed that fin aspect ratio explained 52% of the variation in size-corrected swimming speed, but the angle of attachment of the pectoral fin only explained an additional 2%. Labrid locomotor diversity appears to be related to a trade-off between efficiency of fast swimming and maneuverability in slow swimming species. Slow swimmers typically swim closer to the reef while fast swimmers dominate the water column and shallow, high-flow habitats. Planktivory was the most common trophic associate with high aspect ratio fins and fast swimming, apparently evolving six times.     

Elongation of the body in eels

The shape of the body affects how organisms move, where they live, and how they feed. One body plan that has long engaged the interest of both evolutionary biologists and functional morphologists is axial elongation. There is a growing interest in the correlates and evolution of elongation within different terrestrial and aquatic vertebrate clades. At first glance, Anguilliformes may appear to exhibit a single cylindrical form but there is considerable diversity underlying this seemingly simplified body plan. Here, we explore evolution of the axial skeleton in 54 anguilliform taxa and some close relatives. We describe the diversity of axial elongation as well as investigate how characters such as head length, branchial-arch length, and shape of the pectoral fins correlate with vertebral number to possibly facilitate changes in absolute diameter of the body. Overall, we find that precaudal vertebral numbers and caudal vertebral numbers are evolving independently across elopomorph fishes. We also find that precaudal and caudal vertebral aspect ratios are evolving together across elopomorph fishes. When focusing within Anguilliformes we find striking diversity in the mechanisms of elongation of the body, including almost every trend for axial elongation known within actinopterygian fishes. The three major clades of eels we examined have slightly different mechanisms of elongation. We also find a suite of morphological characters associated with elongation in anguilliform fishes that appears to coincide with a more fossorial lifestyle such as high elongation ratios, a more posteriorly extended-branchial region, and a reduction in the size of the pectoral fins. Lastly, we point out that a diverse range of derived behaviors such as head- and tail-first burrowing, rotational feeding, and knotting around prey are only found in long cylindrical vertebrates.     

How puffers (Teleostei: Tetraodontidae) swim

Two species of marine Indo-Pacific puffers, Arothron meleagris and A. nigropunctatus , were filmed with a high-speed motion picture camera while swimming in a Brett-type water tunnel at speeds of 1-3.5 body lengths (BL) s⁻¹. The puffers generated thrust by use of their pectoral fins in addition to their dorsal and anal fins; the long axis of the body tilted, mouth upwards, by 3–10) while the fishes swam; antero-ventral body profiles of the fishes changed as swimming speeds increased; pectoral fins undulated and moved 180) out of phase from each other, while dorsal and anal fins oscillated in phase with each other; frequencies of fin movements ( F ) increased linearly in relation to swimming speeds ( Uc(rel) ) and were described by the equation F =1.48 Uc(rel) +1.66; stride lengths also increased at higher Uc(rel) ; and, at swimming speeds above 3.0 BL s⁻¹ puffers began to move their tails in sub carangiform-like modes of burst swimming. These results modify significantly the accepted view of the tetraodonti form mode of median and paired fin swimming.     

Turbulence: does vorticity affect the structure and shape of body and fin propulsors?

Over the past century, many ideas have been developed on the relationships between water flow and the structure and shape of the body and fins of fishes, largely during swimming in relatively steady flows. However, both swimming by fishes and the habitats they occupy are associated with vorticity, typically concentrated as eddies characteristic of turbulent flow. Deployment of methods to examine flow in detail suggests that vorticity impacts the lives of fishes. First, vorticity near the body and fins can increase thrust and smooth variations in thrust that are a consequence of using oscillating and undulating propulsors to swim. Second, substantial mechanical energy is dissipated in eddies in the wake and adaptations that minimize these losses would be anticipated. We suggest that such mechanisms may be found in varying the length of the propulsive wave, stiffening propulsive surfaces, and shifting to using median and paired fins when swimming at low speeds. Eddies in the flow encountered by fishes may be beneficial, but when eddy radii are of the order of 0.25 of the fish's total length, negative impacts occur due to greater difficulties in controlling stability. The archetypal streamlined "fish" shape reduces destabilizing forces for fishes swimming into eddies.     

Nonlinear muscles, passive viscoelasticity and body taper conspire to create neuromechanical phase lags in anguilliform swimmers

Locomotion provides superb examples of cooperation among neuromuscular systems, environmental reaction forces, and sensory feedback. As part of a program to understand the neuromechanics of locomotion, here we construct a model of anguilliform (eel-like) swimming in slender fishes. Building on a continuum mechanical representation of the body as an viscoelastic rod, actuated by a traveling wave of preferred curvature and subject to hydrodynamic reaction forces, we incorporate a new version of a calcium release and muscle force model, fitted to data from the lamprey Ichthyomyzon unicuspis, that interactively generates the curvature wave. We use the model to investigate the source of the difference in speeds observed between electromyographic waves of muscle activation and mechanical waves of body curvature, concluding that it is due to a combination of passive viscoelastic and geometric properties of the body and active muscle properties. Moreover, we find that nonlinear force dependence on muscle length and shortening velocity may reduce the work done by the swimming muscles in steady swimming.     

Kinematics of swimming in two burrowing anguilliform fishes

Anguilliform or eel-like fishes are typically bottom dwellers, some of which are specialized burrowers. Although specializations for burrowing are predicted to affect the kinematics of swimming, it remains unknown to what extent this is actually the case. Here we examine swimming kinematics and efficiency of two burrowing anguilliform species, Pisodonophis boro and Heteroconger hassi, with different degrees of specialization for burrowing. Our data suggest that differences in the swimming kinematics may indeed be related to the differences in burrowing specialization and style between both species. The resemblance between the swimming kinematics of P. boro and previously published data for Anguilla anguilla and Anguilla rostrata may be linked with the relatively limited burrowing specialization of P. boro and suggests an overall stereotypy in anguilliform forward-swimming patterns. The body of H. hassi, in contrast, is more specialized for tail-first burrowing and backward swimming bears a striking resemblance to the backward burrowing motions observed in this species. These motions differ significantly from backward swimming in Anguilla and in P. boro. The kinematics of forward swimming are, however, comparable across species. Thus, our data suggest that specializations for burrowing may affect swimming kinematics in anguilliform fishes, but also that forward swimming and burrowing are not necessarily incompatible. Future studies comparing the kinematics and mechanics of burrowing in these and other anguilliform fishes are needed to better understand how specializations for burrowing constrain backward swimming in H. hassi.     

Locomotor Patterns in the Evolution of Actinopterygian Fishes

SYNOPSIS. Locomotor adaptations in actinopterygian fishes aredescribed for (a) caudal propulsion, used in cruising and sprintswimming, acceleration, and fast turns and (b) median and pairedfin propulsion used for slow swimming and in precise maneuver.Caudal swimming is subdivided into steady (time independent)and unsteady (time dependent acceleration and turning) locomotion. High power caudal propulsion is the major theme in actinopterygianswimming morphology because of its role in predator evasionand food capture. Non-caudal slow swimming appears to be secondaryand is not exploited before the Acanthopterygii. Optimal morphological requirements for unsteady swimming are(a) large caudal fin and general body area, (b) deep caudalpeduncle, often enhanced by posterior dorsal and anal fins,(c) an anterior stabilizing body mass and\or added mass, (d)flexible body and (e) large ratio of muscle mass to body mass.Optimal morphological requirements for steady swimming are (a)high aspect ratio caudal fin, (b) narrow caudal peduncle, (c)small total caudal area, (d) anterior stabilizing body massand added mass, and (e) a stiff body. Small changes in morphologycan have large effects on performance. Exclusive morphological requirements for steady versus unsteadyswimming are partially overcome using collapsible fins, butcompromises remain necessary. Morphologies favoring unsteadyperformance are a recurring theme in actinopterygian evolution.Successive radiations at chondrostean, halecostome and teleosteanlevels are associated with modifications in the axial and caudalskeleton. Strength of ossified structures probably limited maximum propulsionforces early in actinopterygian evolution, so that specializationsfor fast cruising (carangiform and thunmform modes) followedstructural advances especially in the caudal skeleton. No suchlimits apply to eel-like forms which consequently recur in successiveactinopterygian radiations. Slow swimming using mainly non-caudal propulsion probably firstoccurred among neopterygians in association with reduced andneutral buoyancy. Slow swimming adaptations can add to and extendthe scope of caudal swimming, but specialization is associatedwith reduced caudal swimming performance. Marked exploitationof slow swimming opportunities does not occur prior to the anterodorsallocation of pectoral and pelvic girdles and the vertical rotationof the base of the pectoral fin, as found in the Acanthopterygii.     

Fish functional design and swimming performance

Classifications of fish swimming are reviewed as a prelude to discussing functional design and performance in an ecological context. Webb (1984a , 1998 ) classified fishes based on body shape and locomotor mode into three basic categories: body and caudal fin (BCF) periodic, BCF transient (fast‐starts, turns) and median and paired fin (MPF) swimmers. Swimming performance and functional design is discussed for each of these categories. Webb hypothesized that specialization in any given category would limit performance in any other. For example, routine MPF swimmers should be penalized in BCF transient (fast‐start propulsion). Recent studies offer much support for Webb's construct but also suggest some necessary amendments. In particular, design and performance compromises for different swimming modes are associated with fish that employ the same propulsor for more than one task (coupled, e.g. the same propulsor for routine steady swimming and fast‐starts). For example, pike (BCF transient specialist) achieve better acceleration performance than trout (generalist). Pike steady (BCF periodic) performance, however, is inferior to that of trout. Fish that employ different propulsors for different tasks (decoupled, e.g. MPF propulsion for low‐speed routine swimming and BCF motions for fast‐starts) do not show serious performance compromises. For example, certain MPF low‐speed swimmers show comparable fast‐start performance to BCF forms. Arguably, the evolution of decoupled locomotor systems was a major factor underlying the adaptive radiation of teleosts. Low‐speed routine propulsion releases MPF swimmers from the morphological constraints imposed by streamlining allowing for a high degree of variability in form. This contrasts with BCF periodic swimming specialists where representatives of four vertebrate classes show evolutionary convergence on a single, optimal ‘thunniform’ design. However, recent experimental studies on the comparative performance of carangiform and thunniform swimmers contradict some of the predictions of hydromechanical models. This is addressed in regard to the swimming performance, energetics and muscle physiology of tuna. The concept of gait is reviewed in the context of coupled and decoupled locomotor systems. Biomimetic approaches to the development of Autonomous Underwater Vehicles have given a new context and impetus to research and this is discussed in relation to current views of fish functional design and swimming performance. Suggestions are made for possible future research directions.     

Design Features and Mechanics of Axial Locomotion in Fish

SYNOPSIS. Locomotion is the result of transfer of momentum fromthe fish musculature to the surrounding water. The present paperdiscusses some basic principles of this momentum transfer andshows the effects of various adaptations of body shape and finshape, size and positioning. Muscles take up a large part of the fish body volume in manycases. The effects of distribution of muscle mass on externalshape, and drag (with its reciprocal influence on the muscularsystem) are analysed. Fins provide an effective means of momentumtransfer, by allowing large amounts of water to be moved bysmall body masses. Fin shape, variable flexibility and positioningall interact to influence thrust producing performance. A frameworkfor understanding the various combinations of fins, their shapesand motion is presented. Reasons for shifting the center ofpropulsion to the rear part of the fish, in anguilliform, andmuch more so in carangiform swimmers are discussed. This shiftis shown to result from considerations of propulsive efficiency.Double-tailed fin configurations, defined as dorsal and ventralfins placed at the same longitudinal positions so as to producea "continuous" are analysed. Examples of both fast starters(such as esocids) and cruising species (scombrids, etc.) areused to point out the advantages of such fin placement.     

Effect of body roll amplitude and arm rotation speed on propulsion of arm amputee swimmers

Only a limited amount of research has gone into evaluating the contribution made by the upper arm to the propulsion of elite swimmers with an amputation at elbow level. With assistance of computational fluid dynamics (CFD) modelling, the swimming technique of competitive arm amputee swimmers can be assessed through numerical simulations which test the effect of various parameters on the effectiveness of the swimming propulsion.This numerical study investigates the effect of body roll amplitude and of upper arm rotation speed on the propulsion of an arm amputee swimmer, at different mean swimming speeds. Various test cases are simulated resulting in a thorough analysis of the complex body/fluid interaction with a detailed quantitative assessment of the effect of the variation of each parameter on the arm propulsion. It is found that a body roll movement with an amplitude of 45° enhances greatly the propulsive contribution from the upper arm with an increase of about 70% in the propulsive force compared to the no roll condition. An increase in the angular velocity of the upper arm also leads to a concomitant increase in the propulsive forces produced by the arm.Such results have direct implications for competitive arm amputee front crawl swimmers and for those who coach them. One important message that emerges in this present work is that there exists, for any given swimming speed, a minimum angular velocity at which the upper arm must be rotated to generate effective propulsion. Below this velocity, the upper arm will experience a net resistive drag force which adversely affects swimming performance.     

The evolution of underwater flight: The redistribution of pectoral fin rays,in manta rays and their relatives (Myliobatidae)

Batoids are a diverse clade of flat cartilaginous fishes that occur primarily in benthic marine habitats. The skates and rays typically use their flexible pectoral fins for feeding and propulsion via undulatory swimming. However, two groups of rays have adopted a pelagic or bentho‐pelagic lifestyle and utilize oscillatory swimming—the Myliobatidae and Gymnuridae. The myliobatids have evolved cephalic lobes, anteriorly extended appendages that are optimized for feeding, while their pectoral fins exhibit several modifications that likely arose in association with functional optimization of pelagic cruising via oscillatory flight. Here, we examine variation in fin ray distribution and ontogenetic timing of fin ray development in batoid pectoral fins in an evolutionary context using the following methods: radiography, computed tomography, dissections, and cleared and stained specimens. We propose an index for characterizing variation in the distribution of pectoral fin rays. While undulatory swimmers exhibit symmetry or slight anterior bias, we found a posterior shift in the distribution of fin rays that arose in two distinct lineages in association with oscillatory swimming. Undulatory and oscillatory swimmers occupy nonoverlapping morphospace with respect to fin ray distribution illustrating significant remodeling of pectoral fins in oscillatory swimmers. Further, we describe a derived skeletal feature in anterior pectoral fins of the Myliobatidae that is likely associated with optimization of oscillatory swimming. By examining the distribution of fin rays with clearly defined articulation points, we were able to infer evolutionary trends and body plan remodeling associated with invasion of the pelagic environment. Finally, we found that the number and distribution of fin rays is set early in development in the little skate, round stingray, and cownose ray, suggesting that fin ray counts from specimens after birth or hatching are representative of adults and therefore comparable among species.     

Swimming dynamics and propulsive efficiency of squids throughout ontogeny

Squids encounter vastly different flow regimes throughout ontogeny as they undergo critical morphological changes to their two locomotive systems: the fins and jet. Squid hatchlings (paralarvae) operate at low and intermediate Reynolds numbers (Re) and typically have rounded bodies, small fins, and relatively large funnel apertures, whereas juveniles and adults operate at higher Re and generally have more streamlined bodies, larger fins, and relatively small funnel apertures. These morphological changes and varying flow conditions affect swimming performance in squids. To determine how swimming dynamics and propulsive efficiency change throughout ontogeny, digital particle image velocimetry (DPIV) and kinematic data were collected from an ontogenetic range of long-finned squid Doryteuthis pealeii and brief squid Lolliguncula brevis swimming in a holding chamber or water tunnel (Re = 20-20 000). Jet and fin wake bulk properties were quantified, and propulsive efficiency was computed based on measurements of impulse and excess kinetic energy in the wakes. Paralarvae relied predominantly on a vertically directed, high frequency, low velocity jet as they bobbed up and down in the water column. Although some spherical vortex rings were observed, most paralarval jets consisted of an elongated vortical region of variable length with no clear pinch-off of a vortex ring from the trailing tail component. Compared with paralarvae, juvenile and adult squid exhibited a more diverse range of swimming strategies, involving greater overall locomotive fin reliance and multiple fin and jet wake modes with better defined vortex rings. Despite greater locomotive flexibility, jet propulsive efficiency of juveniles/adults was significantly lower than that of paralarvae, even when juvenile/adults employed their highest efficiency jet mode involving the production of periodic isolated vortex rings with each jet pulse. When the fins were considered together with the jet for several juvenile/adult swimming sequences, overall propulsive efficiency increased, suggesting that fin contributions are important and should not be overlooked in analyses of the swimming performance of squids. The fins produced significant thrust and consistently had higher propulsive efficiency than did the jet. One particularly important area of future study is the determination of coordinated jet/fin wake modes that have the greatest impact on propulsive efficiency. Although such research would be technically challenging, requiring new, powerful, 3D approaches, it is necessary for a more comprehensive assessment of propulsive efficiency of the squid dual-mode locomotive system.     

Three-dimensional analysis of finlet kinematics in the chub mackerel (Scomber japonicus)

Finlets, which are small non-retractable fins located on the body margins between the second dorsal and anal fins and the caudal fin of scombrid fishes, have been hypothesized to improve swimming performance. The kinematics of three posterior finlets of the chub mackerel, Scomber japonicus, were examined using three-dimensional measurement techniques to test hypotheses on finlet rigidity and function during steady swimming. Finlet bending and finlet planar orientation to the xz, yz, and xy planes were measured during steady swimming at 1.2 lengths s(-1) in a flow tank. Despite very similar morphology among the individual finlets, there was considerable variability in finlet flexure during a stroke. Several of the finlets were relatively rigid and flat (with intrafinlet angles close to 180 degrees during the stroke), although intrafinlet angle of the proximal portion of the most posterior finlet varied considerably over the stroke and was as low as 140 degrees midstroke. Finlets showed complex orientations in three-dimensional space over a stroke, and these orientations differed among the finlets. For example, during tail deceleration the proximal portion of the fifth finlet achieves a mean angle of approximately 75 degrees with the xz plane, while the distal portion of this finlet is oriented at 110 degrees. Our data suggest that the trajectory of local water flow varies among finlets and that the most posterior finlet is oriented to redirect flow into the developing tail vortex, which may increase thrust produced by the tail of swimming mackerel.     

The effect of three recovery protocols on blood lactate clearance after race-paced swimming

ABSTRACT: Lomax, M. The effect of three recovery protocols on blood lactate clearance after race-paced swimming. J Strength Cond Res 26(10): 2771-2776, 2012-The purpose of the present study was to assess the impact of 3 recovery protocols on blood lactate clearance after maximal intensity swimming. Thirty-three regional standard swimmers were tested throughout the course a year and were required to complete a race-paced 200-m swim in their main stroke or individual medley. After the race-paced swim, swimmers were assigned a self-paced continuous steady rate swim of 20 minutes (self-prescribed); a 20-minute coach-administered modified warm-up consisting of various swimming modes, intensities, and rest intervals (coach prescribed); or a 20-minute land-based recovery consisting of light-intensity walking, skipping, and stretching (land based). Blood lactate concentration was measured from the fingertip before and after the race-paced swim and after the recovery activity. The concentration of blood lactate was higher (p < 0.01) after race-paced swimming (range of 10.5-11.0 mmol·L) compared with baseline (range 1.3-1.4 mmol·L). However, there were no differences (p > 0.05) between the groups (recovery protocols) at these time points. Conversely, differences were observed between groups after the recovery activities (p < 0.01). Specifically, blood lactate concentration was higher after the land-based activity (3.7 ± 1.8 mmol·L) than either the self-prescribed (2.0 ± 1.2 mmol·L) or coach-prescribed (1.8 ± 0.9 mmol·L) swimming protocols. The results of the present study suggest that it does not matter whether a self-paced continuous steady rate swimming velocity or a swimming recovery consisting of various strokes, intensities, and rest intervals is adopted as a recovery activity. As both swimming recoveries removed more blood lactate than the land-based recovery, swimmers should therefore be advised to undertake a swimming-based recovery rather than a land-based recovery.