Volumetric imaging of shark tail hydrodynamics reveals a three-dimensional dual-ring vortex wake structure

Understanding how moving organisms generate locomotor forces is fundamental to the analysis of aerodynamic and hydrodynamic flow patterns that are generated during body and appendage oscillation. In the past, this has been accomplished using two-dimensional planar techniques that require reconstruction of three-dimensional flow patterns. We have applied a new, fully three-dimensional, volumetric imaging technique that allows instantaneous capture of wake flow patterns, to a classic problem in functional vertebrate biology: the function of the asymmetrical (heterocercal) tail of swimming sharks to capture the vorticity field within the volume swept by the tail. These data were used to test a previous three-dimensional reconstruction of the shark vortex wake estimated from two-dimensional flow analyses, and show that the volumetric approach reveals a different vortex wake not previously reconstructed from two-dimensional slices. The hydrodynamic wake consists of one set of dual-linked vortex rings produced per half tail beat. In addition, we use a simple passive shark-tail model under robotic control to show that the three-dimensional wake flows of the robotic tail differ from the active tail motion of a live shark, suggesting that active control of kinematics and tail stiffness plays a substantial role in the production of wake vortical patterns.     

The fish tail motion forms an attached leading edge vortex

The tail (caudal fin) is one of the most prominent characteristics of fishes, and the analysis of the flow pattern it creates is fundamental to understanding how its motion generates locomotor forces. A mechanism that is known to greatly enhance locomotor forces in insect and bird flight is the leading edge vortex (LEV) reattachment, i.e. a vortex (separation bubble) that stays attached at the leading edge of a wing. However, this mechanism has not been reported in fish-like swimming probably owing to the overemphasis on the trailing wake, and the fact that the flow does not separate along the body of undulating swimmers. We provide, to our knowledge, the first evidence of the vortex reattachment at the leading edge of the fish tail using three-dimensional high-resolution numerical simulations of self-propelled virtual swimmers with different tail shapes. We show that at Strouhal numbers (a measure of lateral velocity to the axial velocity) at which most fish swim in nature (approx. 0.25) an attached LEV is formed, whereas at a higher Strouhal number of approximately 0.6 the LEV does not reattach. We show that the evolution of the LEV drastically alters the pressure distribution on the tail and the force it generates. We also show that the tail''s delta shape is not necessary for the LEV reattachment and fish-like kinematics is capable of stabilising the LEV. Our results suggest the need for a paradigm shift in fish-like swimming research to turn the focus from the trailing edge to the leading edge of the tail.     

五种淡水鱼类幼鱼游泳能力的比较

为了探讨栖息于不同生境中鱼类的游泳能力和偏好游泳速度及其生理机制,本研究以中华倒刺鲃(Spinibarbus sinensis)、异育银鲫(Carassius auratus gibelio)、岩原鲤(Procypris rabaudi)、青鱼(Mylopharyngodon piceus)和胭脂鱼(Myxocryprinus asiaticus) 5种鱼的幼鱼为对象,在(25±1)℃条件下测定了5种鱼类的标准代谢率(SMR)、最大代谢率(MMR)、有氧代谢范围(MS)、临界游泳速度(U_crit)、最大匀加速游泳速度(U_cat)和偏好游泳速度(U_pref)。结果发现:5种实验鱼中,中华倒刺鲃的游泳能力最强,游泳能力较差的为青鱼和胭脂鱼; 5种鱼之间的代谢和游泳能力差异显著,其偏好游泳速度主要集中在(10～24.5cm·s^-1)区域。研究表明,鱼类游泳能力的种间差异可能主要由心鳃系统相关的呼吸能力和体型相关的游泳效率所决定。本研究提供的有关鱼类游泳能力、偏好游泳速度等资料对于鱼道设计等有一定的参考价值...     

Linking behaviour and performance: intermittent locomotion in a climbing fish

How locomotory performance is influenced by prior experience and behaviour is of adaptive significance. The relationship between kinematics, behaviour and performance was investigated by assessing a previously undescribed mode of climbing locomotion performed by adult Pacific lamprey. The lampreys were challenged with a 1.4 m vertical weir under an experimental setting. The majority of ascents used intermittent bouts of climbing (on an average approximately one-fifth of total ascent time) via powerful cycles of axial undulation at 0.35–1.25 Hz, interspersed with periods of stationary attachment with the oral disk. However, two of the most rapid ascents (57 and 85 s) occurred during one continuous bout at a low cycle frequency ( c . 0.38 and 0.50 Hz). Probability of success and ascent time was positively related to experience climbing the weir. The ratio of time spent actively climbing to time spent resting decreased with distance travelled, indicating fatigue. Ascents with long periods of activity had correspondingly high durations of recovery. Moreover, time to ascend was positively related to the proportion of time spent stationary in ascents that took <300 s. The findings suggest that modification of intermittent locomotion allows Pacific lamprey to compensate for variation in climbing performance and can extend distance travelled before exhaustion.     

Use of a self-propelled,fish-shaped,computer model to study the effects of shape and tail-beat frequency on torque and velocity in salmon-shaped fish

The relationship between fish shape, swimming ability and energy consumption during swimming in fish is complex and not well understood. In this paper, we show how a self-propelled 3-D fish model can be used to examine the effect of controlled changes in some shape parameters. Parameters of the model fish are modified and the resulting fish activated for short swimming episodes during which swimming velocity, torque and energy expenditure are calculated in the computer environment. The effect of shape was determined for two different fish shapes swimming at three different tail-beat frequencies (1.43, 0.94 and 0.64?Hz). The simulation results indicate that fish model one (based on a salmon) has stronger swimming ability than fish model two (a modified salmon fish shape) even though energy expenditure of fish shape two is greater than that of fish shape one. In the same fish types, the fish-swimming velocity and energy expenditure are proportional to tail-beat frequency. This model has the potential to be useful, particularly for predicting fish behavior in fish swim ways and the tail-water of energy turbines.     

Kinematic Comparison of Forward and Backward Swimming and Maneuvering in a Self-Propelled Sub-Carangiform Robotic Fish

We make a thorough kinematic comparison of forward and backward swimming and maneuvering on a self-propelled robot platform that uses sub-carangifbrm swimming as the primary propulsor. An improved Central Pattern Generator （CPG） model allowing free adjustment of phase relationship and directional bias is employed to achieve flexible swimming and smooth transition. Considering the characteristics of forward swimming in carangiform fish and backward swimming in anguilliform fish, various backward swimming patterns for the sub-carangiform robotic fish are suitably created by reversing the direction of propagating propulsive waves. Through a combined use of the CPG control and closed-loop swimming direction control strategy, flexible and precise turning maneuvers in both forward and backward swimming are implemented and compared. By contrast with forward swimming, backward swimming requires a higher frequency or an increased lateral displacement to reach the same relative swimming speed. Noticeably, the phase difference shows a greater impact on forward swimming than on backward swimming. Our observations also indicate that the robotic fish achieves a larger turning rate in forward maneuvering than in backward maneuvering, yet these two maneuvers display comparable turning precision.     

Relationship between osteology and aquatic locomotion in birds: determining modes of locomotion in extinct Ornithurae

The evolutionary history of aquatic invasion in birds would be incomplete without incorporation of extinct species. We show that aquatic affinities in fossil birds can be inferred by multivariate analysis of skeletal features and locomotion of 245 species of extant birds. Regularized discriminant analyses revealed that measurements of appendicular skeletons successfully separated diving birds from surface swimmers and flyers, while also discriminating among different underwater modes of swimming. The high accuracy of this method allows detection of skeletal characteristics that are indicative of aquatic locomotion and inference of such locomotion in bird species with insufficient behavioural information. Statistical predictions based on the analyses confirm qualitative assessments for both foot‐propelled (Hesperornithiformes) and wing‐propelled (Copepteryx) underwater locomotion in fossil birds. This is the first quantitative inference of underwater modes of swimming in fossil birds, enabling future studies of locomotion in extinct birds and evolutionary transitions among locomotor modes in avian lineage.     

Analysis of cell locomotion

The methods of statistical physics have been applied to the analysis of cell movement. Human polymorphonuclear leukocytes were exposed to different surfaces possessing parallel oriented physical stuctures (scratched glass surface, machine drilled aluminium surface, optical grid and stretched polyethylene foil) and cell migration was observed using time-lapse photography.We demonstrate that in cell migration along physical structures, referred to as contact guidance, two subgroups can be distinguished: 1) The nematic type where the cell size is large in relation to the grid distance of the undulate surface. 2) The smectic type where the cell size is small in relation to the grid distance of the substrate.Nematic contact guidance is characterized by an anisotropic random walk. In all substrates investigated the diffusion process parallel to the lines was faster than the diffusion process perpendicular to them. The angular dependent diffusion coefficient was described by an ellipse. Deviation from a circle defined an apolar order parameter, whose value was about 0.3. The amount of information which the cells collected from, the undulate surface was very low, between 0.1 and 0.2 bits. We demonstrate that cells do not recognize all the details of their surroundings and that their migration can be compared to the groping around of a short sighted man. The blurred environment can be described by a mean field whose strength is proportional to the aploar order parameter. It is argued that the anisotropic surface tension is the basic source for nematic contact guidance.Smectic contact guidance is characterized by an anisotropic random walk and is quantified by a density order paramter which is 0.28 in the case of the scratched glass surface of a Neubauer counting chamber. The information which the cells collect from their environment is very low (0.03 bits). The lines seen by the cell can be described by a mean field whose strength is proportional to the density oder parameter.Finally, we demonstrate that the locomotion of granulocytes is governed by an internal clock and internal programs. After migrating for a certain time (32 s) in a particular direction, a new direction of locomotion is determined by an internal program. The cell decides basically between left or right, thereby preferring a turn angle such that the cell migrates either parallel or perpendicular to the lines. the angles are nearly equally probable but the cell moves, in the case of nematic guidance, with different velocities in the +or-direction. The cell also has directional memories with characteristic times of 32 s and greater than 100 s.     

Ontogeny of form and function: locomotor morphology and drag in zebrafish (Danio rerio)

Many fish species transform in body shape during growth, but it remains unclear how this influences the mechanics of locomotion. Therefore, the present study focused on understanding how drag generation during coasting is affected by ontogenetic changes in the morphology of zebrafish (Danio rerio). The shapes of the body and fins were measured from photographs of fish ranging in size from small larvae to mature adults and these morphometrics were compared to drag coefficients calculated from high-speed video recordings of routine swimming. We found that the viscous drag coefficient of larval and juvenile fish increased by more than an order of magnitude during growth and the inertial drag coefficient decreased at a comparable rate in adults. These hydrodynamic changes occurred as zebrafish disproportionately increased the span of their fins and their body changed shape from elongated to streamlined, as reflected by the logistic growth of a newly defined streamlining index, SL. These results suggest that morphological changes incur a performance cost by generating greater drag when larvae and juveniles operate in the viscous regime, but later provide a performance benefit by reducing pressure drag in the inertial regime of the adult stage.     

Shape plasticity in response to water velocity in the freshwater blenny Salaria fluviatilis

A non‐random association between an environmental factor and a given trait could be explained by directional selection (genetic determinism) and by phenotypic plasticity (environmental determinism). A previous study showed a significant relationship between morphology and water velocity in Salaria fluviatilis that conformed to functional expectations. The objective of this study was to test whether this relationship could be explained by phenotypic plasticity. Salaria fluviatilis from a Corsican stream were placed in four experimental channels with different water velocities (0, 10, 20 and 30 cm s^?1) to test whether there was a morphological response associated with this environmental factor. After 28 days, fish shape changed in response to water velocity without any significant growth. Fish in higher water velocities exhibited a more slender body shape and longer anal and caudal fins. These results indicate a high degree of morphological plasticity in riverine populations of S. fluviatilis and suggest that the previous relationship between morphology and water velocity observed in the field may largely be due to an environmental determinism.     

Amphibious adaptations in a newly recognized amphibious fish: Terrestrial locomotion and the influences of body size and temperature

Amphibious animals are adapted for both aquatic and terrestrial habitats. The conflicting requirements for dual habitats are perhaps most pronounced in the air‐breathing fishes, which represent an intermediate stage between the totally aquatic habitat and terrestrial colonization. A key requirement for amphibious fishes is terrestrial locomotion. The different densities and compositions of air and water impose constraints for efficient terrestrial locomotion that differ from those required for aquatic locomotion. I investigated terrestrial locomotion in a small South African fish, Galaxias ‘nebula’, by exposing 60 individual fish to air in specially designed raceways and quantifying movement type and occurrence as a function of availability of water, fish size and environmental temperature. Nebula showed a sustained undulating form of terrestrial locomotion characteristic of amphibious fishes and also a transient ballistic locomotion (jumps) typical of fully aquatic species. Terrestrial movement was influenced by fish size, with medium‐sized fish undertaking more jumps towards water, and fewer jumps away from water, than their smaller or larger conspecifics. In contrast, axial undulation was mainly influenced by temperature. However, there was no consistent pattern in temperature effects presumably because temperature is just one of a suit of environmental factors that may affect terrestrial locomotion. Nebula's amphibious adaptations allow it to cope with the unpredictability inherent in its natural environment.     

Single-shot optical projection tomography for high-speed volumetric imaging of dynamic biological samples

A single-shot adaptation of Optical Projection Tomography (OPT) for high-speed volumetric snapshot imaging of dynamic mesoscopic biological samples is presented. Conventional OPT has been applied to in vivo imaging of animal models such as D. rerio, but the sequential acquisition of projection images typically requires samples to be immobilized during the acquisition. A proof-of-principle system capable of single-shot tomography of a ~1 mm³ volume is presented, demonstrating camera-limited rates of up to 62.5 volumes/s, which has been applied to 3D imaging of a freely swimming zebrafish embryo. This is achieved by recording eight projection views simultaneously on four low-cost CMOS cameras. With no stage required to rotate the sample, this single-shot OPT system can be implemented with a component cost of under £5000. The system design can be adapted to different sized fields of view and may be applied to a broad range of dynamic samples, including high throughput flow cytometry applied to model organisms and fluid dynamics studies.     

Terrestrial locomotion in pterosaurs

On the basis of a well‐preserved pelvis of Anhanguera sp. from the Lower Cretaceous (Aptian) of the Chapada do Araripe, Brazil, the problem of terrestrial locomotion in pterosaurs is discussed. A three‐dimensional reconstruction of the pelvis led to a lateral, dorsal and posterior orientation of the acetabula. By use of the preserved proximal ends of the femora of the same individual, the articulation in the hip socket could be tested. The normal articulation of the femur resulted in a horizontal position of the femur shaft, probably during flight. For constructional reasons the femur could not be brought down to a vertical position. Therefore, a parasagittal swing of the femora necessary for a bird‐like stance and gait must have been impossible. It is suggested that in pterosaurs the wing membrane was attached to the upper leg, which helped in stretching, steering and cambering.

Moreover, on the basis of comparisons of the fossil preservation of pterosaurs Compsognathus and Archaeopteryx in the Solnhofen limestone, it is concluded that the femora of pterosaurs were splayed out laterally, and that they had a semi‐erect gait. They were not bipedal animals, but had to use their fore limbs as well on the ground. Nevertheless, as vertebrates extremely adapted to flight, they could not have been able quadrupeds, either.     

Drag reduction of fish skin mucus: Relationship to mode of swimming and size

Drag reduction by skin mucus was measured from Gulf of Eilat fish. Activity of burst swimmers was greater than manoeuvre swimming fish. Large fish from the same species had higher mucus drag reducing activity than smaller specimens.     

Effects of temperature on larval fish swimming performance: the importance of physics to physiology

Temperature influences both the physiology offish larvae and the physics of the flow conditions under which they swim. For small larvae in low Reynolds number (Re) hydrodynamic environments dominated by frictional drag, temperature‐induced changes in the physics of water flow have the greatest effect on swimming performance. For larger larvae, in higher Re environments, temperature‐induced changes in physiology become more important as larvae swim faster and changes in swimming patterns and mechanics occur. Physiological rates at different temperatures have been quantified using Q₁₀s with the assumption that temperature only affected physiological variables. Consequently, Q₁₀s that did not consider temperature‐induced changes in viscosity overestimated the effect of temperature on physiology by 58% and 56% in cold‐water herring and cod larvae respectively. In contrast, in warm‐water Danube bleak larvae, Q₁₀s overestimated temperature‐induced effects on physiology by only 5–7%. This may be because in warm water, temperature‐induced changes affect viscosity to a smaller degree than in cold water. Temperature also affects muscle contractility and efficiency and at high swimming velocities, efficiency decreases more rapidly in cold‐exposed than in warm‐exposed muscle fibres. Further experiments are needed to determine whether temperature acts differently on swimming metabolism in different thermal environments. While hydrodynamic factors appear to be very important to larval fish swimming performance in cold water, they appear to lose importance in warm water where temperature effects on physiology dominate. This may suggest that major differences exist among locomotory capacities of larval fish that inhabit cold, temperate waters compared to those that live in warm tropical waters. It is possible that fish larvae may have developed strategies that affect dispersal and recruitment in different aquatic habitats in order to cope not only with temperature‐induced physiological challenges, but physical challenges as well.     

Measuring Ucrit and endurance: equipment choice influences estimates of fish swimming performance

This study compared the critical swimming speed (U_crit) and endurance performance of three Australian freshwater fish species in different swim‐test apparatus. Estimates of U_crit measured in a large recirculating flume were greater for all species compared with estimates from a smaller model of the same recirculating flume. Large differences were also observed for estimates of endurance swimming performance between these recirculating flumes and a free‐surface swim tunnel. Differences in estimates of performance may be attributable to variation in flow conditions within different types of swim chambers. Variation in estimates of swimming performance between different types of flumes complicates the application of laboratory‐based measures to the design of fish passage infrastructure.     

Predator-induced morphology enhances escape locomotion in crucian carp

Fishes show a remarkable diversity of shapes which have been associated with their swimming abilities and anti-predator adaptations. The crucian carp (Carassius carassius) provides an extreme example of phenotypic plasticity in body shape which makes it a unique model organism for evaluating the relationship between body form and function in fishes. In crucian carp, a deep body is induced by the presence of pike (Esox lucius), and this results in lower vulnerability to gape-limited predators, such as pike itself. Here, we demonstrate that deep-bodied crucian carp attain higher speed, acceleration and turning rate during anti-predator responses than shallow-bodied crucian carp. Therefore, a predator-induced morphology in crucian carp enhances their escape locomotor performance. The deep-bodied carp also show higher percentage of muscle mass. Therefore, their superior performance in escape swimming may be due to a combination of higher muscle power and higher thrust.     

Experimentation of Fish Swimming Based on Tracking Locomotion Locus

There are many kinds of swimming mode in the fish world, and we investigated two of them, used by cyprinids and bulltrout. In this paper we track the locomotion locus by marks in different flow velocity from 0.2 m·s^-1 to 0.8 m·s^-1. By fit the data above we could find out the locomotion mechanism of the two kinds of fish and generate a mathematical model of fish kine- matics. The cyprinid fish has a greater oscillation period and amplitude compared with the bulltrout, and the bulltrout changes velocity mainly by controlling frequency of oscillation.     

Behavioural asymmetry affects escape performance in a teleost fish

Escape performance is fundamental for survival in fish and most other animals. While previous work has shown that both intrinsic (e.g. size, shape) and extrinsic (e.g. temperature, hypoxia) factors can affect escape performance, the possibility that behavioural asymmetry may affect timing and locomotor performance in startled fish is largely unexplored. Numerous studies have found a relationship between brain lateralization and performance in several cognitive tasks. Here, we tested the hypothesis that behavioural lateralization may affect escape performance in a teleost, the shiner perch Cymatogaster aggregata. Escape responses were elicited by mechanical stimulation and recorded using high-speed video (250 Hz). A number of performance variables were analysed, including directionality, escape latency, turning rate and distance travelled within a fixed time. A lateralization index was obtained by testing the turning preference of each subject in a detour test. While lateralization had no effect on escape directionality, strongly lateralized fish showed higher escape reactivity, i.e. shorter latencies, which were associated with higher turning rates and longer distances travelled. Therefore, lateralization is likely to result in superior ability to escape from predator attacks, since previous work has shown that escape timing, turning rate and distance travelled are among the main determinants of escape success.     

Modulation of polymorphonuclear leukocyte locomotion by synthetic amphiphiles

The capacity of synthetic amphiphiles, poly(ethyleneglycol) 6000 (PEG) esterified with saturated fatty acids (C₂–C₁₈), to modify polymorphonuclear leukocyte (PMNL) locomotion has been investigated. It was noticed that PEG-myristate (M-PEG; C₁₄) stimulated the random locomotion of PMNL populations in concentrations up to about 1 g/L. The esters with shorter aliphatic chains had negligible effects, whereas those with longer chains, PEG-palmitate (P-PEG; C₁₆) and PEG-stearate (S-PEG; C₁₈) reduced the locomotion, irrespectively of concentration. The ability of the PMNL to be stimulated by an attractant liberated from normal human serum was slightly impaired by M-PEG, but not by P-PEG. The response to M-PEG of individual PMNL was heterogeneous in that some cells were stimulated and others were inhibited. However, the average result was a reduction of the motility. This indicates that methods used for the study of the locomotion of cell populations may not always reflect the average behavior of the whole population. It was also concluded that the different effects of M-PEG and P-PEG owed to dissimilar effects on the membrane structure of the PMNL since (1) M-PEG perturbated the PMNL membrane more than P-PEG, as assayed by the release of superoxide anion (0 ₂ ⁻ , although the binding was smaller, and (2) M-PEG and P-PEG increased and decreased the membrane fluidity, respectively, as measured with fluorescent bleaching and recovery after bleaching of labeled PMNL. The results indicate a subtle coupling between membrane structure and PMNL locomotion.