Swimming Direction Research Articles

Exploring the swimming performance and the physical mechanisms ofTomopterislocomotion.

Tomopterids are mesmerizing holopelagic swimmers. They use two modes of locomotion simultaneously: drag-based metachronal paddling and bodily undulation.Tomopterishas two rows of flexible legs (parapodia) positioned on opposite sides of its body. Each row performs metachronal paddling out of phase to the other. Both paddling behaviors occur in concert with a lateral bodily undulation. However, when looked at independently, each mode appears in tension with the other. The direction of the undulatory wave is opposite of what one may expect for forward swimming and appears to actively work act against the direction of swimming initiated by metachronal paddling. To investigate how these two modes of locomotion synergize to generate effective swimming, we created an self-propelled, fluid-structure interaction model of an idealizedTomopteris. We holistically explored swimming performance over a 3D mechanospace comprising parapodia length, paddling amplitude, and undulatory amplitude using a machine learning framework based on polynomial chaos expansions. Although undulatory amplitude minimally affected forward swimming speeds, it helped mitigate larger costs of transport which arise from either using more mechanically expensive (larger) paddling amplitudes and/or having longer parapodia.

Description and Analysis of Horse Swimming Strategies in a U-Shaped Pool.

Aquatic training has been integrated into equine rehabilitation and training programs for several decades. While the cardiovascular effects of this training have been explored in previous studies, limited research exists on the locomotor patterns exhibited during the swimming cycle. This study aimed to analyze three distinct swimming strategies, identified by veterinarians, based on the propulsion phases of each limb: (S1) two-beat cycle with lateral overlap, (S2) two-beat cycle with diagonal overlap, and (S3) four-beat cycle. 125 underwater videos from eleven horses accustomed to swimming were examined to quantify the differences in locomotor patterns between these strategies. Initially, a classifier was developed to categorize 125 video segments into four groups (CatA to CatD). The results demonstrated that these categories correspond to specific swimming strategies, with CatA aligning with S1, CatB with S2, and CatC and CatD representing variations of S3. This classification highlights that two key parameters, lateral and diagonal ratios, are indeed effective in distinguishing between the different swimming strategies. Additionally, coordination patterns were analyzed in relation to these swimming strategies. One of the primary findings is the variability in swimming strategies both within and between individual horses. While five horses consistently maintained the same strategy throughout their swimming sessions, six others exhibited variations in their strategy between laps. This suggests that factors such as swimming direction, pauses between laps, and fatigue may influence the selection of swimming strategy. This study offers new insights into the locomotor patterns of horses during aquatic training and has implications for enhancing the design of rehabilitation protocols.

Directional Swimming of B. Subtilis Bacteria Near a Switchable Polar Surface.

The dynamics of swimming bacteria depend on the properties of their habitat media. Recently it is shown that the motion of swimming bacteria dispersed directly in a non-toxic water-based lyotropic chromonic liquid crystal can be controlled by the director field of the liquid crystal. Here,we investigate whether the macroscopic polar order of a ferroelectric nematic liquid crystal (NF) can be recognized by bacteria B. Subtilis swimming in a water dispersion adjacent to a glassy NF film by surface interactions alone.Our results show that B. Subtilis tends to move in the direction antiparallel to the spontaneous electric polarization at the NF surface. Their speed is found to be the same with or without a polar NF layer. In contrast to observation on crystal ferroelectric films, the bacteria do not get immobilized. These observations may offer a pathway to creation of polar microinserts to direct bacterial motion in vivo.

On the backward excursions in the free-swimming magnetotactic multicellular prokaryote 'Candidatus Magnetoglobus multicellularis'.

Magnetotactic bacteria align to magnetic field lines while swimming in a behavior known as magnetotaxis. They are diverse phylogenetically and morphologically and include both unicellular and multicellular morphologies. The magnetotactic multicellular prokaryote (MMP) 'Candidatus Magnetoglobus multicellularis' has been extensively studied, even though it remains uncultured up to now. It swims back and forth along magnetic field lines, exhibiting a preferential swimming direction that is usually south-seeking, as described for most magnetotactic microorganisms from the Southern Hemisphere. In order to understand the effects of the magnetic field intensity on the backward excursions of 'Ca. M. multicellularis', we applied magnetic fields ranging from 0.09 to 3.4 mT and recorded their movements. Each microorganism was followed frame by frame generating position coordinates, which were used to calculate the frequency of reversal events, as well as the time, distance, and velocity. The velocities in forward movements before and after backward excursions are similar, but no relation was found with the velocity in backward movements. The shapes of the trajectories are distinct in forward and backward movements. In addition, the backward velocities are usually higher. The sharp changes in direction (approximately 180°) indicate that reversal of the flagella rotation direction is the probable mechanism for swimming backward. In conclusion, the backward excursions provide additional freedom of movement to the microorganism, especially when it is constrained by magnetic fields stronger than the Earth's. Backward movements integrate the 'Ca. M. multicellularis' behavioral toolbox, which includes also negative phototaxis, photokinesis, magnetotaxis and possibly helical klinotaxis.

Hydrodynamics investigation of a three-dimensional fish swimming in oblique flows by a ghost cell method

Fish in nature can encounter various flow environments. This paper numerically simulated a 3D (three-dimensional) carangiform fish swimming in oblique flow. The numerical model adopts a robust ghost cell method with graphics processing unit acceleration. The dynamic performance and the 3D wake evolutions are discussed under different Strouhal numbers and attack angles. It is found that the thrust along the swimming direction would get enhanced with more energy consumption as the Strouhal number (St) rises. The attack angle can get the similar but less significant effect. Also, the stall angle of θ = 40° is approximately determined, which is independent of the Strouhal number. However, the flexible deformation can reduce the adverse effects of the stall. In terms of the wake structures, they are transitioned from the two rows of vortex streets at St = 0.2 to the three rows at St = 0.6, and even to the four rows at St = 1. The connected oblique vortex ring rows induced by the undulating caudal fin contributes to the thrust and lateral forces dominantly. As the St rises, the vortex ring rows is transformed from the typical von Karman vortex streets to the reverse one, indicating the generation of thrust. The slender, parallel vortex contrails are caused by the detachment of leading-edge vortices (LEVs), and they induce the high-order harmonic components in force coefficients. The oblique angle of the vortex rings grows with the Strouhal number, while it is hardly affected by the attack angle. As the attack angle grows, the wake is turned from the disconnected hairpin vortices to the intertwined vortex rings and losses the spanwise symmetry. Moreover, the reattachment of the LEV is not observed after the stall angle.

Lake shape and the characteristics of migration behavior modify Atlantic salmon smolt migration success through lakes.

Migration is a high-risk behavior. For the Atlantic salmon, Salmo salar, migrating from its river nursery area to marine feeding grounds, the magnitude of risk varies with habitat type. Passage through lakes, in particular, is associated with low rates of migration success. Downstream migrating salmon smolts are rheotactic when migrating in rivers, but lakes typically provide poorer directional currents for migrating salmon. In this study we tested if, in the absence of clear navigational cues in lakes, Atlantic salmon smolts switch to a random search strategy to find the outflowing river. We constructed random search simulations to test if lake basin shape has an effect on migration success. We also compared simulated migration characteristics with migrations of salmon smolts through five real lakes for which there are telemetry data for migrating salmon. Correlated random walk simulations showed that a random search strategy could be successful for all lake shapes tested but was more successful in curved (round and elliptical) than rectangular basin shapes. Rectangular basins with the migration start and stoppoints at the ends of the lake had a higher success than those where these points were perpendicular to the axis of the lake. In general, a random walk model predicted the migration success rate of fish tracked through real lakes. However, for two lakes the simulated migration success exceeded that of actual success, suggesting that fish passing through these lakes were not adopting a random search strategy. We speculate that this is the result of either conflicting navigational cues which inhibit smolts from finding the lake outlet or that they temporarily suspend migration (e.g., to feed). Modelling predicted that for small lakes, directional swimming in short steps (ca. 100 m) followed by turns with very low variation from the direction of travel resulted in the highest migration success. For larger lakes, longer step lengths but also with low turn variation (simulated turning angle drawn from distributions of standard deviation 2° and 5° around a mean of 0°) resulted in the highest migration success. We conclude that navigation in downstream migrating salmon smolts switches from rheotaxis in rivers to a random search tactic in lakes except where residual flow cues in some lakes prevent this, at times resulting in suboptimal navigation outcomes.

Hydromechanical properties of metachronal swimming in polychaetes

Free-swimming polychaetes are common in marine habitats and exhibit a unique form of swimming whereby a metachronal wave occurs simultaneously with a bending body wave. This body wave is unusual among swimming animals because it travels in the same direction as the animal’s swimming direction. However, we currently lack a mechanistic understanding of this unusual form of locomotion. In this study we use a combination of high-speed, high-resolution video and particle image velocimetry (PIV) to quantify kinematics and fluid dynamics for three species of swimming polychaetes, spanning two orders of magnitude in size. We find that in all species, flows generated by metachronal waves of parapodia dominate while typical flows associated with body bending is absent. However, the parapodia are less flexible than propulsive structures in other metachronal swimmers. This creates a localized, but substantial upstream flow during the recovery stroke. Using body bending, the recovery stroke can occur mostly beneath the bulk flow from the power strokes, resulting in minimal inference while the subsequent power stroke can benefit from the pressure field generated during recovery. These results may have implications for future vehicle designs that incorporate metachronal locomotion.

Light-steerable locomotion using zero-elastic-energy modes

Driving synthetic materials out of equilibrium via dissipative mechanisms paves the way towards autonomous, self-sustained robotic motions. However, obtaining agile movement in diverse environments with dynamic steerability remains a challenge. Here we report a light-fuelled soft liquid crystal elastomer torus with self-sustained out-of-equilibrium movement. Under constant light excitation, the torus undergoes spontaneous rotation arising from the formation of zero-elastic-energy modes. By exploiting dynamic friction or drag, the zero-elastic-energy-mode-based locomotion direction can be optically controlled in various dry and fluid environments. We demonstrate the ability of the liquid crystal elastomer torus to laterally and vertically swim in the Stokes regime. The torus navigation can be extended to three-dimensional space with full steerability of the swimming direction. These results demonstrate the possibilities enabled by prestrained topological structures towards robotic functions of out-of-equilibrium soft matter.

Simulating vortex generation to investigate the propulsive and braking mechanisms of breaststroke kick using computational fluid dynamics on a breaststroke swimmer

Swimmers primarily increase their forward velocity through lower limb motion in breaststroke, making the breaststroke kick crucial for optimizing race times. Recent studies have highlighted the generation of vortices around the swimmer’s entire body to propel forward during swimming. However, the investigation of vortex generation during breaststroke kicks remains unexplored. This study aimed to reveal the propulsive and braking mechanisms of breaststroke kicks by simulating vortex generation using computational fluid dynamics (CFD). Kinematic data during the breaststroke kick and a three-dimensional digital model were collected to conduct CFD for a male breaststroke swimmer. Vortex generation was determined during one breaststroke kick from the CFD results. Vortices, which potentially induce a decrease in forward velocity, were generated by the swimmer’s lower legs and feet during the recovery phase. The swimmer generated vortices on the dorsal side of the feet and the posterior and lateral sides of the lower legs to increase the forward velocity during the out-sweep phase. The swimmer generated vortices on the lateral sides of the thighs and lower legs and the dorsal and lateral sides of the feet during the in-sweep phase to maintain forward velocity. Moreover, vortices generated from the out-sweep to the in-sweep merged and were shed backward relative to the swimming direction after the in-sweep phase. This study is the first to reveal the propulsive and braking mechanisms of breaststroke kicks by analyzing the vortex generation.

Finite-Time Line-of-Sight Guidance-Based Path-Following Control for a Wire-Driven Robot Fish.

This paper presents an adaptive line-of-sight (LOS) guidance method, incorporating a finite-time sideslip angle observer to achieve precise planar path tracking of a bionic robotic fish driven by LOS. First, an adaptive LOS guidance method based on real-time cross-track error is presented. To mitigate the adverse effects of the sideslip angle on tracking performance, a finite-time observer (FTO) based on finite-time convergence theory is employed to observe the time-varying sideslip angle and correct the target yaw. Subsequently, classical proportional-integral-derivative (PID) controllers are utilized to achieve yaw tracking, followed by static and dynamic yaw angle experiments for evaluation. Finally, the yaw-tracking-based path-tracking control strategy is applied to the robotic fish, whose motion is generated by an improved central pattern generator (CPG) and equipped with a six-axis inertial measurement unit for real-time swimming direction. Quantitative comparisons in tank experiments validate the effectiveness of the proposed method.

Animal navigation: Jellyfish dodge the drift

Orientation in the ocean can be challenging because of a lack of landmarks. Evidence is accumulating that jellyfish, once considered to be passive drifters, can also show directional swimming to avoid stranding ashore, using ocean waves for orientation, just like hatchling turtles.

Directional swimming patterns in jellyfish aggregations

Having a profound influence on marine and coastal environments worldwide, jellyfish hold significant scientific, economic, and public interest.1,2,3,4,5 The predictability of outbreaks and dispersion of jellyfish is limited by a fundamental gap in our understanding of their movement. Although there is evidence that jellyfish may actively affect their position,6,7,8,9,10 the role of active swimming in controlling jellyfish movement, and the characteristics of jellyfish swimming behavior, are not well understood. Consequently, jellyfish are often regarded as passively drifting or randomly moving organisms, both conceptually2,11 and in process studies.12,13,14 Here we show that the movement of jellyfish is modulated by distinctly directional swimming patterns that are oriented away from the coast and against the direction of surface gravity waves. Taking a Lagrangian viewpoint from drone videos that allows the tracking of multiple adjacent jellyfish, and focusing on the scyphozoan jellyfish Rhopilema nomadica as a model organism, we show that the behavior of individual jellyfish translates into a synchronized directional swimming of the aggregation as a whole. Numerical simulations show that this counter-wave swimming behavior results in biased correlated random-walk movement patterns that reduce the risk of stranding, thus providing jellyfish with an adaptive advantage critical to their survival. Our results emphasize the importance of active swimming in regulating jellyfish movement and open the way for a more accurate representation in model studies, thus improving the predictability of jellyfish outbreaks and their dispersion and contributing to our ability to mitigate their possible impact on coastal infrastructure and populations.

Dynamics of Purcell-type microswimmers with active-elastic joints.

Purcell's planar three-link microswimmer is a classic model of swimming in low-Reynolds-number fluid, inspired by motion of flagellated microorganisms. Many works analyzed this model, assuming that the two joint angles are directly prescribed in phase-shifted periodic inputs. In this work, we study a more realistic scenario by considering an extension of this model which accounts for joints' elasticity and mechanical actuation of periodic torques so that the joint angles are dynamically evolving. Numerical analysis of the swimmer's dynamics reveals multiplicity of periodic solutions, depending on parameters of the inputs-frequency and amplitude of excitation, joints' stiffness ratio, as well as joint's activation. We numerically study swimming direction reversal, as well as bifurcations, stability transitions, and symmetry breaking of the periodic solutions, which represent the effect of buckling instability observed in swimming microorganisms. The results demonstrate that this variant of Purcell's simple model displays rich nonlinear dynamic behavior with actuated-elastic joints. Similar results are also obtained when studying an extended model of a six-link microswimmer.

Correlation between bioluminescent blinks and swimming behavior in the splitfin flashlight fish Anomalops katoptron

BackgroundThe light organs of the splitfin flashlight fish Anomalops katoptron are necessary for schooling behavior, to determine nearest neighbor distance, and to feed on zooplankton under dim light conditions. Each behavior is coupled to context-dependent blink frequencies and can be regulated via mechanical occlusion of light organs. During shoaling in the laboratory individuals show moderate blink frequencies around 100 blinks per minute. In this study, we correlated bioluminescent blinks with the spatio-temporal dynamics of swimming profiles in three dimensions, using a stereoscopic, infrared camera system.ResultsGroups of flashlight fish showed intermediate levels of polarization and distances to the group centroid. Individuals showed higher swimming speeds and curved swimming profiles during light organ occlusion. The largest changes in swimming direction occurred when darkening the light organs. Before A. katoptron exposed light organs again, they adapted a nearly straight movement direction.ConclusionsWe conclude that a change in movement direction coupled to light organ occlusion in A. katoptron is an important behavioral trait in shoaling of flashlight fish.

A longitudinal behavioral analysis of aquarium whale sharks (Rhincodon typus): insights into anticipatory cues, individual variation, and social interaction

Rhincodon typus, or the whale shark, is the largest extant fish in the world and is classified as endangered on the IUCN’s Red List. Due to their enormous size and conservation status, whale sharks are rarely housed in aquaria. Here we present a behavioral analysis culminating from a large effort by 89 observers from 2008–2012 to study four R. typus (ID codes: AL, TA, TR, YU) longitudinally in an aquarium setting. We found that relatively simple behavioral metrics such as swim speed, depth occupation, swimming direction, and lead-follow interactions demonstrated R. typus individual variation and responses to habitat changes. All sharks displayed increased swim speeds 30-minutes before regimented feed times, when there was scent of food being fed to other animals in the habitat. Consistently in the habitat, one male shark (YU) was recorded swimming more at depth, faster, almost exclusively clockwise, and engaged in fewer close proximity interactions with others than expected by chance. In contrast, a larger female shark (AL) was observed swimming the slowest, at the surface more than others, led other sharks more than she followed, and had strong lead-follow interactions with another shark of the opposite sex (TA). TA and TR did not differ from each other in depth profiles or speed, but did differ in their proclivity to lead or follow. Depth preferences and lead-follow interactions suggest some partitioning of the habitat and the possibility of social hierarchy in this species. These results represent the first longitudinal behavioral analysis of aquarium R. typus, offering meaningful similarities and contrasts to field observations.

Magnetically controlled bacterial turbulence

Concentrated active agents can exhibit turbulent-like flows reminiscent of hydrodynamic turbulence. Despite its importance, the influence of external fields on active turbulence remains largely unexplored. Here we demonstrate the ability to control the swimming direction and active turbulence of Bacillus subtilis bacteria using external magnetic fields. The control mechanism leverages the magnetic torque experienced by the non-magnetic, rod-shaped bacteria in a magnetizable medium containing superparamagnetic nanoparticles. This allows aligning individual bacteria with the magnetic field, leading to a nematically aligned state over millimetric scales with minute transverse undulations and flows. Turning off the field releases the alignment constraint, leading to directly observable hydrodynamic instability of the dipole pushers. Our theoretical model predicts the intrinsic length scale of this instability, independent of the magnetic field, and provides a quantitative control strategy. Our findings suggest that magnetic fields and torques can be excellent tools for controlling non-equilibrium phase transitions in active systems.

Exploring sperm cell motion dynamics: Insights from genetic algorithm-based analysis

Accurate analysis of sperm cell flagellar dynamics plays a crucial role in understanding sperm motility as flagella parameters determine cell behavior in the spatiotemporal domain. In this study, we introduce a novel approach by harnessing Genetic Algorithms (GA) to analyze sperm flagellar motion characteristics and compare the results with the traditional decomposition method based on Fourier analysis. Our analysis focuses on extracting key parameters of the equation approximating flagellar shape, including beating period time, bending amplitude, mean curvature, and wavelength. Additionally, we delve into the extraction of phase constants and initial swimming directions, vital for the comprehensive study of sperm cell pairs and bundling phenomena. One significant advantage of GA over Fourier analysis is its ability to integrate sperm cell motion data, enabling a more comprehensive analysis. In contrast, Fourier analysis neglects sperm cell motion by transitioning to a sperm-centered coordinate system (material system). In our comparative study, GA consistently outperform the Fourier analysis-based method, yielding a remarkable reduction in fitting error of up to 70% and on average by 45%. An in-depth exploration of the sperm cell motion becomes indispensable in a wide range of applications from complexities of reproductive biology and medicine, to developing soft flagellated microrobots.

A novel protocol for three-dimensional mapping of sand tiger shark (Carcharias taurus) enclosure use in aquaria: Implications for management.

This study investigated sand tiger shark (STS; Carcharias taurus) spatial use and exclusion in public aquarium enclosures using a novel protocol for three-dimensional mapping. Fifty-one STS were observed in 14 enclosures, and swimming pattern, depth, and location were recorded in ZooMonitor. Data were converted into quantitative, three-dimensional representations using ArcGIS® Pro v. 2.9. All observed STS except one swam in circular patterns, and 80% (n = 41) showed a directional swimming bias. Most STS (80%; n = 41) predominantly utilized the top two-thirds of the enclosures, though 83% (n = 34) of those had swimming obstructions in the bottom of the enclosure. Avoidance of obstructed areas, sections <7 m wide, as well as behavioral spatial separation, resulted in utilization of between 27% and 66% of available enclosure space. STS underutilized corners, pinch-points, and obstructed areas requiring abrupt directional changes and instead exhibited continual, unimpeded swimming patterns. In addition, this study found no relationship between directional swimming bias or use of smaller enclosure volumes and spinal deformity, a health issue affecting 26% of STS 10 years ago but now with an incidence of 6%. Using novel protocols for three-dimensional mapping and volume estimation, this study demonstrated that enclosures facilitating unimpeded, continuous swimming are most usable for STS and provides important information that will be useful for future enclosure design.

Catch Composition and Selectivity Drift Gillnet in Pambang Pesisir Village Bantan Subdistrict Bengkalis Regency

Gill nets are placed perpendicular to the water to block the swimming direction of the fish. Fish are caught by being entangled in the meshes or entangled (spun) in the body of the net. This research was conducted in Pambang Pesisir Village, Bantan District, Bengkalis Regency, to know the composition of the catch and the selectivity of drift gill nets, comparing the composition of the number, type, weight, and size of the catch from different mesh sizes, and knowing how to catch fish (entangled, gilled, snagged, wedged) on the same mesh used. This research was carried out in December 2020 using the experimental fishing method, which is a research method that uses samples of research objects caught on fishing gear for observation. The research results of drift gill nets are species-selective fishing gear. Moreover, drift gill nets with a mesh size of 7.62 cm are more selective than nets of 5.72 cm because they have a catch ratio value closer to 1 and catch more large fish (worth catching). How to catch fish with a mesh size of 5.72 cm, many fish were caught by snagged; namely, 65 fish (30%), wedged 61 fish (28%), gilled 59 fish (27%), and 33 fish entangled (15%). Meanwhile, for the mesh size of 7.62 cm, 30 fish (31%) were caught wedged, 27 fish (29%) snagged, 27 fish (29%) gilled, and ten fish entangled (11%).

A ray-inspired flexible robot fish with stable controllability actuated by photo -responsive composite hydrogels with poly(N-isopropylacrylamide) and multi-walled carbon nanotubes

Drawing inspiration from the movement behaviour of rays in nature, we have successfully developed a ray-inspired flexible robot fish driven by visible light. A composite made of poly(N-isopropylacrylamide) (PNIPAM) and multi-walled carbon nanotubes (MWCNTs) has excellent biocompatibility and photo-responsive deformability. The PNIPAM hydrogel flexible material of the robot fish was prepared by light curing printing technology. Under the control of visible light, the robot fish swims in a straight line at an average speed of about 0.42 mm/s. The photoinduced asymmetric deformation mechanism is used to control the deformation of the fins on both sides of the robot fish, so that the robot fish can turn and realize directional swimming control. These findings have important implications for the development of flexible bionic robots and provide valuable insights for the research of bionic robots driven by visible light.