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.     

Thermal acclimation effects differ between voluntary, maximum, and critical swimming velocities in two cyprinid fishes

Temperature acclimation may be a critical component of the locomotor physiology and ecology of ectothermic animals, particularly those living in eurythermal environments. Several studies of fish report striking acclimation of biochemical and kinetic properties in isolated muscle. However, the relatively few studies of whole-animal performance report variable acclimation responses. We test the hypothesis that different types of whole-animal locomotion will respond differently to temperature acclimation, probably due to divergent physiological bases of locomotion. We studied two cyprinid fishes, tinfoil barbs (Puntius schwanenfeldii) and river barbels (Barbus barbus). Study fish were acclimated to either cold or warm temperatures for at least 6 wk and then assayed at four test temperatures for three types of swimming performance. We measured voluntary swimming velocity to estimate routine locomotor behavior, maximum fast start velocity to estimate anaerobic capacity, and critical swimming velocity to estimate primarily aerobic capacity. All three performance measures showed some acute thermal dependence, generally a positive correlation between swimming speed and test temperature. However, each performance measure responded quite differently to acclimation. Critical speeds acclimated strongly, maximum speeds not at all, and voluntary speeds uniquely in each species. Thus we conclude that long-term temperature exposure can have very different consequences for different types of locomotion, consistent with our hypothesis. The data also address previous hypotheses that predict that polyploid and eurythermal fish will have greater acclimation abilities than other fish, due to increased genetic flexibility and ecological selection, respectively. Our results conflict with these predictions. River barbels are eurythermal polyploids and tinfoil barbs stenothermal diploids, yet voluntary swimming acclimated strongly in tinfoil barbs and minimally in river barbels, and acclimation was otherwise comparable.     

Phospholipase D is essential for keratocyte-like migration of NBT-II cells

NBT-II cells on collagen-coated substrates move rapidly and persistently, maintaining a semi-circular shape with a large lamellipodium, in a manner similar to fish keratocytes. The inhibitor of phospholipase D (PLD), n-butanol, completely blocked the migration and disturbed the characteristic localization of actin along the edge of lamellipodia. To investigate the functional difference between the two isozymes of PLD (PLD1 and PLD2), we transfected NBT-II cells with vectors expressing shRNA to deplete PLD1 or PLD2. Depletion of both PLD1 and 2 by RNA interference reduced the velocity of the migration, but depletion of PLD2 inhibited motility more severely than that of PLD1. Furthermore, GFP-PLD2 was localized to the protruding regions of lamellipodia in migrating cells. Thus, PLD is essential for the maintenance of keratocyte-like locomotion of NBT-II cells, presumably by regulating the actin cytoskeleton.     

Locomotor synergies in fish

The kinematic characteristics {f(v), A(v), w(v)} allow a first-approximation representation of locomotor synergies in the swimming of fish: f is the frequency of the transverse oscillations, A is the amplitude of the caudal fin sweep, w is the velocity of the locomotor wave, and v is the locomotion speed. The additional compared characteristics included the step length L(v) and the wavelength λ(v), where L ≡ vT is the distance covered by the fish during the period T ≡ 1/f, and λ ≡ wT. These kinematic characteristics were derived from video recordings of swimming in six fish species. Three of the species investigated belonged to the anguilliform type, while the three others belonged to the carangiform type. The constant value of the wavelength λ at all speeds v was the common feature of the two types. The anguilliform fish performed a oneparameter version of locomotion control: the locomotion speed v changed due to the change of the wave velocity w and the undulatory amplitude remained constant. The carangioid fish used a two-parameter version of control, with changes in both the wave velocity w and the amplitude of undulations of the body and tail fin.     

The effects of vision on the general locomotor behaviour of the goldfish, Carassius auratus

Comparison of the locomotor behaviour of normal, unilaterally and bilaterally blinded goldfish (Carassius auratus) demonstrated the roles of perspective vision (depth perception), which requires binocular vision, and of vision provided by only one eye, in the control of locomotion. Because normal and bilaterally blinded fish exhibited similar size and direction of angles of turn, a similar number of consecutive turns in the same direction and the same turning frequency, normal, binocular vision plays no role in the control of turning behaviour. Unilaterally blinded fish exhibited a strong bias in turning behaviour which resulted in their displaying circus movements toward the blinded side, a direction opposite to that reported by others for both invertebrates and vertebrates with unilateral sensory elimination. The mean step length was significantly increased by both uni- and bilateral blinding, and its temporal relationship with turning frequency and distance swum was also changed. Perspective vision (binocular) therefore controls these parameters. The significantly lower velocity of bilaterally blinded fish and the similarity between the other two test groups, indicated that sight by one eye only was sufficient to mediate velocity control.     

Tracking retrograde flow in keratocytes: news from the front

Actin assembly at the leading edge of the cell is believed to drive protrusion, whereas membrane resistance and contractile forces result in retrograde flow of the assembled actin network away from the edge. Thus, cell motion and shape changes are expected to depend on the balance of actin assembly and retrograde flow. This idea, however, has been undermined by the reported absence of flow in one of the most spectacular models of cell locomotion, fish epidermal keratocytes. Here, we use enhanced phase contrast and fluorescent speckle microscopy and particle tracking to analyze the motion of the actin network in keratocyte lamellipodia. We have detected retrograde flow throughout the lamellipodium at velocities of 1-3 microm/min and analyzed its organization and relation to the cell motion during both unobstructed, persistent migration and events of cell collision. Freely moving cells exhibited a graded flow velocity increasing toward the sides of the lamellipodium. In colliding cells, the velocity decreased markedly at the site of collision, with striking alteration of flow in other lamellipodium regions. Our findings support the universality of the flow phenomenon and indicate that the maintenance of keratocyte shape during locomotion depends on the regulation of both retrograde flow and actin polymerization.     

Locomotion Generation and Motion Library Design for an Anguilliform Robotic Fish

In this paper, modeling, locomotion generation, motion library design and path planning for a real prototype of an Anguilliform robotic fish are presented. The robotic fish consists of four links and three joints, and the driving forces are the torques applied to the joints. Considering kinematic constraints and hydrodynamic forces, Lagrangian formulation is used to obtain the dynamic model of the fish. Using this model, three major locomotion patterns of Anguilliform fish, including forward locomotion, backward locomotion and turning locomotion are investigated. It is found that the fish exhibits different locomotion patterns by giving different reference joint angles, such as adding reversed phase difference, or adding deflections to the original reference angles. The results are validated by both simulations and experiments. Furthermore, the relations among the speed of the fish, angular frequency, undulation amplitude, phase difference, as well as the relationship between the turning radius and deflection angle are investigated. These relations provide an elaborated motion library that can be used for motion planning of the robotic fish.     

Functional consequences of phenotypic variation between locally adapted populations: Swimming performance and ventilation in extremophile fish

Natural selection drives the evolution of traits to optimize organismal performance, but optimization of one aspect of performance can influence other aspects of performance. Here, we asked how phenotypic variation between locally adapted fish populations affects locomotion and ventilation, testing for functional trade‐offs and trait–performance correlations. Specifically, we investigated two populations of livebearing fish (Poecilia mexicana) that inhabit distinct habitat types (hydrogen‐sulphide‐rich springs and adjacent nonsulphidic streams). For each individual, we quantified different metrics of burst swimming during simulated predator attacks, steady swimming and gill ventilation. Coinciding with predictions, we documented significant population differences in all aspects of performance, with fish from sulphidic habitats exhibiting higher steady swimming performance and higher ventilation capacity, but slower burst swimming. There was a significant functional trade‐off between steady and burst swimming, but not between different aspects of locomotion and ventilation. Although our findings about population differences in locomotion performance largely parallel the results from previous studies, we provide novel insights about how morphological variation might impact ventilation and ultimately oxygen acquisition. Overall, our analyses provided insights into the functional consequences of previously documented phenotypic variation, which will help to disentangle the effects of different sources of selection that may coincide along complex environmental gradients.     

Quantification of flow during suction feeding in bluegill sunfish

Nearly all aquatic-feeding vertebrates use some amount of suction to capture prey items. Suction prey capture occurs by accelerating a volume of water into the mouth and taking a prey item along with it. Yet, until recently, we lacked the necessary techniques and analytical tools to quantify the flow regime generated by feeding fish. We used a new approach; Digital Particle Image Velocimetery (DPIV) to measure several attributes of the flow generated by feeding bluegill sunfish. We found that the temporal pattern of flow was notably compressed during prey capture. Flow velocity increased rapidly to its peak within 20 ms of the onset of the strike, and this peak corresponded to the time that the prey entered the mouth during capture. The rapid acceleration and deceleration of water suggests that timing is critical for the predator in positioning itself relative to the prey so that it can be drawn into the mouth along with the water. We also found that the volume of water affected by suction was spatially limited. Only rarely did we measure significant flow beyond 1.75 cm of the mouth aperture (in 20 cm fish), further emphasizing the importance of mechanisms, like locomotion, that place the fish mouth in close proximity to the prey. We found that the highest flows towards the mouth along the fish midline were generated not immediately in front of the open mouth, but approximately 0.5 cm anterior to the mouth opening. Away from the midline the peak in flow was closer to the mouth. We propose that this pattern indicates the presence of a bow wave created by the locomotor efforts of the fish. In this scheme, the bow wave acts antagonistically to the flow of water generated by suction, the net effect being to push the region of peak flow away from the open mouth. The peak was located farther from the mouth opening in strikes accompanied by faster locomotion, suggesting faster fish created larger bow waves.     

A GIM-Based Biomimetic Learning Approach for Motion Generation of a Multi-Joint Robotic Fish

In this paper, we propose a biomimetic learning approach for motion generation of a multi-joint robotic fish. Based on a multi-joint robotic fish model, two basic Carangiform swimming patterns, namely ＂cruise＂ and ＂C sharp turning＂, are extracted as training samples from the observations of real fish swimming. A General Internal Model （GIM）, which is an imitation of Central Pattern Generator （CPG） in nerve systems, is adopted to learn and to regenerate coordinated fish behaviors. By virtue of the universal function approximation ability and the temporal/spatial scalabilities of GIM, the proposed learning approach is able to generate the same or similar fish swimming patterns by tuning two parameters. The learned swimming patterns are implemented on a multi-joint robotic fish in experiments. The experiment results verify the effectiveness of the biomimetic learning approach in generating and modifying locomotion patterns for the robotic fish.     

溶氧水平对鲫鱼代谢模式的影响

为了探讨水体溶氧水平对鲫幼鱼(Carassius carassius)运动、消化能力及其交互作用的影响,在(25.0±0.5)℃温度条件下,测定了8(饱和溶氧水平)、2和1mg/L溶氧水平下摄食(饱足摄食)和空腹组(空腹2 d)鲫鱼的临界游泳速度(Ucrit)、运动前耗氧率(MO2pre-exercise)、活跃耗氧率(MO2active)和代谢范围(MS)。摄食诱导的耗氧率上升在各溶氧水平下无显著差异。在饱和溶氧水平下,摄食组和空腹组的Ucrit没有显著差异,但在1和2 mg/L条件下,摄食组的Ucrit显著低于空腹组(P<0.05)。在饱和溶氧水平条件下,消化和运动诱导的耗氧率上升在各个游泳水平均能完全叠加,且摄食组鱼类与空腹组鱼类具有相似的MS和Ucrit和更高的MO2active,提示鲫鱼在常氧下为添加代谢模式。随着溶氧水平下降至2和1mg/L,呼吸能力(摄食组的MO2active)对溶氧水平下降较运动耗氧率更为敏感,消化诱导的耗氧率增加只能在较低游泳速度叠加,与空腹组鱼类比较,摄食组鱼类的MS和Ucrit显著下降,MO2active无显著差异,提示低氧下消化和运动对氧气需求竞争的加剧使其代谢模式转化为消化优先。     

Formal analysis of resonance entrainment by central pattern generator

The neuronal circuit controlling the rhythmic movements in animal locomotion is called the central pattern generator (CPG). The biological control mechanism appears to exploit mechanical resonance to achieve efficient locomotion. The objective of this paper is to reveal the fundamental mechanism underlying entrainment of CPGs to resonance through sensory feedback. To uncover the essential principle, we consider the simplest setting where a pendulum is driven by the reciprocal inhibition oscillator. Existence and properties of stable oscillations are examined by the harmonic balance method, which enables approximate but insightful analysis. In particular, analytical conditions are obtained under which harmonic balance predicts existence of an oscillation at a frequency near the resonance frequency. Our result reveals that the resonance entrainment can be maintained robustly against parameter perturbations through two distinct mechanisms: negative integral feedback and positive rate feedback.     

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.     

Compliant leg behaviour explains basic dynamics of walking and running

The basic mechanics of human locomotion are associated with vaulting over stiff legs in walking and rebounding on compliant legs in running. However, while rebounding legs well explain the stance dynamics of running, stiff legs cannot reproduce that of walking. With a simple bipedal spring-mass model, we show that not stiff but compliant legs are essential to obtain the basic walking mechanics; incorporating the double support as an essential part of the walking motion, the model reproduces the characteristic stance dynamics that result in the observed small vertical oscillation of the body and the observed out-of-phase changes in forward kinetic and gravitational potential energies. Exploring the parameter space of this model, we further show that it not only combines the basic dynamics of walking and running in one mechanical system, but also reveals these gaits to be just two out of the many solutions to legged locomotion offered by compliant leg behaviour and accessed by energy or speed.     

Dynamic patterns in the locomotion and feeding behaviors by the placozoan Trichoplax adhaerence

The placozoan Trichoplax adhaerence is one of the most primitive multi-cellular organisms, and moves about accompanying perpetual changes in its shape. Changes in position, locomotion velocity and the outer shape of the organism were monitored quantitatively with use of a computer image analysis, and their dynamic patterns in free locomotion and upon feeding were analyzed in terms of non-linear dynamics. The organism changed its behavioral patterns discontinuously in response to various concentrations of yeast extracts (food). (1) At low concentrations, the organism moved fast with perpetual random changes in shape. Both locomotion velocity and shape changes exhibited 1/f fluctuations. (2) At high concentrations, the shape of the organism as well as the locomotion exhibited oscillations with periods of about 8 min. These limit cycle oscillations bifurcated into the period 2 at the highest concentration tested. The organism flattened more strongly and the locomotion was more reduced on the whole at higher concentrations. (3) At the intermediate concentrations, two patterns as monitored above appeared: one pattern continued for a while and switched to the other abruptly. (4) The average square displacement of the organism increased linearly with time in all cases, indicating that the locomotion is a Brownian movement. In this way, the feeding behaviors by the placozoan are organized as successive co-operative transitions among non-linear dynamic states.     

Various characteristics of the control of cyclic movements

It was shown by studying control forces and phasic trajectories during oscillation of human forearm, locomotion and rocking of the body on the support that there was an image of accomplished movement in the central nervous system. This image seems to be realized by linear connected displacements of the muscle tension level and threshold of tonic stretch reflex. During the control process, velocity of the threshold and tension level is similarly transformed to that of the body part. The piece constant similarity coefficient is regulated centrally. The main result of such control is moving of the body along energy optimal trajectories.     

Aerial and aquatic visual acuity of the grey bichir Polypterus senegalus,as estimated by optokinetic response

The present study assessed the aerial and aquatic visual abilities of juvenile grey bichir Polypterus senegalus, fish capable of terrestrial locomotion, by measuring the optokinetic response to stimuli of varying speed and spatial frequency. In water, fish tracked slow-moving (2° s⁻¹) stimuli moderately well and fast-moving stimuli very poorly. Spatial acuity was very low compared with many other species, with maximum response observed at 0.05–0.075 stimulus cycles per degree of visual arc; however, it should be noted that adult fish, with their larger eyes, are likely to have somewhat improved spatial acuity. Low spatial acuity and limited stimulus tracking ability might be expected in a nocturnal ambush predator such as P. senegalus, where gaze stabilization may be less crucial and other sensory inputs may have greater importance in perception of the environment. In air, spatial and temporal acuity were both poorer by every measure, but some visual ability persisted. As the eye shows no anatomical specialization for aerial vision, poor vision was expected; however, the large decrease in saccade velocity observed in air trials was unexpected. Stimulus parameters typically have little effect on the characteristics of the saccade, so this finding may suggest that the function of the reflex system itself could be compromised in the aerial vision of some fishes capable of terrestrial locomotion.     

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

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

鱼类摄食代谢和运动代谢研究进展

摄食和运动不仅是动物最主要的生理活动,同时也是机体代谢能量消耗的主要过程。相关研究表明鱼类摄食代谢主要由营养物质同化过程的耗能组成,其食物蛋白质同化耗能远低于陆生脊椎动物,而摄入营养物质不平衡可能导致摄食代谢耗能增加;鱼类摄食代谢和运动代谢上可能存在能量消耗与性能维持之间的权衡,且都可能受最大代谢能力限制。鱼类不仅在摄食和运动代谢的相对大小及其他特征上存在差异,而且在摄食和运动代谢竞争上存在不同的模式。从功率分配的角度,研究鱼类摄食和运动代谢特征及其与物种生态习性的关系将成为鱼类能量学研究的重要方向之一。