Locomotion of Gymnarchus Niloticus： Experiment and Kinematics

In addition to forward undulatory swimming, Gymnarchus niloticus can swim via undulations of the dorsal fin while the body axis remains straight; furthermore, it swims forward and backward in a similar way, which indicates that the undulation of the dorsal fin can simultaneously provide bidirectional propulsive and maneuvering forces with the help of the tail fin. A high-resolution Charge-Coupled Device （CCD） imaging camera system is used to record kinematics of steady swimming as well as maneuvering in G. niloticus. Based on experimental data, this paper discusses the kinematics （cruising speed, wave speed, cycle frequency, amplitude, lateral displacement） of forward as well as backward swimming and maneuvering. During forward swimming, the propulsive force is generated mainly by undulations of the dorsal fin while the body axis remains straight. The kinematic parameters （wave speed, wavelength, cycle frequency, amplitude） have statistically significant correlations with cruising speed. In addition, the yaw at the head is minimal during steady swimming. From experimental data, the maximal lateral displacement of head is not more than 1% of the body length, while the maximal lateral displacement of the whole body is not more than 5% of the body length. Another important feature is that G. niloticus swims backwards using an undulatory mechanism that resembles the forward undulatory swimming mechanism. In backward swimming, the increase of lateral displacement of the head is comparatively significant; the amplitude profiles of the propulsive wave along the dorsal fin are significantly different from those in forward swimming. When G. niloticus does fast maneuvering, its body is first bent into either a C shape or an S shape, then it is rapidly unwound in a travelling wave fashion. It rarely maneuvers without the help of the tail fin and body bending.     

Unilateral ablation of trunk superficial neuromasts increases directional instability during steady swimming in the yellowtail kingfish Seriola lalandi

Detailed swimming kinematics of the yellowtail kingfish Seriola lalandi were investigated after unilateral ablation of superficial neuromasts (SNs). Most kinematic variables, such as tail‐beat frequency, stride length, caudal fin‐beat amplitude and propulsive wavelength, were unaffected but lateral amplitude at the tip of the snout (A₀) was significantly increased in SN‐disrupted fish compared with sham‐operated controls. In addition, the orientation of caudal fin‐tip relative to the overall swimming direction of SN‐disrupted fish was significantly deflected (two‐fold) in comparison with sham‐operated control fish. In some fish, SN disruption also led to a phase distortion of the propulsive body‐wave. These changes would be expected to increase both hydrodynamic drag and thrust production which is consistent with the finding that SN‐disrupted fish had to generate significantly greater thrust power when swimming at ≥1·3 fork lengths (L_F) s^?1. In particular, hydrodynamic drag would increase as a result of any increase in rotational (yaw) perturbation and sideways slip resulting from the sensory disturbance. In conclusion, unilateral SN ablation produced directional instability of steady swimming and altered propulsive movements, suggesting a role for sensory feedback in correcting yaw and slip disturbances to maintain efficient locomotion.     

Red muscle recruitment during steady swimming correlates with rostral-caudal patterns of power production in trout

Rainbow trout (Oncorhynchus mykiss) and brook trout (or charr, Salvelinus fontinalis) display different rostral-caudal patterns of power production by the red or aerobic muscle during steady swimming. The anterior muscle of rainbow trout produces much less power for swimming than the posterior, while in brook trout there is no variation in power output. To determine if red muscle recruitment is associated with anterior-posterior patterns of power production, electromyography (EMG) was used to record red muscle activity at three body positions across a range of swimming speeds in fish of each species. The initial recruitment of the anterior red muscle in swimming rainbow trout was predicted to lag behind, i.e. occur at higher speeds, that of the posterior due to the variation in power production, but no variation in recruitment was expected for brook trout. Burst of red muscle EMG activity occurring with each tailbeat was analyzed for frequency (tailbeat frequency), duty cycle (DC) (duration of burst relative to the period of the tailbeat) and burst intensity (BI) (magnitude of the measured EMG activity). Brook trout swam with higher tailbeat frequencies and longer values of DC than rainbow trout. Both species showed a pattern of longitudinal variation in DC, with longer DC values in the anterior red muscle. BI also differed significantly along the length of rainbow trout but not brook trout. In the former, BI of anterior muscle was significantly less than the posterior at lower steady swimming speeds. The EMG data suggest that power production and muscle recruitment are related. In rainbow trout, where there is longitudinal variation in muscle power output, there are also significant rostral-caudal differences in red muscle recruitment.     

A hydro-mechanical approach to the scaling of swimming performance in the sand flathead Platycephalus bassensis Cuvier: effects of changes in morphological features based on fish size

The swimming performance of Platycephalus bassensis at steady speed was assessed with an emphasis on hydrodynamics. The minimum swimming speed to maintain hydrostatic equilibrium for P. bassensis of 0·271 m total length ( L _T) was calculated to be 1·06 L _T s⁻¹. At this speed, the required lift to support the mass of the fish was equivalent to 6·6% of the fish mass; 82·7% of which was created by the body as a hydrofoil, and the rest of which was created by the pelvic fins as hydrofoils. The minimum swimming speed decreased with the L _T of the fish and ranged from 1·15 L _T s⁻¹ for a fish of 0·209 m to 0·89 L _T s⁻¹ for a fish of 0·407 m. The forward movement per tail-beat cycle ( i.e. stride length) was described with an equation including quantities of morphological and hydro-mechanical relevance. This equation explained that stride length was increased by the effect of turbulence characterized by the Reynolds number and demonstrated the morphological and hydro-mechanical functional design of the fish for maximizing thrust and minimizing drag. The larger span of the caudal fin and caudal tail-beat amplitude was associated with larger stride length, whereas greater frictional drag was associated with smaller stride length.     

Heterochrony and the development of the escape response: prehatching movements in the rainbow trout Oncorhynchus mykiss

Teleost fishes produce coordinated escape responses (C-starts) at hatching. This implies that essential swimming morphologies and motor behaviors develop during the incubation interval while the embryo is in the chorion. We examined prehatching motor behaviors in rainbow trout Oncorhycus mykiss (considered morphologically mature at hatching) and compared this species with zebrafish Danio rerio (considered morphologically immature) and assessed two hypotheses concerning the development of escape behavior. (1) Escape behavior is associated with the formation of key elements of the musculoskeletal and nervous systems; thus, the escape response appears early in ontogeny, when these elements form. (2) Escape behavior is not directly associated with the formation of underlying morphological elements; instead, it appears at hatching (i.e. when needed). We find that rainbow trout, like zebrafish, respond to touch early in the incubation interval, but do not demonstrate a complete C-start (including the second, propulsive stage) until shortly before hatching. At hatching, rainbow trout and zebrafish are similar in the degree of development of the chondocranium, paired fins and visceral arches (which comprise the larval jaw and gill support); however, rainbow trout have incipient rays in their unpaired fins (dorsal, anal and caudal), whereas zebrafish retain the embryonic fin fold. Although rainbow trout are more mature in axial swimming morphology at hatching, the essential neural and musculoskeletal systems that produce a coordinated escape response are functional at hatching in both species. This finding supports the evolutionary hypothesis that an effective escape response is critical for the survival of newly hatched teleost fishes.     

Locomotion of free-swimming ghost knifefish: anal fin kinematics during four behaviors

The maneuverability demonstrated by the weakly electric ghost knifefish (Apteronotus albifrons) is a result of its highly flexible ribbon-like anal fin, which extends nearly three-quarters the length of its body and is composed of approximately 150 individual fin rays. To understand how movement of the anal fin controls locomotion we examined kinematics of the whole fin, as well as selected individual fin rays, during four locomotor behaviors executed by free-swimming ghost knifefish: forward swimming, backward swimming, heave (vertical) motion, and hovering. We used high-speed video (1000 fps) to examine the motion of the entire anal fin and we measured the three-dimensional curvature of four adjacent fin rays in the middle of the fin during each behavior to determine how individual fin rays bend along their length during swimming. Canonical discriminant analysis separated all four behaviors on anal fin kinematic variables and showed that forward and backward swimming behaviors contrasted the most: forward behaviors exhibited a large anterior wavelength and posterior amplitude while during backward locomotion the anal fin exhibited both a large posterior wavelength and anterior amplitude. Heave and hover behaviors were defined by similar kinematic variables; however, for each variable, the mean values for heave motions were generally greater than for hovering. Individual fin rays in the middle of the anal fin curved substantially along their length during swimming, and the magnitude of this curvature was nearly twice the previously measured maximum curvature for ray-finned fish fin rays during locomotion. Fin rays were often curved into the direction of motion, indicating active control of fin ray curvature, and not just passive bending in response to fluid loading.     

基于Matlab的鱼类游泳动力学分析

鱼类游泳动力学分析研究对解决鱼道等工程应用中水力学设计方面的关键问题有着重要的意义,利用计算机技术对鱼类游泳动力学进行分析有助于研究目标鱼类的生理特性、游泳能力及其与水力环境因子的响应关系。基于MATLAB软件对我国特有鱼类鲢幼鱼进行游泳动力学分析,借助鲢幼鱼游泳时的摆尾行为,得到不同水流速度下鲢幼鱼的摆尾频率、摆尾幅度、游泳速度和加速度;对比人工计数和手动跟踪分析方法,从实际操作复杂程度和实验数据准确性的角度,分析各数据采集方法的优劣性。结果表明基于Matlab软件采用跟踪鱼的身体中线的思路能更高效的获取大量的运动参数,比如摆尾频率、摆尾幅度、游泳速度和加速度等指标。文章介绍了一种基于Matlab开发的鱼类游泳动力学分析方法,有助于为以后鱼类游泳动力学研究提供依据。     

Assessing the ecological relevance of swimming performance traits: a case study of bluegill sunfish (<Emphasis Type="Italic">Lepomis macrochirus</Emphasis>)

A variety of fish species show habitat-related variation in traits associated with swimming performance and foraging behavior. This commonly manifests as a distinction between open water and shallow water littoral ecotypes. In bluegill sunfish (Lepomis macrochirus), open water fish exhibit greater energy economy and speed during sustained locomotion than those from the littoral, whereas littoral fish were more maneuverable than their open water counterparts. These distinctions are associated with variation in diet and foraging behavior and may represent a resource polyphenism that enhances fitness through more effective exploitation of particular habitat types. A lack of field data means that polyphenisms have not been placed in context with swimming behavior in the field. We have used 3D videography to quantify bluegill field swimming performance in open water and littoral habitats. This revealed patterns of performance variation that parallel the trait variation previously established in the laboratory. Open water fish utilized faster average swimming speeds than inshore fish, while indicators of nonlinearity and unsteadiness were greater in the littoral fish. There are, however, differences in propulsive behavior between the field and laboratory. Pectoral-fin-powered, median-paired fin swimming is rarely employed by open water fish. Field body-caudal fin swimming involves short sequences of propulsive tail beats interspersed with gliding, rather than the repeated propulsive cycles employed under steady-state conditions. This suggests a need to re-evaluate the applicability of steady-state performance traits to behavior and fitness in the field and highlights the general importance of obtaining field performance data.     

Red muscle function during steady swimming in brook trout, Salvelinus fontinalis.

Red muscle function during steady swimming in brook trout was studied through both in vivo swimming and in vitro muscle mechanics experiments. In the swimming experiments, red muscle activity was characterized through the use of electromyography and sonomicrometry, allowing the determination of several parameters such as tailbeat frequency, EMG burst duration, muscle length change patterns and relative phase of EMG activity and length change. Brook trout do show some shifts in these variables along their length during steady swimming, but the magnitude of these shifts is relatively small. In the muscle mechanics experiments, the in vivo muscle activity data were used to evaluate patterns of power production by red muscle during swimming. Unlike many fish species, the red muscle along the length of brook trout shows little change in isometric kinetic variables such as relaxation rate and twitch time. Furthermore, there is no rostral-caudal shift in red muscle mass-specific power output during steady swimming. This last result contrasts sharply with rainbow trout and with a variety of other fish species that power steady swimming primarily with the posterior red myotome.     

Exercise training and the stress response in rainbow trout, Salmo gairdneri Richardson

Plasma levels of catecholamines, cortisol, and glucose were monitored in rainbow trout during a 6-week forced swimming exercise programme. Compared to resting non-exercised controls, resting trained fish had lower levels of epinephrine, norephinephrine, cortisol, and glucose during the last 3 weeks of training. Initially, trained fish that were swimming had higher levels of epinephrine than resting trained fish. After 2 weeks of exercise, swimming did not significantly elevate epinephrine levels in trained fish. Glucose levels were consistently greater in swimming fish than in resting fish. At the end of the training period, exercised trout had lower (15–20%) oxygen consumption rates while resting or swimming than unexercised fish.
After a 5-month forced swimming exercise programme plasma levels of catecholamines and glucose were monitored in trained and untrained cannulated rainbow trout after 2 min of mild agitation. Trained fish showed an immediate (within 1 min) increase in the levels of epinephrine, but not norepinephrine and a delayed (within 15 min) increase in the levels of plasma glucose. Epinephrine levels returned to pre-stress levels within 15 min. Untrained fish had no significant increase in the plasma levels of norepinephrine, epinephrine, or glucose.     

The Importance of Body Stiffness in Undulatory Propulsion

During steady swimming in fish, the dynamic form taken by theaxial undulatory wave may depend on the bending stiffness ofthe body. Previous studies have suggested the hypothesis thatfish use their muscles to modulate body stiffness. In orderto expand the theoretical and experimental tools available fortesting this hypothesis, we explored the relationship betweenbody stiffness, muscle activity, and undulatory waveform inthe mechanical context of dynamically bending beams. We proposethat fish minimize the mechanical cost of bending by increasingtheir body stiffness, which would allow them to tune their body'snatural frequency to match the tailbeat frequency at a givenswimming speed. A review of the literature reveals that theform of the undulatory wave, as measured by propulsive wavelength,is highly variable within species, a result which calls intoquestion the use of propulsive wavelength as a species-specificindicator of swimming mode. At the same time, the smallest wavelengthwithin a species is inversely proportional to the number ofvertebrae across taxa (r² = 0.21). In order to determine ifintact fish bodies are capable of increasing bending stiffness,we introduce a method for stimulating muscle in the body ofa dead fish while it is being cyclically bent at physiologicalfrequencies. The bending moment (N m) and angular displacement(radians) are measured during dynamic bending with and withoutmuscle stimulation. Initial results from these whole body workloops demonstrate that largemouth bass possess the capabilityto increase body stiffness by using their muscles to generatenegative mechanical work.     

Constraints of body size and swimming velocity on the ability of juvenile rainbow trout to endure periods without food

The hypothesis that body size and swimming velocity affect proximate body composition, wet mass and size‐selective mortality of fasted fish was evaluated using small (107 mm mean total length, L _T) and medium (168 mm mean L _T) juvenile rainbow trout Oncorhynchus mykiss that were sedentary or swimming ( c . 1 or 2 body length s⁻¹) and fasted for 147 days. The initial amount of energy reserves in the bodies of fish varied with L _T. Initially having less lipid mass and relatively higher mass‐specific metabolic rates caused small rainbow trout that were sedentary to die of starvation sooner and more frequently than medium‐length fish that were sedentary. Swimming at 2 body length s⁻¹ slightly increased the rate of lipid catabolism relative to 1 body length s⁻¹, but did not increase the occurrence of mortality among medium fish. Death from starvation occurred when fish had <3·2% lipid remaining in their bodies. Juvenile rainbow trout endured long periods without food, but their ability to resist death from starvation was limited by their length and initial lipid reserves.     

An ultrasonic biotelemetry system for the continuous monitoring of tail-beat rate from free-swimming fish

A telemetry system for the continuous monitoring of tail beats, and hence swimming activity, from loch-dwelling brown trout, Salmo trutta L., is described. Tail beats are detected by electromyography and are transmitted using a specially-developed miniature ultrasonic transmitter. The output from the transmitter is relayed to a remote recording station using a radio-transponder buoy. Data analysed to date show that on average fish are active for only 9% of the time. Tail beat rates rarely exceeded 2.5 tail-beats per second (TB/s) corresponding to a velocity of 1 body length per second. The fish showed a 'preferred' tail-beat rate of 1.0–2.0 TB/s and consequently they rarely swam at speeds which would incur oxygen debt.     

Comparative susceptibility of rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta to Myxobolus cerebralis, the cause of salmonid whirling disease.

The susceptibility of rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta to Myxobolus cerebralis, the cause of salmonid whirling disease, was assessed following dosed exposures to the infectious stages (triactinomyxons). Parallel groups of age-matched brown trout and rainbow trout were exposed to 10, 100, 1000 or 10,000 triactinomyxons per fish for 2 h and then placed in aquaria receiving single pass 15 degrees C well water. Severity of infection was evaluated by presence of clinical signs (whirling and/or black tail), prevalence of infection, severity of microscopic lesions, and spore counts 5 mo after exposure. Clinical signs of whirling disease, including a darkened caudal region (black tail) and radical tail chasing swimming (whirling), occurred first among rainbow trout at the highest dose at 6 to 7 wk post exposure. Black tail and whirling occurred among rainbow trout receiving 1000 and 100 triactinomyxons per fish at 8 to 9 wk post exposure. Only 1 of 20 fish had a black tail among rainbow trout receiving 10 triactinomyxons per fish, although 30% of the fish were infected at 5 mo post exposure. Black tails were observed in brown trout at 1000 and 10,000 triactinomyxons per fish beginning at 11 and 7 wk post exposure, respectively. There was no evidence of the tail chasing swimming (whirling) in any group of brown trout. The prevalence of infection, spore numbers, and severity of microscopic lesions due to M. cerebralis among brown trout were less at each exposure dose when compared to rainbow trout. Infections were found among rainbow trout at all doses of exposure but only among brown trout exposed to doses of 100 triactinomyxons per fish or greater. Risk of infection analyses showed that rainbow trout were more apt to be infected at each exposure dose than brown trout. Spore counts reached 1.7 x 10(6) per head among rainbow trout at the highest dose of exposure compared to 1.7 x 10(4) at the same exposure dose among brown trout. Spore numbers increased with dose of exposure in rainbow trout but not in brown trout. As microscopic lesion scores increased from mild to moderate, spore numbers increased in rainbow trout but not brown trout. The mechanisms by which brown trout resist infections with M. cerebralis were not determined. Cellular immune functions, including those of eosinophilic granular leukocytes that were more prominent in brown trout than rainbow trout, may be involved.     

Group size influences foraging effort independent of predation risk: an experimental study on rainbow trout

Foraging effort, swimming activity, vertical position and flight response were recorded in focal juvenile rainbow trout Oncorhynchus mykiss at three group sizes: without company, or in visual and chemical contact with either one or five companion fish at two levels of predation risk: high (simulated aerial predator attack) or low (no attack). The predator attack induced a pronounced flight reaction as well as a reduction in vertical position, feeding and swimming activity. The foraging effort of the focal fish increased with group size independent of the level of predation risk, which suggests that the group-mediated increase in foraging activity is caused by competition rather than by reduction in perceived risk. The flight response to the predator attack, however, was stronger when the focal fish had company, suggesting that individuals may benefit from copying the anti-predator response of other group members.     

Flesh qualities and muscle fiber characteristics in triploid and diploid rainbow trout

Analyzed with regard to their slaughter weights and flesh quality 78‐month‐old diploid and triploid rainbow trout (full sibs) were reared together in a pond after tagging at an age of 12 months. Triploids had higher body weights and carcass percentages than diploids (6 kg vs 4 kg and 66% vs 52%). Triploid fish also displayed lower electrical conductivity values and darker (L* value) and redder (a* value) flesh color. The fillets of the triploid trout contained more crude fat and less moisture than the diploids (6% vs 3% and 68% vs 74%, respectively). No effect of ploidy was found with regard to the protein contents. Triploid rainbow trout had larger mean white and intermediate muscle fiber areas than diploid fish in the dorsal and pelvic fin regions. In the pelvic fin part, the white muscle fiber areas were larger than in the dorsal fin part. In conclusion, adult triploid rainbow trout grow faster especially by fiber hypertrophy and have better flesh quality parameters than diploid fish.     

Functional morphology of the fin rays of teleost fishes

Ray‐finned fishes are notable for having flexible fins that allow for the control of fluid forces. A number of studies have addressed the muscular control, kinematics, and hydrodynamics of flexible fins, but little work has investigated just how flexible ray‐finned fish fin rays are, and how flexibility affects their response to environmental perturbations. Analysis of pectoral fin rays of bluegill sunfish showed that the more proximal portion of the fin ray is unsegmented while the distal 60% of the fin ray is segmented. We examined the range of motion and curvatures of the pectoral fin rays of bluegill sunfish during steady swimming, turning maneuvers, and hovering behaviors and during a vortex perturbation impacting the fin during the fin beat. Under normal swimming conditions, curvatures did not exceed 0.029 mm^?1 in the proximal, unsegmented portion of the fin ray and 0.065 mm^?1 in the distal, segmented portion of the fin ray. When perturbed by a vortex jet traveling at approximately 1 ms^?1 (67 ± 2.3 mN s.e. of force at impact), the fin ray underwent a maximum curvature of 9.38 mm^?1. Buckling of the fin ray was constrained to the area of impact and did not disrupt the motion of the pectoral fin during swimming. Flexural stiffness of the fin ray was calculated to be 565 × 10^?6 Nm². In computational fluid dynamic simulations of the fin‐vortex interaction, very flexible fin rays showed a combination of attraction and repulsion to impacting vortex dipoles. Due to their small bending rigidity (or flexural stiffness), impacting vortices transferred little force to the fin ray. Conversely, stiffer fin rays experienced rapid small‐amplitude oscillations from vortex impacts, with large impact forces all along the length of the fin ray. Segmentation is a key design feature of ray‐finned fish fin rays, and may serve as a means of making a flexible fin ray out of a rigid material (bone). This flexibility may offer intrinsic damping of environmental fluid perturbations encountered by swimming fish. J. Morphol. 274:1044–1059, 2013. © 2013 Wiley Periodicals, Inc.     

Rainbow trout display a developmental shift in red muscle kinetics, swimming kinematics and myosin heavy chain isoform

Both activation and relaxation times of rainbow trout Oncorhynchus mykiss red muscle were shorter in parr than in older juveniles. Furthermore, parr red muscle had a faster maximum shortening velocity than that of older fish, as estimated with the force-clamp technique. Parr swam with higher tailbeat frequencies and lower tailbeat amplitude than did older fish across a range of length-specific steady swimming speeds. The developmental shift in contraction kinetics of red muscle and steady swimming kinematics was associated with a reduction from two or three myosin heavy chain isoforms in parr to one in older juveniles. This transition provides a mechanism to explain the variations in muscle contraction kinetics and swimming performance.     

A long wavelength solution for a microorganism swimming in a channel

The hydrodynamics of a microorganism swimming in a channel is investigated. The microorganism is modeled as a two-dimensional sheet swimming at low Reynolds numbers between two rigid walls. The wavelengths of the propulsive waves passing down the sheet are assummed to be very large compared to the channel spacing, but the amplitude of the propulsive waves is arbitrary. Explicit analytical solutions for the propulsive velocity and the rate of energy dissipated in terms of the wave amplitude, channel spacing, wave number, and wave speeds are given.     

Mechanical properties of a bio-inspired robotic knifefish with an undulatory propulsor

South American electric knifefish are a leading model system within neurobiology. Recent efforts have focused on understanding their biomechanics and relating this to their neural processing strategies. Knifefish swim by means of an undulatory fin that runs most of the length of their body, affixed to the belly. Propelling themselves with this fin enables them to keep their body relatively straight while swimming, enabling straightforward robotic implementation with a rigid hull. In this study, we examined the basic properties of undulatory swimming through use of a robot that was similar in some key respects to the knifefish. As we varied critical fin kinematic variables such as frequency, amplitude, and wavelength of sinusoidal traveling waves, we measured the force generated by the robot when it swam against a stationary sensor, and its velocity while swimming freely within a flow tunnel system. Our results show that there is an optimal operational region in the fin's kinematic parameter space. The optimal actuation parameters found for the robotic knifefish are similar to previously observed parameters for the black ghost knifefish, Apteronotus albifrons. Finally, we used our experimental results to show how the force generated by the robotic fin can be decomposed into thrust and drag terms. Our findings are useful for future bio-inspired underwater vehicles as well as for understanding the mechanics of knifefish swimming.