Tail Beat Frequency Research Articles

Kinematic study and implementation of a bio-inspired robotic fish underwater vehicle in a Lighthill mathematical framework

This paper has focused on the formulation of the biological fish propulsion mechanism given by Sir J. Lighthill mathematical slender body theory for a bio-inspired robotic fish. A 2-joint, 3-link multibody vehicle model biologically inspired by a body caudal fin (BCF) carangiform fish propulsion is designed. The objective is to investigate and show that a machine mimicking real fish behavior can navigate efficiently over a given distance with a good balance of speed and maneuverability. The robotic fish model (kinematics and dynamics) is integrated with the Lighthill (LH) mathematical model framework. Different mathematical propulsive waveforms are combined with an inverse kinematics-based approach for generating fish body motion. Comparative studies are undertaken among a non-LH model, a LH model, and the proposed propulsive wave models based on a distance-based performance index. Proposed LH cubic and NURB quadratic functions are found to be 16.32% and 17.94% efficient than a non-LH function, respectively. With the help of the simulation results, closed-loop experiments are done and an operating region is established for critical kinematic parameters tail-beat frequency and propulsive wavelength. The simulation and experimental plots are compared and found to be similar to the kinematic behavior study of the biological yellowfin tuna.

Fish swimming in schools save energy regardless of their spatial position

For animals, being a member of a group provides various advantages, such as reduced vulnerability to predators, increased foraging opportunities and reduced energetic costs of locomotion. In moving groups such as fish schools, there are benefits of group membership for trailing individuals, who can reduce the cost of movement by exploiting the flow patterns generated by the individuals swimming ahead of them. However, whether positions relative to the closest neighbours (e.g. ahead, sided by side or behind) modulate the individual energetic cost of swimming is still unknown. Here, we addressed these questions in grey mullet Liza aurata by measuring tail-beat frequency and amplitude of 15 focal fish, swimming in separate schools, while swimming in isolation and in various positions relative to their closest neighbours, at three speeds. Our results demonstrate that, in a fish school, individuals in any position have reduced costs of swimming, compared to when they swim at the same speed but alone. Although fish swimming behind their neighbours save the most energy, even fish swimming ahead of their nearest neighbour were able to gain a net energetic benefit over swimming in isolation, including those swimming at the front of a school. Interestingly, this energetic saving was greatest at the lowest swimming speed measured in our study. Because any member of a school gains an energetic benefit compared to swimming alone, we suggest that the benefits of membership in moving groups may be more strongly linked to reducing the costs of locomotion than previously appreciated.

Water quality monitoring using abnormal tail-beat frequency of crucian carp

Fish are rapidly becoming favored as convenient sentinels for behavioral assays of toxic chemical exposure. Tail-beat frequency (TBF) of fish is highly correlated with swimming speed, which has been used to detect toxicants. Here we examined the effect on TBF of exposure to two chemicals, and evaluated the ability of this novel behavioral parameter to accurately monitor water quality. To further refine our approach, the Wall-hitting rate (WHR) was used to characterize behavioral avoidance after exposure. Overall, exposure to test chemicals at different levels induced significant increase in both behavioral parameters of the red crucian carp during 1-h exposure periods. Furthermore, the TBF achieved better performance as an indicator when it was calculated in cases where the fish hit the tank wall. Collectively, this study demonstrates the capacity of the TBF of fish to assess water quality in a reliable manner.

Temperature influences sociality and activity of freshwater fish

Temperature is a critical environmental factor in the ecology of fish, significantly influencing their physiology and behavior. Previous studies on the effect of temperature have focused on the metabolic and growth rates of individual fish and on the social behavior of fish shoals in placid water. In this paper, we investigate the effect of changing temperature on shoals of giant danios as they swim in a water tunnel at 22, 25, and 28 °C. Fish activity is quantified in terms of rheotaxis and tail-beat frequency measured automatically by tracking fish shape. Fish social behavior is quantified in terms of average nearest neighbor distance (ANND) and polarization. Results show that both social behavior and individual activity are significantly affected by change in temperature. In particular, fish maximize their activity and ANND at 28 °C, while their polarization is maximized at 22 °C. These findings suggest that temperature influences both the social behavior and the energy expenditure of fish, whereby lower temperatures lead to more cohesive shoals with reduced fish activity.

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 (LF ) 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.

Neural Control and Modulation of Swimming Speed in the Larval Zebrafish

Vertebrate locomotion at different speeds is driven by descending excitatory connections to central pattern generators in the spinal cord. To investigate how these inputs determine locomotor kinematics, we used whole-field visual motion to drive zebrafish to swim at different speeds. Larvae match the stimulus speed by utilizing more locomotor events, or modifying kinematic parameters such as the duration and speed of swimming bouts, the tail-beat frequency, and the choice of gait. We used laser ablations, electrical stimulation, and activity recordings in descending neurons of the nucleus of the medial longitudinal fasciculus (nMLF) to dissect their contribution to controlling forward movement. We found that the activity of single identified neurons within the nMLF is correlated with locomotor kinematics, and modulates both the duration and oscillation frequency of tail movements. By identifying the contribution of individual supraspinal circuit elements to locomotion kinematics, we build a better understanding of how the brain controls movement.

Swimming fish stick to same Strouhal number

Fish swimming at a certain speed appear to adopt a narrow range of swimming styles instinctively. Robert Nudds and colleagues from the University of Manchester, UK, explain that fish seem to adapt their undulations so that the product of their tail beat frequency and the maximum displacement of the tail tip when divided by the fish's forward velocity almost always converges to a number ranging from 0.2 to 0.4, known as the Strouhal number. This means that, at a certain swimming speed, if the fish beats its tail faster it compensates by dropping the amplitude of the tail's undulation, or if the tail beats become broader, they slow down. The same phenomenon, where movements are conserved to a narrow range of Strouhal numbers during locomotion, has also been found in bird flight, leading scientists to conclude that animal movements have been tightly constrained by evolution to maximise propulsive efficiency. However, Nudds points out that none of the observations that have directed scientists to this conclusion had been collected systematically, so Nudds, Emma John, Adam Keen and Holly Shiels decided to resolve the problem by investigating how trout adjust their swimming styles in warmer waters (p. 2244).The team explains that ectothermic fish are susceptible to the environmental temperature, so when the temperature rises, the fish's metabolic rate rises also, reducing the amount of energy that they can invest in swimming at higher speeds and affecting how they beat their tails. With that in mind, the scientists filmed young trout swimming at speeds from 0.28 to 1.11 m s−1 in water at temperatures of 11 and 20°C while recording the fish's tail beat frequency and amplitude.After painstakingly analysing hours of swimming data to calculate the fish's Strouhal number at different speeds and temperatures, the team could see that the fish maintained the same Strouhal number when swimming at both the low and high temperatures at any given speed. The hotter fish beat their tails faster than the cooler fish, but they compensated by reducing the amplitude of each tail beat to maintain a constant Strouhal number at that speed. ‘This is the first experimental evidence for an apparent adherence to a preferred (perhaps optimum) Strouhal number for an animal using oscillatory propulsion’, the team says.However, when they calculated how the fish's Strouhal number varied as the animals speeded up, they saw that the number gradually increased from 0.19 at the lowest speeds to 0.22 at the highest. Although the fish continued beating their tails at the same rate, they increased their speed by sweeping the tail further. The team suggests that the fish's apparent inability to increase their tail beat frequency indicates that their muscle contraction frequency might be finely tuned to a very narrow range at any given temperature. And when they measured the metabolic rate of the fish, although the animals' basal metabolic rate increased with temperature, they did not have to increase the amount of effort they put into fast swimming at higher temperatures. The team suggests that small increases in water temperature may even benefit trout swimming performance. They conclude by saying, ‘Future predictions of changes to water temperature of lakes and rivers are only 5–10°C over the next 100 years and it appears that rainbow trout, at least, can cope with this easily in terms of swimming biomechanics.’

Rainbow trout provide the first experimental evidence for adherence to a distinct Strouhal number during animal oscillatory propulsion.

The relationship between tail (or wing) beat frequency (f(tail)), amplitude (A) and forward velocity (U) in animals using oscillatory propulsion, when moving at a constant cruising speed, converges upon an optimum range of the Strouhal number (St = f(tail) · A/U). Previous work, based on observational data and supported by theory, shows St falling within the broad optimum range (0.2<St<0.4) and considers this adequate to indicate its importance in governing wing or tail kinematics. This study presents the first evidence using an experimental manipulation that supports the importance of maintaining kinematics at a single optimum (or preferred) St. The tail beat kinematics of rainbow trout, Oncorhynchus mykiss, were disturbed by increasing water temperature (T(water)) from 11 ± 1 to 20 ± 1 °C. Elevated T(water) increased f(tail) and decreased A, whilst St at any given U was conserved. St increased with U, driven by concomitant increases in A, whilst f(tail) was unaffected by U. An increase in T(water) also increased basal metabolic costs, but did not affect the incremental increase in metabolic cost with increasing U. Predicted future changes to T(water) of lakes and rivers (5-10 °C over the next 100 years) may not present major locomotory problems to salmonids.

Dietary selenomethionine exposure alters swimming performance, metabolic capacity and energy homeostasis in juvenile fathead minnow

Selenium (Se) is known to cause chronic toxicity in aquatic species. In particular, dietary exposure of fish to selenomethionine (SeMet), the primary form of Se in the diet, is of concern. Recent studies suggest that chronic exposure to elevated dietary SeMet alters energy and endocrine homeostasis in adult fish. However, little is known about the direct effects of dietary SeMet exposure in juvenile fish. The objective of the present study was to investigate sublethal physiological effects of dietary SeMet exposure in juvenile fathead minnow (Pimephales promelas). Twenty days-post-hatch fathead minnow were exposed for 60 days to different measured concentrations (2.8, 5.4, 9.9, 26.5μgSe/g dry mass [dm]) of Se in food in the form of SeMet. After exposure, samples were collected for Se analysis and fish were subjected to a swimming performance challenge to assess critical swim speed (Ucrit), tail beat frequency and tail beat amplitude, oxygen consumption (MO2), cost of transport (COT), standard metabolic rate (SMR), active metabolic rate (AMR), and factorial aerobic scope (F-AS). Ucrit was decreased in the 26.5μgSe/gdm exposure group compared to the control group. Tail beat frequency and tail beat amplitude were significantly reduced in fish fed 9.9 and 26.5μgSe/g. An increase in MO2 and COT was observed in the 9.9 and 26.5μgSe/g exposure groups compared to the control group. While the AMR of the high dose group was increased relative to control, there were no significant differences in SMR and F-AS. Energy storage capacity was measured via whole body triglyceride and glycogen concentrations. Triglyceride concentrations in non-swam fish were elevated in the 5.4μgSe/g group relative to controls. Fatigued (swam) fish had significantly lower whole body triglycerides than non-swam fish. All non-swam SeMet exposure groups had significantly decreased whole body glycogen concentrations compared to controls, while the 5.4 and 26.5μgSe/g exposure groups had significantly greater whole body glycogen concentrations in swam versus non-swam fish. A decrease in whole body cortisol was observed in swam fish in the 5.4μgSe/g exposure group compared to control fish. Whole body cortisol was greater in control, 9.9 and 26.5μgSe/g swam fish compared to non-swam fish. These results suggest that exposure to environmentally relevant concentrations of dietary SeMet impairs swimming performance, aerobic capacity, and energy homeostasis, potentially impacting survivability of juvenile fish in Se impacted aquatic ecosystems.

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.

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.

Analytical insights into optimality and resonance in fish swimming

This paper provides analytical insights into the hypothesis that fish exploit resonance to reduce the mechanical cost of swimming. A simple body-fluid fish model, representing carangiform locomotion, is developed. Steady swimming at various speeds is analysed using optimal gait theory by minimizing bending moment over tail movements and stiffness, and the results are shown to match with data from observed swimming. Our analysis indicates the following: thrust-drag balance leads to the Strouhal number being predetermined based on the drag coefficient and the ratio of wetted body area to cross-sectional area of accelerated fluid. Muscle tension is reduced when undulation frequency matches resonance frequency, which maximizes the ratio of tail-tip velocity to bending moment. Finally, hydrodynamic resonance determines tail-beat frequency, whereas muscle stiffness is actively adjusted, so that overall body-fluid resonance is exploited.

Bio-harmonized Dynamic Model of a Biology Inspired Carangiform Robotic Fish Underwater Vehicle

This paper presents a novel dynamic model of a bio-inspired robotic fish underwater vehicle by unifying conventional rigid body dynamics and bio-fluid-dynamics of a carangiform fish swimming given by Lighthill's (LH) slender body theory It proposes an inclusive mathematical design for better control and energy efficient path travel for the robotic fish. The system is modeled as an 2-link robot manipulator (caudal tail) with a mobile base (head). Lighthill caudal-tail reactive forces and moments are shown to contribute towards thrust generation and yaw balance. These LH reactive forces are shown to generate the inertial added mass during the robotic fish locomotion. This forward thrust drives the robotic fish head represented by a unified non-linear equation of motion in earth fixed frame. Using the proposed dynamic model an open-loop (manual) operating region for the identified kinematic parameter tail beat frequency (TBF) is established. Obtained Kinematic results also resemble with real fish kinematic results. The objective is to mimic the propulsion technique of the carangiform swimming style and to show the fish behavior navigating efficiently over large distances at impressive speeds and its exceptional character in fluid environment.

Undulatory locomotion of flexible foils as biomimetic models for understanding fish propulsion

An undulatory pattern of body bending in which waves pass along the body from head to tail is a major mechanism of creating thrust in many fish species during steady locomotion. Analyses of live fish swimming have provided the foundation of our current understanding of undulatory locomotion, but our inability to experimentally manipulate key variables such as body length, flexural stiffness and tailbeat frequency in freely swimming fish has limited our ability to investigate a number of important features of undulatory propulsion. In this paper we use a mechanical flapping apparatus to create an undulatory wave in swimming flexible foils driven with a heave motion at their leading edge, and compare this motion with body bending patterns of bluegill sunfish (Lepomis macrochirus) and clown knifefish (Notopterus chitala). We found similar swimming speeds, Reynolds and Strouhal numbers, and patterns of curvature and shape between these fish and foils, suggesting that flexible foils provide a useful model for understanding fish undulatory locomotion. We swam foils with different lengths, stiffnesses and heave frequencies while measuring forces, torques and hydrodynamics. From measured forces and torques we calculated thrust and power coefficients, work and cost of transport for each foil. We found that increasing frequency and stiffness produced faster swimming speeds and more thrust. Increasing length had minimal impact on swimming speed, but had a large impact on Strouhal number, thrust coefficient and cost of transport. Foils that were both stiff and long had the lowest cost of transport (in mJ m(-1) g(-1)) at low cycle frequencies, and the ability to reach the highest speed at high cycle frequencies.

Development of the ultrastructure of sonic muscles: a kind of neoteny?

BackgroundDrumming muscles of some sound-producing fish are ‘champions’ of contraction speed, their rate setting the fundamental frequency. In the piranha, contraction of these muscles at 150 Hz drives a sound at the same frequency. Drumming muscles of different not closely related species show evolutionary convergences. Interestingly, some characters of sonic muscles can also be found in the trunk muscles of newly hatched larvae that are able to maintain tail beat frequencies up to 100 Hz. The aim of this work was to study the development of sound production and sonic and epaxial muscles simultaneously in the red bellied piranhas (Pygocentrus nattereri) to seek for possible common characteristics.ResultsCall, pulse and period durations increased significantly with the fish size, but the call dominant frequencies decreased, and the number of pulses and the call amplitude formed a bell curve. In epaxial muscles, the fibre diameters of younger fish are first positioned in the graphical slope corresponding to sonic muscles, before diverging. The fibre diameter of older fish trunk muscles was bigger, and the area of the myofibrils was larger than in sonic muscles. Moreover, in two of the biggest fish, the sonic muscles were invaded by fat cells and the sonic muscle ultrastructure was similar to the epaxial one. These two fish were also unable to produce any sound, meaning they lost their ability to contract quickly.ConclusionsThe volume occupied by myofibrils determines the force of contraction, the volume of sarcoplasmic reticulum sets the contraction frequency, and the volume of mitochondria sets the level of sustained performance. The functional outcomes in muscles are all attributable to shifts in the proportions of those structures. A single delay in the development restricts the quantity of myofibrils, maintains a high proportion of space in the sarcoplasm and develops sarcoplasmic reticulum. High-speed sonic muscles could thus be skeletal muscles with delayed development. This hypothesis has the advantage that it could easily explain why high-speed sonic muscles have evolved so many times in different lineages.

Computational and mathematical modeling of the effects of tailbeat frequency and flexural stiffness in swimming fish

In this paper we describe how we combine computational and mathematical models to form virtual fish to explore different hypotheses about the impact of centra. We show how we create simulation models using a combination of a mathematical model of a fish-like robot using caudal fin propulsion, a propulsion model, and an optimizer, to explore the impact of centra under various scenarios. The optimizer uses the mathematical model to construct valid configurations of the digital robot and uses the utility function and propulsion model to evaluate the performance of each configuration. The evaluations are used to explore the adaptive landscape and find high-performing configurations. Our results show that the high-performing configurations have both increased (flexural) stiffness of the tail and higher tailbeat frequencies.

Temperature and fatigue effect on the maximum swimming speed of jack mackerel Trachurus japonicus

Swimming performance of jack mackerel Trachurus japonicus (18.2 ± 0.8 cm fork length (FL), n = 185) was examined in a flume tank by measuring the stride length at low and high tail beat frequencies with electromyogram monitoring and a muscle twitch experiment. Stride length was analyzed by monitoring the tail beat frequency according to the swimming speed at different temperatures of 10, 15 and 22 °C. In the electromyographic observations, the initiation of ordinary muscle activity occurred between 71.4 and 99.6 cm/s, that is 3.7 to 5.3 FL/s, when the tail beat frequency was over 6 Hz. The swimming speeds increased rectilinearly with the tail beat frequency at each water temperature both for the low and high tail beat frequency. Lower stride length was observed at the lowest temperature (10 °C) tested. The forced swimming exercise significantly affected the muscle contraction time to become longer than the control fish, which indicated a reduction of the maximum swimming speed performance.

Fish and robots swimming together in a water tunnel: robot color and tail-beat frequency influence fish behavior.

The possibility of integrating bioinspired robots in groups of live social animals may constitute a valuable tool to study the basis of social behavior and uncover the fundamental determinants of animal functions and dysfunctions. In this study, we investigate the interactions between individual golden shiners (Notemigonus crysoleucas) and robotic fish swimming together in a water tunnel at constant flow velocity. The robotic fish is designed to mimic its live counterpart in the aspect ratio, body shape, dimension, and locomotory pattern. Fish positional preference with respect to the robot is experimentally analyzed as the robot's color pattern and tail-beat frequency are varied. Behavioral observations are corroborated by particle image velocimetry studies aimed at investigating the flow structure behind the robotic fish. Experimental results show that the time spent by golden shiners in the vicinity of the bioinspired robotic fish is the highest when the robot mimics their natural color pattern and beats its tail at the same frequency. In these conditions, fish tend to swim at the same depth of the robotic fish, where the wake from the robotic fish is stronger and hydrodynamic return is most likely to be effective.

Collective response of zebrafish shoals to a free-swimming robotic fish.

In this work, we explore the feasibility of regulating the collective behavior of zebrafish with a free-swimming robotic fish. The visual cues elicited by the robot are inspired by salient features of attraction in zebrafish and include enhanced coloration, aspect ratio of a fertile female, and carangiform/subcarangiform locomotion. The robot is autonomously controlled with an online multi-target tracking system and swims in circular trajectories in the presence of groups of zebrafish. We investigate the collective response of zebrafish to changes in robot speed, achieved by varying its tail-beat frequency. Our results show that the speed of the robot is a determinant of group cohesion, quantified through zebrafish nearest-neighbor distance, which increases with the speed of the robot until it reaches . We also find that the presence of the robot causes a significant decrease in the group speed, which is not accompanied by an increase in the freezing response of the subjects. Findings of this study are expected to inform the design of experimental protocols that leverage the use of robots to study the zebrafish animal model.

Effect of temperature on swimming performance of juvenile Schizothorax prenanti

The migration of Schizothorax prenanti, an ecologically important and commercially valuable species, is impeded by dams. Effective fishways would contribute to conservation of wild populations, and swimming performance data are necessary for fishway design. The swimming performance of S. prenanti was investigated at four temperatures (15, 19, 23, 27 °C), and numerical models were used to characterize the effect of temperature on swimming performance. As temperature increases, critical swimming speed (U crit) increases from 15 to 23 °C and then decreases significantly. The highest U crit (7.71 BL/s) occurs at 24 °C, as estimated by interpolation. Swimming efficiency was similar from 19 to 23 °C, but decreases significantly at 27 °C. The temperature range 15-23 °C is suitable for S. prenanti. However, the excess post-exercise oxygen consumption values of Q 10 for the four temperature increments indicate that 19-23 °C is the optimal range for swimming performance. Maximum tail beat amplitude increased >25 % (0.35-0.45 BL) over the temperature range considered, but variation of tail beat frequency was erratic. White muscle fiber begins to contribute to swimming at swimming speeds ~40 % U crit at the lower three temperatures, but increases to almost 60 % at 27 °C, and the contribution is relatively small. The results of this investigation advance the knowledge of fish metabolism while swimming provides data critical for fishway design.