Tail Beat Amplitude Research Articles

Thyroid hormone regulates muscle function during cold acclimation in zebrafish (Danio rerio)

Thyroid hormone (TH) is a universal regulator of growth, development and metabolism during cold exposure in mammals. In zebrafish (Danio rerio), TH regulates locomotor performance and metabolism during cold acclimation. The influence of TH on locomotor performance may be via its effect on metabolism or, as has been shown in mammals, by modulating muscle phenotypes. Our aim was to determine whether TH influences muscle phenotypes in zebrafish, and whether this could explain changes in swimming capacity in response to thermal acclimation. We used propylthiouracil and iopanoic acid to induce hypothyroidism in zebrafish over a 3-week acclimation period to either 18 or 28°C. To verify that physiological changes following hypothyroid treatment were in fact due to the action of TH, we supplemented hypothyroid fish with 3,5-diiodothryronine (T2) or 3,5,3'-triiodothyronine (T3). Cold-acclimated fish had significantly greater sustained swimming performance (Ucrit) but not burst speed. Greater Ucrit was accompanied by increased tail beat frequency, but there was no change in tail beat amplitude. Hypothyroidism significantly decreased Ucrit and burst performance, as well as tail beat frequency and SERCA activity in cold-acclimated fish. However, myofibrillar ATPase activity increased in cold-acclimated hypothyroid fish. Hypothyroid treatment also decreased mRNA concentrations of myosin heavy chain fast isoforms and SERCA 1 isoform in cold-acclimated fish. SERCA 1 mRNA increased in warm-acclimated hypothyroid fish, and SERCA 3 mRNA decreased in both cold- and warm-acclimated hypothyroid fish. Supplementation with either T2 or T3 restored Ucrit, burst speed, tail beat frequency, SERCA activity and myosin heavy chain and SERCA 1 and 3 mRNA levels of hypothyroid fish back to control levels. We show that in addition to regulating development and metabolism in vertebrates, TH also regulates muscle physiology in ways that affect locomotor performance in fish. We suggest that the role of TH in modulating SERCA1 expression during cold exposure may have predisposed it to regulate endothermic thermogenesis.

Function of dorsal fins in bamboo shark during steady swimming

To gain insight into the function of the dorsal fins in white-spotted bamboo sharks (Orectolobiformes: Hemiscyillidae) during steady swimming, data on three-dimensional kinematics and electromyographic recordings were collected. Bamboo sharks were induced to swim at 0.5 and 0.75 body lengths per second in a laminar flow tank. Displacement, lag and angles were analyzed from high-speed video images. Onset, offset, duration, duty cycle and asynchrony index were calculated from three muscle implants on each side of each dorsal fin. The dorsal fins were displaced more laterally than the undulating body. In addition, the dorsal tips had larger lateral displacement than the trailing edges. Increased speed was accompanied by an increase in tail beat frequency with constant tail beat amplitude. However, lateral displacement of the fins and duration of muscle bursts remained relatively constant with increased speed. The range of lateral motion was greater for the second dorsal fin (mean 33.3°) than for the first dorsal fin (mean 28.4°). Bending within the fin was greater for the second dorsal fin (mean 43.8°) than for the first dorsal fin (mean 30.8°). Muscle onset and offset among implants on the same side of each dorsal fin was similar. Three-dimensional conformation of the dorsal fins was caused by interactions between muscle activity, material properties, and incident flow. Alternating bilateral activity occurred in both dorsal fins, further supporting the active role of these hydrofoils in thrust production during steady swimming. The dorsal fins in bamboo sharks are capable of thrust production during steady swimming and do not appear to function as stabilizing structures.

Recovery bags reduce post-release impairments in locomotory activity and behavior of bonefish (Albula spp.) following exposure to angling-related stressors

Bonefish (Albula spp.) are a group of species targeted by recreational anglers in shallow tropical and sub-tropical seas worldwide. Although bonefish angling is almost entirely catch-and-release, mortality can occur because the stress associated with angling and handling causes locomotory impairment that promotes post-release predation. We used tri-axial accelerometer loggers to compare the locomotor activity and behavior of bonefish exposed to angling-related stressors and immediately released (n=10, 39.9±1.1cm FL), to those retained in a recovery bag for 15min prior to release (n=10, 39.6±1.0cm FL) in a tidal creek in Eleuthera, The Bahamas. We also validated the use of reflex action mortality predictors (RAMP) as an impairment index for evaluating bonefish condition upon release. Following release, bonefish were visually tracked for 30min with floats to evaluate short-term survival, after which the accelerometer was retrieved. Bonefish held in recovery bags exhibited significantly less locomotory impairment immediately post-release, and higher maximum tail beat frequencies and amplitudes up to 15min post-release, which was likely due to the time spent in the recovery bag. Bonefish in the recovery bag treatment also spent more time resting in possible refuge areas, which may facilitate further recovery and avoidance from predation. RAMP provided a gradient of impairment scores that were correlated with stressor duration. Retaining bonefish in recovery bags improved swimming abilities during the critical time period where the majority of post-release predation occurs, and one fish that was not placed in the recovery bag was preyed upon during the monitoring period. Further testing is needed to determine if the locomotory and behavioral benefits of retaining bonefish in recovery bags translate into improved survival from predation in more predator rich environments.

The effects of caudal fin loss and regeneration on the swimming performance of three cyprinid fish with different swimming capacities

In nature, the caudal fins of fish species are frequently lost to some extent by aggressive behaviour, predation and diseases. To test whether the swimming performance of fish with different swimming capacities would be differentially affected due to caudal fin loss and regeneration, we investigated the critical swimming speed (Ucrit), swimming metabolic rate (M(O2)), tail beat frequency (f(TB)) and tail beat amplitude (A(TB)) after caudal fin loss and regeneration (20 days) in juveniles of three cyprinid fish species: the qingbo (Spinibarbus sinensis; strong swimmer), the common carp (Cyprinus carpio; intermediate swimmer) and the goldfish (Carassius auratus; poor swimmer). The Ucrit values of the caudal-fin-lost qingbo, common carp and goldfish were 49, 32 and 35% significantly lower than those of the control groups, respectively. The maximum tail beat amplitude (A(TBmax)) (all three fishes), the maximum tail beat frequency (f(TBmax)) (only the common carp and the goldfish) and/or the active metabolic rate (M(O2active)) (only the common carp) of the caudal-fin-lost fish were significantly higher than those of the control groups. After 20 days of recovery, the caudal fins recovered to 41, 47 and 24% of those of the control groups for the qingbo, the common carp and the goldfish, respectively. However, the Ucrit values of the fin-regenerated qingbo, common carp and goldfish recovered to 86, 91 and 95% of those of the control group, respectively. The caudal-fin-regenerated qingbo and common carp showed a significantly higher A(TBmax) and f(TBmax), respectively, compared with those of the control groups. The qingbo had a higher f(TBmax) but a lower A(TBmax) than the common carp and the goldfish, which suggested that a strong swimmer may maintain swimming speed primarily by maintaining a greater f(TBmax), for which the caudal fin plays a more important role during swimming, than a poor swimmer. The M(O2active) of fish (common carp) with a redundant respiratory capacity could increase due to caudal fin loss to meet the increase in energy expenditure required by an increase in f(TBmax). In addition, the sustained swimming performance may not be the only selective pressure acting on caudal fin size in these three species, and the present caudal fin size may be a trade-off between sustain swimming performance and other factors (e.g. sexual selection, escape responses).

The effect of flow speed and body size on Kármán gait kinematics in rainbow trout

We have little understanding of how fish hold station in unsteady flows. Here, we investigated the effect of flow speed and body size on the kinematics of rainbow trout Kármán gaiting behind a 5 cm diameter cylinder. We established a set of criteria revealing that not all fish positioned in a vortex street are Kármán gaiting. By far the highest probability of Kármán gaiting occurred at intermediate flow speeds between 30 and 70 cm s(-1). We show that trout Kármán gait in a region of the cylinder wake where the velocity deficit is about 40% of the nominal flow. We observed that the relationships between certain kinematic and flow variables are largely preserved across flow speeds. Tail-beat frequency matched the measured vortex shedding frequency, which increased linearly with flow speed. Body wave speed was about 25% faster than the nominal flow velocity. At speeds where fish have a high probability of Kármán gaiting, body wavelength was about 25% longer than the cylinder wake wavelength. Likewise, the lateral (i.e. cross-stream) amplitude of the tail tip was about 50% greater than the expected lateral spacing of the cylinder vortices, while the body center amplitude was about 70% less. Lateral body center acceleration increased quadratically with speed. Head angle decreased with flow speed. While these values are different from those found in fish swimming in uniform flow, the strategy for locomotion is the same; fish adjust to increasing flow by increasing their tail-beat frequency. Body size also played a role in Kármán gaiting kinematics. Tail-beat amplitudes of Kármán gaiting increased with body size, as in freestream swimming, but were almost three times larger in magnitude. Larger fish had a shorter body wavelength and slower body wave speed than smaller fish, which is a surprising result compared with freestream swimming, where body wavelength and wave speed increased with size. In contrast to freestream swimming, tail-beat frequency for Kármán gaiting fish did not depend on body size and was a function of the vortex shedding frequency.

The effects of caudal fin amputation on metabolic interaction between digestion and locomotion in juveniles of three cyprinid fish species with different metabolic modes

Metabolic competitive modes between digestion and locomotion are classified into three categories, termed the additive, digestion- and locomotion-priority modes. In nature, the caudal fin is frequently observed to sustain damage as a result of social rank, predation or disease. To test whether the metabolic mode changed differently for fish with different metabolic mode after caudal fin amputation as a consequence of intensified energy competition, we investigated the swimming performance of fasting and fed fish with and without the caudal fin in juveniles of three cyprinid fish species: qingbo (Spinibarbus sinensis, locomotion-priority mode), common carp (Cyprinus carpio, additive mode) and goldfish (Carassius auratus, digestion-priority mode). The critical swimming speed (Ucrit) of fasting qingbo, common carp and goldfish decreased significantly by 49%, 32% and 35% after caudal fin amputation. The maximum tail beat amplitude (TBAmax) (all three fishes), maximum tail beat frequency (TBFmax) (only common carp and goldfish) and (or) active metabolic rate (M˙O2active) (only common carp) increased significantly after caudal fin amputation. In the control fish, digestion let to a significantly lower Ucrit in goldfish but not in qingbo and common carp, and the M˙O2active of digesting common carp was higher than that of fasting fish, suggesting locomotion-priority, additive and digestion-priority metabolic modes in qingbo, common carp and goldfish, respectively. However, after fin amputation, digestion showed no effect on Ucrit in any of the three fishes, and only the digesting common carp showed a higher M˙O2active than their fasting counterparts. This result suggested that the metabolic mode of the goldfish changed from the digestion- to the locomotion-priority mode, whereas the metabolic mode of the other two fishes remained the same after fin amputation. The metabolic mode of the common carp showed no change after fin amputation likely due to the high flexibility of the cardio-respiratory capacity of this fish, as indicated by the increased M˙O2active. Although the metabolic mode remained the same, the feeding metabolism in the fin-amputated qingbo was down-regulated at a lower swimming speed than that of the control group due to the intensified competition between digestion and locomotion. The underlying mechanism for the metabolic mode change in the goldfish is not clear and needs further investigation. However, we speculated that in caudal-fin-intact goldfish, the decreased swimming efficiency, rather than irreducible digestive loading, caused a decreased Ucrit in digesting fish (i.e. false digestion-priority mode), and the metabolic mode should not be judged simply by the relative magnitude of the metabolic rates of fasting and digesting fish.

How well do muscle biomechanics predict whole-animal locomotor performance? The role of Ca2+ handling

It is important to determine the enabling mechanisms that underlie locomotor performance to explain the evolutionary patterns and ecological success of animals. Our aim was to determine the extent to which calcium (Ca(2+)) handling dynamics modulate the contractile properties of isolated skeletal muscle, and whether the effects of changing Ca(2+) handling dynamics in skeletal muscle are paralleled by changes in whole-animal sprint and sustained swimming performance. Carp (Cyprinus carpio) increased swimming speed by concomitant increases in tail-beat amplitude and frequency. Reducing Ca(2+) release from the sarcoplasmic reticulum (SR) by blocking ryanodine receptors with dantrolene decreased isolated peak muscle force and was paralleled by a decrease in tail-beat frequency and whole-animal sprint performance. An increase in fatigue resistance following dantrolene treatment may reflect the reduced depletion of Ca(2+) stores in the SR associated with lower ryanodine receptor (RyR) activity. Blocking RyRs may be detrimental by reducing force production and beneficial by reducing SR Ca(2+) depletion so that there was no net effect on critical sustained swimming speed (U(crit)). In isolated muscle, there was no negative effect on force production of blocking Ca(2+) release via dihydropyridine receptors (DHPRs) with nifedipine. Nifedipine decreased fatigue resistance of isolated muscle, which was paralleled by decreases in tail-beat frequency and U(crit). However, sprint performance also decreased with DHPR inhibition, which may indicate a role in muscle contraction of the Ca(2+) released by DHPR into the myocyte. Inhibiting sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) activity with thapsigargin decreased fatigue resistance, suggesting that SERCA activity is important in avoiding Ca(2+) store depletion and fatigue. We have shown that different molecular mechanisms modulate the same muscle and whole-animal traits, which provides an explanatory model for the observed variations in locomotor performance within and between species.

Maximum sustainable speed, energetics and swimming kinematics of a tropical carangid fish, the green jack Caranx caballus

Maximum sustained swimming speeds, swimming energetics and swimming kinematics were measured in the green jack Caranx caballus (Teleostei: Carangidae) using a 41 l temperature-controlled, Brett-type swimming-tunnel respirometer. In individual C. caballus [mean ±s.d. of 22·1 ± 2·2 cm fork length (L(F) ), 190 ± 61 g, n = 11] at 27·2 ± 0·7° C, mean critical speed (U(crit)) was 102·5 ± 13·7 cm s⁻¹ or 4·6 ± 0·9 L(F) s⁻¹. The maximum speed that was maintained for a 30 min period while swimming steadily using the slow, oxidative locomotor muscle (U(max,c)) was 99·4 ± 14·4 cm s⁻¹ or 4·5 ± 0·9 L(F) s⁻¹. Oxygen consumption rate (M in mg O₂ min⁻¹) increased with swimming speed and with fish mass, but mass-specific M (mg O₂ kg⁻¹ h⁻¹) as a function of relative speed (L(F) s⁻¹) did not vary significantly with fish size. Mean standard metabolic rate (R(S) ) was 170 ± 38 mg O₂ kg⁻¹ h⁻¹, and the mean ratio of M at U(max,c) to R(S) , an estimate of factorial aerobic scope, was 3·6 ± 1·0. The optimal speed (U(opt) ), at which the gross cost of transport was a minimum of 2·14 J kg⁻¹ m⁻¹, was 3·8 L(F) s⁻¹. In a subset of the fish studied (19·7-22·7 cm L(F) , 106-164 g, n = 5), the swimming kinematic variables of tailbeat frequency, yaw and stride length all increased significantly with swimming speed but not fish size, whereas tailbeat amplitude varied significantly with speed, fish mass and L(F) . The mean propulsive wavelength was 86·7 ± 5·6 %L(F) or 73·7 ± 5·2 %L(T) . Mean ±s.d. yaw and tailbeat amplitude values, calculated from lateral displacement of each intervertebral joint during a complete tailbeat cycle in three C. caballus (19·7, 21·6 and 22·7 cm L(F) ; 23·4, 25·3 and 26·4 cm L(T) ), were 4·6 ± 0·1 and 17·1 ± 2·2 %L(T) , respectively. Overall, the sustained swimming performance, energetics, kinematics, lateral displacement and intervertebral bending angles measured in C. caballus were similar to those of other active ectothermic fishes that have been studied, and C. caballus was more similar to the chub mackerel Scomber japonicus than to the kawakawa tuna Euthynnus affinis.

A Flexible Fin with Bio-Inspired Stiffness Profile and Geometry

Biological evidence suggests that fish use mostly anterior muscles for steady swimming while the caudal part of the body is passive and, acting as a carrier of energy, transfers the momentum to the surrounding water. Inspired by those findings we hypothesize that certain swimming patterns can be achieved without copying the distributed actuation mechanism of fish but rather using a single actuator at the anterior part to create the travelling wave. To test the hypothesis a pitching flexible fin made of silicone rubber and silicone foam was designed by copying the stiffness distribution profile and geometry of a rainbow trout. The kinematics of the fin was compared to that of a steadily swimming trout. Fin's propulsive wave length and tail-beat amplitude were determined while it was actuated by a single servo motor. Results showed that the propulsive wave length and tail-beat amplitude of a steadily swimming 50 cm rainbow trout was achieved with our biomimetic fin while stimulated using certain actuation parameters (frequency 2.31 Hz and amplitude 6.6 degrees). The study concluded that fish-like swimming can be achieved by mimicking the stiffness and geometry of a rainbow trout and disregarding the details of the actuation mechanism.

Movement and function of the pectoral fins of the larval zebrafish (Danio rerio) during slow swimming

Pectoral fins are known to play important roles in swimming for many adult fish; however, their functions in fish larvae are unclear. We examined routine pectoral fin movement during rhythmic forward swimming and used genetic ablation to test hypotheses of fin function in larval zebrafish. Fins were active throughout bouts of slow swimming. Initiation was characterized by asymmetric fin abduction that transitioned to alternating rhythmic movement with first fin adduction. During subsequent swimming, fin beat amplitude decreased while tail beat amplitude increased over swimming speeds ranging from 1.47 to 4.56 body lengths per second. There was no change in fin or tail beat frequency with speed (means ± s.d.: 28.2±3.5 and 29.6±1.9 Hz, respectively). To examine potential roles of the pectoral fins in swimming, we compared the kinematics of finless larvae generated with a morpholino knockdown of the gene fgf24 to those of normal fish. Pectoral fins were not required for initiation nor did they significantly impact forward rhythmic swimming. We investigated an alternative hypothesis that the fins function in respiration. Dye visualization demonstrated that pectoral fin beats bring distant fluid toward the body and move it caudally behind the fins, disrupting the boundary layer along the body's surface, a major site of oxygen absorption in larvae. Larval zebrafish also demonstrated more fin beating in low oxygen conditions. Our data reject the hypothesis that the pectoral fins of larval zebrafish have a locomotor function during slow, forward locomotion, but are consistent with the hypothesis that the fins have a respiratory function.

Aerobic swimming performance of juvenile Schizothorax chongi (Pisces, Cyprinidae) in the Yalong River, southwestern China

Schizothorax chongi (locally known as Xilian Yu), a fish species commonly found in Yalong River, has been declining quickly in recent years. One of the important factors, among many, is the interruption of the free flowing river by dams. To obtain data that can be applied to the design of a fishway for S. chongi and other species in the community, a laboratory study of juvenile S. chongi’s swimming energetics and kinematics was conducted in a flume-type respirometer equipped with a high speed video camera system to record swimming behavior. The aerobic metabolic rate, tail beat frequency (TBF) and tail beat amplitude (TBA) were measured during steady swimming at varying flow rates for fish of similar mass. A power function accurately describes the relationship between oxygen consumption rate (MO2) and swimming speed (U). The estimated standard metabolic rate (SMR) calculated from the power function was 445.34 mg O2 kg−1 h−1, similar to the experimental result of 431.5 mg O2 kg−1 h−1. The relationship between cost of transport (COT) and U was, characteristically, inverse bell-shaped, with COTmin = 44.6 J kg−1 m−1 at Uopt = 5.5 body lengths per second (bl s−1). There was a significant positive linear correlation between TBF and U. The slope of the correlation (0.33) was lower than for many other species, implying that S. chongi swim efficiently. The TBA, ranging from 0.15 to 0.2 bl, was found to be independent of U. Kinematic analyses indicates that S. chongi primarily depends on the caudal fin to generate forward thrust and employs three velocity-dependent swimming gaits. This investigation provides data on the swimming ability of S. chongi that will add to the basic science required for fishway design.

Acute exposure to 2,4-dinitrophenol alters zebrafish swimming performance and whole body triglyceride levels

While swimming endurance (critical swimming speed or U crit) and lipid stores have both been reported to acutely decrease after exposure to a variety of toxicants, the relationship between these endpoints has not been clearly established. In order to examine these relationships, adult zebrafish ( Danio rerio) were aqueously exposed to solvent control (ethanol) or two nominal concentrations of 2,4-dinitrophenol (DNP), a mitochondrial electron transport chain uncoupler, for a 24-h period. Following exposure, fish were placed in a swim tunnel in clean water for swimming testing or euthanized immediately without testing, followed by analysis of whole body triglyceride levels. U crit decreased in both the 6 mg/L and 12 mg/L DNP groups, with 12 mg/L approaching the LC 50. A decrease in tail beat frequency was observed without a significant change in tail beat amplitude. In contrast, triglyceride levels were elevated in a concentration-dependent manner in the DNP exposure groups, but only in fish subjected to swimming tests. This increase in triglyceride stores may be due to a direct interference of DNP on lipid catabolism as well as increased triglyceride production when zebrafish were subjected to the co-stressors of swimming and toxicant exposure. Future studies should be directed at determining how acute DNP exposure combines with swimming to cause alterations in triglyceride accumulation.

Dietary selenomethionine exposure in adult zebrafish alters swimming performance, energetics and the physiological stress response

Selenomethionine (Se-Met) is the major form of organoselenium present in food. Early life stages of oviparous vertebrate species, especially fish, are highly susceptible to dietary selenium (Se) exposure; however less is known concerning effects in adults. The present study was designed to investigate behavioral and physiological consequences of dietary Se-Met exposure to adult zebrafish ( Danio rerio). Adult fish were fed either control food (1.3 μg Se/g, dry weight or dw) or food spiked with varying measured concentrations of Se (3.7, 9.6 and 26.6 μg Se/g, dw) in the form of Se-Met for 60 days at 5% body weight/day ration, and an additional 30–40 days with equal ration (2.5%) of control or Se-Met spiked foods and clean chironomids. At the end of the exposure period, critical swimming speed (Ucrit), oxygen consumption (MO 2), cost of transport (COT), tail beat amplitude, tail beat frequency, and whole body cortisol, triglyceride and glycogen levels were determined. Significantly reduced Ucrit was observed in fish fed 3.7, 9.6 and 26.6 μg Se/g when compared to control fish. Although MO 2 of fish fed >3 μg Se/g was consistently greater than control fish, those values were not statistically significant. There was no difference in COT among different treatment groups. Tail beat amplitudes of fish fed >3 μg Se/g were lower than control fish, however tail beat frequencies were not altered. Fish fed 3.7, 9.6 and 26.6 μg Se/g had greater whole body triglycerides and glycogen levels than control fish. Fish fed the highest concentration of Se (26.6 μg Se/g) had elevated levels of whole body cortisol compared to control fish. Our results suggest that environmentally relevant dietary Se-Met exposure can alter both behavioral and physiological responses in adult fish, and such consequences could threaten fitness of adult fish in Se impacted aquatic ecosystems.

The effect of temperature and ammonia exposure on swimming performance of brook charr (Salvelinus fontinalis)

The effects of water temperature and ammonia concentration on swimming capacity of brook charr (Salvelinus fontinalis, Mitchill, 1814) were determined by measuring gait transition speed (Ugt, cms−1), maximum burst speed (Umax, cms−1), tail-beat amplitude (a, cm), tail-beat frequency (f, Hz), maximum acceleration of bursts (Amax, cms−2), number of bursts, distance of bursts (cm) and total swimming distance (cm) in a 4.5m long experimental raceway with increasing upstream water velocity. Temperatures other than the acclimation temperature of 15°C significantly reduced swimming characteristics of gait transition, i.e. Ugt and Amax, while increased ammonia concentration reduced the measures of swimming after Ugt: Umax, the relationship between f and swimming speed above Ugt, a, Amax and the distance travelled with each swimming burst above Ugt. This study, using a novel raceway set-up shows various effects of temperature and ammonia exposure on the swimming performance of brook charr and can be used to establish threshold values for environmental management.

Swimming and posture control of common carp when penetrating mesh nets in a water tunnel

Successful capture of actively swimming fishes by towed net is a complex process. Quantitative studies of fish behavior and swimming kinematics near and in towed nets under field conditions are almost impossible. This paper reports a laboratory study of a model system that provides insight these matters. Behavioral and swimming kinematic responses of juvenile common carp to variously oriented flat panels of netting were studied under conditions of rapid water flow in a precision water tunnel. Responses of groups of fish were recorded by digital video camera; their maneuvers and kinematic responses were analyzed. Netting panels were positioned in three directions: vertically transverse to flow, vertically and horizontally parallel to flow. Panels of diamond mesh netting (both horizontal and vertical diamonds) were mounted in rigid frames. When fish passed through the nets tail beat frequencies and amplitudes both increased above base line levels. Penetration ratios, moving speeds, yawing turns and rolling angles all varied with the positions of the netting panels or the mesh hanging ratios. The penetration process had several stages: fish initially adjusted positions using yawing and side-slip; they then made yawing turns or rolled; propulsive accelerations followed; then fish rolled and stabilized in relation to the water flow. Penetration failures were due to lack of one or more of the main maneuvers. Fish penetration and selectivity in towed fishing gear may relate to both difficulties with swimming maneuverability and to the sizes and shapes of both the fish and the netting.

Numerical investigation of the hydrodynamics of anguilliform swimming in the transitional and inertial flow regimes

We employ numerical simulation to investigate the hydrodynamic performance of anguilliform locomotion and compare it with that of carangiform swimming as the Reynolds number (Re) and the tail-beat frequency (Strouhal number, St) are systematically varied. The virtual swimmer is a 3-D lamprey-like flexible body undulating with prescribed experimental kinematics of anguilliform type. Simulations are carried out for three Reynolds numbers spanning the transitional and inertial flow regimes, Re=300, 4000 (viscous flow), and infinity (inviscid flow). The net mean force is found to be mainly dependent on the tail-beat frequency rather than the tail-beat amplitude. The critical Strouhal number, St, at which the net mean force becomes zero (constant-speed self-propulsion) is, similar to carangiform swimming, a decreasing function of Re and approaches the range of St numbers at which most anguilliform swimmers swim in nature (St approximately 0.45) only as Re increases. The anguilliform swimmer's force time series is characterized by significantly smaller fluctuations above the mean than that for carangiform swimmers. In stark contrast with carangiform swimmers, the propulsive efficiency of anguilliform swimmers at St is not an increasing function of Re but instead is maximized in the transitional regime. Furthermore, the power required for anguilliform swimming is less than that for the carangiform swimmer at the same Re. We also show that the form drag decreases while viscous drag increases as St increases. Finally, our simulations reinforce our previous finding for carangiform swimmers that the 3-D wake structure depends primarily on the Strouhal number.

Muscle bioenergetics of speeding fish: In vivo 31P‐NMR studies in a 4.7 T MR scanner with an integrated swim tunnel

AbstractEnergetic studies on exercising animals are usually limited to oxygen consumption measurements in respirometers followed by invasive tissue sampling and analysis of metabolites. Noninvasive studies of exercising animals like through the use of 31P NMR are typically restricted to “stop and go” measurements. Furthermore, magnetic resonance studies of marine animals are hampered by sea water, a highly electric conductive and dielectric medium, resulting in heavy loading and strong RF loss. In this work, we present a set‐up for online determination of muscle bioenergetics in swimming marine fish, Atlantic cod (Gadus morhua), using in vivo 31P NMR spectroscopy, which overcome these limitations. Special hardware and RF coils were developed for this purpose. A birdcage resonator adapted to high loadings was used for signal excitation. An insulated inductive coil (2 cm diameter) was fixed onto the surface of the fish tail and placed opposite a watertight, passively decoupled 9 × 6 cm2 elliptic and curved surface coil for signal recordings. This arrangement led to enhanced penetration of the RF signal and an almost 10‐fold increase in S/N ratio compared to the exclusive use of the elliptic surface coil. Monitoring of tail beat allowed to set trigger values resulted in an improved quality of in vivo 31P NMR spectra of swimming fish. We report the first successful NMR experiments recording simultaneously tissue energetic and acid–base parameters on swimming cod depending on tail beat frequency and amplitude to determine critical swimming speeds. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 33B: 62–73, 2008

Flow patterns of larval fish: undulatory swimming in the intermediate flow regime

Fish larvae, like many adult fish, swim by undulating their body. However, their body size and swimming speeds put them in the intermediate flow regime, where viscous and inertial forces both play an important role in the interaction between fish and water. To study the influence of the relatively high viscous forces compared with adult fish, we mapped the flow around swimming zebrafish (Danio rerio) larvae using two-dimensional digital particle image velocimetry (2D-DPIV) in the horizontal and transverse plane of the fish. Fish larvae initiate a swimming bout by bending their body into a C shape. During this initial tail-beat cycle, larvae shed two vortex pairs in the horizontal plane of their wake, one during the preparatory and one during the subsequent propulsive stroke. When they swim ;cyclically' (mean swimming speed does not change significantly between tail beats), fish larvae generate a wide drag wake along their head and anterior body. The flow along the posterior body is dominated by the undulating body movements that cause jet flows into the concave bends of the body wave. Patches of elevated vorticity form around the jets, and travel posteriorly along with the body wave, until they are ultimately shed at the tail near the moment of stroke reversal. Behind the larva, two vortex pairs are formed per tail-beat cycle (the tail beating once left-to-right and then right-to-left) in the horizontal plane of the larval wake. By combining transverse and horizontal cross sections of the wake, we inferred that the wake behind a cyclically swimming zebrafish larva contains two diverging rows of vortex rings to the left and right of the mean path of motion, resembling the wake of steadily swimming adult eels. When the fish larva slows down at the end of a swimming bout, it gradually reduces its tail-beat frequency and amplitude, while the separated boundary layer and drag wake of the anterior body extend posteriorly to envelope the entire larva. This drag wake is considerably wider than the larval body. The effects of the intermediate flow regime manifest as a thick boundary layer and in the quick dying-off of the larval wake within less than half a second.

Vertebral function during tadpole locomotion

Most anuran larvae show large lateral oscillations at both the tip of the tail and the snout while swimming in a straight line. Although the lateral deflections at the snout have long been considered an inefficient aspect of tadpole locomotion, a recent hydrodynamic model suggests that they may in fact help generate thrust. It is not clear though exactly where this bending takes place. The vertebral column is extremely short and seemingly inflexible in anurans, and any axial flexion that might occur there is hidden within the globose body of the tadpole. Here we test the hypothesis that lateral deflections of the snout correlate with bending of the vertebral column within the torso of tadpoles. To quantify vertebral curvature, three sonomicrometry crystals were surgically implanted along the dorsal midline in locations corresponding to the anterior, middle, and posterior region of the presacral vertebral column. Swimming trials were conducted in a flume where synchronized video recordings were collected in dorsal view. Our results confirm that cyclic lateral bending occurs along the vertebral column during swimming and indicate that vertebral curvature is temporally in phase with lateral oscillation of the snout. Lateral oscillation of the snout increased significantly with increasing vertebral curvature. Similarly, tail beat amplitude also increases significantly with increasing vertebral curvature. Our results suggest that cyclic lateral flexion of the vertebral column, activated by the axial muscle within the torso of tadpoles contributes to snout oscillations and the generation of thrust during undulatory swimming in anuran larvae.

Effects of Partial Ablation of the Cerebellum on Sustained Swimming in Goldfish

To investigate the role of the corpus cerebelli in the control of sustained swimming or cruising in goldfish, Carassius auratus, we conducted experiments examining the effects of partial ablation of the corpus cerebelli (CC) on swimming performance against constant water flow at various speeds. Ten out of 15 CC-ablated fish successfully maintained sustained swimming against water flow even at the highest speed tested (3.0 body lengths per second). This result showed that the CC is not crucial for generating the simple swimming motor pattern, although some effects of the surgical operation itself on the capability of the sustained swimming were found in both sham-operated and CC-ablated fish. However, we found that both tail-beat amplitude and frequency in CC-ablated goldfish tended to be greater than that of control fish at the same swimming speeds. The thrust index (square of the value obtained by multiplying the tail beat frequency (Hz) by twice the tail beat amplitude (mm)) was significantly larger in CC-ablated fish than in control fish at higher swimming speeds (≧2.0 body length per second). This result suggests that CC-ablated goldfish produced more thrust by tail beats than control fish to maintain sustained swimming at higher speeds. We concluded that in goldfish the CC plays no major role in the posture control and generation of simple forward swimming movement, although the integrity of the CC is important for execution of normal swim gait.