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PubMed2004

Spectrum and frequency of cardiac channel defects in swimming-triggered arrhythmia syndromes.

BACKGROUND: Swimming is a relatively genotype-specific arrhythmogenic trigger for type 1 long-QT syndrome (LQT1). We hypothesize that mimickers of concealed LQT1, namely catecholaminergic polymorphic ventricular tachycardia (CPVT), may also underlie swimming-triggered cardiac events. METHODS AND RESULTS: Between August 1997 and May 2003, 388 consecutive, unrelated patients were referred specifically for LQTS genetic testing. The presence of a personal and/or family history of a near-drowning or drowning was determined by review of the medical records and/or phone interviews and was blinded to genetic test results. Comprehensive mutational analysis of the 5 LQTS-causing channel genes, KCNQ1 (LQT1), KCNH2 (LQT2), SCN5A (LQT3), KCNE1 (LQT5), and KCNE2 (LQT6), along with KCNJ2 (Andersen-Tawil syndrome) and targeted analysis of 18 CPVT1-associated exons in RyR2, was performed with the use of denaturing high-performance liquid chromatography and direct DNA sequencing. Approximately 11% (43 of 388) of the index cases had a positive swimming phenotype. Thirty-three of these 43 index cases had a "Schwartz" score (> or =4) suggesting high clinical probability of LQTS. Among this subset, 28 patients (85%) were LQT1, 2 patients (6%) were LQT2, and 3 were genotype negative. Among the 10 cases with low clinical probability for LQTS, 9 had novel, putative CPVT1-causing RyR2 mutations. CONCLUSIONS: In contrast to previous studies that suggested universal LQT1 specificity, genetic heterogeneity underlies channelopathies that are suspected chiefly because of a near-drowning or drowning. CPVT1 and strategic genotyping of RyR2 should be considered when LQT1 is excluded in the pathogenesis of a swimming-triggered arrhythmia syndrome.

Adolescent↗
PubMed2006

Allopregnanolone reduces immobility in the forced swimming test and increases the firing rate of lateral septal neurons through actions on the GABAA receptor in the rat.

Since allopregnanolone reduces the total time of immobility in rats submitted to the forced swimming test, we decided to explore whether this neuroactive steroid shares other antidepressant-like actions, such as increasing the neuronal firing rate in the lateral septal nucleus (LSN). In order to discard the influence of the oestrous cycle on immobility and on the firing rate of LSN neurons, all Wistar rats used in the study underwent ovariectomy before treatments. A group of rats received different doses of allopregnanolone (0.5, 1.0, 2.0 and 3.0 mg/kg, i.p.) 1 hour before being forced to swim in order to identify the minimum effective dose diminishing immobility. None of the tested doses of allopregnanolone produced significant changes in motor activity in the open-field test. The minimum dose of allopregnanolone producing a significant reduction in the total time of immobility (p<0.05) against the vehicle was 1.0 mg/kg, while 2.0 mg/kg and above also increased the latency to the first period of immobility (p<0.05). The minimum effective dose of allopregnanolone reducing immobility in the forced swimming test (1.0 mg/kg) significantly (p <0.05) produced a higher (twofold) neuronal firing rate in LSN neurons, but did not produce any change in septofimbrial nucleus neurons, which fired at a rate similar to that of vehicle-treated rats. The pretreatment with the non-competitive GABAA receptor antagonist, picrotoxin (1.0 mg/kg), blocked the aforementioned actions of allopregnanolone on both immobility and LSN firing rate. In conclusion, allopregnanolone produces an antidepressant-like effect in the forced swimming test, associated with an increase in the LSN neuronal firing rate, seemingly mediated by the GABAA receptor.

Action Potentials↗
PubMed1999

Swimming and central venous catheter-related infections in the child with cancer.

Although there have been many studies evaluating risk factors for catheter-related infections in children with cancer, none have examined whether swimming presents such a risk. Families of children with cancer were asked about specific swimming practices and central line care to determine whether there is an association between swimming and infection. Parents completed a self-report questionnaire and medical records were reviewed to document catheter-related intraluminal, tunnel, and exit-site infections. Ninety-one children with a total of 101 tunneled catheters participated in the study. Forty-nine children with a total of 50 catheters were swimmers; 46 children with 51 catheters were nonswimmers (four children had two catheters and swam with one catheter but not the other, therefore, these children were counted twice). There were no statistically significant differences in rates of catheter-related infections between the two groups (0.04/catheter-month in swimmers versus 0.25/in non-swimmers, relative risk; RR = 1.6, p = .16). When the analysis was confined to summertime infections per summertime catheter month, there were no significant differences in the rates of infections per summer month (0.06 for swimmers vs. 0.05 for non-swimmers, RR = 1.4; p = .50). When the analyses were performed to compare frequent swimmers with infrequent/non-swimmers, once again there were no differences found in rates of catheter-related infections between the two groups. These results suggest that swimming does not increase the risk of catheter-related infections in children with tunneled catheters.

Adolescent↗
PubMed2003

Comparative studies of high performance swimming in sharks I. Red muscle morphometrics, vascularization and ultrastructure.

Tunas (family Scombridae) and sharks in the family Lamnidae are highly convergent for features commonly related to efficient and high-performance (i.e. sustained, aerobic) swimming. High-performance swimming by fishes requires adaptations augmenting the delivery, transfer and utilization of O(2) by the red myotomal muscle (RM), which powers continuous swimming. Tuna swimming performance is enhanced by a unique anterior and centrally positioned RM (i.e. closer to the vertebral column) and by structural features (relatively small fiber diameter, high capillary density and greater myoglobin concentration) increasing O(2) flux from RM capillaries to the mitochondria. A study of the structural and biochemical features of the mako shark (Isurus oxyrinchus) RM was undertaken to enable performance-capacity comparisons of tuna and lamnid RM. Similar to tunas, mako RM is positioned centrally and more anterior in the body. Another lamnid, the salmon shark (Lamna ditropis), also has this RM distribution, as does the closely related common thresher shark (Alopias vulpinus; family Alopiidae). However, in both the leopard shark (Triakis semifasciata) and the blue shark (Prionace glauca), RM occupies the position where it is typically found in most fishes; more posterior and along the lateral edge of the body. Comparisons among sharks in this study revealed no differences in the total RM quantity (approximately 2-3% of body mass) and, irrespective of position within the body, RM scaling is isometric in all species. Sharks thus have less RM than do tunas (4-13% of body mass). Relative to published data on other shark species, mako RM appears to have a higher capillary density, a greater capillary-to-fiber ratio and a higher myoglobin concentration. However, mako RM fiber size does not differ from that reported for other shark species and the total volume of mitochondria in mako RM is similar to that reported for other sharks and for tunas. Lamnid RM properties thus suggest a higher O(2) flux capacity than in other sharks; however, lamnid RM aerobic capacity appears to be less than that of tuna RM.

Adaptation, Biological↗
PubMed2003

Swimming performance studies on the eastern Pacific bonito Sarda chiliensis, a close relative of the tunas (family Scombridae) II. Kinematics.

The swimming kinematics of the eastern Pacific bonito Sarda chiliensis at a range of sustained speeds were analyzed to test the hypothesis that the bonito's swimming mode differs from the thunniform locomotor mode of tunas. Eight bonito (fork length FL 47.5+/-2.1 cm, mass 1.25+/-0.15 kg) (mean +/- S.D.) swam at speeds of 50-130 cm s(-1) at 18+/-2 degrees C in the same temperature-controlled water tunnel that was used in previous studies of tunas. Kinematics variables, quantified from 60 Hz video recordings and analyzed using a computerized, two-dimensional motion analysis system, were compared with published data for similar sized tunas at comparable speeds. Bonito tailbeat frequency, tailbeat amplitude and stride length all increased significantly with speed. Neither yaw (6.0+/-0.6%FL) nor propulsive wavelength (120+/-65% fish total length) varied with speed, and there were no mass or body-length effects on the kinematics variables for the size range of bonitos used. Relative to similar sized yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tunas at similar speeds, the bonito has a lower tailbeat frequency, a higher yaw and a greater stride length. The lateral displacement and bending angle of each intervertebral joint during a complete tailbeat cycle were determined for the bonito at a swimming speed of 90 cm s(-1). The pattern of mean maximum lateral displacement (z(max)) and mean maximum bending angle (beta(max)) along the body in the bonito differed from that of both chub mackerel Scomber japonicus and kawakawa tuna Euthynnus affinis; z(max) was highest in the bonito. This study verifies that S. chiliensis is a carangiform swimmer and supports the hypothesis that the thunniform locomotor mode is a derived tuna characteristic associated with changes in this group's myotomal architecture. The finding that yaw and z(max) were greater in the bonito than in both mackerels and tunas suggests that swimming kinematics in the bonito is not intermediate between that of tunas and mackerels, as would be predicted on the basis of morphological characteristics.

Animals↗
PubMed2003

Comparative studies of high performance swimming in sharks II. Metabolic biochemistry of locomotor and myocardial muscle in endothermic and ectothermic sharks.

Metabolic enzyme activities in red (RM) and white (WM) myotomal muscle and in the heart ventricle (HV) were compared in two lamnid sharks (shortfin mako and salmon shark), the common thresher shark and several other actively swimming shark species. The metabolic enzymes measured were citrate synthase (CS), an index of aerobic capacity, and lactate dehydrogenase (LDH), an index of anaerobic capacity. WM creatine phosphokinase (CPK) activity, an index of rapid ATP production during burst swimming, was also quantified. Enzyme activities in RM, WM and HV were similar in the two lamnid species. Interspecific comparisons of enzyme activities at a common reference temperature (20 degrees C) show no significant differences in RM CS activity but higher CS activity in the WM and HV of the lamnid sharks compared with the other species. For the other enzymes, activities in lamnids overlapped with those of other shark species. Comparison of the HV spongy and compact myocardial layers in mako, salmon and thresher sharks reveals a significantly greater spongy CS activity in all three species but no differences in LDH activity. Adjustment of enzyme activities to in vivo RM and WM temperatures in the endothermic lamnids elevates CS and LDH in both tissues relative to the ectothermic sharks. Thus, through its enhancement of both RM and WM enzyme activity, endothermy may be an important determinant of energy supply for sustained and burst swimming in the lamnids. Although lamnid WM is differentially warmed as a result of RM endothermy, regional differences in WM CS and LDH activities and thermal sensitivities (Q(10) values) were not found. The general pattern of the endothermic myotomal and ectothermic HV muscle metabolic enzyme activities in the endothermic lamnids relative to other active, ectothermic sharks parallels the general pattern demonstrated for the endothermic tunas relative to their ectothermic sister species. However, the activities of all enzymes measured are lower in lamnids than in tunas. Relative to lamnids, the presence of lower WM enzyme activities in the thresher shark (which is in the same order as the lamnids, has an RM morphology similar to that of the mako and salmon sharks and may be endothermic) suggests that other factors, such as behavior and swimming pattern, also affect shark myotomal organization and metabolic function.

Adaptation, Biological↗
PubMed2004

Neuromuscular control of trout swimming in a vortex street: implications for energy economy during the Karman gait.

Approximating the complexity of natural locomotor conditions provides insight into the diversity of mechanisms that enable animals to successfully navigate through their environment. When exposed to vortices shed from a cylinder, fishes hold station by adopting a mode of locomotion called the Kármán gait, whereby the body of the fish displays large, lateral oscillations and the tail-beat frequency matches the vortex shedding frequency of the cylinder. Although field studies indicate that fishes often prefer turbulent flows over uniform currents, the effect of hydrodynamic perturbations on the mechanics, control and energetics of locomotion is still poorly understood. In this study, electromyography is used to measure red and white axial muscle activity for rainbow trout (Oncorhynchus mykiss) holding station in a vortex street. When trout Kármán gait, they show a significantly reduced but still rhythmic pattern of muscle activity compared with that seen when they swim steadily in uniform flow. Specifically, trout selectively activated only their anterior red axial muscles and abandoned the antero-posterior wave of red muscle activity that drives undulatory locomotion in uniform flow. This supports a previously proposed hypothesis that trout are not just swimming in the reduced flow behind a cylinder (drafting). Anterior axial muscle activity was correlated to head amplitude during steady swimming but not during the Kármán gait, indicating that while activation of muscles during the Kármán gait may aid in stability and control, vortices determined overall head motion. Furthermore, anterior red axial muscle activity, the only region of muscle activity shared between both the Kármán gait and steady swimming, had a lower intensity and longer duration during the Kármán gait. At times when paired fins were active during the Kármán gait, there was no axial muscle activity measured, lending support to a passive mechanism of thrust generation in oscillating flows. Comparisons with dead trout towed behind a cylinder confirm this intriguing observation that live trout may temporarily adopt the Kármán gait with no axial muscle activity, revealing paradoxically that at times fish can passively move against turbulent flow. To Kármán gait for prolonged periods, however, trout must adapt to the demands of turbulence by eliciting a shift in neural control strategy. By decoupling motor output both down and across the body, the pattern of rhythmic Kármán gait muscle activity may reflect the entrainment of a central pattern generator to environmental vortices.

Animals↗
PubMed2005

Linking swimming performance, cardiac pumping ability and cardiac anatomy in rainbow trout.

We exploited the inherent individual diversity in swimming performance of rainbow trout Oncorhynchus mykiss to investigate the hypothesis that maximum cardiac performance is linked to active metabolic rate (AMR) and critical swimming speed (U crit). Six hundred juveniles (body mass approximately 150 g) were screened using a swimming challenge of 1.2 m s(-1) to identify 'poor swimmers' and 'good swimmers', i.e. the first and last 60 fish to fatigue, respectively. These 120 fish were individually tagged and then reared in common tanks for 9 months, where they grew at similar rates and achieved a similar body mass of approximately 1100 g. Critical swimming speed (U crit) was then measured individually in tunnel respirometers, with simultaneous recordings of cardiac output via a ventral aortic flow probe. The group of individuals that were screened as poor swimmers remained so, with a significantly (27%) lower U crit than good swimmers [89+/-10 cm s(-1) vs 123+/-5 cm s(-1) (mean +/-s.e.m.), respectively, N = 6], a 19% lower AMR (147+/-12 micromol min(-1) kg(-1) vs 181+/-11 micromol min(-1) kg(-1), respectively), and a 30% lower maximum in vivo cardiac output (47.3+/-4.7 ml min(-1) kg(-1) vs 68.0+/-5.2 ml min(-1) kg(-1), respectively). When cardiac performance was compared with an in situ heart preparation, hearts from poor swimmers had a significantly (26%) lower maximum cardiac output (45.9+/-1.9 ml min(-1) kg(-1) vs 56.4+/-2.3 ml min(-1) kg(-1), respectively) and a 32% lower maximum cardiac power output at a high afterload (3.96+/-0.58 mW g(-1) vs 5.79+/-1.97 mW g(-1), respectively). Cardiac morphology was visualised in vivo by Doppler echography on anaesthetised individual fish and revealed that poor swimmers had a significantly more rounded ventricle (reduced ventricle length to height ratio) compared with good swimmers, which in turn was correlated with fish condition factor. These results provide clear evidence that maximum cardiac performance is linked to AMR and U crit and indicate that a simple screening test can distinguish between rainbow trout with lower active metabolic rate, U crit, maximal cardiac pumping capacity and a more rounded ventricular morphology. These distinguishing traits may have been retained for 9 months despite a common growing environment and growth.

Analysis of Variance↗
PubMed2005

Patterns of red muscle strain/activation and body kinematics during steady swimming in a lamnid shark, the shortfin mako (Isurus oxyrinchus).

The dynamics of steady swimming were examined in the shortfin mako (Isurus oxyrinchus), a member of the cartilaginous fish family Lamnidae, a family known for their morphological adaptations for high-performance locomotion and their similarity in hydromechanical design to tunas. Patterns of red muscle (RM) strain (i.e. relative length change) and activation were quantified at two axial positions ( approximately 0.4 and 0.6L, where L is total body length), using sonomicrometry and electromyography (EMG), and correlated with simultaneous measurements of dorsal midline kinematics during steady swimming ( approximately 0.5-1 L s(-1)). RM strain varied longitudinally with strain amplitudes ranging from 5.5+/-1.1% (s.e.m.) in the anterior to 8.7+/-0.9% in the posterior. We found no significant longitudinal variation in patterns of RM activation, with mean onset of activation occurring at 83-84 degrees (90 degrees is peak length) and offset at 200-210 degrees at both body positions. Likewise, duty cycles were similar: 35.5+/-1.0% in the anterior and 32.2+/-1.6% in the posterior. Comparison of the timing of waves of dorsal midline curvature and predicted strain relative to measured RM strain revealed a phase shift between RM shortening and local body bending. Furthermore, when the body is bent passively, RM shortens synchronously with the surrounding white muscle (WM) and skin, as expected. During active swimming, peaks in RM strain were delayed relative to peaks in WM strain by a mean of approximately 10% of the tailbeat cycle, with one individual as high as approximately 17% in the anterior and nearly 50% in the posterior. The longitudinal consistency in the EMG/strain phase relationship in the mako is similar to that in the leopard shark, suggesting a consistent trend among sharks using different locomotor modes. However, unlike in the leopard shark, RM shortening in the mako is physically uncoupled from deformation of the surrounding body during steady swimming, a characteristic shared between the mako and tunas.

Animals↗
PubMed2006

Cardiorespiratory physiology and swimming energetics of a high-energy-demand teleost, the yellowtail kingfish (Seriola lalandi).

This study utilizes a swimming respirometer to investigate the effects of exercise and temperature on cardiorespiratory function of an active teleost, the yellowtail kingfish (Seriola lalandi). The standard aerobic metabolic rate (SMR) of S. lalandi (mean body mass 2.1 kg) ranges from 1.55 mg min(-1) kg(-1) at 20 degrees C to 3.31 mg min(-1) kg(-1) at 25 degrees C. This 2.1-fold increase in SMR with temperature is associated with a 1.5-fold increase in heart rate from 77 to 117 beats min(-1), while cardiac stroke volume remains constant at 0.38 ml beat(-1) kg(-1) and the difference in oxygen content between arterial and mixed venous blood [(Ca(O2)-Cv(O2))] increases marginally from 0.06 to 0.08 mg ml(-1). During maximal aerobic exercise (2.3 BL s(-1)) at both temperatures, however, increases in cardiac output are limited to about 1.3-fold, and increases in oxygen consumption rates (up to 10.93 mg min(-1) kg(-1) at 20 degrees C and 13.32 mg min(-1) kg(-1) at 25 degrees C) are mediated primarily through augmentation of (Ca(O2)-Cv(O2)) to 0.29 mg ml(-1) at 20 degrees C and 0.25 mg ml(-1) at 25 degrees C. It seems, therefore, that the heart of S. lalandi routinely works close to its maximum capacity at a given temperature, and changes in aerobic metabolism due to exercise are greatly reliant on high blood oxygen-carrying capacity and (Ca(O2)-Cv(O2)). Gross aerobic cost of transport (GCOT) is 0.06 mg kg(-1) BL(-1) at 20 degrees C and 0.09 mg kg(-1) BL(-1) at 25 degrees C at the optimal swimming velocities (U(opt)) of 1.2 BL s(-1) (opt) and 1.7 BL s(-1), respectively. These values are comparable with those reported for salmon and tuna, implying that the interspecific diversity in locomotor mode (e.g. subcarangiform, carangiform and thunniform) is not concomitant with similar diversity in swimming efficiency. A low GCOT is maintained as swimming velocity increases above U(opt), which may partly result from energy savings associated with the progressive transition from opercular ventilation to ram ventilation.

Analysis of Variance↗
PubMed2006

Pectoral fin coordination and gait transitions in steadily swimming juvenile reef fishes.

A common feature of animal locomotion is its organization into gaits with distinct patterns of movement and propulsor use for specific speeds. In terrestrial vertebrates, limb gaits have been extensively studied in diverse taxa and gait transitions have been shown to provide efficient locomotion across a wide range of speeds. In contrast, examination of gaits in fishes has focused on axial gaits and the transition between synchronous paired fin locomotion and axial propulsion. Because many fishes use their pectoral fins as their primary propulsors, we aimed to examine more broadly the use of pectoral fin gaits in locomotion. We used juvenile reef fishes in these experiments because their swimming could be recorded readily across a wide range of Reynolds numbers, which we thought would promote gait diversity. Based on previous work in larval fishes, we hypothesized that juveniles have alternating pectoral fin movements rather than the synchronous, or in-phase, coordination pattern of adults. In flow tank swim studies, we found that juvenile sapphire damselfish Pomacentrus pavo used two fin gaits during steady swimming. Below approximately 3 BL s(-1), P. pavo primarily swam with alternating fin strokes 180 degrees out of phase with one another. At speeds in the range of 3-4 BL s(-1), they performed a gait transition to synchronous fin coordination. Between approximately 4 and 8 BL s(-1), P. pavo primarily beat their fins synchronously. At around 8 BL s(-1) there was another gait transition to body-caudal fin swimming, in which the pectoral fins were tucked against the body. We suggest that the transition from alternating to synchronous fin coordination occurs due to mechanical limits of gait performance rather than to energy efficiency, stability or transitions in hydrodynamic regime. To determine whether this gait transition was species-specific, we surveyed pectoral fin locomotion in juveniles from 11 species in three reef fish families (Pomacentridae, Labridae and Scaridae). We found that this gait transition occurred in every species examined, suggesting that it may be a common behavior of juvenile reef fishes. Greater inclusion of early life history stages in the study of fin-based locomotion should significantly enhance and inform the growing body of work on these behaviors.

Analysis of Variance↗
PubMed2006

Jet propulsion in the cold: Mechanics of swimming in the Antarctic scallop Adamussium colbecki.

Unlike most bivalves, scallops are able to swim, relying on a shell with reduced mass and streamlined proportions, a large fast-twitch adductor muscle and the elastic characteristics of the shell's hinge. Despite these adaptations, swimming in scallops is never far from failure, and it is surprising to find a swimming scallop in Antarctica, where low temperature increases the viscosity of seawater, decreases the power output of the adductor muscle and potentially compromises the energy storage capability of the hinge material (abductin, a protein rubber). How does the Antarctic scallop, Adamussium colbecki, cope with the cold? Its shell mass is substantially reduced relative to that of temperate and tropical scallops, but this potential advantage is more than offset by a drastic reduction in adductor-muscle mass. By contrast, A. colbecki's abductin maintains a higher resilience at low temperatures than does the abductin of a temperate scallop. This resilience may help to compensate for reduced muscle mass, assisting the Antarctic scallop to maintain its marginal swimming ability. However, theory suggests that this assistance should be slight, so the adaptive value of increased resilience remains open to question. The high resilience of A. colbecki abductin at low temperatures may be of interest to materials engineers.

Animals↗
PubMed1985

Differences between upstroke and downstroke in swimming dolphins.

Steady swimming movements of dolphins were recorded in a search for direct evidence of asymmetry between upstrokes and downstrokes. Kinematic swimming and gliding data from frame-by-frame analysis of ciné pictures taken at constant frame rates with a camera in a fixed position are presented. We estimated the propulsive forces generated by the tail blade with a simple hydrodynamic model. Dolphins accelerate during the downstroke and decelerate during the upstroke: the net hydrodynamic force in the animal is always positive during the downstroke and negative during the upstroke. Both parts of the stroke cycle are equally long. The propulsive forces of downstrokes are on average larger than the forces of the upstrokes. Occasionally the average forces within an upstroke are greater than within a downstroke of the same sequence. Our data suggest that the drag on the body during the upstroke exceeds the drag in the course of the downstroke. The specific swimming speed or stride length of dolphins swimming at low speeds is about 0.9 body lengths per tail beat.

Animals↗
PubMed1986

Blood oxygen transport in the free-swimming hagfish, Eptatretus cirrhatus.

Arterial and mixed venous blood were sampled through chronically implanted cannulae from rested and swimming hagfish. PaO2 remained high when hagfish were swum for 15 min at a velocity of 20 cm s-1. PvO2 fell from 17.2 mmHg at rest to 3.5 mmHg after swimming, and the arteriovenous pH difference increased from 0.15 to 0.25 pH units. Whole blood oxygen equilibrium curves were essentially hyperbolic (Hill's n value = 1.38) and gave a half-saturation PO2 (P50) value of 12.3 mmHg at pH 7.8 and 16 degrees C. A CO2-Bohr factor (phi = delta logP50/delta pH) of -0.43 and a limited buffering capacity of the blood, amounting to approx. 4 slykes, were observed. The role of the blood in transporting oxygen and carbon dioxide both at rest and after swimming is established by in vivo blood gas measurements and in vitro oxygen-binding data. The low internal PvO2 at rest is close to the P50 measured under similar conditions and the hyperbolic equilibrium curve permits further oxygen unloading when PvO2 falls during swimming.

Acid-Base Equilibrium↗
PubMed1997

The metabolic cost of swimming in marine homeotherms.

This paper describes a model of the metabolic cost of swimming in pinnipeds and its application to other marine homeotherms. The model takes account of both hydrodynamic and thermal processes. The thermal component incorporates both free and forced convection and takes account of the effect of hair on free convection. Using data from the literature to evaluate all but two of the parameters, we apply the model to metabolic rate data on phocid seals, otariids (sea lions), penguins and minke whales. We show that the model is able to reproduce two unusual features of the data; namely, a very rapid increase in metabolic rate at low velocities and an overall rise in metabolic rate with velocity which is slower than the rise in hydrodynamic drag force. The work shows the metabolic costs of propulsion and thermoregulation in a swimming homeotherm to be interlinked and suggests differing costs of propulsion for different modes of swimming. This is potentially of ecological significance since the swimming speed that minimises the cost of transport for an animal will change with changes in water temperature.

Animals↗
PubMed1999

Mechanical versus physiological determinants of swimming speeds in diving Brünnich's guillemots.

For fast flapping flight of birds in air, the maximum power and efficiency of the muscles occur over a limited range of contraction speeds and loads. Thus, contraction frequency and work per stroke tend to stay constant for a given species. In birds such as auks (Alcidae) that fly both in air and under water, wingbeat frequencies in water are far lower than in air, and it is unclear to what extent contraction frequency and work per stroke are conserved. During descent, compression of air spaces dramatically lowers buoyant resistance, so that maintaining a constant contraction frequency and work per stroke should result in an increased swimming speed. However, increasing speed causes exponential increases in drag, thereby reducing mechanical versus muscle efficiency. To investigate these competing factors, we have developed a biomechanical model of diving by guillemots (Uria spp.). The model predicted swimming speeds if stroke rate and work per stroke stay constant despite changing buoyancy. We compared predicted speeds with those of a free-ranging Brünnich's guillemot (U. lomvia) fitted with a time/depth recorder. For descent, the model predicted that speed should gradually increase to an asymptote of 1.5-1.6 m s-1 at approximately 40 m depth. In contrast, the instrumented guillemot typically reached 1.5 m s-1 within 10 m of the water surface and maintained that speed throughout descent to 80 m. During ascent, the model predicted that guillemots should stroke steadily at 1.8 m s-1 below their depth of neutral buoyancy (62 m), should alternate stroking and gliding at low buoyancies from 62 to 15 m, and should ascend passively by buoyancy alone above 15 m depth. However, the instrumented guillemot typically ascended at 1.25 m s-1 when negatively buoyant, at approximately 1.5 m s-1 from 62 m to 25 m, and supplemented buoyancy with stroking above 25 m. Throughout direct descent, and during ascent at negative and low positive buoyancies (82-25 m), the guillemot maintained its speed within a narrow range that minimized the drag coefficient. In films, guillemots descending against high buoyancy at shallow depths increased their stroke frequency over that of horizontal swimming, which had a substantial glide phase. Model simulations also indicated that stroke duration, relative thrust on the downstroke versus the upstroke, and the duration of gliding can be varied to regulate swimming speed with little change in contraction speed or work per stroke. These results, and the potential use of heat from inefficient muscles for thermoregulation, suggest that diving guillemots can optimize their mechanical efficiency (drag) with little change in net physiological efficiency.

Animals↗
PubMed1999

Large-amplitude undulatory fish swimming: fluid mechanics coupled to internal mechanics.

The load against which the swimming muscles contract, during the undulatory swimming of a fish, is composed principally of hydrodynamic pressure forces and body inertia. In the past this has been analysed, through an equation for bending moments, for small-amplitude swimming, using Lighthill's elongated-body theory and a 'vortex-ring panel method', respectively, to compute the hydrodynamic forces. Those models are outlined in this review, and a summary is given of recent work on large-amplitude swimming that has (a) extended the bending moment equation to large amplitude, which involves the introduction of a new (though probably usually small) term, and (b) developed a large-amplitude vortex-ring panel method. The latter requires computation of the wake, which rolls up into concentrated vortex rings and filaments, and has a significant effect on the pressure on the body. Application is principally made to the saithe (Pollachius virens). The calculations confirm that the wave of muscle activation travels down the fish much more rapidly than the wave of bending.

Animals↗
PubMed2000

Hydrodynamics of unsteady fish swimming and the effects of body size: comparing the flow fields of fish larvae and adults.

Zebra danios (Brachydanio rerio) swim in a burst-and-coast mode. Most swimming bouts consist of a single tail flick and a coasting phase, during which the fish keeps its body straight. When visualising the flow in a horizontal section through the wake, the effects of the flow regime become apparent in the structure of the wake. In a two-dimensional, medio-frontal view of the flow, larvae and adults shed two vortices at the tail during the burst phase. These vortices resemble a cross section through a large-core vortex ring: two vortex cores packed close together with the central flow directed away from the fish. This flow pattern can be observed in larvae (body length approximately 4 mm) at Reynolds numbers below 100 as well as in adult fish (body length approximately 35 mm) at Reynolds numbers above 1000. Larval vortices differ from those of adult zebra danios mainly in their relatively wider vortex cores (higher ratio of core radius to ring radius) and their lower vortex circulation. Both effects result from the increased importance of viscosity on larval flows. During the coasting phase, larval and adult flows again differ because of the changing importance of viscosity. The high viscosity of the water causes large vortical flows adjacent to the larva's body. These regions of high vorticity represent the huge body of water dragged along by the larva, and they cause the larva to stop almost immediately after thrust generation ceases. No such areas of high vorticity are visible adjacent to adult zebra danios performing a comparable swimming manoeuvre. The rapid decrease in vortex circulation and the severe reduction in the coasting distance due to viscous drag contribute to the high cost that larvae - unlike adult fish - face when using a burst-and-coast swimming style.

Animals↗