Maximum Sustained Swimming Speed Research Articles

Swimming Performance Assessments of Fish Species of Greatest Conservation Need to Inform Future Stream Crossing Designs in Texas

Conventional structures associated with stream crossings such as bridges and culverts can lead to zones of high-velocity water flow that impede fish passage. Such obstacles are likely to harm native fish populations by impacting migrations critical to their life history strategies, causing habitat fragmentation and extirpation, thereby limiting population growth and distribution. Due to the high rates of human population growth and development occurring in Texas, this is an issue of particular concern for fish designated as species of greatest conservation need (SGCN). This project focused on four SGCN fishes native to the Edwards Plateau Ecoregion, namely the Guadalupe Bass, Guadalupe Roundnose Minnow, Guadalupe Darter, and Plateau Shiner, at both adult (all species) and juvenile (Guadalupe Bass only) life stages. Our primary aim was to aid in the design of future culverts associated with stream crossings (or the modification of existing culverts) so that the water velocities through these structures do not exceed the swimming capacities of our target SGCN fishes. To this end, we assessed their maximum sustained swimming speeds (Ucrit) under a typical range of Edwards Plateau stream temperatures (15, 22.5, and 30 °C) to be used in site-specific calculations of the maximum allowable culvert water velocities (Vf). A secondary objective was to collect physiological endpoints of relevance to the overall swimming performance including the maximum burst swimming speeds (Umax), metabolic rate measurements (i.e., standard metabolic rate (SMR), maximum metabolic rate (MMR), and aerobic scope (AS)), cost of transport (COT), and optimal swimming speed (Uopt). Temperature-related effects were observed that can be used to inform site-specific culvert designs. In general, the highest Ucrit values for the tested species were near, or possibly between, 22.5 and 30 °C, while Umax stayed relatively consistent among treatments.

Accelerometer-based swimming metabolism of smallmouth bass (Micropterus dolomieu).

Bioenergetics is informative for a range of fundamental and applied resource management questions, but findings are often constrained by a lack of ecological realism due to the challenges of remotely estimating key parameters such as metabolic rate. To enable field applications, we conducted a calibration study with smallmouth bass (Micropterus dolomieu, 0.7-2 kg) surgically implanted with accelerometer transmitters and exposed to a ramp-Ucrit swimming protocol in a swim tunnel respirometer across a range of water temperatures (6, 12, 18, and 24°C). There was an exponential increase in fish acceleration with swimming speed, and acceleration per speed was higher in smaller fish and female fish, and at colder temperatures. Mass-specific fish metabolic rate (MO2; mg O2 kg-1 h-1) increased with swimming speed, acceleration, and temperature, and decreased with fish mass, which when combined were strong predictors of MO2. Maximum metabolic rate (MMR) was estimated to peak at 22°C, but maximum sustained swimming speed (Ucrit) remained high at c. 90-100 m s-1 above 20°C, based on second-order polynomial functions. Aerobic scope (AS) estimates peaked at 20°C (>90% AS at 17-24°C; >50% AS at 11-28°C). Males exhibited marginally higher MMR, AS, and Ucrit than females at higher temperatures. Larger fish generally exhibited higher Ucrit, but smaller fish had a marginally broader performance range (AS, Ucrit) among temperatures, benefiting from higher MMR despite a steeper increase in resting metabolic rate with temperature. These findings enable field studies to estimate metabolic metrics of smallmouth bass in situ to characterize their ecological energetics and inform bioenergetics models.

Energy conservation by collective movement in schooling fish

Many animals moving through fluids exhibit highly coordinated group movement that is thought to reduce the cost of locomotion. However, direct energetic measurements demonstrating the energy-saving benefits of fluid-mediated collective movements remain elusive. By characterizing both aerobic and anaerobic metabolic energy contributions in schools of giant danio (Devario aequipinnatus), we discovered that fish schools have a concave upward shaped metabolism–speed curve, with a minimum metabolic cost at ~1 body length s-1. We demonstrate that fish schools reduce total energy expenditure (TEE) per tail beat by up to 56% compared to solitary fish. When reaching their maximum sustained swimming speed, fish swimming in schools had a 44% higher maximum aerobic performance and used 65% less non-aerobic energy compared to solitary individuals, which lowered the TEE and total cost of transport by up to 53%, near the lowest recorded for any aquatic organism. Fish in schools also recovered from exercise 43% faster than solitary fish. The non-aerobic energetic savings that occur when fish in schools actively swim at high speed can considerably improve both peak and repeated performance which is likely to be beneficial for evading predators. These energetic savings may underlie the prevalence of coordinated group locomotion in fishes.

Energy conservation by collective movement in schooling fish.

Many animals moving through fluids exhibit highly coordinated group movement that is thought to reduce the cost of locomotion. However, direct energetic measurements demonstrating the energy-saving benefits of fluid-mediated collective movements remain elusive. By characterizing both aerobic and anaerobic metabolic energy contributions in schools of giant danio (Devario aequipinnatus), we discovered that fish schools have a concave upward shaped metabolism-speed curve, with a minimum metabolic cost at ~1 body length s-1. We demonstrate that fish schools reduce total energy expenditure (TEE) per tail beat by up to 56% compared to solitary fish. When reaching their maximum sustained swimming speed, fish swimming in schools had a 44% higher maximum aerobic performance and used 65% less non-aerobic energy compared to solitary individuals, which lowered the TEE and total cost of transport by up to 53%, near the lowest recorded for any aquatic organism. Fish in schools also recovered from exercise 43% faster than solitary fish. The non-aerobic energetic savings that occur when fish in schools actively swim at high speed can considerably improve both peak and repeated performance which is likely to be beneficial for evading predators. These energetic savings may underlie the prevalence of coordinated group locomotion in fishes.

Swimming Performance of Schizothorax sp. and Planning of Fish Passages in Nepal

Swimming performance of migrating fish is crucial for the planning and design of effective fish passages. Commonly the fish swimming speeds are classified into five categories: 1) Optimum Swimming Speed, 2) Maximum Sustained Swimming Speed, 3) Critical Swimming Speed, 4) Maximum Domed Swimming Speed, and 5) Burst Swimming Speed. Swimming characteristics are related to the different species' adaptions to the environmental conditions. A variety of different factors affect the swimming capacity of fish which is directly related to fish size and species-specific morphology. A crucial abiotic factor is water temperature, which affects the fish physiology and thereby the swimming speed of the fish. This means that the fish's swimming speed can increase with increased water temperature. The swimming speed also increases with fish size. Fish often use burst speeds when passing a step in a fish ladder or entering a culvert. Burst speed is the highest speed attainable for fish, and it is the maximum energy output to be gained by using the white muscle (red muscle in salmonids). The burst speed can only be maintained for short periods of time (seconds). In the Himalayas, the main objective of many fisheries development plans is to secure future habitats and ensure up- and downstream migration of fish. Schizothorax richardsonii is often a targeted species in the area due to its importance as a food resource. If a fish passage is prepared for the upstream migration of fish, it is also crucial for the fish population development to ensure a safe downstream passage. Data on swimming performance for many of the native fish species in Nepal are scarce which complicates the design of suitable ecologically adapted fishways. In general, nature-like fish passes allow most of the species to migrate, followed by vertical slot fishways, meander fishways, and thereafter fish ladders of the pool-and-weir type. The key factor is to construct fish-passes that under all naturally required environmental circumstances can allow appropriate passage conditions of the targeted fish species.

No difference between critical and sprint swimming speeds for two galaxiid species.

Researchers have used laboratory experiments to examine how fish might be affected by anthropogenic alterations and conclude how best to adjust fish passage and culvert remediation designs in response. A common way to document swimming performance for this purpose is measuring fish critical swimming speed (Ucrit ). Nonetheless, the Ucrit protocol as defined by Brett [(1964) Journal of the Fisheries Research Board of Canada, 21, 1183-1226] may be inappropriate for studying swimming performance and determining how it relates to upstream migration in benthic fish, as they may not actively swim throughout the entire Ucrit test. An alternative method to estimate swimming performance is sprint swimming speed (Usprint ), which is suggested to be a measure of the burst speed of fish rather than maximum sustained swimming speed. The authors conducted comparative swimming performance experiments to evaluate whether Usprint can be used to compare swimming performance of benthic species to that of pelagic, actively swimming species. They measured individual swimming speeds of īnanga (Galaxias maculatus), an actively swimming pelagic species, and banded kōkopu (Galaxias fasciatus), a fish that exhibits benthic station-holding behaviour, using both the Usprint and Ucrit test. Experiments revealed that no significant statistical difference between swimming speeds was estimated using the Ucrit and Usprint test protocols for both G. maculatus and G. fasciatus. The result of this study suggests that fish swimming speeds obtained using these two methods are comparable for the species used in this study. By using Usprint for benthic-associated fish and Ucrit for pelagic fish, we may be able to compare a broader range of species' swimming abilities for use in a fish passage context.

Behavior and swimming performance of local fish in the ecosystem waters of rivers, oxbow and peat swamps

The four fish species, Trichogaster pectoralis, Barbodes schwanenfeldii, Osphronemus gouramy, and Wallago leeri have the same body size, representing different habitats. Therefore, this study aimed to determine the four species swimming abilities and speeds, including sustained, maximum sustained, prolonged swimming speed, and burst speed. The four species were brought using oxygenated plastic bags to the Aquatic Resources Utilization Laboratory at Riau University. Then it was acclimated in an aquarium measuring 100×50×50 cm with an aeration and filtering system to maintain water quality. The four groups of species were forced to swim in the swimming channel of the flume tank, with different current speeds for each individual tested. The swimming activity of the fish was recorded using a high-speed video camera (Casio HS Exlim, EX-ZR400, Casio Computer Co. LTD, Japan). The results showed that the swimming speed of B. schwanenfeldii was higher than O. gouramy, T. pectoralis, and W. leeri. The maximum sustained swimming speed of B. schwanenfeldii is about 5.1 BL/s, and 14.2 BL/s for the burst speed. Meanwhile, the sustained swimming speed of O. gouramy (1.6 BL/s) and the burst speed is 7.2 BL/s. The maximum sustained swimming speed of T. pectoralis was 1.6 BL/s, and the burst speed was 5.7 BL/s. In addition, the maximum sustained swimming speed of W. leeri is only 0.5 BL/s and 2.4 BL/s for the burst speed. The ability of these four fish to swim was influenced by the morphology of the tail fin, body shape, and the habitat where they live.

Fish Specialize Their Metabolic Performance to Maximize Bioenergetic Efficiency in Their Local Environment: Conspecific Comparison Between Two Stocks of Pacific Chub Mackerel (Scomber japonicus)

Species-specific ecological traits in fishes are likely to vary between populations or stocks due to differences in regional oceanic conditions, such as latitudinal temperature. We examined potential intraspecific differences in the swimming performance and metabolism of Pacific chub mackerel (Scomber japonicus) from the Northwest and Northeast Pacific stocks, which are distributed on opposite sides of the North Pacific at similar latitudes, but where the temperature contrast is large. Swimming bioenergetics and metabolic data of Northwest stock mackerel were measured at 14, 18, and 24°C using variable-speed swim-tunnel respirometers, and then the resulting bioenergetic parameters were compared with previous findings from the Northeast stock. At a given size, the maximum sustainable swimming speed (Umax) of the Northwest stock showed no significant difference compared to the Northeast stock at 18 and 24°C, but was lower at 14°C. In addition, the oxygen consumption rate (MO2) of the Northwest stock showed lower mass dependence and different temperature dependence at a given swimming speed than in the Northeast stock. Combined with stock-specific data on growth and experienced temperatures in the wild, these bioenergetic differences indicate that the swimming performance and metabolism of the two stocks are specific to their local environment to maximize bioenergetic efficiency.

Physiological mechanisms linking cold acclimation and the poleward distribution limit of a range-extending marine fish.

Extensions of species’ geographical distributions, or range extensions, are among the primary ecological responses to climate change in the oceans. Considerable variation across the rates at which species’ ranges change with temperature hinders our ability to forecast range extensions based on climate data alone. To better manage the consequences of ongoing and future range extensions for global marine biodiversity, more information is needed on the biological mechanisms that link temperatures to range limits. This is especially important at understudied, low relative temperatures relevant to poleward range extensions, which appear to outpace warm range edge contractions four times over. Here, we capitalized on the ongoing range extension of a teleost predator, the Australasian snapper Chrysophrys auratus, to examine multiple measures of ecologically relevant physiological performance at the population’s poleward range extension front. Swim tunnel respirometry was used to determine how mid-range and poleward range edge winter acclimation temperatures affect metabolic rate, aerobic scope, swimming performance and efficiency and recovery from exercise. Relative to ‘optimal’ mid-range temperature acclimation, subsequent range edge minimum temperature acclimation resulted in absolute aerobic scope decreasing while factorial aerobic scope increased; efficiency of swimming increased while maximum sustainable swimming speed decreased; and recovery from exercise required a longer duration despite lower oxygen payback. Cold-acclimated swimming faster than 0.9 body lengths sec−1 required a greater proportion of aerobic scope despite decreased cost of transport. Reduced aerobic scope did not account for declines in recovery and lower maximum sustainable swimming speed. These results suggest that while performances decline at range edge minimum temperatures, cold-acclimated snapper are optimized for energy savings and range edge limitation may arise from suboptimal temperature exposure throughout the year rather than acute minimum temperature exposure. We propose incorporating performance data with in situ behaviour and environmental data in bioenergetic models to better understand how thermal tolerance determines range limits.

Reduced swimming and metabolic fitness of aquaculture-reared California Yellowtail (Seriola dorsalis) in comparison to wild-caught conspecifics

Aspects of swimming and metabolic physiology were measured in aquaculture-reared California Yellowtail (Seriola dorsalis) in comparison to wild-caught individuals in order to examine potential differences in health and fitness associated with captive rearing, and to help identify areas for targeted improvement in Seriola aquaculture. Incremental swimming velocity trials using a swim tunnel respirometer on small yellowtail (mean body length=18.9cm, mass=80.1g) showed that aquaculture-reared fish had a significantly slower mean maximum sustainable swimming speed (Ucrit) (4.16±0.62BLs−1) in comparison to that of wild-caught fish (4.80±0.52BLs−1). In addition, oxygen consumption (ṀO2) measurements at varying swimming speeds allowed for estimation of standard metabolic rate, which was significantly higher in aquaculture-reared yellowtail (7.31±2.32 vs. 3.94±1.60mgO2kg−1min−1 at 18°C). Aquaculture fish also had a lower aerobic scope (9.20±3.44mgO2kg−1min−1) in comparison to wild-caught yellowtail (15.80±5.78mgO2kg−1min−1), which likely contributed to their reduced capacity for fast sustainable swimming. Reduced physical fitness is commonplace in aquaculture-reared fishes, and the examination of wild-caught yellowtail in this study provides baseline metrics that can be used to gauge the health and fitness of future S. dorsalis production. In particular, the lower standard metabolic rate and higher aerobic scope of wild-caught fish represent desirable metabolic characteristics that if achievable in aquaculture through better-rearing practices could allow for increased feed conversion efficiencies and potentially faster growth. At a minimum, a 35–40% reduction in metabolic costs at low swimming speeds (to those observed for wild-caught yellowtail) should result in substantial cost savings for feed in aquaculture operations.

Quantitative genetic variation for post-stress cortisol and swimming performance in growth-selected and control populations of European sea bass (Dicentrarchus labrax)

Sea bass is a major species in Mediterranean aquaculture, and is now being subject to selective breeding programmes for faster growth. In terrestrial species, it was demonstrated that fast growth may be linked to a correlated degradation of fitness traits. In this experiment, we evaluated 600 young sea bass from a factorial mating of 76 sires and 13 dams. The sires were from four genetic groups, wild (W), domesticated (D), and selected for growth (2 groups, M and P). The 600 offspring were submitted to two acute confinement stress challenges at 6weeks intervals, and plasma cortisol at one hour post stress was measured. The same fish were also submitted to two swimming challenges at a 5days interval, where the maximum sustained swimming speed (Umax) of each fish was evaluated. Parentage was assessed by genotyping of 12 microsatellites. 554 fish had both valid parentage and phenotypes. Cortisol had a low repeatability (r=0.30 between the two successive measurements) while repeatability was moderate for Umax (r=0.62). However, genetic correlations between successive measurements were very high (>0.96) for both traits, indicating that successive measurements were related to the same trait. Heritability was moderate for mean post-stress cortisol (h2=0.34±0.09) and Umax (h2=0.48±0.08). When Umax was expressed in m.s−1, it was negatively correlated to cortisol (rA=−0.48±0.08) and weakly correlated to body weight (rA=0.12±0.16), but figures changed when it was expressed in Body Lengths.s−1 (h2=0.55±0.08, rA=−0.10±0.19 with cortisol and rA=−0.64±0.07 with body weight, respectively). Cortisol was moderately negatively correlated with body weight (rA=−0.36±0.18). The four lines did not differ for cortisol or Umax, but when Umax was expressed in BL.s−1 it tended to be lower in the two selected lines — which were also significantly larger. However, this is likely due to a phenotypic decrease of relative Umax with increasing body size. We conclude that selection for growth and/or domestication should not impact maximum sustained swimming speed in the European sea bass, but may tend to favour animals with low cortisol responsiveness. These traits could be used to orientate functional capabilities other than productivity in sea bass. Statement of relevanceWe estimate heritability of cortisol stress response and (for the first time) in European sea bass, as well as their correlations with growth. We show moderate correlations, and no correlated response to selection for growth. We also provide methods to evaluate these traits on large number of fishes. This can be useful to monitor and design breeding programmes.

Intraspecific variation in aerobic and anaerobic locomotion: gilthead sea bream (Sparus aurata) and Trinidadian guppy (Poecilia reticulata) do not exhibit a trade-off between maximum sustained swimming speed and minimum cost of transport.

Intraspecific variation and trade-off in aerobic and anaerobic traits remain poorly understood in aquatic locomotion. Using gilthead sea bream (Sparus aurata) and Trinidadian guppy (Poecilia reticulata), both axial swimmers, this study tested four hypotheses: (1) gait transition from steady to unsteady (i.e., burst-assisted) swimming is associated with anaerobic metabolism evidenced as excess post exercise oxygen consumption (EPOC); (2) variation in swimming performance (critical swimming speed; Ucrit) correlates with metabolic scope (MS) or anaerobic capacity (i.e., maximum EPOC); (3) there is a trade-off between maximum sustained swimming speed (Usus) and minimum cost of transport (COTmin); and (4) variation in Usus correlates positively with optimum swimming speed (Uopt; i.e., the speed that minimizes energy expenditure per unit of distance traveled). Data collection involved swimming respirometry and video analysis. Results showed that anaerobic swimming costs (i.e., EPOC) increase linearly with the number of bursts in S. aurata, with each burst corresponding to 0.53 mg O2 kg−1. Data are consistent with a previous study on striped surfperch (Embiotoca lateralis), a labriform swimmer, suggesting that the metabolic cost of burst swimming is similar across various types of locomotion. There was no correlation between Ucrit and MS or anaerobic capacity in S. aurata indicating that other factors, including morphological or biomechanical traits, influenced Ucrit. We found no evidence of a trade-off between Usus and COTmin. In fact, data revealed significant negative correlations between Usus and COTmin, suggesting that individuals with high Usus also exhibit low COTmin. Finally, there were positive correlations between Usus and Uopt. Our study demonstrates the energetic importance of anaerobic metabolism during unsteady swimming, and provides intraspecific evidence that superior maximum sustained swimming speed is associated with superior swimming economy and optimum speed.

Evaluation approaches of fish swimming performance

Swimming speeds are the most important index for the evaluation of the fish swimming performance. The terminologies and classifications of the fish swimming performance were summarized in this paper. Taking into consideration of the widely used evaluation approaches of the fish swimming performance by different researchers, a recommended classification methodology of the fish swimming performance was proposed by the authors. And a new concept of the swimming speed, the Maximum Domed Swimming Speed (DSS), was introduced into this new classification framework together with a discussion on its calculation method and the practical significance. According to the classification system, the fish swimming speeds are classified into five categories: Optimum Swimming Speed, Maximum Sustained Swimming Speed, Critical Swimming Speed, Maximum Domed Swimming Speed, and Burst Swimming Speed. Other concepts of swimming speeds are generally merged into the above five categories, respectively. Furthermore, possible relevancies among the Maximum Sustained Swimming Speed (MSS), the Critical Swimming Speed (CSS), and the Maximum Domed Swimming Speed (DSS) were discussed. It was concluded that these three swimming speeds, in a sense, can be regarded as the equivalent indices for the evaluation of fish swimming performance.

Growth, feed utilization, body composition and swimming performance of giant croaker,Nibea japonicaTemminck and Schlegel, fed at different dietary protein and lipid levels

A 50-day feeding trial was conducted to examine the effects of dietary protein and lipid levels on growth, feed utilization, body composition and swimming performance of giant croaker, Nibea japonica. Fish (initial body weight 44.6 g ind−1) were fed ten test diets which were formulated at 5 crude protein levels (360, 400, 440, 480 and 520 g kg−1) and 2 crude lipid levels (90 and 150 g kg−1). In addition, a raw fish diet (fillet of small yellow croaker) served as the reference. The weight gain (WG) increased, whereas the feed intake (FI) and feed conversion ratio (FCR) decreased, with increasing dietary protein level from 360 to 520 g kg−1. At the same dietary protein level, no significant difference was found in the WG between fish fed the diets containing 90 or 150 g kg−1 crude lipid. Fish fed the diet containing 480 g kg−1 crude protein and 90 g kg−1 crude lipid exhibited higher WG, nitrogen retention efficiency (NRE) and energy retention efficiency (ERE) but lower nitrogen wastes output (TNW). At the end of the feeding trial, the hepatosomatic index (HSI) and viscerosomatic index (VSI) decreased, whereas the body protein content increased, with increase in dietary protein level. The body lipid content was higher in fish fed at the 150 g kg−1 lipid level than in fish fed at the 90 g kg−1 lipid level. No significant difference was found in the maximum sustained swimming speed (MSS) between fish fed at different dietary protein and lipid levels. The WG, NRE, ERE and condition factor (CF) were higher, whereas the FI, FCR, HSI, VSI and TNW were lower, in fish fed the raw fish diet than in fish fed the diet containing 480 g kg−1 crude protein and 90 g kg−1 crude lipid. No significant difference was detected in the MSS between fish fed the raw fish diet and diet containing 480 g kg−1 crude protein and 90 g kg−1 crude lipid. The results of this study suggest that the suitable dietary crude protein and crude lipid levels are 480 g kg−1 and 90 g kg−1 for giant croaker reared in net pens.

Critical swimming speed and maximum sustainable swimming speed of juvenile Pacific bluefin tuna, Thunnus orientalis

Tank wall collision is one of the major causes of mortality during the early-stage rearing of Pacific bluefin tuna, Thunnus orientalis (PBT). Therefore, to design a rearing environment that meets the needs of juvenile PBT, it is important to gather information about their swimming capabilities. We conducted experiments to examine the relative critical swimming speed (RCSS) and maximum sustainable swimming speed (MSSS) of early-stage PBT. The fish were kept in 3-tonne tanks and fed on artificial pellets every 2 h from dusk to dawn. We conducted two sets of experiments to measure swimming speed; the fish were introduced one at a time into a water funnel, and the water current velocity was gradually increased over time to estimate RCSS, or the water current was kept at a constant velocity to estimate MSSS. We measured the RCSS of 72 PBT juveniles (24–29 days after hatching (DAH); standard length (SL), 15.0 ± 2.3 mm) and the MSSS of 32 PBT juveniles (28–37 DAH; SL, 20.0 ± 5.1 mm) in the laboratory. The RCSS ranged from 4.7 to 20.3 SL/s (average, 12.4 ± 3.3 SL/s), and the MSSS was estimated to be approximately 4 SL/s. We speculate that introducing a water current in the rearing tank of no more than 4 SL/s could positively affect the survival of juvenile PBT.

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.

The trade-off between steady and unsteady swimming performance in six cyprinids at two temperatures

The purpose of this study was to investigate whether a functional trade-off (as assessed by a negative phenotypic relationship) between steady and unsteady swimming performance exists in six selected cyprinids and whether the possible trade-off changed with temperature. We measured the critical swimming speed (Ucrit, i.e., the water speed at which a fish can no longer maintain its position or its maximum sustainable swimming speed), metabolic rate (ṀO2) and fast-start performance in juvenile grass carp (Ctenopharyngodon idellus), crucian carp (Carassius auratus), qingbo (Spinibarbus sinensis), Chinese bream (Parabramis pekinensis), common carp (Cyprinus carpio) and sharp-jaw barbel (Onychostoma sima) at 15 and 25°C. Steady swimming performance as indicated by Ucrit and unsteady swimming performance as indicated by maximum linear velocity (Vmax), maximum linear acceleration (Amax) and the escape distance during 120ms (S120ms) varied significantly among species and between temperatures (P<0.05). There was no significant relationship between steady and unsteady swimming performance at low temperature. Ucrit was positively related to Vmax at 25°C. These findings clearly demonstrated that the relationship between steady and unsteady swimming performance changed with temperature. Both steady and unsteady swimming performance increased significantly with temperature. However, the thermal sensitivity of Ucrit was negatively related to that of the fast-start variables. This result suggested that a trade-off exists in the temperature reaction norm of the two types of swimming performance among the six cyprinids.

Optimal shape and motion of undulatory swimming organisms.

Undulatory swimming animals exhibit diverse ranges of body shapes and motion patterns and are often considered as having superior locomotory performance. The extent to which morphological traits of swimming animals have evolved owing to primarily locomotion considerations is, however, not clear. To shed some light on that question, we present here the optimal shape and motion of undulatory swimming organisms obtained by optimizing locomotive performance measures within the framework of a combined hydrodynamical, structural and novel muscular model. We develop a muscular model for periodic muscle contraction which provides relevant kinematic and energetic quantities required to describe swimming. Using an evolutionary algorithm, we performed a multi-objective optimization for achieving maximum sustained swimming speed U and minimum cost of transport (COT)--two conflicting locomotive performance measures that have been conjectured as likely to increase fitness for survival. Starting from an initial population of random characteristics, our results show that, for a range of size scales, fish-like body shapes and motion indeed emerge when U and COT are optimized. Inherent boundary-layer-dependent allometric scaling between body mass and kinematic and energetic quantities of the optimal populations is observed. The trade-off between U and COT affects the geometry, kinematics and energetics of swimming organisms. Our results are corroborated by empirical data from swimming animals over nine orders of magnitude in size, supporting the notion that optimizing U and COT could be the driving force of evolution in many species.

Swimming performance and behaviour of young-of-the-year shortnose sturgeon (Acipenser brevirostrum) under fixed and increased velocity swimming tests

Swimming performance and behaviour in fish has been shown to vary depending on the investigation method. In this study, an endurance swimming curve was generated for young-of-the-year shortnose sturgeon (Acipenser brevirostrum LeSueur, 1818) (~7 cm total length, ~2 g) and compared with values determined in a separate incremental swimming (critical swimming, Ucrit) test. Using video, tail-beat frequency (TBF) was quantified and compared for fish swimming under both swimming tests. From the endurance-curve analysis, it was found that sturgeon did not display a statistically significant burst swimming phase. Maximum sustainable swimming speed (calculated to be 18.00 cm·s–1) from the endurance curve occurred at ~80% of Ucrit(22.30 cm·s–1). TBF was similar at all speeds for both swimming tests, except at speeds approaching Ucrit, where fish displayed TBFs of 4.29 Hz for the endurance protocol and 2.26 Hz for the Ucritprotocol. TBF was more variable between individuals swimming at the same speed within the Ucritcompared with the endurance protocol. Finally, a significant negative correlation was found between TBF and Ucritin individual fish, suggesting that station-holding may be an important energy saving strategy during swimming in this size class of sturgeon.

Sustained swimming increases the mineral content and osteocyte density of salmon vertebral bone

This study addresses the effects of increased mechanical load on the vertebral bone of post-smolt Atlantic salmon by forcing them to swim at controlled speeds. The fish swam continuously in four circular tanks for 9 weeks, two groups at 0.47 body lengths (bl) × s(-1) (non-exercised group) and two groups at 2 bl × s(-1) (exercised group), which is just below the limit for maximum sustained swimming speed in this species. Qualitative data concerning the vertebral structure were obtained from histology and electron microscopy, and quantitative data were based on histomorphometry, high-resolution X-ray micro-computed tomography images and analysis of bone mineral content, while the mechanical properties were tested by compression. Our key findings are that the bone matrix secreted during sustained swimming had significantly higher mineral content and mechanical strength, while no effect was detected on bone in vivo architecture. mRNA levels for two mineralization-related genes bgp and alp were significantly upregulated in the exercised fish, indicating promotion of mineralization. The osteocyte density of the lamellar bone of the amphicoel was also significantly higher in the exercised than non-exercised fish, while the osteocyte density in the cancellous bone was similar in the two groups. The vertebral osteocytes did not form a functional syncytium, which shows that salmon vertebral bone responds to mechanical loading in the absence of an extensive connecting syncytial network of osteocytic cell processes as found in mammals, indicating the existence of a different mechanosensing mechanism. The adaptive response to increased load is thus probably mediated by osteoblasts or bone lining cells, a system in which signal detection and response may be co-located. This study offers new insight into the teleost bone biology, and may have implications for maintaining acceptable welfare for farmed salmon.