The effect of progressive hypoxia on swimming activity and schooling in Atlantic herring

Schools of herring exposed to progressive hypoxia show a peak in velocity during severe hypoxia, at 15–34% oxygen saturation, followed by a decrease in swimming speed until school disruption occurred. The observed increase in swimming speed during severe hypoxia reveals a graded response, since the lower the fish's swimming speed prior to severe hypoxia ( U ₉₅₋₅₀, the speed at oxygen saturations between 95 and 50%), the greater the relative increase in swimming speed. The oxygen saturations at which both peak velocity and school disruption occurred were lower for fish with lowest U ₉₅₋₅₀, suggesting that the fish with the slowest speed U ₉₅₋₅₀ reach their critical P_O2 (at which there is respiratory distress) last, i.e. at lower oxygen saturation. At a functional level, it is suggested that herring encountering hypoxia increase their speed in order to find more favourable conditions, and the magnitude of this increase is modulated by their respiratory distress. It is also hypothesised that the observed increase in speed may be related to an increase in the rate of position shifting within the school. Since the oxygen saturation at which the response to hypoxia occurs and the magnitude of the response are related to the fish's preferred speed prior to severe hypoxia, it is suggested that such a preferred speed should be measured in experiments testing the effect of hypoxia on fish behaviour.     

The swimming abilities of recently settled post-larvae of Sillaginodes punctata

Sixty-four post-larvae of the King George whiting Sillaginodes punctata were tested in swimming chambers, against one of five flow-through velocities (2, 4, 6, 8 or 10 cm s ⁻¹) for up to a maximum of 120 min. Fish were determined by regression to have an FV₅₀ (50% fatigue velocity) of 6.0 cm s⁻¹. No fish survived the full 120 min at 10 cm s⁻¹. Sixteen individuals were tested in a swimming chamber against a flow-through velocity of 6 cm s ⁻¹ and allowed to swim to exhaustion. Fish swam between 25 and 538 min with a peak at c . 6–8 h. Total swimming time was not correlated with standard length of fish although the size range examined was narrow. Relative to recent studies on the swimming abilities of late-stage larvae of reef fishes, this study indicates that post-larval King George whiting are weak swimmers. The weak swimming ability of post-larval King George whiting is consistent with studies showing passive dispersal and recruitment of this species.     

Effects of the brain parasite Myxobolus arcticus on sockeye salmon

Parasitism with Myxobolus arcticus did not affect smolt size of sockeye salmon or their osmocompetence, but had a deleterious effect ( P <0.001) on the swimming speed of naturally infected smolts. Parasitized fish had a mean swimming speed of 2.89 fork length s⁻¹ (L_F s⁻¹) compared with 4.37 L _F s⁻¹ for unparasitized fish. The parasite probably impairs swimming ability by affecting the central nervous system, but this effect does not appear severe enough to limit the parasite's usefulness in stock separation.     

Field-based measurements of oxygen uptake and swimming performance with adult Pacific salmon using a mobile respirometer swim tunnel

Novel field measurements of critical swimming speed ( U _crit) and oxygen uptake (  M o₂) in three species of adult Pacific salmon Oncorhynchus spp. up to 3·5 kg in body mass were made using two newly designed, mobile Brett-type swim tunnel respirometers sited at a number of field locations in British Columbia, Canada. Measurements of U _crit, which ranged from 1· 68 to 2·17 body lengths s⁻¹, and maximum M o₂, which ranged from 8·74 to 12·63 mg O₂ kg⁻¹ min⁻¹ depending on the species and field location, were judged to be of similar quality when compared with available data for laboratory-based studies. Therefore high quality respirometry studies were possible in the field using adult wild swimming salmonids. In addition, the recovery of wild adult Pacific salmon from the exhaustive U _crit swim test was sufficiently rapid that swimming performance could be repeated with <1 h of recovery time between the termination of the initial swim test and the start of the second test. Moreover, this repeat swimming performance was possible without routine M o₂ being reestablished. This result suggests that wild adult salmon are capable of carrying a moderate excess post-exercise oxygen consumption without adversely affecting U _crit, maximum M o₂ or swimming economy. Such capabilities may be extremely important for timely migratory passages when salmonids face repetitive hydraulic challenges on their upstream migration.     

Repeat UCrit and endurance swimming in juvenile shortnose sturgeon (Acipenser brevirostrum)

Previous results show that juvenile shortnose sturgeon are steady swimmers and, compared with salmonids, generally have low critical swimming (UCrit) and endurance swimming capacities. Most studies on swimming capacities of sturgeon, and other fishes, include those where fish have only been swum once and the metrics of swimming performance are assessed (e.g., time swum, speed achieved). Under natural conditions, there are ample instances where fish undergo multiple swimming cycles when traversing fish ways, culverts and other sources of fast water flow. While some evidence exists for salmonids, the effects of repeat swimming are not well known for sturgeon. The current study consisted of two experiments. The first examined the UCrit of juvenile shortnose sturgeon following three consecutive swimming trials with a 30 min recovery period between subsequent tests. The second examined the endurance swimming capacities of juvenile shortnose sturgeon following three consecutive swimming trials with a 60 min recovery period between subsequent tests. Our findings indicate that (i) UCrit was consistent (~2 body lengths/s) among swimming trials; (ii) significant individual variation exists between individuals in the endurance swimming trials; and (iii) consistent results exist for individuals across swimming trials in both the UCrit and the endurance swimming tests. These results suggest that juvenile shortnose sturgeon have a high recovery capacity, and their behaviour and morphology likely reflect aspects of their swimming capacities.     

Diurnal Variations in Swimming Activity of Rutilus rutilus (Cyprinidae) in a Group under Tank Conditions

Measurements of the swimming activity of a group of roach (12–19 cm TL, average) in a circular swimming chamber revealed two distinct activity patterns: a diurnal and a nocturnal one. The experiments showed that, having the choice, two factors stimulated the rhythmicity of the swimming behaviour of the fish, i.e. light intensity and the presence of a current field in the proximity of the fish. During daytime (bright light conditions) the fish moved into the current field and swam on average at 0.4 BL/s (resting swimming). The roach remained swimming at this speed even if no current field was established, however, then distributed evenly in the basin. By contrast, during night (dim light conditions) the fish predominantly chose the still water section but swam on average with a cruising speed of 1.6 BL/s (night swimming). Accordingly, they did not seek the still water section for night swimming if the light was kept on. Then again, the fish distributed more or less evenly in the basin. The results support the hypothesis that the fish migrate during night-time and do this preferably in still water.     

The effect of temperature and acclimation period on repeat swimming performance in cutthroat trout

Hatchery cutthroat trout Oncorhynchus clarki clarki were used to examine the effects of 48 h and 3 week temperature acclimation periods on critical swimming speed ( U _crit). The U _crit was determined for fish at acclimation temperatures of 7, 14 and 18° C using two consecutive ramp‐ U _crit tests in mobile Brett‐type swim tunnels. An additional group was tested at the stock's ambient rearing temperature of 10° C. The length of the temperature acclimation period had no significant effect on either the first or the second U _crit( U _crit‐1 and U _crit‐2, respectively) or on the recovery ratio (the quotient of U _crit‐2  U _crit‐1⁻¹). As anticipated, there was a significant positive relationship between U _crit‐1 and temperature ( P  < 0·01) for both acclimation periods, and an increasing, though non‐significant, trend between U _crit‐2 and temperature ( P  = 0·10). Acclimation temperature had no significant effect ( P  = 0·71) on the recovery ratio. These results indicate that a 48 h acclimation to experimental temperatures within the range of −3 to +8° C of the acclimation temperature may be sufficient in studies of swimming performance with this species. This ability to acclimate rapidly is probably adaptive for cutthroat trout and other species that occupy thermally variable environments.     

Comparisons of swimming performance in rainbow trout using constant acceleration and critical swimming speed tests

Maximum swimming performance of seasonally acclimated rainbow trout Oncorhynchus mykiss was compared among short-duration constant acceleration tests ( U _max) and with the well established, but longer duration critical swimming speed ( U _crit) test. The present results show that U _max was insensitive to a range of acceleration rates that differed by more than three-fold. Thus, test duration could be reduced from 58 to 18 min without affecting the estimate of U _max. The value of U _max, however, was up to 57% higher than U _crit. Only the slowest acceleration rate tested (an increase of 1 cm s⁻¹ every min) had a significantly lower U _max, and this was up to 19% higher than U _crit. Even so, the potential saving in the test duration was small (70 v. 90 min) when compared with a ramp- U _crit test (a standard U _crit test but with the water velocity initially ramped to c . 50% of the estimated U _crit). Therefore, swim tests that are appreciably shorter in duration than a ramp- U _crit test result in U _max being appreciably greater than U _crit. An additional discovery was that the ramp- U _crit performance of cold-acclimated rainbow trout was independent of the recovery period between tests. These results may prove useful in making comparisons among different swim test protocols and in designing swim tests that assess fish health and toxicological impacts.     

Movements of ultrasonically tagged brown trout (Sulmo trutta L.) in Lake Constance

In Lake Constance from September 1986 to May 1988 13 adult lake dwelling brown trout ( Sulmo trutta L.) were tagged with ultrasonic transmitters and tracked almost continuously for up to 13 days. Two behaviour types were observed: (a) random movement in locally restricted areas and (b) excursions of up to 40 km distance. Swimming activity during the day was significantly higher than at night in most experiments. In summer swimming depth ranged between 8 and 16 m, and in winter between 0 and 3m. The preferred water temperature was about 14°C in the thermally stratified waterbody. During the experiments mean swimming speed ranged between 0.3 km h⁻¹ (0.1 bodylengths s⁻¹) and 0.9 km h⁻¹ (0.6 bodylengths s⁻¹).     

Swimming performance and metabolism of 0+ year Thymallus arcticus

The prolonged swimming speed and metabolic rate of 0+ year Arctic grayling Thymallus articus were examined with respect to current velocity, water temperature and fish size, and compared to conditions fish occupy in the river. Oxygen consumption (mg O₂ h⁻¹) increased with fish mass and temperature (6–23° C), with a steep increase in metabolic rate between 12 and 16° C. Absolute prolonged swimming speed (cm s⁻¹) increased rapidly with fish size (total length, L _T, and mass), however, fish in the natural stream habitat occupied current velocities between 15 and 25 cm s⁻¹ or 4  L _T s⁻¹, approximately half their potential prolonged swimming speed (10  L _T s⁻¹).     

实验室条件下唐鱼两性异形及其与游泳能力关系

为了解唐鱼两性异形及其与游泳能力关系,检测了性成熟阶段唐鱼躯干部和鱼鳍形态特征以及爆发游泳速度(U_burst)和临界游泳速度(U_crit)在雌雄之间的差异,旨在从形态适应角度探究长期进化中雌雄唐鱼各自面对选择压力所产生的游泳能力差异及其机制,从而为野生唐鱼保护提供基础数据.结果表明: 雌性唐鱼的体长、头高、头宽、尾鳍面积以及吻端至枕骨后末端、腹鳍起点至背鳍末端等长度均与雄性无显著差异.而体高、体宽、腹鳍起点至背鳍起点等反映腹腔大小的形态参数以及吻端至背鳍起点、吻端至臀鳍起点、枕骨后末端至背鳍起点等反映躯干部大小的形态参数均显示为雌性显著大于雄性,但头长以及胸鳍面积、腹鳍面积、背鳍面积和臀鳍面积均显示为雄性显著大于雌性.对所有数据进行主成分分析,结果显示第1主成分贡献率为74.2%,负载量较大的是体长、头长、头高、体高、头宽、体宽以及各鳍之间距离等主要反映唐鱼躯干整体特征的参数;第2主成分贡献率为15.7%,负载量较大的是胸鳍面积、腹鳍面积、背鳍面积和臀鳍面积等主要反映鱼鳍特征的参数.唐鱼性别在第1主成分上无法区分,但在第2主成分却可以明显区分.根据体宽、胸鳍面积、腹鳍面积、背鳍面积和臀鳍面积等建立的性别判别方程对雌雄判断准确率达到91.8%～92.5%.唐鱼游泳能力测定结果显示,雌性U_burst与雄性无显著差异,但U_crit显著小于雄性.以上结果表明,雌雄唐鱼两性异形主要集中在与游泳能力相关的鱼鳍特征上.相比雄性,雌性唐鱼虽然胸鳍等鱼鳍面积较小导致其U_crit小于雄性,却具有更长的躯干部以保证其同样具有较高的爆发游泳能力,从而有利于在流速波动很大的溪流中躲避捕食和进行其他应急活动;相比雌性,雄性唐鱼则具有较大的鱼鳍面积保证其U_crit高于雌性,以利于日常活动及在繁殖过程中追逐雌性等相对持久性游泳运动.     

The muscle twitch and the maximum swimming speed of giant bluefin tuna, Thunnus thynnus L.

Sustained swimming of bluefin tuna was analysed from video recordings made of a captive patrolling fish school [lengths (L) 1.7–3.3 m, body mass (M) 54–433 kg]. Speeds ranged from 0.6 to 1.2 L s⁻¹ (86–260 km day⁻¹) while stride length during steady speed swimming varied between 0.54 and 0.93 L. Maximum swimming speed was estimated by measuring twitch contraction of the anaerobic swimming muscle in pithed fish 5 min after death. Muscle contraction time increased from the shortest just behind the head (30–50 ms at 20% L) to the longest at the tail peduncle (80–90 ms at 80% L) (all at 28°C). A fish (L = 2.26 m) with a muscle contraction time of 50 ms at 25% L can have a maximum tail beat frequency of 10 Hz and maximum swimming speed of 15m s⁻¹ (54km h⁻¹) with a stride length of 0.65L. With a stride length of 1 L a speed of 22.6 m s⁻¹ (81.4 km h⁻¹) is possible. Power used at maximum speed was estimated for this fish at between 10 and 40 kW, with corresponding values for the drag coefficient at a Reynolds number of 4.43 × 10⁷ of 0.0007 and 0.0027.     

Endurance swimming of diploid and triploid Atlantic salmon

When groups of diploid (mean ±  s . e . fork length, L _F) 33·0 ± 1·4 cm and triploid (35·3 ± 0·5 cm) Atlantic salmon Salmo salar were forced to swim at controlled speeds in a carefully monitored 10 m diameter 'annular' tank no significant difference was found between the maximum sustained swimming speeds ( U _ms, maintainable for 200 min) where the fish swam at the limit of their aerobic capability. Diploids achieved 2·99 body lengths per second (bl s⁻¹)(0·96 m s⁻¹) and triploids sustained 2·91 bl s⁻¹(1·02 m s⁻¹). The selection of fish for the trials was based on their ability to swim with a moving pattern projected from a gantry rotating at the radius of the tank and the selection procedure did not prove to be significant by ploidy. A significant difference was found between the anaerobic capabilities of the fish measured as endurance times at their prolonged swimming speeds. During the course of the experimentation the voluntary swimming speed selected by the fish increased and the schooling behaviour improved. The effect of the curvature of the tank on the fish speeds was calculated (removing the curved effect of the tank increased the speed in either ploidy by 5·5%). Implications of the endurance times and speeds are discussed with reference to the aquaculture of triploid Atlantic salmon.     

Mechanical understanding of hunting waves generated by killer whales

The wave wash hunting employed by Orcinus orca, also known as killer whales, is unique in that the prey is hunted outside of the water by generating waves. To quantitatively analyze the specific mechanism of the wave wash, data were obtained using computational fluid dynamics (CFD), and wave theory was introduced as the theoretical background to clarify the mechanism. The relationships between the swimming characteristics and wave parameters are defined in this paper. The results obtained by numerical investigation revealed that the wavelength increased with the swimming speed. Additionally, the wave height increased as the swimming speed increased and the swimming depth became shallower, and subsequently converged to a maximum of 2.42 m. The success of hunting is determined by two wave parameters, which indicate the intensity of the wave wash: the wave height and force exerted on the prey. The metabolic rate and the drag force are considered to evaluate the efficiency of the locomotion, which varied according to the swimming speed (V) and swimming depth (d) of the whales. To generate hunting waves efficiently, the optimal ranges of V and d were estimated to be 3 ~ 5 m/s and 0.5 m ~ 1.1 m respectively.     

Effect of temperature on swimming performance of sea bass juveniles

At four temperatures ( T= 15, 20, 25 and 28° C) swimming performance of Dicentrarchus labrax was significantly correlated with total length (23–43 mm L _T); r²=0.623–0.829). The relative critical swimming speed ( RU _crit= U _crit L _T⁻¹), where U _crit is the critical swimming speed, was constant throughout the L _T range studied. The significant effect of temperature on the relative critical swimming speed was described binomially: RU _crit=−0.0323T²+ 1.578 T −10.588 (r²=1). The estimated maximum RU _crit (8.69 L _T s⁻¹) was achieved at 24.4° C, and the 90% performance level was estimated between 19.3 and 29.6° C.     

Swimming performance and associated ionic disturbance of juvenile pink salmon Oncorhynchus gorbuscha determined using different acceleration profiles

Swimming performance was assessed in juvenile pink salmon Oncorhynchus gorbuscha (body mass <5·0 g) using five different protocols: four constant acceleration tests each with a different acceleration profile (rates of 0·005, 0·011, 0·021 and 0·053 cm s^?2) and a repeated ramped‐critical swimming speed test. Regardless of the swim protocol, the final swimming speeds did not differ significantly (P > 0·05) among swim tests and ranged from 4·54 to 5·20 body lengths s^?1. This result supports the hypothesis that at an early life stage, O. gorbuscha display the same fatigue speeds independent of the swimming test utilized. Whole body and plasma [Na⁺] and [Cl^?] measured at the conclusion of these tests were significantly elevated when compared with control values (P < 0·05) and appear to be predominantly associated with dehydration rather than net ion gain. Given this finding for a small salmonid, estimates of swim performance can be accurately measured with acceleration tests lasting <10 min, allowing a more rapid processing than is possible with a longer critical swim speed test.     

Effects of age and size on critical swimming speed of juvenile Chinese sturgeon Acipenser sinensis at seasonal temperatures

Changes in the critical swimming speed (U_crit, cm s^?1) with ontogeny of 2·5–12·5 month‐old juvenile anadromous Chinese sturgeon Acipenser sinesis were measured in a modified Blazka‐type swimming tunnel. The absolute U_crit increased with length, mass and age; the relative U^′_crit (body lengths, s^?1), however, decreased. Juvenile A. sinesis did not display a parr–smolt transformation at the length or age threshold to tolerate full‐strength seawater.     

Swimming activity and behaviour of European Anguilla anguilla glass eels in response to photoperiod and flow reversal and the role of energy status

To better understand migratory divergences among Anguilla anguilla glass eels, the behaviour of individuals caught at the time of their estuary entrance was studied through their response to a light:dark cycle and then to both water current reversal and light:dark cycle. In a first experiment, fish moving with the flow in response to dusk (M⁺ fish) and fish that had not exhibited any movement (M⁻ fish) were distinguished. Anguilla anguilla from these two groups were then individually marked and their response to water current reversal compared. M⁺ individuals mainly exhibited negative rheotaxis with a tidal periodicity, whereas positive rheotaxis was mainly exhibited by M⁻ individuals. Thus, M⁺ A. anguilla glass eels showing negative rheotaxis appear to have the strongest propensity to migrate, the converse applies to M⁻ ones showing positive rheotaxis. A small percentage of individuals (5%) were hyperactive, alternately swimming with and against the current with almost no resting phase. These fish lost c . 2 mg wet mass day⁻¹, whereas individuals which were almost inactive lost c . 1 mg day⁻¹. Wet and dry mass changes in relation to activity levels were compared with previous experiments and it was concluded that A. anguilla glass eel energy status might be involved in differences in migratory tendencies but other factors that might be important are discussed. It is proposed that any decrease in A. anguilla glass eel energy stores associated with global warming might lead to an increase in the proportion of sedentary individuals and thus be involved in the decrease in the recruitment to freshwater habitats.     

The behavioural and physiological response of Atlantic cod Gadus morhua L. to short-term acute hypoxia

The average rate of swimming speed and the physiological status or stress of individual Atlantic cod Gadus morhua was monitored in response to short-term acute (STA) hypoxia ( i.e. partial pressure of oxygen,     , reduced from 20·9 to 4·3 kPa within 1 h at 10° C). The STA hypoxic response of Atlantic cod was associated with a large primary increase (+29%) and a large secondary decrease (−54%) in swimming speed as well as major physiological stress ( e.g. plasma cortisol = 214·7 ng ml⁻¹ and blood lactate = 2·41 mmol l⁻¹).     

Pelvic girdle shape predicts locomotion and phylogeny in batoids

In terrestrial vertebrates, the pelvic girdle can reliably predict locomotor mode. Because of the diminished gravitational effects on positively buoyant bony fish, the same relationship does not appear to exist. However, within the negatively buoyant elasmobranch fishes, benthic batoids employ pelvic fin bottom‐walking and punting as primary or supplementary forms of locomotion. Therefore, in this study, we employed geometric and linear morphometrics to investigate if their pelvic girdles exhibit shape characteristics similar to those of sprawling terrestrial vertebrates. We tested for correlates of pelvic girdle shape with 1) Order, 2) Family, 3) Swim Mode, and/or 4) Punt Mode. Landmarks and semilandmarks were placed along outlines of dorsal views of 61 batoid pelvic girdles (3/3 orders, 10/13 families, 35/72 genera). The first three relative warps explained 88.45% of the variation among individuals (P < 0.01%). Only Order and Punt Mode contained groups that were all significantly different from each other (P < 0.01%). Discriminant function analyses indicated that the majority of variation within each category was due to differences in extension of lateral and prepelvic processes and puboischiac bar angle. Over 60% of the original specimens and 55% of the cross‐validated specimens were correctly classified. The neutral angle of the propterygium, which articulates with the pelvic girdle, was significantly different among punt modes, whereas only pectoral fin oscillators had differently shaped pelvic girdles when compared with batoids that perform other swimming modes (P < 0.01). Pelvic girdles of batoids vary greatly, and therefore, likely function in ways not previously described in teleost fishes. This study illustrates that pelvic girdle shape is a good predictor of punt mode, some forms of swimming mode, and a species' Order. Such correlation between locomotor style and pelvic girdle shape provides evidence for the convergent evolution of morphological features that support both sprawled‐gait terrestrial walking and aquatic bottom‐walking. J. Morphol. 275:100–110, 2014. © 2013 Wiley Periodicals, Inc.