Critical swimming speed of sterlet (Acipenser ruthenus): Does intraspecific hybridization affect swimming performance?

We studied the effect of intraspecific hybridization on swimming performance in sterlet, hypothesizing that such hybridization increases the performance by inducing the hybrid vigor. A total of 12 purebred and hybrid crosses were reproduced from Danube (D) and Volga (V) populations of Acipenser ruthenus. Within each cross, one group of fish was exposed to temperature challenges mimicking the temperature variation in the natural environment during summer. Temperature challenges comprised a constant increase from 19°C to 24°C and then return to 19°C within 12 hr (dT<1°C/hr), and were carried out every third day over the experimental period of 20 days. As a control, fish from each cross were kept at a constant temperature of 19°C. Critical swimming speed (U_crit) was assessed on day 0 (29 days post hatch, dph), 10 (39 dph) and 20 (49 dph). The critical swimming speeds ranged from 5.12 cm/s (1.63 TL/s) to 16.44 cm/s (2.4 TL/s) during the experimental period (29–49 dph). There were no significant differences observed in U_crit between repeatedly temperature challenged and control groups, indicating that the temperature challenge did not alter the swimming performance. The critical swimming speed showed positive relationship with total body length. Comparing intraspecific hybrid crosses with purebred crosses, no significant difference in swimming performance was observed. It is thus concluded that swimming performance is a family specific trait. There is no indication that intraspecific hybridization affects swimming performance nor that close‐to‐natural temperature regimes increase swimming performance.     

Can winter swimming cause people to prefer lower room temperatures?

Preferred room temperatures were determined for 16 winter swimmers who had been exposed to cold shock daily by bathing in the sea (0–6°C) during at least two winter seasons. Each subject participated in one comfort experiment (2 1/2 h) in an environmental test chamber, where the preferred ambient temperature was determined by adjusting it according to his wishes. The subjects were sedentary and clothed in a standard uniform. Skin temperatures, rectal temperature and evaporative weight loss were measured. The results were compared with similar data for two other groups: (a) a control group of 64 normal subjects and (b) 16 persons who had been working 8 h a day at 8°C during at least 6 months in the meat packing industry. The results showed no significant differences between the ambient temperatures preferred by the three groups of subjects. This indicated that man cannot be adapted to prefer lower ambient temperatures by exposing him daily to cold.     

Four flippers or two? Tetrapodal swimming with an aquatic robot

To understand how to modulate the behavior of underwater swimmers propelled by multiple appendages, we conducted surge maneuver experiments on our biologically-inspired robot, Madeleine. Robot Madeleine is a self-contained, self-propelled underwater vehicle with onboard processor, sensors and power supply. Madeleine's four flippers, oscillating in pitch, can be independently controlled, allowing us to test the impact of flipper phase on performance. We tested eight gaits, four four-flippered and four two-flippered. Gaits were selected to vary the phase, at either 0 or pi rad, between flippers on one side, producing a fore-aft interaction, or flippers on opposite sides, producing a port-starboard interaction. During rapid starting, top-speed cruising, and powered stopping, the power draw, linear acceleration and position of Madeleine were measured. Four-flippered gaits produced higher peak start accelerations than two, but did so with added power draw. During cruising, peak speeds did not vary by flipper number, but power consumption was double in four flippers compared to that of two flippers. Cost of transport (J N(-1) m(-1)) was lower for two-flippered gaits and compares favorably with that of aquatic tetrapods. Two four-flippered gaits produce the highest surge scope, a measure of the difference in peak forward and reverse acceleration. Thus four flippers produce superior surge behavior but do so at high cost; two flippers serve well for lost-cost cruising.     

Power requirements of swimming: do new methods resolve old questions?

A recurring question in the study of fish biomechanics and energeticsis the mechanical power required for tail-swimming at the highspeeds seen among aquatic vertebrates. The quest for answershas been driven by conceptual advances in fluid dynamics, startingwith ideas on the boundary layer and drag initiated by Prandtl,and in measurement techniques starting with force balances focussingon drag and thrust. Drag (=thrust) from measurements on physicalmodels, carcasses, kinematics as inputs to hydromechanical models,and physiological power sources vary from less than that expectedfor an equivalent rigid reference to over an order of magnitudegreater. Estimates of drag and thrust using recent advanceslargely made possible by increased computing power have notresolved the discrepancy. Sources of drag and thrust are notseparable in axial undulatory self propulsion, are open to interpretationand Froude efficiency is zero. Wakes are not easily interpreted,especially for thrust evaluation. We suggest the best measuresof swimming performance are velocity and power consumption forwhich 2D inviscid simulations can give realistic predictions.Steady swimming power is several times that required for towingan equivalent flat plate at the same speed.     

Light-induced swimming of Daphnia: can laboratory experiments predict diel vertical migration?

Vertical displacement velocity of a Daphniagaleata × hyalina clone was quantified inrelation to changes in the relative rate of lightchange. An increase in the latter variable triggers anenhanced swimming response, and this response is againelicited when a second increase in the rate ofrelative light increase is applied. Decreases in therate of light increase affect phototactic swimming ina similar way. The acceleration/deceleration assistedstimulus-response system is an extension of the ideaof phototaxis as the underlying behavioural mechanismfor vertical migration, and suggests that continuousaccelerations in light change also affect verticaldisplacements observed in the field. A simple dielvertical migration simulation model was used tocalculate the vertical displacement of Daphniain relation to the natural light change at sunrise.The calculated vertical displacement fits nicely inthe temporal range of the observed averaged downwardmigration of adult Daphnia in Lake Maarsseveen.The calculated migration amplitude, however, islarger than the change in mean population depthobserved in nature.     

Inflamed adult pharynx tissues and swimming larva of Ciona intestinalis share CiTNFα-producing cells

In situ hybridisation and immunohistochemistry analyses have shown that the Ciona intestinalis tumour necrosis factor alpha gene (CiTNFα), which has been previously cloned and sequenced, is expressed either during the inflammatory pharynx response to lipopolysaccharide (LPS) or during the swimming larval phase of development. Granulocytes with large granules and compartment/morula cells are CiTNFα-producing cells in both inflamed pharynx and larvae. Pharynx vessel endothelium also takes part in the inflammatory response. Haemocyte nodules in the vessel lumen or associated with the endothelium suggest the involvement of CiTNFα in recruiting lymphocyte-like cells and promoting the differentiation of inflammatory haemocytes. Specific antibodies against a CiTNFα peptide have identified a 43-kDa cell-bound form of the protein. Observations of pharynx histological sections (at 4 and 8 h post-LPS inoculation) from naive and medium-inoculated ascidians have confirmed the CiTNFα-positive tissue response. Larval histological sections and whole-mount preparations have revealed that CiTNFα is expressed by trunk mesenchyme, preoral lobe and tunic cells, indicating CiTNFα-expressing cell immigration events and an ontogenetic role.     

The first world swimming championships of roseobacters—Phylogenomic insights into an exceptional motility phenotype

Many marine Alphaproteobacteria of the Roseobacter group show a characteristic swim-or-stick lifestyle, for which motility is a crucial trait. Three phylogenetically distinct flagellar gene clusters (FGCs) have been identified in Rhodobacteraceae that have been named fla1, fla2 and fla3 according to their relative abundance. In addition to the flagellar-dependent swimming and swarming motility, pilus-dependent twitching mediates bacterial locomotion. Furthermore, filament independent modes of motility, namely gliding and sliding, have been described for various microorganisms. However, no mode of motility other than swimming has so far been described for roseobacters. In the present study, we investigated motility, distribution of flagellar systems and the phylogeny of 120 genome-sequenced Rhodobacteraceae. The phylogenetically broad taxon sampling that included 114 type strains revealed the presence of at least ten distinct clades that were statistically well supported. The investigation of the actual physiological capacity for swimming motility on soft agar plates showed that only about half of the 120 tested strains were motile under the tested conditions. Seven strains developed a conspicuous dendritic motility phenotype that was reminiscent of the swarming motility in Pseudomonas aeruginosa. The observed dendritic motility in two strains (i.e. Sulfitobacter pseudonitzschiae DSM 26842 and Roseovarius pacificus DSM 29589) was particularly surprising because they did not harbor any genes of the FGC. Accordingly, it was concluded that this form of dendritic motility was independent of a flagellum. A comparative genomics approach allowed a remarkable number of pilus-related candidate genes to be identified for this novel type of motility in Rhodobacteraceae.     

Locomotion at –1.0°C: burst swimming performance of five species of Antarctic fish

We investigated the burst swimming performance of five species of Antarctic fish at −1.0°C. The species studied belonged to the suborder, Notothenioidei, and from the families, Nototheniidae and Bathydraconidae. Swimming performance of the fish was assessed over the initial 300 ms of a startle response using surgically attached miniature accelerometers. Escape responses in all fish consisted of a C-type fast start; consisting of an initial pronounced bending of the body into a C-shape, followed by one or more complete tail-beats and an un-powered glide. We found significant differences in the swimming performance of the five species of fish examined, with average maximum swimming velocities (U_max) ranging from 0.91 to 1.39 m s⁻¹ and maximum accelerations (A_max) ranging from 10.6 to 15.6 m s⁻². The cryopelagic species, Pagothenia borchgrevinki, produced the fastest escape response, reaching a U_max and A_max of 1.39 m s⁻¹ and 15.6 m s⁻², respectively. We also compared the body shapes of each fish species with their measures of maximum burst performance. The dragonfish, Gymnodraco acuticeps, from the family Bathdraconidae, did not conform to the pattern observed for the other four fish species belonging to the family Nototheniidae. However, we found a negative relationship between buoyancy of the fish species and burst swimming performance.     

Morphological predictors of swimming speed performance in river and reservoir populations of Australian smelt Retropinna semoni

Dam construction is a major driver of ecological change in freshwater ecosystems. Fish populations have been shown to diverge in response to different flow velocity habitats, yet adaptations of fish populations to river and reservoir habitats created by dams remains poorly understood. We aimed to evaluate divergence of morphological traits and prolonged swimming speed performance between lotic and lentic populations of Australian smelt Retropinna semoni and quantify the relationship between prolonged swimming speed performance and morphology. Prolonged swimming speed performance was assessed for 15 individuals from each of three river and two reservoir populations of R. semoni using the critical swimming speed test (U_crit). Body shape was characterized using geometric morphometrics, which was combined with fin aspect ratios and standard length to assess morphological divergence among the five populations. Best subsets model-selection was used to identify the morphological traits that best explain U_crit variation among individuals. Our results indicate R. semoni from river populations had significantly higher prolonged swimming speed performance (U_crit = 46.61 ± 0.98 cm s⁻¹) than reservoir conspecifics (U_crit = 35.57 ± 0.83 cm s⁻¹; F_1,74 = 58.624, Z = 35.938, P < 0.001). Similarly, R. semoni sampled from river populations had significantly higher fin aspect ratios (AR_caudal = 1.71 ± 0.04 and 1.29 ± 0.02 respectively; F_(1,74) = 56.247, Z = 40.107, P < 0.001; AR_pectoral = 1.85 ± 0.03 and 1.33 ± 0.02 respectively; F_(1,74) = 7.156, Z = 4.055, P < 0.01). Best-subset analyses revealed U_crit was most strongly correlated with pectoral and caudal fin aspect ratios (R²_adj = 0.973, AIC_c = 41.54). Body shape, however, was subject to a three-way interaction among population, habitat and sex effects (F_3,74 = 1.038. Z = 1.982; P < 0.05). Thus sexual dimorphism formed a significant component of unique and complex variation in body shape among populations from different habitat types. This study revealed profound effects of human-altered flow environments on locomotor morphology and its functional link to changes in swimming performance of a common freshwater fish. While past studies have indicated body shape may be an important axis for divergence between lotic and lentic populations of several freshwater fishes, fin aspect ratios were the most important predictor of swimming speed in our study. Differences in body morphology here were inconsistent between river and reservoir populations, suggesting this aspect of phenotype may be more strongly influenced by other factors such as predation and sexual dimorphism.     

Exercise challenge in Antarctic fishes: do haematology and muscle metabolite levels limit swimming performance?

 Burst swimming increased haematocrit (partly from erythrocyte swelling) in the cryopelagic nototheniid Pagothenia borchgrevinki, but not in the benthic species Trematomus bernacchii. Erythrocyte nucleotides, which regulate haemoglobin-oxygen affinity, remained constant. Plasma cortisol was high in all captive fish and raised questions about the effects of chronic stress on metabolic measurements from Antarctic fish held in captivity. Glycogen was reduced in white trunk muscle, but not in the red pectoral muscle of exercised P. borchgrevinki. Red pectoral muscle glycogen was nearly 3 times higher in T. bernacchii than in P. borchgrevinki but post-exercise lactate rises were modest. Lactate values were, however, higher in exercised P. borchgrevinki white muscle than in T. bernacchii, and correlated with muscle-buffering capacity. Resting adenylate energy charge (AEC) was unexpectedly low in both species and reduced with exercise only for white muscle in P. borchgrevinki. While it appears that the capacity for burst swimming is limited by endogenous metabolic fuels, confirmation of low resting values of ATP and AEC in Antarctic fishes requires the development of methods that maintain high phosphocreatine levels in the muscle. Received: 12 February 1996/Accepted:1 May 1996     

Polymorphism and multiple correlated characters: Do flatfish asymmetry morphs also differ in swimming performance and metabolic rate?

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Just keep swimming? Observations of resting behavior in gray reef sharks Carcharhinus amblyrhynchos (Bleeker, 1856)

Understanding the respiratory modes of sharks has important implications for studying the metabolism, energetics, and behavioral strategies of different species. Here we provide the first reported observations of resting behavior in the gray reef shark Carcharhinus amblyrhynchos, a species typically considered an obligate ram ventilator. Observations were made at several locations in the Republic of Seychelles, where sharks were found resting under reef ledges and were unresponsive to the presence of divers. These findings update our understanding of the respiratory mode of this species and have implications for future research.     

The significance of heart rate in free swimming cod,Gadus morhua: Some observations with ultra‐sonic tags

Ultra sonic transmitters (cylindrical, 1.5 cm diameter × 7 cm long) with three‐week battery life were used to examine the heart rate and electrocardiogram (ECG) of cod in swimming experiments. The maximum heart rate was observed when the period between the recovery (T) wave and the initial wave (P) of the ECG was zero and was limited by the P to T period which was not observed to vary in an individual. Low heart rates were observed in resting fish and maximum rates were associated with exhaustion and cruising swimming. Maximum rates continued during periods of oxygen debt repayment and during anaesthesia as long as oxygen was supplied to the gills. Brief inhibition of heart rate was associated with sudden stimuli and during maximum swimming exertion. The significance of rate change and its relation to the aerobic and anaerobic states is discussed.     

A novel crustacean swimming stroke: coordinated four-paddled locomotion in the cypridoidean ostracode Cypridopsis vidua (Müller)

Despite the diversity and ecological importance of cypridoidean ostracodes, there have been no kinematic studies of how they swim. We used regular and high-speed video of tethered ostracodes to document locomotion in the cypridoidean species Cypridopsis vidua. Swimming in this species is drag-based, with thrust provided by both antennulae and antennae. About 15 complete power and recovery strokes occur per second; maximal speeds for the limb tips were about 30 mm/s for the antennulae and 50 mm/s for the antennae. These speeds correspond to Reynolds numbers on the order of 10(-1) to 10(0) for the limb tips and 10(-2) to 10(-1) for the setae that extend outward from the swimming limbs and provide much of the surface area of the limb. The strokes of the four thrust-producing limbs are coordinated in a manner that seems to be unique among aquatic arthropods. When viewed from the anterior, power strokes are synchronized diagonally: left antennula and right antenna power strokes start at the same time and terminate just as the power strokes for the right antennula and left antenna begin. Because power strokes occur throughout the stroke cycle, swimming in this species is smoothly continuous, without the rapid accelerations and decelerations characteristic of most small aquatic arthropods.     

Does among‐population variation in burst swimming performance of sockeye salmon Oncorhynchus nerka fry reflect early life migrations?

Using a fixed‐speed test, burst swimming performance was found to vary among nine populations of emergent sockeye salmon Oncorhynchus nerka fry reared in a common‐garden environment. No consistent relationship was, however, detected between difficulty of fry migration (upstream v. downstream) to rearing areas and total burst swimming duration or bursting rate.