流速对细鳞裂腹鱼游泳行为及能量消耗影响的研究

通过自制密封的鱼类游泳实验装置, 研究了流速对细鳞裂腹鱼游泳行为和能量消耗的影响。结果显示,细鳞裂腹鱼的摆尾频率随游泳速度的变化有明显的变化规律, 摆尾频率随着流速的增加而显著性的增加,而摆尾幅度有减小趋势, 差异性不显著。结果还表明, (26±1) ℃时, (10.60±0.54) cm 细鳞裂腹鱼的相对临界游泳速度为(11.5±0.5) BL/s, 绝对临界游泳速度为(110.28±2.02) cm/s。测定的相对临界流速较其他的鲤科鱼大,是对生存水流环境(流速0.5—1.5m/s)适应性的表现。这一结果表明鱼类的游泳能力是能够训练的。运动代谢率与相对流速的关系为, AMR = 93.08e(0.307v) + 314.33, R2= 0.994; 单位距离能耗与流速的指数关系为COT =28e (-1.03V) +6.05, R2= 0.998。流速达到8 BL/s 时, 裂腹鱼耗氧率开始下降, 从流速7 BL/s 时, (1245.57±90.97 )mg O2/(kg·h)最大, 下降到(978.78±189.38) mg O2/(kg·h)。1—7 BL/s 流速范围内, 裂腹鱼单位时间内的耗氧率随着游泳速度的增加而增加, 而且随着游泳速度的增加, 单位距离能耗(COT)逐渐减少, 最小能耗在6 倍体长流速, 0.68 m/s 时, 为(6.00±1.57) J/(kg·m), 其能量利用效率最大。       

Effect of swimming on protein degradation: 3-methylhistidine and creatinine excretion

The effect of 5-km noncompetitive swimming (moderate exercise) and 2-km competitive speed swimming (intensive exercise) on protein breakdown was studied in a group of young male volunteers (16-20 years old) who followed a 3-MH-free diet throughout the study. Urinary 3-MH and creatinine were determined over a period of 24 and 48 hr as an index of protein degradation. Basal 3-MH levels in the two groups of swimmers were 2.85 and 3.07 mumole X kg-1 X day-1. Mean rates of 3-MH excretion were, respectively, 1.54 and 1.94 mumole X kg-1 X day-1 for the 48 hr after moderate exercise and the 24 hr after intensive exercise. The decrease in 3-MH urinary excretion was still evident when calculated as the urinary 3-MH-to-creatinine ratio.     

基于雅砻江两种裂腹鱼游泳能力的鱼道设计

为探究雅砻江两种裂腹鱼的游泳能力,给过鱼设施设计和鱼类游泳行为学研究提供基础参数,本研究采用递增流速法对长丝裂腹鱼、齐口裂腹鱼的感应流速、临界游泳速度、突进游泳速度进行测试,采用固定流速法对长丝裂腹鱼的耐久游泳速度进行测试。结果表明: 长丝裂腹鱼与齐口裂腹鱼的感应流速随着体长的增加均出现了先增加后平稳的趋势,但最大感应流速均小于0.2 m·s^-1;长丝裂腹鱼的临界游泳速度与突进游泳速度分别为(0.81±0.20)和(1.49±0.26) m·s^-1,相对临界游泳速度为(4.90±1.73) BL·s^-1,相对突进游泳速度为(9.77±1.72) BL·s^-1(BL为体长);齐口裂腹鱼的临界游泳速度与突进游泳速度分别为(0.73±0.24)和(1.17±0.39) m·s^-1,相对临界游泳速度为(6.88±2.82) BL·s^-1,相对突进游泳速度为(11.75±2.77) BL·s^-1。耐久测试发现,随着流速增加(0.7～1.5) m·s^-1,长丝裂腹鱼持续游泳时间与水流速度呈负相关,疲劳时间(T)与水流速度(V)的关系可以拟合为lgT=-2.52V+5.59,预测鱼道长度(d)与鱼道内可通过的最大平均水流速度(V_fmax)的关系式为V_{f max}=-0.17lnd+1.74。根据试验结果,当以长丝裂腹鱼和齐口裂腹鱼为主要过鱼对象时,建议鱼道内最小水流速度应大于0.2 m·s^-1,进口及竖缝处水流速度为0.73～1.67 m·s^-1,休息池主流水流速度为0.2～0.7 m·s^-1。     

Consumption, growth and evacuation in the Pacific cod, Gadus macrocephalus

Growth of Pacific cod was related to energy consumption (cal g⁻¹ day⁻¹) and was well described by linear equations. Maintenance ration was 11 and 12 cal g⁻¹ day⁻¹ at 4.5 and 6.5° C, respectively. Cod between 200 and 5000 g had similar growth rates when growth was expressed as a function of consumption (cal g⁻¹ day⁻¹). Laboratory consumption of food averaged 0.9 and 1.3% body weight per day at 4.5 and 6.5° C, respectively. At these temperatures growth was 0.34–0.38% body weight day⁻¹.
Maximum stomach volumes equated to approximately 4.7% of body weight with shrimp as prey. At this meal size Pacific cod did not feed the next day. A multiple meal evacuation experiment was used to verify the consumption estimates. A return-to-hunger estimate of the meal size evacuated was 1.5% body weight day⁻¹ at 6.5° C, similar to the 1.3% consumption estimate. For Pacific cod fed a single meal of 1% body weight the estimated instantaneous evacuation rate was 0.63 body weight day⁻¹ at 6.5° C. Meal size markedly affected the evacuation rate.
Measured consumption and growth rates are similar to those of Atlantic cod, Gadus morhua .     

Development of enteropeptidase activity in mouse small intestine: influence of hormones

The postnatal development of enteropeptidase activity has been examined on mucosal scrapping of the proximal part of the mouse small intestine. The activity was present at birth and remained low during the first 15 days of life. Then it rapidly increased reaching adult level within 2 days. Daily administration of cortisone acetate (25 micrograms X g body weight (bw)-1 X day-1), insulin (12.5 mU X g bw-1 X day-1), or epidermal growth factor (4 micrograms X g bw-1 X day-1) during 3 days to 8-day-old mice induced a premature increase of enteropeptidase. The maximal increase was observed with cortisone treatment, the enzymic activity representing 70% of the adult level. Thyroxine alone (1 microgram X g bw-1 X day-1) had no significant effect on enteropeptidase activity. Hormonal interactions have been evaluated by studying the effects of different hormonal combinations. Finally, cortisone acetate which has a major effect on this activity during suckling period was unable to influence adult small intestinal enteropeptidase activity.     

Cyclic feeding and subsequent compensatory growth do not significantly impact standard metabolic rate or critical swimming speed in rainbow trout

Standard metabolic rate ( R _s) and critical swimming speed ( U _crit) were used to assess the aspects of physiological status (stamina) of rainbow trout Oncorhynchus mykiss . Fish were fed either 1·5% body mass daily, 1·5% body mass cyclically (3 weeks of food deprivation followed by 3 weeks of refeeding), a ration based on Stauffer's formula (a maximum temperature-specific ration level) daily or on Stauffer's ration cyclically for 18 weeks. It was hypothesized that if cyclic feeding had no impact on the status of the fish, R _s and U _crit would not cycle with the feeding regime. This hypothesis was supported. No significant difference was found between the mean mass and the fork length of the four groups at the end of the experiment ( P > 0·05). Feeding had no effect on changes in R _s among the four groups, which were significantly different throughout the experiment ( P ≤ 0·05). No significant difference in U _crit was found ( P > 0·05) until at week 12 between groups fed 1·5% body mass ration cyclically and Stauffer's ration daily ( P ≤ 0·05). For groups fed a 1·5% body mass ration cyclically and daily, significant differences occurred at week 15 ( P ≤ 0·05) but no significant difference was found by week 18 ( P > 0·05), suggesting that cyclic feeding does not affect the aspects of physiological status (stamina) of the fish.     

Ligand binding equilibrium and kinetic measurements on the dimeric myoglobin of Busycon canaliculatum and the comparative ligand binding of diverse non-cooperative heme proteins

The rate constants and delta H degrees for the non-cooperative dimeric Busycon myoglobin are: oxygen, k' = 4.75 X 10(7) M-1 sec-1, k = 71 sec-1, and CO, l'= 3.46 X 10(5) M-1 sec-1, l = 0.0052 sec-1 at 20 degrees C, pH 7, delta H degrees = -3 kcal/mol for O2 and CO.2. Log-log plots of k vs K for oxygen and of l' vs L for CO binding for numerous non-cooperative hemoglobins and myoglobins point to a large steric influence of the protein on heme ligation reactions. Many of the proteins behave as "R" state for one ligand, but "T" for the other.     

不同程度的尾损伤对镇海林蛙(Rana zhenhaiensis)蝌蚪游泳速度的影响

无尾两栖类蝌蚪的尾巴通过产生强大的游泳速度在反捕食中起到了重要的作用。以镇海林蛙(Rana zhenhaiensis)蝌蚪为实验动物来评估断尾的运动代价。以74尾具有完整尾蝌蚪作为实验组,通过截去不同尾长片段,人为分成轻微尾损伤组(30%)和严重尾损伤组(30%)并测定两组蝌蚪在断尾前后的游泳速度。以16尾完整尾蝌蚪作为对照组在实验组断尾前后同时进行游泳速度的测定。实验结果显示断尾影响蝌蚪的游泳速度,但仅在尾损伤程度达到尾长的30%以上时才产生不利的影响。这表明轻微尾损伤并不对镇海林蛙蝌蚪的游泳速度产生严重影响。在断尾前后实验组蝌蚪的游泳速度均与尾长呈正相关。在相同尾长状态下,尾损伤蝌蚪的相对游泳速度明显快于完整尾蝌蚪。因此,尾损伤的镇海林蛙蝌蚪有可能通过改变尾和身体的摆动频次等方式在断尾后对游泳速度进行了一定的补偿。尾损伤在野外频繁发生于蝌蚪的尾远端,据此推测镇海林蛙蝌蚪在自然条件下的尾损伤并不会产生严重运动代价。     

Kinetics and mechanism of Zn(II) complexation with reduced glutathione

The kinetics of formation and dissociation of mono and bis complexes of Zn(II) with reduced glutathione (H4L+ = fully protonated form) were studied in aqueous solution at 25.0 +/- 0.1 degrees C and ionic strength 0.30 M (NaNO3) in the pH range 4.58 to 4.98 by temperature-jump. The reaction was found to proceed via two different mechanisms depending on degree of ligand protonation. In both cases, complex formation is predominantly if not completely through the sulfur. Reaction with the form HL-2 (only the amino nitrogen protonated), the dominant form of this species, proceeds by the expected rat limiting water loss (dissociative or Eigen) mechanism with rate constants of 9.3 X 10(7) M-1 sec-1 (+/- 24%) for mono and 5.1 X 10(7) M-1 sec-1 (+/- 25%) for bis complex formation. Reaction with H2L--(sulfur protonated) yields rate constants of 3.9 X 10(3) M-1 sec-1 (+/- 43%) for mono and 1.95 X 10(3) M-1 sec-1 (+/- 43%) for bis complex formation. The decrease in rate constant is attributed to blockage of the complexing site on reduced glutathione by intramolecular hydrogen bonding, with proton removal being the rate determining step.     

Bcl-2 over-expression reduces growth rate and prolongs G1 phase in continuous chemostat cultures of hybridoma cells.

Recent studies have suggested that Bcl-2 can affect cell cycle re-entry by inhibiting the transition from G0/G1 to S phase. In this study, we have taken a novel route to the study of the relationship between Bcl-2 expression and cell cycle progression. Continuous cultures of pEF (control) and Bcl-2 transfected murine hybridoma cells were operated at a range of dilution rates from 0.8 day-1 down to 0.2 day-1. The specific growth rate of the pEF cell line was the same as the dilution rate down to a value of 0.6 day-1. However, as the dilution rate was reduced stepwise to 0.2 day-1, the growth rate levelled-off at approximately 0.55 day-1 and this coincided with a fall in culture viability. By contrast, the specific growth rate of the Bcl-2 transfected cell line followed the dilution rate down to a value of 0.3 day-1 with high levels of cell survival. At high dilution rates, the cell cycle distributions were very similar for both cell lines. However, the distributions diverged as the dilution rate was reduced and, at a rate of 0.2 day-1, the percentage of G1 cells in the Bcl-2 culture was 80%, compared to only 56% in the pEF cell population. This corresponded with a greater extension in the duration of the G1 phase in the Bcl-2 cells, which was 1.7 days at the lowest dilution rate tested, compared to only 0.6 day for the pEF cell line. The durations of the G2/M and S phases remained constant throughout the culture. The maximum doubling time was 1.2 days in the pEF culture compared to 2.3 days in the Bcl-2 culture. Analysis of amino acids, ammonia and lactate concentrations indicated that the observed effects on cell cycle dynamics were probably not due to differences in the culture environment. It is suggested that the expression of Bcl-2 can effect G1 to S phase transition in continuously cycling cells, but this is only apparent at suboptimal growth rates.     

The effects of temperature and swimming speed on instantaneous fuel use and nitrogenous waste excretion of the Nile tilapia.

The effects of acclimation temperature (30 degrees, 20 degrees, and 15 degrees C) and swimming speed on the aerobic fuel use of the Nile tilapia (Oreochromis niloticus; 8-10 g, 8-9-cm fork length) were investigated using a respirometric approach. As acclimation temperature was decreased from 30 degrees C to 15 degrees C, resting oxygen consumption (Mo2) and carbon dioxide excretion (Mco2) decreased approximately twofold, while nitrogenous waste excretion (ammonia-N plus urea-N) decreased approximately fourfold. Instantaneous aerobic fuel usage was calculated from respiratory gas exchange. At 30 degrees C, resting Mo2 was fueled by 42% lipids, 27% carbohydrates, and 31% protein. At 15 degrees C, lipid use decreased to 21%, carbohydrate use increased greatly to 63%, and protein use decreased to 16%. These patterns at 30 degrees C and 15 degrees C in tilapia paralleled fuel use previously reported in rainbow trout acclimated to 15 degrees C and 5 degrees C, respectively. Temperature also had a pronounced effect on critical swimming speed (UCrit). Tilapia acclimated to 30 degrees C had a UCrit of 5.63+/-0. 06 body lengths/s (BL/s), while, at 20 degrees C, UCrit was significantly lower at 4.21+/-0.14 BL/s. Tilapia acclimated to 15 degrees C were unable or unwilling to swim. As tilapia swam at greater speeds, Mo2 increased exponentially; Mo2min and Mo2max were 5.8+/-0.6 and 21.2+/-1.5 micromol O2/g/h, respectively. Nitrogenous waste excretion increased to a lesser extent with swimming speed. At 30 degrees C, instantaneous protein use while swimming at 15 cm/s ( approximately 1.7 BL/s) was 23%, and at UCrit (5.6 BL/s), protein use dropped slightly to 17%. During a 48-h swim at 25 cm/s (2.7 BL/s, approximately 50% UCrit), Mo2 and urea excretion remained unchanged, while ammonia excretion more than doubled by 24 h and remained elevated 24 h later. These results revealed a shift to greater reliance on protein as an aerobic fuel during prolonged swimming.     

Bioenergetics of growth of a cyprinid, Phoxinus phoxinus (L.): the effect of ration and temperature on growth rate and efficiency

Growth of minnows, Phoxinus phoxinus , weighing 1-5.5 g was studied experimentally at five ration levels from starvation to ad libitum and four temperatures ranging from 5 to 15°C. The relationship between specific growth rate (SGR) and ration was a decelerating curve. SGR at maximum rations increased with increased temperature, but at restricted rations it decreased with increased temperature. Predictive models for the specific growth rates were developed using multiple regression. Maintenance rations and optimum rations both increased with increased temperature. Maintenance rations were less sensitive to temperature than optimum rations and mostly lay between 1 and 2% of body weight per day. Conversion efficiencies increased with increased ration from zero value at the maintenance ration to a peak at the optimum ration, then decreased with further increases in ration. At a given restricted ration level, conversion efficiencies generally decreased with increased temperature. At maximum rations, conversion efficiencies were relatively insensitive to temperature. Growth in wet weight, dry weight and energy content showed similar responses to ration, temperature and body weight.     

The effects of body mass and feeding on metabolic rate in small juvenile Atlantic cod

Apparent specific dynamic action (SDA) amplitude in young juvenile Atlantic cod Gadus morhua (1 to 8 g wet mass), fed a standardized meal and then exercised in a circular swimming respirometer at a constant swimming speed of 0·5 ± 0·3 body lengths s^-1, occurred within l h after feeding in all juveniles. SDA amplitude were 1·4 to 1·8 times higher in fed fish compared to unfed fish, and rates of oxygen consumption decreased as body mass increased. SDA duration had a tendency to decrease with increasing body mass and was shortest, at 6 h, in the smallest fish (1–1·5 g), but increased to 10–11 h in the largest fish. Apparent SDA in fed fish ( R _r) scaled with a mass exponent of 0·89, while maximum metabolic rate ( R _max) determined by chasing fish to exhaustion and then measuring oxygen consumption for 12 h, and unfed routine metabolic rate (R_r) scaled with a mass exponent of 0·79 and 0·76 respectively. Relative aerobic scope ( R _max– unfed R _r) did not appear to vary over the 1 to 8 g increase in wet mass. These results show that as body mass increased in young juvenile Atlantic cod: (1) apparent SDA ( R _f) increased more rapidly than R _max, and (2) apparent SDA took up >98% of the relative aerobic scope and that young Atlantic cod allocated most of the energy to growth, and left little for other metabolic activities.     

The reversible reduction of horse metmyoglobin by the iron(II) complex of trans-1,2-diaminocyclohexane-N,N,N,n-tetraacetate.

The reduction of metmyoglobin by the iron(II) complex of trans-1,2-diaminocyclohexane-N,N,N'N'-tetraacetate (FeCDTA2-) has been investigated. The equilibrium constant, measured spectrophotometrically, is 0.21 with a resulting reduction potential of 0.050 V for Mb0. The rate constant for the reduction is 28 M-1 sec-1 with a deltaH ++ of 13 kcal M-1 and deltaS ++ of -11 eu. Both CN- and OH- inhibit the reduction because of the relatively low reactivity of cyanometmyoglobin (Mb+CN-) and ionized metmyglobin (Mb+OH-). The rate constant for the reduction of Mb+CN- by FeCDTA2- is 4.0 X 10(-2) M-1 sec-1 and that for reduction of Mb+OH- is 4.8 M-1 sec-1. The nitric oxide complex of metmyoglobin is reduced with a rate constant of 10 M-1 sec-1. The kinetics of oxidation of oxymyoglobin by FeCDTA- were studied. The data are consistent with a mechanism where oxidation takes place entirely through the deoxy form. A rate constant of 1.45 X 10(2) M-1 sec-1 was calculated for the oxidation of deoxymyoglobin by FeCDTA-, in equilibrium constant and rate constant for reduction. The above data are discussed in terms of a simple outer-sphere reduction reaction.     

Bioenergetics of acclimation to permethrin (NRDC-143) by rainbow trout

Metabolic rates associated with sustained, prolonged and critical swimming speeds were examined in 10 g trout exposed to 5% 96 hr LC50 (0.75 microgram X l-1) and 10% 96 hr LC50 (1.50 micrograms X l-1) at 12 degrees C. Permethrin did not influence the metabolic cost for swimming at sustained and prolonged speeds. Basal metabolic rate increased on initial exposure to permethrin reaching maximum values after 7 days and declined to the control level after 13 days in 5% and after 32 days in 10% 96 hr LC50. Critical swimming speeds were adversely affected in a manner reflective of the effects of permethrin on basal metabolic rate. Elevation in basal metabolic rate in fish exposed to permethrin was a result of increased energy requirements due to physiological stress, detoxication and tissue repair.     

Spirillum swimming: theory and observations of propulsion by the flagellar bundle.

The hydrodynamics and energetics of helical swimming by the bacterium Spirillum sp. is analysed using observations from medium speed cine photomicrography and theory. The photographic records show that the swimming organism's flagellar bundles beat in a helical fashion just as other bacterial flagella do. The data are analysed according to the rotational resistive theory of Chwang & Wu (1971) in a simple-to-use parametric form with the viscous coefficients Cs and Cn calculated according to the method of Lighthill (1975). Results of the analysis show that Spirillum dissipated biochemical energy in performing work against fluid resistance to motion at an average rate of about 6 X 10(-8) dyne cm s-1 with some 62-72% of the power dissipation due to the non-contractile body. These relationships yield a relatively low hydromechanical efficiency which is reflected in swimming speeds much smaller than a representative eukaryote. In addition the Cn/Cs ratio for the body is shown to lie in the range 0-86-1-51 and that for the flagellar bundle in the range 1-46-1-63. The implications of the power calculations for the Berg & Anderson (1973) rotating shaft model are discussed and it is shown that a rotational resistive theory analysis predicts a 5-cross bridge M ring for each flagellum of Spirillum.     

Power isn't everything: muscle function and energetic costs during steady swimming in Atlantic cod (Gadus morhua)

Power produced by red myotomal muscles of fish during cruise swimming appears seldom maximized, so we sought to investigate whether economy may impact or dominate muscle function. We measured cost of transport (COT) using oxygen consumption and the strain trajectories and electromyographic activity of red muscle measured at anterior (ANT) and posterior (POST) locations while Atlantic cod (Gadus morhua) swam steadily at speeds between 0.3 and 1.0 body lengths (BL) s(-1). We then measured the power produced by isolated segments of red muscle when activated either as in the swimming cod or such that maximal net power was produced. Patterns of activation during swimming were not optimal for power output and were highly variable between tail beats, particularly at the ANT location and at slow swim speeds. Muscle strain amplitude did not increase until swimming speed reached 0.9 (ANT) versus 0.5 (POST) BL s(-1). These limited power to only 53% (ANT) and 71% (POST) of maximum at slower swim speeds and to 70%-80% of maximum at high swim speeds. COT (resting metabolism subtracted) was minimal at the slowest swim speed, surprisingly, where power was most impaired by activation and strain. Thus, production of powered forces for maneuverability/stability appeared to greatly impact red muscle function during cruise swimming in cod, particularly at slow speeds and in ANT muscle.     

Growth and morphological development of laboratory-reared larval and juvenile climbing perch <Emphasis Type="Italic">Anabas testudineus</Emphasis>

Morphological development, including fin and labyrinth organ, body proportions and pigmentation, in laboratory-reared larval and juvenile climbing perch Anabas testudineus was described and behavioral features under rearing condition were observed. Body lengths (BL) of larvae and juveniles were 1.9 ± 0.1 (mean ± SD) mm just after hatching (day-0), 8.7 ± 1.3 mm on day-19, reaching 18.4 ± 2.1 mm on day-35 after hatching. Aggregate fin ray numbers attained full complements in juveniles larger than 8.3 mm BL. Preflexion larvae started feeding on day-2 following formation of the upper and lower jaws, the yolk being completely absorbed by day-7 after hatching. Teeth appeared in flexion larvae larger than 5 mm BL on day-6, with cannibalism starting shortly after and continuing with further growth. Melanophores on the body increased with growth, a large dark spot developing on the lateral midline around caudal margin of the body in the postflexion and juvenile stages. The labyrinth organ differentiated in postflexion larvae larger than 7.2 mm BL on day-16, with air-breathing starting at the same time. Body proportions attained constant in postflexion larvae larger than 7.0 mm BL, and habitat of fish shifted from bottom to mid-layer. With the exception of fin ray numbers, the above morphological developments corresponded to behavioral shifts that occurred in the postflexion stage (ca. 7 mm BL), their subsequent continuity illustrating that the species possessed most juvenile-equivalent functions from ca. 7 mm BL.     

Thermoregulatory responses to low-intensity prolonged swimming in water at various temperatures and treadmill walking on land

The purpose of the present study was to examine the effect of water temperature on the human body during low-intensity prolonged swimming. Six male college swimmers participated in this study. The experiments consisted of breast stroke swimming for 120 minutes in 23 degrees C, 28 degrees C and 33 degrees C water at a constant speed of 0.4 m.sec-1 in a swimming flume. The same subjects walked on a treadmill at a rate of approximately 50% of maximal oxygen uptake (VO2max) at the same relative intensity as the three swimming trials. Rectal temperature (Tre) in 33 degrees C water was unchanged during swimming for 120 minutes. Tre during treadmill walking increased significantly compared to the three different swimming trials. Tre, mean skin temperature (Tsk) and mean body temperature (Tb) in 23 degrees C and 28 degrees C water decreased significantly more than in both the 33 degrees C water and walking on land. VO2 during swimming in 23 degrees C water increased more than during swimming in the 28 degrees C and 33 degrees C trials; however, there were no significant differences in VO2 between the 23 degrees C swimming trial and treadmill walking. Heart rate (HR) during treadmill walking on land increased significantly compared with HR during the three swimming trials. Plasma adrenaline concentration at the end of the treadmill walking was higher than that at the end of each of the three swimming trials. Noradrenaline concentrations at the end of swimming in the 23 degrees C water and treadmill walking were higher than those during the other two swimming trials. Blood lactate concentration during swimming in 23 degrees C water was higher than that during the other two swimming trials and walking on land. These results suggest that the balance of heat loss and heat production is maintained in the warm water temperature. Therefore, a relatively warm water temperature may be desirable when prolonged swimming or other water exercise is performed at low intensity.