Fasting goldfish, Carassius auratus, and common carp, Cyprinus carpio, use different metabolic strategies when swimming

Fish need to balance their energy use between digestion and other activities, and different metabolic compromises can be pursued. We examined the effects of fasting (7days) on metabolic strategies in goldfish and common carp at different swimming levels. Fasting had no significant effect on swimming performance (U(crit)) of either species. Feeding and swimming profoundly elevated total ammonia (T(amm)) excretion in both species. In fed goldfish, this resulted in increased ammonia quotients (AQ), and additionally plasma and tissue ammonia levels increased with swimming reflecting the importance of protein contribution for aerobic metabolism. In carp, AQ did not change since oxygen consumption (MO(2)) and T(amm) excretion followed the same trend. Plasma ammonia did not increase with swimming suggesting a balance between production and excretion rate except for fasted carp at U(crit). While both species relied on anaerobic metabolism during exhaustive swimming, carp also showed increased lactate levels during routine swimming. Fasting almost completely depleted glycogen stores in carp, but not in goldfish. Both species used liver protein for basal metabolism during fasting and muscle lipid during swimming. In goldfish, feeding metabolism was sacrificed to support swimming metabolism with similar MO(2) and U(crit) between fasted and fed fish, whereas in common carp feeding increased MO(2) at U(crit) to sustain feeding and swimming independently.     

The effects of dissolved oxygen levels on the metabolic interaction between digestion and locomotion in Cyprinid fishes with different locomotive and digestive performances

To test whether the effects of water oxygen concentration ([O(2)]) on the metabolic interaction between locomotion and digestion differ between fish species with different locomotive and digestive behaviours in normoxia, we investigated the swimming performance of fasted and fed fish at water [O(2)] of 1, 2 and 8 (normoxia) mg L(-1) (2.5, 5 and 20 kPa) at 25°C in three juvenile Cyprinidae fish species: goldfish (Carassius auratus), common carp (Cyprinus carpio) and qingbo (Spinibarbus sinensis). Digestion, taxon and water [O(2)] all had significant effects on the pre-exercise oxygen consumption rate [Formula: see text] and the swimming performance (P < 0.05). Among the three fishes, qingbo showed the highest swimming performance and the lowest feeding [Formula: see text] at the saturated water [O(2)], and its active oxygen consumption rate [Formula: see text] and critical swimming speed (U (crit)) decreased the most with decreases in water [O(2)]. Qingbo exhibited a locomotion-priority metabolic mode at all three water [O(2)]. Digestion was sacrificed to locomotion in a postprandial swimming situation, but fed qingbo could not maintain their U (crit) at water [O(2)] of 2 and 1 mg L(-1). Goldfish showed the lowest swimming performance and the highest feeding [Formula: see text] at the saturated water [O(2)]. They exhibited a digestion-priority metabolic mode at high water [O(2)]. However, with a decrease in water [O(2)], the feeding [Formula: see text] decreased more acutely than the respiratory capacity; thus, digestion and locomotion performed independently in a postprandial swimming situation (i.e., an additive metabolic mode) at a water [O(2)] of 1 mg L(-1). The common carp showed moderate and balanced swimming performance and feeding [Formula: see text] at the saturated water [O(2)], and exhibited an additive metabolic mode at all 3 water [O(2)], because digestion, swimming and respiratory capacities decreased in parallel with the decrease in water [O(2)].     

Gastrointestinal blood flow and postprandial metabolism in swimming sea bass Dicentrarchus labrax

In trout and salmon, the metabolic costs of exercise and feeding are additive, which would suggest that gastrointestinal blood flow during exercise is maintained to preserve digestive and absorptive processes related to the specific dynamic action (SDA) of food. However, in most published studies, gastrointestinal blood flow drops during swimming, hypoxia, and general stress. To test whether gastrointestinal blood flow is spared during exercise after feeding, sea bass were instrumented with flow probes to measure cardiac output and celiacomesenteric blood flow while swimming in a respirometer before and after feeding. Swimming at 2 body lengths per second (bl s(-1)) increased metabolic rate considerably more than did feeding (208% vs. 32% increase, respectively, relative to resting), and a similar pattern was observed for cardiac output. In unfed fish, resting gastrointestinal blood flow was 13.8+/-0.5 mL min(-1) kg(-1). After feeding, resting gastrointestinal blood flow increased by 82% but then decreased progressively with increasing swimming speeds. At 2 bl s(-1), gastrointestinal blood flow in fed fish was not significantly different compared with that in unfed swimming fish, and, therefore, the data do not support the gastrointestinal sparing hypothesis. The magnitude of the SDA was maintained despite the decrease in gastrointestinal blood flow and the consequent reduction in oxygen supply to the gut. An estimate of maximal oxygen flow to the gastrointestinal tract after feeding yielded 2.6 mmol O(2) h(-1) kg(-1), but this amount is not able to cover the oxygen demand of 3.16 mmol O(2) h(-1) kg(-1). Therefore, the SDA must reflect metabolic processes in tissues other than those directly perfused by the celiacomesenteric artery.     

溶氧水平对鲫鱼代谢模式的影响

为了探讨水体溶氧水平对鲫幼鱼(Carassius carassius)运动、消化能力及其交互作用的影响,在(25.0±0.5)℃温度条件下,测定了8(饱和溶氧水平)、2和1mg/L溶氧水平下摄食(饱足摄食)和空腹组(空腹2 d)鲫鱼的临界游泳速度(Ucrit)、运动前耗氧率(MO2pre-exercise)、活跃耗氧率(MO2active)和代谢范围(MS)。摄食诱导的耗氧率上升在各溶氧水平下无显著差异。在饱和溶氧水平下,摄食组和空腹组的Ucrit没有显著差异,但在1和2 mg/L条件下,摄食组的Ucrit显著低于空腹组(P<0.05)。在饱和溶氧水平条件下,消化和运动诱导的耗氧率上升在各个游泳水平均能完全叠加,且摄食组鱼类与空腹组鱼类具有相似的MS和Ucrit和更高的MO2active,提示鲫鱼在常氧下为添加代谢模式。随着溶氧水平下降至2和1mg/L,呼吸能力(摄食组的MO2active)对溶氧水平下降较运动耗氧率更为敏感,消化诱导的耗氧率增加只能在较低游泳速度叠加,与空腹组鱼类比较,摄食组鱼类的MS和Ucrit显著下降,MO2active无显著差异,提示低氧下消化和运动对氧气需求竞争的加剧使其代谢模式转化为消化优先。     

The effects of temperature on metabolic interaction between digestion and locomotion in juveniles of three cyprinid fish (Carassius auratus, Cyprinus carpio and Spinibarbus sinensis)

To test whether the effects of temperature on the metabolic mode changed among different fish species, we investigated the specific dynamic action (SDA) and swimming performance of fasting and fed fish at 15 and 25°C in three juvenile Cyprinidae fish species: goldfish (Carassius auratus), common carp (Cyprinus carpio) and qingbo (Spinibarbus sinensis). Both taxon and temperature had significant effects on the resting oxygen consumption rate (M˙O(rest)), SDA and swimming performance (p<0.05). In addition, the effect of temperature differed significantly among the different species (interaction effect, p<0.05). Under the low temperature condition, digestion had no effect on either critical swimming speed (U(crit)) or the active MO(2) (MO(active)) for all fish species (additive metabolic mode). When the temperature was increased from 15 to 25°C, the metabolic scope (MS) for digestion increased approximately 182, 49 and 17%, and the MS for locomotion increased approximately 129, 58 and 138% in goldfish, common carp and qingbo, respectively. The total metabolic demands for both digestion and locomotion (i.e., the sum of digestive MS and locomotive MS) increased approximately 143, 56 and 112% in goldfish, common carp and qingbo, respectively. The total MS for both digestion and locomotion (the difference between MO(active) in fed fish and MO(rest) in fasting fish) increased approximately 106, 58 and 78% in goldfish, common carp and qingbo, respectively. Thus, the MS for locomotion in fed goldfish decreased due to the large increase in digestive function at the high temperature, and the U(crit) of fed goldfish decreased by 11% compared to that of fasting fish (p<0.05) (digestion-priory metabolic mode). The metabolic mode of qingbo changed to locomotion-priority mode, as illustrated by the large increase in locomotive MS in response to the increase in temperature. In the common carp, temperature had no effect on metabolic mode as illustrated by the parallel increases in cardio-respiratory capacity and metabolic capacity of digestive and locomotive organs. A discussion on the changes in metabolic mode in response to temperature and its possible relationship with the metabolic characteristics of a given fish species was also documented in this paper.     

锦鲫的摄食代谢与运动代谢及其相互影响

为了探讨锦鲫(Carassius auratus)幼鱼摄食后特殊动力作用(SDA)的变化特征及运动代谢与摄食代谢之间的相互影响,实验首先灌喂锦鲫4%体重的饲料和等体积的纤维素(湿重),测定灌喂前后的耗氧率;另设灌喂饲料、灌喂纤维素、空腹组(对照组)3个组,测定3组的临界游泳速度(Ucrit)和运动耗氧率(MO2);然后在70%、0%临界游泳速度下,分别测定饱足摄食组和空腹组的耗氧率。结果显示:1灌喂饲料后代谢率快速上升,达到峰值后又迅速下降,代谢时间较短,没有一个相对稳定的平台期,灌喂纤维素后代谢率没有显著性变化(P0.05)。提示锦鲫幼鱼的特殊动力作用功率曲线为一个典型的"三角型"模型,且在特殊动力作用总耗能中,生化特殊动力作用占特殊动力作用总耗能的绝大部分,而机械特殊动力作用只占特殊动力作用的极少部分。2锦鲫幼鱼在摄食后临界游泳速度显著下降(P0.05),代谢率显著升高(P0.05)。摄食后的运动过程中,代谢率从摄食开始到代谢率回落至空腹组代谢的标准误范围内的首个数据所对应的时间长度均为6.5 h,且摄食代谢无显著性差异。提示,对锦鲫幼鱼来说,摄食代谢降低了其运动能力,而运动代谢并没有影响摄食代谢。     

溶氧水平对瓦氏黄颡鱼幼鱼静止耗氧率和临界游泳运动能力的影响

为了研究瓦氏黄颡鱼(Peltebagrus vachelli)在不同溶氧水平(DO)下的游泳运动能力、限制性机制及能量适应对策, 在25℃分别对不同溶氧水平(125%、100%、75%、50%和25% 空气饱和度)条件下瓦氏黄颡鱼幼鱼静止耗氧率、临界游泳速度(Ucrit)、活跃耗氧率进行了测定。研究发现瓦氏黄颡鱼的静止耗氧率随溶氧水平下降而显著下降(P2crit)为14.52%空气饱和度(1.16 mg/L)。当溶氧水平从100%下降到25%空气饱和度时, 其活跃耗氧率随溶氧的下降而显著下降(PPP<0.05)。研究结果提示: 在低氧条件下, 瓦氏黄颡鱼的临界游泳速度受中心的心鳃系统的限制, 而在常氧条件下,受外周的运动系统(肌肉组织)的限制。       

Effect of fasting on nychthemeral concentrations of plasma growth hormone (GH), insulin-like growth factor I (IGF-I), and cortisol in channel catfish (Ictalurus punctatus)

This experiment was conducted to characterize the effect of fasting versus satiety feeding on plasma concentrations of GH, IGF-I, and cortisol over a nychthemeron. Channel catfish fingerlings were acclimated for two weeks under a 12L:12D photoperiod, then fed or fasted for 21 d. On day 21, blood samples were collected every 2 h for 24 h. Weight of fed fish increased an average of 66.2% and fasted fish lost 21.7% of body weight on average. Average nychthemeral concentrations of plasma GH were not significantly different between fed (24.7 ng/mL) and fasted (26.8 ng/mL) fish, but average nychthemeral IGF-I concentrations were higher in fed (23.4 ng/mL) versus fasted (17.8 ng/mL) fish. An increase in plasma IGF-I concentrations was observed in fasted fish 2 h after a peak in plasma GH, but not in fed fish. Average nychthemeral plasma cortisol concentrations were higher in fed (14.5 ng/mL) versus fasted (11.0 ng/mL) fish after 21 d. Significant fluctuations and a postprandial increase in plasma cortisol were observed in fed fish and there was an overall increase in plasma cortisol of both fasted and fed fish during the scotophase. The present experiment indicates little or no effect of 21-d fasting on plasma GH levels but demonstrates fasting-induced suppression of plasma IGF-I and cortisol levels in channel catfish.     

速度增量及持续时间对瓦氏黄颡鱼幼鱼临界游泳速度的影响

为了考查速度增量(△v)和持续时间(△t)2个参数变化对鱼类临界游泳速度(critical swimming speed,Ucrit)的影响,于25℃条件下,首先以15%临界游泳速度作为△v,设置不同的持续时间(△t:5,10,15,30,60min);再以20min作为△t,设置不同的速度增量(△v:5%,10%,15%,20%,30%Ucrit),测定瓦氏黄颡鱼(Pelteobag vachelli)幼鱼的临界游泳速度。结果表明:随△t的增加Ucrit整体呈下降趋势,△t由5min增加至60min,绝对游泳速度(absolute swimming speed,Ua)由(47.4±0.7)cm.s-1下降至(39.1±1.5)cm.s-1(P<0.05),除15和30min无显著差异外,其余各组间均存在显著差异(P<0.05);而△v由5%提高至10%Ucrit,Ua由(44.1±0.6)cm.s-1显著增加至(47.0±0.4)cm.s-1(P<0.05),15%和20%Ucrit的Ua分别为(45.2±0.2)cm.s-1和(46.3±0.8)cm.s-1,与10%Ucrit组之间均无显著差异,但△v增...     

Effect of a commercial trout diet on liver ultrastructure of fed and fasted yearling coho salmon, Oncorhynchus kisutch Walbaum

Yearling coho salmon were fed either a commercial trout (TC) diet or a diet consisting of homogenized adult Pacific Ocean coho salmon (PS), supplemented with vitamins and minerals. The hepatosomatic index of the TC-fed fish killed 12 h after the last feed or after 4 or 8 weeks of fasting were significantly larger ( P 0.05) than comparable PS-fed groups.
'Light' and'dark' hepatocyte cell types were evident in all groups although the dark cells were less numerous in the fasted fish. Hepatocytes of fasted fish contained markedly more endoplasmic reticulum than fed fish. Hepatocytic glycogen content of the TC-fed fish was higher than in PS-fed fish. Whereas in the TC-fed group hepatic glycogen was still evident in fish fasted for 8 weeks, the hepatocytes of the fasted PS-fed group contained little or no glycogen. The suitability of commercial fish diets for salmonids is discussed.     

Fasting modulates metabolic responses to cortisol, GH and IGF‐I in Arctic charr hepatocytes

Hepatocytes in primary culture from fed and 2 month fasted Arctic charr Salvelinus alpinus were exposed to physiological doses of either cortisol, salmon growth hormone (GH), salmon insulin‐like growth factor‐I (IGF‐I) or a combination of salmon GH and salmon IGF‐I. Fasting significantly lowered medium glucose levels compared to the fed fish, but had no significant effects on hepatocyte glycogen content or on the activities of enzymes involved in the intermediary metabolism. Cortisol treatment had no effect on hepatocyte glycogen content or on the enzyme activities investigated, but resulted in a significant increase in medium glucose concentration in hepatocytes isolated from fasted, but not fed fish. GH and IGF‐I treatments, both singly and in combination, significantly increased the glycogen content of hepatocytes isolated from fed fish, with less pronounced effects on hepatocytes isolated from fasted fish. The combination of GH and IGF‐I significantly increased lactate dehydrogenase activity regardless of the feeding state and significantly reduced the phosphenolpyruvate carboxykinase activity and medium glucose concentration in hepatocytes isolated from fed fish. Further, GH and IGF‐I significantly increased the activities of alanine aminotransferase and aspartate aminotransferase in hepatocytes isolated from fasted fish, but not fed fish. There were no effects of GH, IGF‐I, or their combination, on glucose 6‐phosphate dehydrogenase or 3‐hydroxyacyl‐CoA dehydrogenase activities. The results demonstrated that nutritional status of the animal modulates hepatocyte responsiveness to metabolic hormones, and suggested a role for GH and IGF‐I in hepatic glycogen conservation.     

Behavioral Thermoregulation by Juvenile Spring and Fall Chinook Salmon, Oncorhynchus Tshawytscha, during Smoltification

Fall chinook salmon evolved to emigrate during the summer months. The shift in the temperature preference we observed in smolting fall chinook but not spring chinook salmon may reflect a phylogenetic adaptation to summer emigration by (1) providing directional orientation as fall chinook salmon move into the marine environment, (2) maintaining optimal gill function during emigration and seawater entry, and/or (3) resetting thermoregulatory set-points to support physiological homeostasis once smolted fish enter the marine environment. Phylogenetically determined temperature adaptations and responses to thermal stress may not protect fall chinook salmon from the recent higher summer water temperatures, altered annual thermal regimes, and degraded cold water refugia that result from hydropower regulation of the Columbia and Snake rivers. The long-term survival of fall chinook salmon will likely require restoration of normal annual thermographs and rigorous changes in land use practices to protect critical thermal refugia and control maximum summer water temperatures in reservoirs.     

Inclusion of low amounts of fructose with an intraportal glucose load increases net hepatic glucose uptake in the presence of relative insulin deficiency in dog

The effect of small amounts of fructose on net hepatic glucose uptake (NHGU) during hyperglycemia was examined in the presence of insulinopenia in conscious 42-h fasted dogs. During the study, somatostatin (0.8 microg.kg(-1).min(-1)) was given along with basal insulin (1.8 pmol.kg(-1).min(-1)) and glucagon (0.5 ng.kg(-1).min(-1)). After a control period, glucose (36.1 micromol.kg(-1).min(-1)) was continuously given intraportally for 4 h with (2.2 micromol.kg(-1).min(-1)) or without fructose. In the fructose group, the sinusoidal blood fructose level (nmol/ml) rose from <16 to 176 +/- 11. The infusion of glucose alone (the control group) elevated arterial blood glucose (micromol/ml) from 4.3 +/- 0.3 to 11.2 +/- 0.6 during the first 2 h after which it remained at 11.6 +/- 0.8. In the presence of fructose, glucose infusion elevated arterial blood glucose (micromol/ml) from 4.3 +/- 0.2 to 7.4 +/- 0.6 during the first 1 h after which it decreased to 6.1 +/- 0.4 by 180 min. With glucose infusion, net hepatic glucose balance (micromol.kg(-1).min(-1)) switched from output (8.9 +/- 1.7 and 13.3 +/- 2.8) to uptake (12.2 +/- 4.4 and 29.4 +/- 6.7) in the control and fructose groups, respectively. Average NHGU (micromol.kg(-1).min(-1)) and fractional glucose extraction (%) during last 3 h of the test period were higher in the fructose group (30.6 +/- 3.3 and 14.5 +/- 1.4) than in the control group (15.0 +/- 4.4 and 5.9 +/- 1.8). Glucose 6-phosphate and glycogen content (micromol glucose/g) in the liver and glucose incorporation into hepatic glycogen (micromol glucose/g) were higher in the fructose (218 +/- 2, 283 +/- 25, and 109 +/- 26, respectively) than in the control group (80 +/- 8, 220 +/- 31, and 41 +/- 5, respectively). In conclusion, small amounts of fructose can markedly reduce hyperglycemia during intraportal glucose infusion by increasing NHGU even when insulin secretion is compromised.     

Osmoregulatory physiology of pyloric ceca: regulated and adaptive changes in chinook salmon

Functions of the anatomically obvious, yet peculiar, pyloric ceca of the fish gut have been a source of conjecture for over two millennia since Aristotle hypothesized on digestive utilities. Here, we demonstrate regulated and adaptive changes in osmoregulatory physiology of ceca from chinook salmon (Onchorhynchus tshawytscha). Transfer of salmon from freshwater to seawater (both short- and long-term) significantly stimulated both fluid uptake from 5.1 to 8.3-9.3 microl/cm2/hr and also Na+/K+ -ATPase from 6.5 to 8.3-9.6 micromol/ADP/mg protein/hr. Similar changes were induced with implants of cortisol, which resulted in high physiological cortisol levels in plasma. Ceca, which can number about 200 in chinook salmon, were estimated to account for the majority of fluid uptake capacity of the intestine and, after long-term seawater adaptation, the proportion of uptake capacity was sixfold higher. Transport physiology of ceca is thus under environmental and endocrine control indicative of an important role in salt and water homeostasis.     

Hepatic autoregulation: response of glucose production and gluconeogenesis to increased glycogenolysis

The effect of increased glycogenolysis, simulated by galactose's conversion to glucose, on the contribution of gluconeogenesis (GNG) to hepatic glucose production (GP) was determined. The conversion of galactose to glucose is by the same pathway as glycogen's conversion to glucose, i.e., glucose 1-phosphate --> glucose 6-phosphate --> glucose. Healthy men (n = 7) were fasted for 44 h. At 40 h, hepatic glycogen stores were depleted. GNG then contributed approximately 90% to a GP of approximately 8 micromol.kg(-1).min(-1). Galactose, 9 g/h, was infused over the next 4 h. The contribution of GNG to GP declined from approximately 90% to 65%, i.e., by approximately 2 micromol.kg(-1).min(-1). The rate of galactose conversion to blood glucose, measured by labeling the infused galactose with [1-(2)H]galactose (n = 4), was also approximately 2 micromol.kg(-1).min(-1). The 41st h GP rose by approximately 1.5 micromol.kg(-1).min(-1) and then returned to approximately 9 micromol.kg(-1).min(-1), while plasma glucose concentration increased from approximately 4.5 to 5.3 mM, accompanied by a rise in plasma insulin concentration. Over 50% of the galactose infused was accounted for in blood glucose and hepatic glycogen formation. Thus an increase in the rate of GP via the glycogenolytic pathway resulted in a concomitant decrease in the rate of GP via GNG. While the compensatory response to the galactose administration was not complete, since GP increased, hepatic autoregulation is operative in healthy humans during prolonged fasting.     

Ontogenetic variations in the type and size of prey consumed by juvenile coho,Oncorhynchus kisutch,and chinook,O. tshawytscha,salmon

Synopsis Stomach contents of juvenile coho,Oncorhynchus kisutch, and chinook,O. tshawytscha, salmon collected in purse seines off the coast of Washington and Oregon were examined for variations related to predator size. There was a general trend toward increasing consumption of fish with increasing body size, due mainly to the increase in northern anchovy biomass consumed by the larger salmon. Most of the major prey taxa showed significant differences among the size classes examined for both salmon species. There was a direct relationship between predator and prey size for both coho and chinook, but considerable variation was found in prey length consumed within each size class. Prey width did not provide as good a fit as prey length for either species. In general, coho consumed larger fish prey in relation to their body length than chinook but there were substantial differences by month or year of collection.     

Effects of nutritional status on metabolic rate, exercise and recovery in a freshwater fish

The influence of feeding on swimming performance and exercise recovery in fish is poorly understood. Examining swimming behavior and physiological status following periods of feeding and fasting is important because wild fish often face periods of starvation. In the current study, researchers force fed and fasted groups of largemouth bass (Micropterus salmoides) of similar sizes for a period of 16 days. Following this feeding and fasting period, fish were exercised for 60 s and monitored for swimming performance and physiological recovery. Resting metabolic rates were also determined. Fasted fish lost an average of 16 g (nearly 12%) of body mass, while force fed fish maintained body mass. Force fed fish swam 28% further and required nearly 14 s longer to tire during exercise. However, only some physiological conditions differed between feeding groups. Resting muscle glycogen concentrations was twofold greater in force fed fish, at rest and throughout recovery, although it decreased in both feeding treatments following exercise. Liver mass was nearly three times greater in force fed fish, and fasted fish had an average of 65% more cortisol throughout recovery. Similar recovery rates of most physiological responses were observed despite force fed fish having a metabolic rate 75% greater than fasted fish. Results are discussed as they relate to largemouth bass starvation in wild systems and how these physiological differences might be important in an evolutionary context.     

Effects of rapid experimental temperature increases on acute physiological stress and behaviour of stream dwelling juvenile chinook salmon

We experimentally heated small streams in summer and investigated the short-term behavioural changes and physiological stress responses of juvenile chinook salmon (Oncorhynchus tshawytscha). We rapidly raised temperatures ∼1–4 °C for 1.5 h above ambient levels of ∼7–15 °C in groundwater fed tributary streams and ∼19–23 °C in side-channel streams. Juvenile chinook rearing in groundwater fed tributaries were generally unaffected behaviourally; however, we found that temperature increase caused fish in the tributary trials to be physiologically stressed (elevations in mean cortisol concentrations ranged from 116% to 253%). Side-channel trials caused some mortality of juvenile chinook and a stronger display of behaviours indicative of stress and avoidance such as erratic swimming, abnormal posture, and aggregative behaviour. Foraging rates increased over 56 times in response to heating in side-channel trials. Cortisol levels did not increase in side-channel trials, but rather showed a trend to levels below control values suggesting an impaired stress response possibly due to chronic stress. Our results may reflect conservative responses in terms of what we may find with other salmonid species since juvenile chinook have been described as the most tolerant of the Pacific salmon species to elevated temperatures.     

Metabolism and thermoregulation during fasting in king penguins, Aptenodytes patagonicus, in air and water

We measured oxygen consumption rate (Vo(2)) and body temperatures in 10 king penguins in air and water. Vo(2) was measured during rest and at submaximal and maximal exercise before (fed) and after (fasted) an average fasting duration of 14.4 +/- 2.3 days (mean +/- 1 SD, range 10-19 days) in air and water. Concurrently, we measured subcutaneous temperature and temperature of the upper (heart and liver), middle (stomach) and lower (intestine) abdomen. The mean body mass (M(b)) was 13.8 +/- 1.2 kg in fed and 11.0 +/- 0.6 kg in fasted birds. After fasting, resting Vo(2) was 93% higher in water than in air (air: 86.9 +/- 8.8 ml/min; water: 167.3 +/- 36.7 ml/min, P < 0.01), while there was no difference in resting Vo(2) between air and water in fed animals (air: 117.1 +/- 20.0 ml O(2)/min; water: 114.8 +/- 32.7 ml O(2)/min, P > 0.6). In air, Vo(2) decreased with M(b), while it increased with M(b) in water. Body temperature did not change with fasting in air, whereas in water, there were complex changes in the peripheral body temperatures. These latter changes may, therefore, be indicative of a loss in body insulation and of variations in peripheral perfusion. Four animals were given a single meal after fasting and the temperature changes were partly reversed 24 h after refeeding in all body regions except the subcutaneous, indicating a rapid reversal to a prefasting state where body heat loss is minimal. The data emphasize the importance in considering nutritional status when studying king penguins and that the fasting-related physiological changes diverge in air and water.     

Routine and active metabolic rates of migrating adult wild sockeye salmon (Oncorhynchus nerka Walbaum) in seawater and freshwater

We present the first data on the differences in routine and active metabolic rates for sexually maturing migratory adult sockeye salmon (Oncorhynchus nerka) that were intercepted in the ocean and then held in either seawater or freshwater. Routine and active oxygen uptake rates (MO2) were significantly higher (27%-72%) in seawater than in freshwater at all swimming speeds except those approaching critical swimming speed. During a 45-min recovery period, the declining postexercise oxygen uptake remained 58%-73% higher in seawater than in freshwater. When fish performed a second swim test, active metabolic rates again remained 28%-81% higher for fish in seawater except at the critical swimming speed. Despite their differences in metabolic rates, fish in both seawater and freshwater could repeat the swim test and reach a similar maximum oxygen uptake and critical swimming speed as in the first swim test, even without restoring routine metabolic rate between swim tests. Thus, elevated MO2 related to either being in seawater as opposed to freshwater or not being fully recovered from previous exhaustive exercise did not present itself as a metabolic loading that limited either critical swimming performance or maximum MO2. The basis for the difference in metabolic rates of migratory sockeye salmon held in seawater and freshwater is uncertain, but it could include differences in states of nutrition, reproduction, and restlessness, as well as ionic differences. Regardless, this study elucidates some of the metabolic costs involved during the migration of adult salmon from seawater to freshwater, which may have applications for fisheries conservation and management models of energy use.