Metabolic measurements and parameter estimations for bioenergetics modelling of Pacific Chub Mackerel Scomber japonicus

As a crucial step in developing a bioenergetics model for Pacific Chub Mackerel Scomber japonicus (hereafter chub mackerel), parameters related to metabolism, the largest dissipation term in bioenergetics modelling, were estimated. Swimming energetics and metabolic data for nine chub mackerel were collected at 14°C, a low temperature within the typical thermal range of this species, using variable‐speed swim‐tunnel respirometry. These new data were combined with previous speed‐dependent metabolic data at 18 and 24°C and single‐speed (1 fork length per second: FL/s) metabolic data at 15 and 20°C to estimate respiration parameters for model development. Based on the combined data, the optimal swimming speed (the swimming speed with the minimum cost of transport, U_opt) was 42.5 cm/s (1.5–3.0 FL/s or 2.1 ± 0.4 FL/s) and showed no significant dependence on temperature or fish size. The daily mass‐specific oxygen consumption rate (R, g O₂ g fish^?1 day^?1) was expressed as a function of fish mass (W), temperature (T) and swimming speed (U): R = 0.0103W^?0.490 e^(0.0457T) e^(0.0235U). Compared to other small pelagic fishes such as Pacific Herring Clupea harengus pallasii, Pacific Sardine Sardinops sagax and various anchovy species, chub mackerel respiration showed a lower dependence on fish mass, temperature and swimming speed, suggesting a greater swimming ability and lower sensitivity to environmental temperature variation.     

Behavioral responses of tilapia (Oreochromis niloticus) to acute fluctuations in dissolved oxygen levels as monitored by computer vision

Behavioral and ventilatory parameters have the possibility of predicting the stress state of fish in vivo and in situ. This paper presents a new image-processing algorithm for quantifying the average swimming speed of a fish school in an aquarium. This method is based on the alteration in projected area caused by the movement of individual fish during frame sequences captured at given time intervals. The image enhancement method increases the contrast between fish and background, and is thus suitable for use in turbid aquaculture water. Behavioral parameters (swimming activity and distribution parameters) and changes in ventilation frequency (VF) of tilapia (Oreochromis niloticus) responded to acute fluctuations in dissolved oxygen (DO) which were monitored continuously in the course of normoxia, falling DO level, maintenance of hypoxia (three levels of 1.5, 0.8 and 0.3 mg l⁻¹) and subsequent recovery to normoxia. These parameters responded sensitively to acute variations in DO level; they displayed significant changes (P < 0.05) during severe hypoxia (0.8 and 0.3 mg l⁻¹ level) compared with normoxic condition, but there was no significant difference under conditions of mild hypoxia (1.5 mg l⁻¹ level). There was no significant difference in VF between two levels of severe hypoxia 0.8 and 0.3 mg l⁻¹ level during the low DO condition. The activity and distribution parameters displayed distinguishable differences between the 0.8 and 0.3 mg l⁻¹ levels. The behavioral parameters are thus capable of distinguishing between different degrees of severe hypoxia, though there were relatively large fluctuations.     

Effect of Sublethal Hypoxia on the Immune Response and Susceptibility of Channel Catfish, Ictalurus punctatus, to Enteric Septicemia

The effect of sublethal hypoxia exposure on stress and immune responses and susceptibility to Edwardsiella ictaluri infection in juvenile channel catfish, Ictalurus punctatus, was investigated. Fish were monitored for temporal changes in glucose and cortisol concentrations before, during, and after 2 h exposure to sublethal hypoxia (<2 mg/L dissolved oxygen [DO]) and when maintained under normoxic conditions (6.0 ± 0.3 mg/L DO). Both blood glucose and plasma cortisol increased significantly in response to hypoxic conditions. Fish exposed to hypoxic or normoxic conditions were challenged with a high dose (1.3 × 10⁷ colony‐forming units [CFU]/mL) or a low dose (1.3 × 10⁵ CFU/mL) of E. ictaluri or sterile culture broth by 30‐min immersion bath. Approximately 1% of fish in both the normoxic and the hypoxic groups died when challenged with the low dose of E. ictaluri. However, when challenged with the high dose of E. ictaluri, catfish exposed to hypoxic conditions had significantly higher cumulative mortality (36 ± 12.1%) than those maintained under normoxic conditions (12 ± 1.1%). Total hemolytic complement and bactericidal activities and antibody response were lower in hypoxia‐exposed channel catfish, indicating that increased susceptibility of channel catfish to E. ictaluri may be the result of the immunosuppressive effects of the stress response to hypoxia.     

Effect of lordosis on the swimming performance of juvenile sea bass (Dicentrarchus labrax L.)

The critical swimming speed (U_crit, cm s⁻¹) value of normal juvenile sea bass (Dicentrarchus labrax) (64.7±6.33) was significantly higher than that of fish with lordosis (60.3±6.66) (P<0.05). Both normal fish and those with lordosis showed increased endurance with increasing length during exercise at a fixed water velocity of 50 cm s⁻¹. This speed was used to investigate the separation possibility of deformed specimen from the normal developed fish based on their swimming performance, and 28% separation was achieved without losing any normal fish by the end of the 10th minute. To achieve a better separation of the deformities from the normal, first grading of the juveniles and then a swimming endurance test is advised.     

Cardiac activity,ventilation rate and acid-base regulation in rainbow trout exposed to hypoxia and combined hypoxia and hypercapnia

A computerised system for non-invasive monitoring of heart and ventilation rates and the time intervals between heart beats and between breaths was developed and used to investigate cardio-respiratory changes in rainbow trout exposed to hypoxia and to combined hypoxia and hypercapnia. Upon exposure to hypoxia and hypoxia-hypercapnia the arterial O₂ tension decreased from about 90 mmHg to about 30 mmHg. Acid-base changes were small in hypoxia whereas exposure to combined hypoxia-hypercapnia caused a large extracellular respiratory acidosis. This acidosis was completely compensated within 24h by accumulation of bicarbonate in plasma to concentrations twice the normoxic values. The ventilation rate was increased to higher values in hypoxic-hypercapnic trout than in hypoxic trout. In contrast to previous reports, the heart rate increased in hypoxia. On top of the tachycardia response to hypoxia, the heart rate was governed by circadian rhythms, with higher heart rates during the day than during the night. The time interval between heart beats varied considerably in normoxic fish. Hypoxia strongly reduced this variability, which may originate in a reduced cholinergic tone to the heart. The width of the frequency distribution of the time intervals between breaths was not affected by hypoxia. The degree of cardio-respiratory synchronization was low in both normoxic and in hypoxic and hypoxic-hypercapnic trout.     

Optimal swimming speeds reflect preferred swimming speeds of brook charr (<Emphasis Type="Italic">Salvelinus fontinalis</Emphasis> Mitchill, 1874)

Several measures have been developed to quantify swimming performance to understand various aspects of ecology and behaviour, as well as to help design functional applications for fishways and aquaculture. One of those measures, the optimal swimming speed, is the speed at which the cost of transport (COT) is minimal, where COT is defined as the cost of moving unit mass over unit distance. The experimental protocol to determine the optimal swimming speed involves forced-swimming in a flume or respirometer. In this study, a 4.5–m-long tilted raceway with gradually increasing upstream water speed is used to determine a novel, behaviourally based swimming parameter: the preferred swimming speed. The optimal swimming speed and the preferred swimming speed of brook charr were determined and a comparison of the two reveals that the optimal swimming speed (25.9 ± 4.5 cm s⁻¹ or 1.02 ± 0.47 bl s⁻¹) reflected the preferred swimming speed (between 20 cm s⁻¹ or 0.78 ± 0.02 bl s⁻¹ and 25 cm s⁻¹ or 0.95 ± 0.03 bl s⁻¹). The preferred swimming speed can be advantageous for the determination of swimming speeds for the use in aquaculture studies.     

Metabolic scope, swimming performance and the effects of hypoxia in the mulloway, Argyrosomus japonicus (Pisces: Sciaenidae)

The culture of the mulloway (Argyrosomus japonicus), like many other Sciaenidae fishes, is rapidly growing. However there is no information on their metabolic physiology. In this study, the effects of various hypoxia levels on the swimming performance and metabolic scope of juvenile mulloway (0.34 ± 0.01 kg, mean ± SE, n = 30) was investigated (water temperature = 22 °C). In normoxic conditions (dissolved oxygen = 6.85 mg l^− 1), mulloway oxygen consumption rate (M·o₂) increased exponentially with swimming speed to a maximum velocity (U_crit) of 1.7 ± < 0.1 body lengths s^− 1 (BL s^− 1) (n = 6). Mulloway standard metabolic rate (SMR) was typical for non-tuna fishes (73 ± 8 mg kg^− 1 h^− 1) and they had a moderate scope for aerobic metabolism (5 times the SMR). Mulloway minimum gross cost of transport (GCOT_min, 0.14 ± 0.01 mg kg^− 1 m^− 1) and optimum swimming velocity (U_opt, 1.3 ± 0.2 BL s^− 1) were comparable to many other body and caudal fin swimming fish species. Energy expenditure was minimum when swimming between 0.3 and 0.5 BL s^− 1. The critical dissolved oxygen level was 1.80 mg l^− 1 for mulloway swimming at 0.9 BL s^− 1. This reveals that mulloway are well adapted to hypoxia, which is probably adaptive from their natural early life history within estuaries. In all levels of hypoxia (75% saturation = 5.23, 50% = 3.64, and 25% = 1 .86 mg l^− 1), M·o₂ increased linearly with swimming speed and active metabolic rate (AMR) was reduced (218 ± 17, 202 ± 14 and 175 ± 10 mg kg^− 1 h^− 1 for 75%, 50% and 25% saturation respectively). However, U_crit was only reduced at 50% and 25% saturation (1.4 ± < 0.1 and 1.4 ± < 0.1 BL s^− 1 respectively). This demonstrates that although the metabolic capacity of mulloway is reduced in mild hypoxia (75% saturation) they are able to compensate to maintain swimming performance. GCOT_min (0.09 ± 0.01 mg kg^− 1 m^− 1) and U_opt (0.8 ± 0.1 BL s^− 1) were significantly reduced at 25% dissolved oxygen saturation. As mulloway metabolic scope was significantly reduced at all hypoxia levels, it suggests that even mild hypoxia may reduce growth productivity.     

温度和重复运动对中华鲟游泳行为的影响

研究温度和重复疲劳运动对中华鲟游泳行为和能量代谢的影响,为中华鲟养殖环境水质量监测管理、物种保护和鱼道的设计等提供参考。在密封鱼类游泳装置中,利用速度递增法测定了不同温度(10、15、20和25℃)、流速条件下中华鲟(Acipenser sinensis)幼鱼(体长8.50~11.00 cm,体重5.10~8.80 g)的摆尾频率(TBF)、呼吸频率(RR),并同时测定了游泳过程中的耗氧率(M_(O_2))。结果表明:随着摆尾频率或呼吸频率的增加,中华鲟幼鱼的耗氧率增加,耗氧率与摆尾频率或呼吸频率呈指数相关(M_(O_2)=a×TBF~b;M_(O_2)=A×RR~B);随着温度增加,b值先减小后增加,15℃和20℃时b值较小;疲劳恢复后,第2次测试b值大于第1次;随着温度的增加,B值逐渐增加;疲劳恢复后,第2次测试B值小于第1次。游泳过程能量消耗随着温度的升高先降低后升高,15~20℃能量消耗较小。疲劳恢复后,第2次测试能量消耗大于第1次,游泳效率降低,特别是在10℃和25℃,15~20℃变化不明显。温度和重复游泳对中华鲟幼鱼游泳行为影响显著,温度不适宜和重复疲劳运动会产生叠加效应,导致游泳效率显著降低。     

A respirometer with controlled water quality and computerized data acquisition for experiments with swimming fish

This paper describes the design of a modified Brett-type respirometer for use with fish up to 2 kg at swimming speeds as high as 2.5 m·s^-1. Control of the respirometer, experimental monitoring and data acquisition are performed by computer. Water velocity, temperature, pH, dissolved oxygen and carbon dioxide can be controlled at predetermined levels to enable experiments to be conducted over several days with minimal deterioration in water quality.     

低氧胁迫对鲻幼鱼生长、能量代谢和氧化应激的影响

为研究低氧胁迫对鲻幼鱼生长、能量代谢和氧化应激的影响,实验将其放在溶解氧(DO,mean±SE)含量分别控制在(1.66±0.41)、(4.35±0.53)、(7.03±0.36)mg/L的条件下养殖10 d,然后恢复至接近饱和溶解氧含量7.0 mg/L的条件下养殖30 d,研究其特定生长率、排氨率、耗氧率、氧氮比和血浆、肌肉、肝脏及鳃组织的总抗氧化能力(T-AOC)、过氧化物歧化酶(SOD)活力、抗超氧阴离子活力(ASOR)、丙二醛(MDA)含量、乳酸(LD)含量、总谷胱甘肽(T-GSH)、还原型谷胱甘肽(GSH)和氧化型谷胱甘肽(GSSG)含量。结果表明:低氧胁迫对鲻幼鱼的生长、能量代谢影响显著,较严重缺氧组鲻的体质量、特定生长率(SGR)、耗氧率和排氨率显著低于其他处理,不具有补偿生长的能力;而轻微缺氧组获得完全补偿生长。低氧胁迫对鲻氧化应激指标影响显著,胁迫结束时鲻通过提高某些抗氧化酶的活力来增强抗氧化能力,以提高其应对恢复正常溶解氧环境可能带来的氧化应激的能力,同时在恢复溶氧后鲻氧化应激反应也较强烈。在恢复溶解氧阶段,肝脏中GSH显著增加,说明鲻体内的保护机制被激活。肝脏和鳃中MDA的含量在低氧胁迫后与溶解氧含量呈明显的负相关性,在复氧30 d后仍然高于对照组,表明低氧胁迫加强鲻肝脏和鳃组织脂质过氧化反应。     

Split-beam target tracking can be used to study the swimming behaviour of deep-living plankton in situ

A scattering layer consisting mainly of krill (Meganyctiphanes norvegica) was studied with a submersible transducer, to assess the behaviour of individual organisms in situ by means of split-beam target tracking. Individuals were resolved and tracked, but a rapid increase in average swimming speeds with depth suggested that inaccuracies in the angular estimates affected the estimates. Attempts were made to smooth the tracks during post-processing. Smoothed speeds suggested that most (>78%) invertebrates swam at speeds below 12 cm s^–1 (mode ~4 cm s^–1), with components of speed larger in the horizontal plane than in the vertical.     

水温、盐度和溶氧对红鳍东方鲀幼鱼游泳能力的影响

为了考查水温、盐度和溶氧对红鳍东方鲀(Takifugu rubripes)幼鱼游泳能力的影响,测定了其在不同水温[15.2、20.2、25.6(对照)和30.4℃]、盐度[0、10、20、32(对照)和40]和溶氧[2.14、4.10、5.81和7.36 mg/L(对照)]条件下的临界游速和最大游速。结果表明,水温和溶氧含量均显著影响实验鱼的临界游速和最大游速(P0.01)。随水温和溶氧含量升高,实验鱼的临界游速和最大游速均逐渐增加。水温(T,℃)与临界游速(U_(crit),cm/s)和最大游速(U_(max),cm/s)均呈二次函数关系,关系式分别为U_(crit)=-0.095T 2+5.450T-47.79,R~2=0.995(P0.01)和U_(max)=-0.018T 2+2.204 T-12.27,R~2=0.981(P0.01)。溶氧含量(DO,mg/L)与临界游速和最大游速也均呈二次函数关系,关系式分别为U_(crit)=0.230DO2+1.561DO+5.84,R~2=0.995(P0.01)和U_(max)=-0.806 DO2+11.10DO-3.919,R~2=0.985(P0.01)。不同盐度下实验鱼的临界游速和最大游速与对照组均无显著差异(P0.05)。结论认为,低温和缺氧会降低红鳍东方鲀放流苗种的游泳能力,进而降低其放流后的捕食成功率,提高被捕食概率。     

Physiological and behavioural responses to hypoxia in an invasive freshwater fish species and a native competitor

The spread of invasive species is one of the major environmental concerns which can have negative effects on biodiversity. While several life history traits have been identified as being important for increasing the invasiveness of introduced species, the physiological factors that allow certain species to become successful invaders remain poorly understood. It has been speculated that good invaders are thriving in disturbed environments. In unfavourable conditions, as during hypoxic events, invasive species might be better adapted in their physiological and behavioural responses towards this stressor. We compared physiological and behavioural traits between two freshwater fish species: the European bullhead (Cottus gobio), an invasive fish species in Scotland, and its native competitor the stone loach (Barbatula barbatula) over different dissolved oxygen concentrations (DO). Contrary to expectations, bullhead displayed a reduced hypoxia tolerance as compared to stone loach, indicated by a higher threshold (P_crit) for the maintenance of standard metabolism. Avoidance behaviour during progressive hypoxia was similar between bullhead and stone loach. When given a choice between an open normoxic zone and a shelter located in hypoxia, both species spent most of their time hiding under the shelter in hypoxic conditions (bullhead: 100%; stone loach: 93.93%–99.73%), although stone loach showed brief excursions into normoxic conditions under 25% DO level. These results suggest that stone loach might be more resistant to hypoxia as compared to bullhead, and thus that increased hypoxia tolerance is likely not a trait by which bullhead have been able to expand their range within the United Kingdom.     

The swimming capacity of juvenile Murray cod (Maccullochella peelii): an ambush predator endemic to the Murray‐Darling Basin,Australia

This study documented the swimming capacity of a large ambush predator, Murray cod Maccullochella peelii, endemic to the Murray‐Darling Basin, Australia. It was evident that the species is a swimming generalist, maintaining moderate ability across all aspects of the swimming capacity parameters that were investigated. For instance, the species was capable of prolonged swimming performance (critical swimming speed, U_crit: absolute, 0.26–0.60 m·s^?1, relative, 1.15–2.20 BL s^?1) that was inferior to active fish species, but comparable with other ambush predators. The species had low energetic demands, maintaining a low mass‐specific standard (21.3–140.3 mg·h^?1 kg^?1) and maximum active metabolic rate (75.5–563.8 mg·h^?1 kg^?1), which lead to a small scope for activity (maximum active metabolic rate–standard metabolic rate; 1.4–5.9). They were reasonably efficient swimmers (absolute and relative optimal swimming speed, 0.17–0.61 m·s^?1 and 0.77–1.93 BL·s^?1, respectively) and capable of repeat bouts of prolonged performance (recovery ratio = 0.99). Allometric changes in aspects of swimming capacity were realised with body mass, whereas broad swimming capacity was maintained across a wide range of temperatures. The swimming capacity demonstrated by M. peelii reflects a sit‐and‐wait foraging strategy that seeks to conserve energy characteristic of ambush predators, but with distinct features (e.g., lack of fast‐start ability) that may reflect their evolution in some of the world's most hydrologically and thermally variable rivers.     

Temperature and dissolved oxygen influence growth and digestive enzyme activities of yellowtail kingfish Seriola lalandi (Valenciennes, 1833)

A 5 week experiment was carried out with juvenile yellowtail kingfish Seriola lalandi to investigate the interactive effects of water temperature (21, 24, or 27°C) and dissolved oxygen regime (normoxic vs. hypoxic) on the growth rate, feed intake and digestive enzyme activity of this species. Specific growth rate (SGR) was highest at 24°C, regardless of oxygen regime, but the SGRs of the fish exposed to hypoxia at 21, 24 and 27°C were 13%, 20% and 17% lower, respectively, than the SGRs recorded for the fish reared under normoxic conditions. The digestive enzyme activities (i.e. trypsin, lipase and α‐amylase) were influenced by temperature but did not appear to be affected by dissolved oxygen concentration. Information about the effects of water temperature and dissolved oxygen on feeding, growth and digestive capacity of juvenile yellowtail kingfish could contribute to improving feed management decisions for production of this fish species under different environmental conditions.     

Effect of stocking density,oxygen level,light regime and swimming velocity on the incidence of sexual maturation in adult Atlantic salmon (Salmo salar)

The effects of various environmental parameters on sexual maturation of two sea-winter Atlantic salmon (Salmo salar) were tested in two separate experiments. In the first experiment Atlantic salmon with initial mean individual weight 1.5 kg (smolt 13 months before) were reared for 8 months from June to February at different oxygen levels and stocking densities using continuous light. Oxygen levels of 5–7, 7.5–9.5 and 10–12 mg O₂ l⁻¹ and stocking densities starting at about 20, 30 and 40 kg m⁻³ and increasing as the fish grew to 80–90 kg m⁻³ for the highest densities were tested in a factorial design. Only male fish matured, and incidence of maturation among males varied from 4.1% to 25% between tanks. The highest percentage of mature males was found in the tanks with low stocking density. No clear effect on oxygen level was found.The second experiment lasted 20 months from seawater transfer in May until the fish weighed 3.3–3.5 kg. Two water current speeds (14–16 and 20–24 cm s⁻¹) and two photoperiod regimes (LD 20:4) and continuous light (LL) were tested in a factorial design. Neither swimming velocity nor photoperiod affected growth rate. Continuous light reduced the incidence of sexual maturation. The average proportion of maturation among males was 8% and 25% under the LL and LD 20:4 regimes respectively. The fish reared under the LD 20:4 light regime had a significant lower condition factor and significant larger hearts than the fish reared under continuous light. Swimming velocity had no significant effect on the incidence of maturation. The results indicate that the swimming velocity must be higher than 0.5 BL s⁻¹ in order to influence the energy stores. An important finding in this study is that light cues are not required for gonadal growth. The results also indicate that environmental factors can affect maturation even after the first sea-winter.     

An analysis of the energetic cost of the branchial and cardiac pumps during sustained swimming in trout

Experimental data are available for the oxygen cost of the branchial and cardiac pumps in fish. These data were used to theoretically analyze the relative oxygen cost of these pumps during rest and swimming in rainbow troutSalmo gairdneri. Efficiency of the heart increases with activity and so the relative oxygen cost of the cardiac pumps decreased from 4.6% at rest to 1.9% at the critical swimming speed. The relative oxygen cost of the branchial pump is significant in the resting and slowly swimming fish, being 10 to 15% of total oxygen uptake. However, when swimming trout switch to a ram mode of ventilation, a considerable saving in oxygen cost is accrued by switching the cost of ventilation from the branchial to the tail musculature. Thus, the relative oxygen cost of the branchial and cardiac pumps actually decreases at critical swimming speed compared to rest and therefore is unlikely to be a major limiting factor in maximum oxygen delivery to the tissues.     

The effects of swimming exercise and dissolved oxygen on growth performance,fin condition and precocious maturation of early‐rearing Atlantic salmon Salmo salar

Swimming exercise, typically measured in body‐lengths per second (BL/s), and dissolved oxygen (DO), are important environmental variables in fish culture. While there is an obvious physiological association between these two parameters, their interaction has not been adequately studied in Atlantic salmon Salmo salar. Because exercise and DO are variables that can be easily manipulated in modern aquaculture systems, we sought to assess the impact of these parameters, alone and in combination, on the performance, health and welfare of juvenile Atlantic salmon. In our study, Atlantic salmon fry were stocked into 12 circular 0.5 m³ tanks in a flow‐through system and exposed to either high (1.5–2 BL/s) or low (<0.5 BL/s) swimming speeding and high (100% saturation) or low (70% saturation) DO while being raised from 10 g to approximately 350 g in weight. Throughout the study period, we assessed the impacts of exercise and DO concentration on growth, feed conversion, survival and fin condition. By study's end, both increased swimming speed and higher DO were independently associated with a statistically significant increase in growth performance (p < .05); however, no significant differences were noted in survival and feed conversion. Caudal fin damage was associated with low DO, while right pectoral fin damage was associated with higher swimming speed. Finally, precocious male sexual maturation was associated with low swimming speed. These results suggest that providing exercise and dissolved oxygen at saturation during Atlantic salmon early rearing can result in improved growth performance and a lower incidence of precocious parr.     

Sex differences in metabolic rate and swimming performance in pink salmon (Oncorhynchus gorbuscha): the effect of male secondary sexual traits

Do secondary sexual traits, such as large dorsal hump and hooked snout, decrease the swimming efficiency of male pink salmon during freshwater migration? This is the first study to address the effects of secondary sexual traits in pink salmon on oxygen uptake and swimming capacity. We conducted a laboratory experiment using a swimming respirometer and a field study using electromyogram (EMG) telemetry in the Shibetsu River, Hokkaido, Japan. We compared the relationship between MO₂ (mg O₂·kg^?1·h^?1) and swimming velocity U (m·s^?1) in male and female fish, and also investigated the effects of morphological traits (secondary sexual characters) on the relationship between MO₂ (mg O₂·kg^?1·h^?1) and swimming velocity U (m·s^?1). Additionally, we compared energy costs and swimming behaviour during upstream migration between male and female pink salmon. The laboratory experiment revealed that MO₂ exponentially increased with increasing U; this increase was described by MO₂ = 167.9e^1.23U for males and 144.9e^1.14U for females. Linear mixed models found that hump height and the upper jaw length in males significantly and positively affected the relationship between MO₂ and U; no effect was found in females. The field study found that swimming velocity for both sexes estimated from EMG calibration was lower than optimal swimming velocity (U_opt) calculated from the laboratory experiment. We suggest that pink salmon in the Shibetsu River do not swim at the optimal swimming velocity because of the short migration distance involved (20 km).     

Respiratory response of grass carp <Emphasis Type="Italic">Ctenopharyngodon idellus</Emphasis> to dissolved oxygen changes at three acclimation temperatures

Respiratory parameters of grass carp were studied during dissolved oxygen (DO) changes from normal DO to hypoxia, then return to normal DO at 15, 25, and 30 °C acclimation, respectively. The results showed that with increases of acclimation temperature at normoxia the respiratory frequency (f_R), oxygen consumption rate (VO₂), respiratory stroke volume (V_S.R), gill ventilation (V_G), and V_G/VO₂ of grass carp increased significantly, but the oxygen extraction efficiency (EO₂) of fish decreased significantly (P < 0.05). With declines of DO levels, the f_R, V_S.R, V_G, and V_G/VO₂ of fish increased significantly at different acclimation temperatures (P < 0.05). A slight increase was found in VO₂, and the EO₂ of fish remained almost constant above DO levels of 3.09, 2.91, and 2.54 mg l^?1 at 15, 25, and 30 °C, while the VO₂ and EO₂ began to decrease significantly with further reductions in DO levels (P < 0.05). After 0.5 h of recovery to normoxia from hypoxia at three acclimation, the f_R, V_S.R, V_G, and V_G/VO₂ of the fish decreased sharply; meanwhile, the VO₂ and EO₂ increased sharply (P < 0.05). The respiratory parameters of fish gradually approached initial values with prolonged recovery time to normoxia, and reached their initial values in 2.5 h at 25 and 30 °C acclimation. The critical oxygen concentrations (C_c) of fish for VO₂ were 2.42 mg l^?1 at 15 °C, 2.02 mg l^?1 at 25 °C, and 1.84 mg l^?1 at 30 °C, respectively. The results suggest that grass carp are highly adapted to varied DO and short-term hypoxia environments.