Comparison of static and dynamic respirometry for the determination of stoichiometric and kinetic parameters of a nitrifying process

Respirometry consists in the measurement of the biological oxygen consumption rate under well-defined conditions and has been used for the characterization of countless biological processes. In the field of biotechnology and applied microbiology, several respirometry methods are commonly used for the determination of process parameters. Dynamic and static respirometry, which are based on oxygen measurements with or without continuous aeration, respectively, are the methods most commonly used. Additionally to several respirometry methods, different methods have also been developed to retrieve process parameters from respirometric data. Among them, methods based on model fitting and methods based on the injection of substrate pulse at increasing concentration are commonly used. An important question is then; what respirometry and data interpretation methods should be preferably used? So far, and despite a growing interest for respirometry, relatively little attention has been paid on the comparison between the different methods available. In this work, both static and dynamic respirometry methods and both interpretation methods; model fitting and pulses of increasing concentration, were compared to characterize an autotrophic nitrification process. A total of 60 respirometry experiments were done and exhaustively analysed, including sensitivity and error analyses. According to the results obtained, the substrate affinity constant (K _S ) was better determined by static respirometry with pulses of increasing concentration and the maximum oxygen uptake rate (OUR _ex.max ) was better determined by dynamic respirometry coupled to fitting procedure. The best method for combined K _S and OUR _ex.max determination was static respirometry with pulses of increasing concentration.     

A model system using confocal fluorescence microscopy for examining real-time intracellular sodium ion regulation

The gills of euryhaline fish are the ultimate ionoregulatory tissue, achieving ion homeostasis despite rapid and significant changes in external salinity. Cellular handling of sodium is not only critical for salt and water balance but is also directly linked to other essential functions such as acid–base homeostasis and nitrogen excretion. However, although measurement of intracellular sodium ([Na⁺]_i) is important for an understanding of gill transport function, it is challenging and subject to methodological artifacts. Using gill filaments from a model euryhaline fish, inanga (Galaxias maculatus), the suitability of the fluorescent dye CoroNa Green as a probe for measuring [Na⁺]_i in intact ionocytes was confirmed via confocal microscopy. Cell viability was verified, optimal dye loading parameters were determined, and the dye–ion dissociation constant was measured. Application of the technique to freshwater- and 100% seawater-acclimated inanga showed salinity-dependent changes in branchial [Na⁺]_i, whereas no significant differences in branchial [Na⁺]_i were determined in 50% seawater-acclimated fish. This technique facilitates the examination of real-time changes in gill [Na⁺]_i in response to environmental factors and may offer significant insight into key homeostatic functions associated with the fish gill and the principles of sodium ion transport in other tissues and organisms.     

Comparison of methods to quantify metabolic rate and its relationship with activity in larval lake sturgeon Acipenser fulvescens

Until recently most studies have focussed on method development for metabolic rate assessment in adult and/or juvenile fish with less focus on measurement of oxygen consumption (ṀO₂) during early life history stages, including fast-growing larval fish and even less focus on nonteleostean species. In the present study we evaluated measurement techniques for standard metabolic rate (SMR), maximum metabolic rate (MMR) and aerobic scope in an Acipenseriform, the lake sturgeon Acipenser fulvescens, throughout the first year of life. Standardized forced exercise protocols to assess MMR were conducted for 5 or 15 min before or after measurement of SMR. We used different levels of oxygen decline during the measurement period of MMR post forced exercise to understand the influence these may have on the calculation of MMR. Opercular rate and tail beat frequencies were recorded by video as measures of behaviours and compared to metabolic rate recorded over a 24 h period. Results indicate that calculated values for aerobic scope were lower in younger fish. Neither exercise sequence nor exercise duration influenced metabolic rate measurements in the younger fish, but exercise duration did affect measurement of MMR in older fish. Finally, there was no strong correlation between metabolic rate and the measured behaviours in the lake sturgeon at either age. Based on the results, we recommend that a minimum of 6 h of acclimation to the respirometry chamber should be given prior to measuring SMR, a chasing protocol to elicit MMR should ideally be performed at the end of experiment, a short chasing time should be avoided to minimize variation and assessment of MMR should balance measurement limitations of the probes along with when and for how long oxygen consumption is measured.     

Open-top static respirometry is a reliable method to determine the routine metabolic rate of barramundi,Lates calcarifer

Closed-system respirometry is a standard technique used to determine aerobic metabolism of aquatic organisms. Open-top systems are rarely used due to concerns of gas exchange across the air–water interface. Here, we evaluated an open-top respirometry system by comparing the mass-specific routine metabolic rate (RMR) of the tropical diadromous finfish barramundi, Lates calcarifer, in both closed-top and open-top respirometers. The RMR of 190?g barramundi was determined across broad temperatures ranging from 18 to 38?°C. There was no significant difference in RMR between barramundi in either closed- or open-top respirometers at any temperature (p?>?0.05). To ensure RMR measurements were not an artifact of the respirometry system, barramundi were reciprocally transplanted into either respective closed-top or open-top respirometer and oxygen consumption re-measured at each temperature treatment. The RMR of transplanted barramundi was found to be virtually identical in either respirometer. RMR increased linearly with increasing temperature; the relationship between RMR and temperature (T; 18–38?°C) can be described as 3.658T?36.294?mg?O₂?kg^?0.8?h^?1. The daily energetic cost of RMR was 1.193T?11.838?kJ?kg^?0.8?day^?1. Q₁₀ for barramundi increased significantly with increasing temperature (p?Q_10(18–28) was the lowest at 1.7 and Q_10(28–38) the highest at 1.9, over the whole experiment temp range Q_10(18–28) was 1.8. The current study demonstrates that open-top respirometry is a reliable and practical alternative to closed-top respirometry for accurate determination of the aerobic metabolism of barramundi and has potential application for a number of different aquatic organisms.     

Metabolic adaptations to hypoxia of two species of polychaeta,Nephtys ciliata and Nephtys hombergii

Summary The respiratory responses to declining oxygen tension in Nephtys ciliata and N. hombergii were investigated using flow respirometry. N. hombergii showed a better regulation of oxygen uptake during declining oxygen tension than N. ciliata. N. ciliata showed no difference in regulatory ability when individuals of different sizes were compared. It is argued that the difference in regulating ability can partly explain the distribution pattern of these two species in Århus Bight, Denmark.Abbreviations B2 regulation index - B2 mean regulation index - C_eO2 excurrent oxygen concentration - C _iO2 incurrent oxygen concentration; dw dry weight - PO ₂ partial pressure (oxygen) - VO₂ oxygen uptake - VO₂ relative oxygen uptake - V_W water flow     

The Diffusion Capacity of the Hematoparenchymal Barrier in Mammalian and Marine Fish Skeletal Muscles

Analysis of own and literature data shows that oxygen tension and mass transfer in skeletal muscles of higher and lower vertebrates (mammals, teleosts) are quite comparable. Oxygen consumption in fish muscles is 2–6 times lower and occurs at higher diffusion gradients of PO₂ (blood ? muscles: 45–57 hPa). Wei ghted mean values of PO₂ in fish muscles (with allowance for muscle composition) are minimum (5–12 hPa). As compared to mammals, they exhibit an extremely low diffusion capacity of the hematoparenchymal barrier (0.0014–0.0055 mLO₂ min^–1 100 g^–1 hPa^–1) which appears to rely on diffusion characteristics of cell membranes. Apparently, this is the main reason that accounts for low values of tissue PO₂ as well as low efficacy and oxygen utilization degree in muscles of this taxonomic group of animals.     

A rationale for the appropriate amount of inoculum in ready biodegradability tests

Several screening methods at the so-called ready biodegradability level are suitable to test poorly soluble substances. Typical for these tests is that mineralization is evaluated from monitoring oxygen uptake or carbon dioxide production. Unfortunately, they suffer from a rather low precision in the calculated percentage of mineralization caused by subtracting a too high inoculum control measurement from the response in the test system. Criteria for blank oxygen consumption, due to the metabolic activity of the inoculum, are proposed from which maximum amounts of activated sludge or secondary effluent per litre test medium can be derived to be used as an appropriate inoculum. Both for current and future standardized tests the precision of the method can be kept within acceptable margins. Inoculum material was sampled from 40 communal biological waste water treatment plants. From endogenous respiration rates it was derived that the concentration of secondary effluent in the Closed Bottle Test can be increased up to 50 mL/L but that in respirometry tests inoculated with activated sludge the appropriate concentration is 10 mg/L dry matter or below, depending of the design of the test system.List of abbreviations BOD biological oxygen demand - CBT Closed Bottle Test - C _as inoculum concentration in mg dry solids of activated sludge per litre test medium - C _ef inoculum concentration in ml secondary effluent per litre test medium - C _ss dry weight content of activated sludge (g/L) - CFU colony forming units - DO_7d dissolved oxygen concentration (mg/L) after 7 days - ISO International Organization for Standardization - NEN Dutch Organization for Standardization - O _c oxygen capacity in mg oxygen per litre vessel volume - OECD Organisation for Economic Co-operation and Development - Ox _as oxygen consumption after one week in mg oxygen per mg dry weight activated sludge - Ox _ef oxygen consumption after one week in mg oxygen per mL secondary effluent - Ox _ef [n] oxygen consumption after one week in mg oxygen per n mL secondary effluent - Ox _flask oxygen uptake in mg per litre flask volume - RBT Ready Biodegradability Test - SLR sludge loading rate in kg O₂/kg dry weight·d - ThOD theoretical oxygen demand - TPCBT Two Phase Closed Bottle Test - V _a volumes of air and water per litre vessel - V _w volume, respectively - _a concentration of oxygen in air at 20° C and 101.5 kPa - _s saturation oxygen concentration in te aqueous phase     

Should I stay or should I go?: Physiological, metabolic and biochemical consequences of voluntary emersion upon aquatic hypoxia in the scaleless fish Galaxias maculatus

Hypoxia represents a significant challenge to most fish, forcing the development of behavioural, physiological and biochemical adaptations to survive. It has been previously shown that inanga (Galaxias maculatus) display a complex behavioural repertoire to escape aquatic hypoxia, finishing with the fish voluntarily emerging from the water and aerially respiring. In the present study we evaluated the physiological, metabolic and biochemical consequences of both aquatic hypoxia and emersion in inanga. Inanga successfully tolerated up to 6?h of aquatic hypoxia or emersion. Initially, this involved enhancing blood oxygen-carrying capacity, followed by the induction of anaerobic metabolism. Only minor changes were noted between emersed fish and those maintained in aquatic hypoxia, with the latter group displaying a higher mean cell haemoglobin content and a reduced haematocrit after 6?h. Calculations suggest that inanga exposed to both aquatic hypoxia and air reduced oxygen uptake and also increased anaerobic contribution to meet energy demands, but the extent of these changes was small compared with hypoxia-tolerant fish species. Overall, these findings add to previous studies suggesting that inanga are relatively poorly adapted to survive aquatic hypoxia.     

Continuous measurement of oxygen tensions in the air-breathing organ of Pacific tarpon (Megalops cyprinoides) in relation to aquatic hypoxia and exercise

The Pacific tarpon is an elopomorph teleost fish with an air-breathing organ (ABO) derived from a physostomous gas bladder. Oxygen partial pressure (PO₂) in the ABO was measured on juveniles (238 g) with fiber-optic sensors during exposure to selected aquatic PO₂ and swimming speeds. At slow speed (0.65 BL s⁻¹), progressive aquatic hypoxia triggered the first breath at a mean PO₂ of 8.3 kPa. Below this, opercular movements declined sharply and visibly ceased in most fish below 6 kPa. At aquatic PO₂ of 6.1 kPa and swimming slowly, mean air-breathing frequency was 0.73 min⁻¹, ABO PO₂ was 10.9 kPa, breath volume was 23.8 ml kg⁻¹, rate of oxygen uptake from the ABO was 1.19 ml kg⁻¹ min⁻¹, and oxygen uptake per breath was 2.32 ml kg⁻¹. At the fastest experimental speed (2.4 BL s⁻¹) at 6.1 kPa, ABO oxygen uptake increased to about 1.90 ml kg⁻¹ min⁻¹, through a variable combination of breathing frequency and oxygen uptake per breath. In normoxic water, tarpon rarely breathed air and apparently closed down ABO perfusion, indicated by a drop in ABO oxygen uptake rate to about 1% of that in hypoxic water. This occurred at a wide range of ABO PO₂ (1.7–26.4 kPa), suggesting that oxygen level in the ABO was not regulated by intrinsic receptors.     

Metabolic responses of the mussels Perna viridis and Perna indica to declining oxygen tension at different salinities

• 1.1. Oxygen uptake and ammonia loss were monitored during responses to reductions of both salinity and oxygen tension (PO₂) in the marine mussels Perna viridis and Perna indica from southern India.
• 2.2. The proportional contribution of protein to total catabolic substrates under natural environmental conditions was as much as 96% in P. viridis, relative to only 19% in P. indica.
• 3.3. Normoxic oxygen consumption remained statistically unchanged in P. viridis conditioned to salinities between 32 and 15‰, with no obvious signs of distress. Although equally unaffected at salinities between 32 and 20‰, P. indica showed significantly reduced oxygen uptake following transfer from 32 to 15‰, and had died within the next 7 days.
• 4.4. At salinities greater than 20‰, P. viridis was better able than P. indica to regulate oxygen consumption independent of PO₂.
• 5.5. P. indica showed a compensatory increase in oxyregulatory capacity at 15‰. This exceeded unstressed abilities, helping to maintain albeit reduced oxygen uptake throughout wider ranges of PO₂.
• 6.6. Different responses recorded in each of these tropical and often intertidal species were in accordance with their natural distributions. Nevertheless, the oxyregulatory capacity in both species was higher than in bivalves from temperate and/or subtidally restricted habitats.

     

Allometric relationship between oxygen consumption and body weight of mosquitofish,Gambusia affinis

Synopsis The allometric relationship between body size and oxygen consumption of Gambusia affinis at 28° C was determined under controlled experimental conditions, using a manometric respirometer. The allometric exponent (b-value) was 0.64 ± 0.02 S.E. (n = 51). Oxygen consumption was not influenced by any time-related factors during the 17 days of measurements. Variance between replicated oxygen consumption trials on individual fish was negligible. Specific oxygen consumption rates of several G. affinis at 28° C that were determined by using a sealed vessel and O₂ electrode respirometry method were similar to the rates measured by the manometric respirometry method in similar-sized G. affinis.     

Influence of experimental set-up and methodology for measurements of metabolic rates and critical swimming speed in Atlantic salmon Salmo salar

In this study, swim-tunnel respirometry was performed on Atlantic salmon Salmo salar post-smolts in a 90 l respirometer on individuals and compared with groups or individuals of similar sizes tested in a 1905 l respirometer, to determine if differences between set-ups and protocols exist. Standard metabolic rate (SMR) derived from the lowest oxygen uptake rate cycles over a 20 h period was statistically similar to SMR derived from back extrapolating to zero swim speed. However, maximum metabolic rate (MMR) estimates varied significantly between swimming at maximum speed, following an exhaustive chase protocol and during confinement stress. Most notably, the mean (±SE) MMR was 511 ± 15 mg O₂ kg⁻¹ h⁻¹ in the swim test which was 52% higher compared with 337 ± 9 mg O₂ kg⁻¹ in the chase protocol, showing that the latter approach causes a substantial underestimation. Performing group respirometry in the larger swim tunnel provided statistically similar estimates of SMR and MMR as for individual fish tested in the smaller tunnel. While we hypothesised a larger swim section and swimming in groups would improve swimming performance, U_crit was statistically similar between both set-ups and statistically similar between swimming alone v. swimming in groups in the larger set-up, suggesting that this species does not benefit hydrodynamically from swimming in a school in these conditions. Different methods and set-ups have their own respective limitations and advantages depending on the questions being addressed, the time available, the number of replicates required and if supplementary samplings such as blood or gill tissues are needed. Hence, method choice should be carefully considered when planning experiments and when comparing previous studies.     

Cation Transport in Escherichia coli : VII. Potassium requirement for phosphate uptake

When Escherichia coli K-12 is grown in media containing limiting amounts of K, growth continues normally until all the extracellular K has been consumed. Thereafter the rates of growth, glucose consumption, and oxygen consumption decrease progressively, and the cell contents of K and P fall. These changes, referred to as K limitation, are all reversed by the addition of K. By specifically altering the ionic composition of the cells it was shown that these metabolic disturbances are not due to changes in the cell content of K or Na, but are directly related to the absence of K from the extracellular medium. The cell pool of inorganic P and the uptake of PO₄ from the medium are low in K-limited cells and are immediately stimulated by the addition of K, suggesting that the primary effect of K limitation is to inhibit PO₄ uptake. All the metabolic effects of K limitation can be attributed to inhibition of PO₄ uptake. The requirement of extracellular K for PO₄ uptake may be due to a coupling between the uptake of K and PO₄.     

Balancing the competing requirements of air-breathing and display behaviour during male–male interactions in Siamese fighting fish Betta splendens

Air-breathing fish of the Anabantoidei group meet their metabolic requirements for oxygen through both aerial and aquatic gas exchange. Siamese fighting fish Betta splendens are anabantoids that frequently engage in aggressive male–male interactions which cause significant increases in metabolic rate and oxygen requirements. These interactions involve opercular flaring behaviour that is thought to limit aquatic oxygen uptake, and combines with the increase in metabolic rate to cause an increase in air-breathing behaviour. Air-breathing events interrupt display behaviour and increase risk of predation, raising the question of how Siamese fighting fish manage their oxygen requirements during agonistic encounters. Using open-flow respirometry, we measured rate of oxygen consumption in displaying fish to determine if males increase oxygen uptake per breath to minimise visits to the surface, or increase their reliance on aquatic oxygen uptake. We found that the increased oxygen requirements of Siamese fighting fish during display behaviour were met by increased oxygen uptake from the air with no significant changes in aquatic oxygen uptake. The increased aerial oxygen uptake was achieved almost entirely by an increase in air-breathing frequency. We conclude that limitations imposed by the reduced gill surface area of air-breathing fish restrict the ability of Siamese fighting fish to increase aquatic uptake, and limitations of the air-breathing organ of anabantoids largely restrict their capacity to increase oxygen uptake per breath. The resulting need to increase surfacing frequency during metabolically demanding agonistic encounters has presumably contributed to the evolution of the stereotyped surfacing behaviour seen during male–male interactions, during which one of the fish will lead the other to the surface, and each will take a breath of air.     

Aerobic scaling and resting metabolism in oviferous and post-spawning Barents Sea capelin Mallotus villosus villosus (Müller, 1776)

As part of the quantitative investigations into the bioenergetic relationships of the Barents Sea capelin, Mallotus villosus villosus (Müller, 1776), resting metabolic rates were examined in the oviferous and post-spawning fish in order to provide insights to aerobic scaling and the basal energetic costs associated with reproduction. Aerobic scaling of the different categories of sexually mature fish (body weight, W=13-54 g) could be expressed as: Q_O2=0.106W^1.049 (oviferous fish; N=11), Q_O2=0.411W^0.430 (post-spawning females; N=9), and Q_O2=0.075W^1.012 (post-spawning males; N=14), where Q_O2 is the oxygen consumption (ml O₂ h⁻¹) per fish. The weight specific oxygen consumption of oviferous capelin was about 30% higher (∼125 ml O₂ kg⁻¹ h⁻¹) compared to those of the post-spawning fish (79-87 ml O₂ kg⁻¹ h⁻¹). The results are discussed in context with other empirical studies on the aerobic scaling and metabolic costs involved with the build-up of roe in the fish.     

Hot hypoxic flies: Whole-organism interactions between hypoxic and thermal stressors in Drosophila melanogaster

The upper critical thermal maximum (CT_max) of metazoans varies over a wide range, and its determinative factors, such as oxygen limitation, remain controversial. Induction of thermoprotective mechanisms after challenge by sublethal heat stress has been well documented in many organisms, including the model fly Drosophila melanogaster. Interestingly, however, other challenges—notably a period of anoxia—induce post-exposure thermoprotective effects in some organisms such as locusts and houseflies. Here I show, using thermolimit respirometry, that acute hypoxia during thermal stress significantly reduced the CT_max of D. melanogaster, but only below an oxygen partial pressure of about 10 kPa (39.0±0.4 SE °C at 9.3 kPa vs. 36.0±0.2 SE °C at 3.5 kPa). Likewise, the scope for voluntary motor activity declined sharply below 10 kPa and was essentially eliminated at 2.3 kPa. Respiratory water loss increased highly significantly below about 10 kPa. The post-CT_max release of a large quantity of CO₂ is shown to be independent of loss of spiracular control, but dependent at least in part on oxygen availability. The results are broadly in accord with Pörtner's oxygen limitation hypothesis, but suggest that acute oxygen limitation only becomes an important factor at partial pressures less than half of typical atmospheric levels.     

Energetic cost of hovering flight in a nectar-feeding bat measured with fast-response respirometry

Hover-feeding glossophagine bats provide, in addition to the hummingbirds, a second vertebrate model for the analysis of hovering flight based on metabolic measurement and aerodynamic theory. In this study, the power input of hovering Glossophaga soricina bats (11.9 g) was measured by standard respirometry and fast-response (<0.2 s) oxygen analysis. Bats needed 5–7 s after a rest-to-flight transition to return to a respiratory steady state. Therefore, only hovering events preceeded by a 7-s flight interval were evaluated. V˙_O2 during hovering fluctuated with a frequency of 3–5 Hz, which corresponded in frequency to the licking movement of the tongue. During hovering, bats often may have hypoventilated as indicated by reduced V˙_O2 and a respiratory exchange ratio (RER) well below the steady-state value of 1. Steady-state oxygen consumption (and derived power input) during hovering was estimated to be 27 (25–29) ml O₂ g⁻¹ h⁻¹ (158 W kg⁻¹ or 1.88 W) in the 11.9-g bats as indicated by three independent findings: (1) V˙_O2 was 26 ml O₂ g⁻¹ h⁻¹ after 6.5 s of hovering, (2) the mean RER during single hovering events was at its steady-state level of 1 only at oxygen uptake rates of 25–29 ml g⁻¹ h⁻¹, and (3) when the oxygen potentially released from estimated oxygen stores was added to the measured oxygen uptake, the upper limit for oxygen consumption during hovering was found to be 29 ml O₂ g⁻¹ h⁻¹. Hovering power input was about 1.2 times the value of minimum flight power input (Winter and von Helversen 1998) and thus well below the 1.7–2.6 difference in power output postulated by aerodynamic theory (Norberg et al. 1993). Mass specific power input was 40% less than in hummingbirds. Thus, within the possible modes of hovering flight, Glossophaga bats seem to operate at the high-efficiency end of the spectrum. Accepted: 28 April 1998     

Responses of the teleost Hoplias malabaricus to hypoxia

Synopsis Oxygen uptake (VO₂) during graded hypoxia, rate of hypoxia acclimation, breathing frequency (f_R), breath volume (V_{S, R}) and gill ventilation (V_G) were measured in Hoplias malabaricus. Normoxia and hypoxia acclimated fish had similar and constant VO₂ and V_G in a range of water PO₂ from 150 to 25 mmHg. Hypoxia acclimated fish showed significantly higher VO₂ in severe hypoxia (PO₂ <15 mmHg). Normoxia acclimated fish showed symptoms similar to hypoxic coma after 1 h of exposure to water PO₂ of 10 mmHg whereas the same symptoms were observed only at PO₂ of 5 mmHg for fish acclimated to hypoxia. Fish required 14 days to achieve full acclimation to hypoxia (PO₂ ≥25 mmHg). Lowering of water PO₂ from 150 to 25 mmHg resulted in normoxic fish showing a 3–2 fold increase in V_G. The increase was the result of an elevation in V_{S, R} rather than f_R. Among normoxia acclimated specimens, small fish showed a higher V_G per unit weight than the large ones in both normoxia (PO₂ =150 mmHg) and hypoxia (PO₂ = 15 mmHg). A decrease in the ventilatory requirement (V_G/VO₂) with increased body weight was recorded in hypoxia (PO₂ = 15 mmHg).     

Rainbow trout Oncorhynchus mykiss consume less energy when swimming near obstructions

The effect of obstructions in steady flow on swimming by rainbow trout Oncorhynchus mykiss was examined in a respirometry swim tunnel to test the prediction that fish interacting with obstructions require less energy to hold station. When an obstruction was present, O. mykiss altered the kinematics of swimming and the rate of oxygen consumption was significantly reduced. The fish employed both entrainment and Kármán gait swimming strategies, permitting greater locomotor efficiency.     

Integrating Water Flow,Locomotor Performance and Respiration of Chinese Sturgeon during Multiple Fatigue-Recovery Cycles

The objective of this study is to provide information on metabolic changes occurring in Chinese sturgeon (an ecologically important endangered fish) subjected to repeated cycles of fatigue and recovery and the effect on swimming capability. Fatigue-recovery cycles likely occur when fish are moving through the fishways of large dams and the results of this investigation are important for fishway design and conservation of wild Chinese sturgeon populations. A series of four stepped velocity tests were carried out successively in a Steffensen-type swimming respirometer and the effects of repeated fatigue-recovery on swimming capability and metabolism were measured. Significant results include: (1) critical swimming speed decreased from 4.34 bl/s to 2.98 bl/s; (2) active oxygen consumption (i.e. the difference between total oxygen consumption and routine oxygen consumption) decreased from 1175 mgO₂/kg to 341 mgO₂/kg and was the primary reason for the decrease in U _crit; (3) excess post-exercise oxygen consumption decreased from 36 mgO₂/kg to 22 mgO₂/kg; (4) with repeated step tests, white muscle (anaerobic metabolism) began contributing to propulsion at lower swimming speeds. Therefore, Chinese sturgeon conserve energy by swimming efficiently and have high fatigue recovery capability. These results contribute to our understanding of the physiology of the Chinese sturgeon and support the conservation efforts of wild populations of this important species.