Standard Metabolic Rate Estimates Research Articles

Chasing away accurate results: exhaustive chase protocols underestimate maximum metabolic rate estimates in European perch Perca fluviatilis.

Metabolic rates are one of many measures that are used to explain species' response to environmental change. Static respirometry is used to calculate the standard metabolic rate (SMR) of fish, and when combined with exhaustive chase protocols it can be used to measure maximum metabolic rate (MMR) and aerobic scope (AS) as well. While these methods have been tested in comparison to swim tunnels and chambers with circular currents, they have not been tested in comparison with a no‐chase control. We used a repeated‐measures design to compare estimates of SMR, MMR and AS in European perch Perca fluviatilis following three protocols: (a) a no‐chase control; (b) a 3‐min exhaustive chase; and (c) a 3‐min exhaustive chase followed by 1‐min air exposure. We found that, contrary to expectations, exhaustive chase protocols underestimate MMR and AS at 18°C, compared to the no‐chase control. This suggests that metabolic rates of other species with similar locomotorty modes or lifestyles could be similarly underestimated using chase protocols. These underestimates have implications for studies examining metabolic performance and responses to climate change scenarios. To prevent underestimates, future experiments measuring metabolic rates should include a pilot with a no‐chase control or, when appropriate, an adjusted methodology in which trials end with the exhaustive chase instead of beginning with it.

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, Ucrit 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.

Development and testing of a simple field-based intermittent-flow respirometry system for riverine fishes.

By understanding range-wide intraspecific variation in metabolic rate we can better understand how organisms have adapted to their environment. However, methods to quantify metabolic rate of fishes from remote areas or those that cannot be brought back to the laboratory because of imperilment status are lacking. Consequently, practical and reliable field-based methods are needed. To address this need, we developed a simple yet robust intermittent-flow respirometry system, adapted from a design commonly used in the laboratory that is readily suited for field use. Standard metabolic rate (SMR), maximum metabolic rate (MMR) and aerobic scope (AS) estimates were obtained from juvenile lake trout (Salvelinus namaycush) and brook trout (Salvelinus fontinalis) using both field- and laboratory-based systems. Whole-fish SMR, MMR and AS estimates from the field and laboratory methods did not differ from one another (ANCOVA and LMM: all P > 0.05) for either species and were comparable to estimates previously reported. Our field setup is a simpler system than the conventional laboratory-based system that requires less power and equipment to operate, yet still offers users the ability to: (1) acclimate fish to the respirometry chamber; (2) measure oxygen consumption during a shorter period (1 h), which yield metabolic rate estimates comparable to systems that take measurements over longer periods; and (3) take repeated oxygen consumption measurements with manual user-defined flush and measurement phase routines. Developing practical and reliable field respirometry methods, as demonstrated here, is important if we wish to improve our ability to predict how imperiled species will respond to changes in their environment. Such knowledge is critical for informing conservation strategies.

Effect of nanosilver on metabolism in rainbow trout (Oncorhynchus mykiss): An investigation using different respirometric approaches.

Nanosilver (nAg) has been incorporated into many consumer products, including clothing and washing machines, because of its antimicrobial properties. Consequently, the potential for its release into aquatic environments is of significant concern. Documented toxic effects on fish include altered gene expression, gill damage, and impaired gas exchange, as well as mortality at high nAg concentrations. The present study reports the effects of nAg on the metabolism of rainbow trout (Oncorhynchus mykiss). Fish were exposed to environmentally relevant concentrations (0.28 ± 0.02 μg/L) and higher (47.60 ± 5.13 μg/L) for 28 d, after which their standard metabolic rate (SMR), forced maximum metabolic rate (MMRf ), and spontaneous maximum metabolic rate (MMRs ) were measured. There was no effect observed in SMR, MMRf , or MMRs , suggesting that nAg is unlikely to directly affect fish metabolism. On average, MMRs tended to be greater than MMRf , and most MMRs occurred when room lighting increased. The timing of MMRf chase protocols was found to affect both MMRf and SMR estimates, in that chasing fish before respirometric experiments caused higher MMRf estimates and lower SMR estimates. Although compounded effects involving nAg and other environmental stressors remain unknown, the present study indicates that the tested range of nAg is unlikely to constrain fish metabolism. Environ Toxicol Chem 2017;36:2722-2729. © 2017 SETAC.

Inbreeding effects on standard metabolic rate investigated at cold, benign and hot temperatures in Drosophila melanogaster

Inbreeding increases homozygosity, which is known to affect the mean and variance of fitness components such as growth, fecundity and mortality rate. Across inbred lines inbreeding depression is typically observed and the variance between lines is increased in inbred compared to outbred lines. It has been suggested that damage incurred from increased homozygosity entails energetic cost associated with cellular repair. However, little is known about the effects of inbreeding on standard metabolic rate. Using stop-flow respirometry we performed repeated measurements of metabolic rate in replicated lines of inbred and outbred Drosophila melanogaster at stressful low, benign and stressful high temperatures. The lowest measurements of metabolic rate in our study are always associated with the low activity period of the diurnal cycle and these measurements therefore serve as good estimates of standard metabolic rate. Due to the potentially added costs of genetic stress in inbred lines we hypothesized that inbred individuals have increased metabolic rate compared to outbred controls and that this is more pronounced at stressful temperatures due to synergistic inbreeding by environment interactions. Contrary to our hypothesis we found no significant difference in metabolic rate between inbred and outbred lines and no interaction between inbreeding and temperature. Inbreeding however effected the variance; the variance in metabolic rate was higher between the inbred lines compared to the outbred control lines with some inbred lines having very high or low standard metabolic rate. Thus genetic drift and not inbreeding per se seem to explain variation in metabolic rate in populations of different size.

Finding the best estimates of metabolic rates in a coral reef fish

Metabolic rates of aquatic organisms are estimated from measurements of oxygen consumption rates ( ) through swimming and resting respirometry. These distinct approaches are increasingly used in ecophysiology and conservation physiology studies; however, few studies have tested whether they yield comparable results. We examined whether two fundamental measures, standard metabolic rate (SMR) and maximum metabolic rate (MMR), vary based on the method employed. Ten bridled monocle bream (Scolopsis bilineata) were exercised using (1) a critical swimming speed (Ucrit) protocol, (2) a 15 min exhaustive chase protocol and (3) a 3 min exhaustive chase protocol followed by brief (1 min) air exposure. Protocol 1 was performed in a swimming respirometer whereas protocols 2 and 3 were followed by resting respirometry. SMR estimates in swimming respirometry were similar to those in resting respirometry when a three-parameter exponential or power function was used to extrapolate the swimming speed- relationship to zero swimming speed. In contrast, MMR using the Ucrit protocol was 36% higher than MMR derived from the 15 min chase protocol and 23% higher than MMR using the 3 min chase/1 min air exposure protocol. For strong steady (endurance) swimmers, such as S. bilineata, swimming respirometry can produce more accurate MMR estimates than exhaustive chase protocols because oxygen consumption is measured during exertion. However, when swimming respirometry is impractical, exhaustive chase protocols should be supplemented with brief air exposure to improve measurement accuracy. Caution is warranted when comparing MMR estimates obtained with different respirometry methods unless they are cross-validated on a species-specific basis.

Influence of respirometry methods on intraspecific variation in standard metabolic rates in newts

Standard metabolic rate (SMR) is both a highly informative and variable trait. Variation in SMR stems not only from diverse intrinsic and extrinsic factors, but also from the use of diverse methods for metabolic measurements. We measured CO2 production (V˙CO2) and oxygen consumption rates (V˙O2) using two flow-through respirometry modes, continuous and intermittent (stop-flow), to evaluate their potential contribution to SMR variation in Alpine newts, Ichthyosaura alpestris. Both respirometry modes yielded similar and repeatable V˙CO2 values. Although V˙O2 was highly repeatable, continuous respirometry produced lower V˙O2 than the intermittent method. During intermittent measurements, the total number of activity bouts was higher than during continuous respirometry trials. Statistical correction for disparate activity levels minimized variation in oxygen consumption between respirometry modes. We conclude that use of either method of flow-through respirometry, if properly applied, introduced less noise to SMR estimates than a variation in activity levels.

Accelerating estimates of activity-specific metabolic rate in fishes: Testing the applicability of acceleration data-loggers

We report the results of a series of experiments to test the utility of acceleration data-loggers for determining the energy expenditure of juvenile hammerhead sharks ( Sphyrna lewini). In one experiment, three sharks were instrumented with miniature acceleration data-loggers and swum in a Brett-style respirometer at a range of speeds. For all three sharks, significant linear relationships were obtained between mean oxygen consumption (M ·o 2) and Partial Dynamic Body Acceleration in the lateral and dorso-ventral axes (PDBA y, z ) with high predictive power ( r 2 > 0.71). In a second experiment, PDBA was measured for sharks swimming freely in circular tanks. The free-swimming sharks exhibited wide ranges of PDBA y, z ; routine swimming was characterised by low PDBA y, z (0.01–0.12 g) whereas unsteady swimming, (especially fast-start swimming of > 1 g) was characterised by high PDBA y, z . Despite initial evidence of linearity in the oxygen consumption vs. PDBA relationship, incorporating previous estimates of standard metabolic rate of hammerhead sharks suggests a non-linear fit. Further work is needed to establish the exact shape of the relationship beyond the narrow range of speeds that hammerhead pups could be exercised in this study, particularly the low swimming speeds which are frequently observed in free-swimming animals.

Effect of isoenergetic diets with different protein and lipid content on the growth performance and heat increment of rainbow trout

The heat increment of feeding (HiE) is the metabolic cost associated with feeding, typically measured in fish as the increase in oxygen consumption (MO2) over some estimate of standard metabolic rate (SMR). The present study sought to accurately measure HiE using a variety of different methods in order to remove the influence of routine fish activity and excitement which could overestimate HiE. Protein handling makes up a large component of HiE. Thus, there is an expectation that variations in dietary protein content could influence HiE. Therefore, growth performance parameters were assessed in juvenile rainbow trout fed daily to satiation one of three isoenergetic diets with equivalent carbohydrate content (12%) but variable protein (P) and lipid (L) content [theoretical protein:lipid levels were: 55%:10% (HP:LL); 45%:15% (MP:ML) and 35%:20% (LP:HL)]. The estimated dietary digestible protein (DP) to digestible energy (DE) ratios of 19.8, 24.8 and 29.8 g/MJ bracketed the recommended levels of 22–25 g/MJ for juvenile rainbow trout. HiE values for the same groups of fish that were maintained on the test diets after the growth trial were subsequently assessed following a single meal (by gavage) of 2% of their body mass so that the growth performance parameters could be compared with the HiE estimates. Some growth performance parameters (i.e., specific growth rate, feed efficiency and dry feed intake) did not vary significantly among fish fed the diets, whereas percent protein deposition was inversely related to dietary protein content and the dietary DP to DE ratio. The dissimilar diet treatments did not result in differences in values for SMR, RMR, peak MO2 or time-to-peak MO2 or in estimates for HiE. The mean SMR from all fish combined across treatments was 50.4±3.4 mg O2/kg/h. MO2 increased significantly above SMR by 4-h postprandial and peaked at 116.2±7.7 mg O2/kg/h, representing an increase of 131%. The metabolic cost of the diets (as a % of DE) was low, and best estimates ranged between 4.0 and 4.8%.

Aerobic metabolic rates of swimming juvenile mako sharks, Isurus oxyrinchus

The shortfin mako shark, Isurus oxyrinchus, is a highly streamlined epipelagic predator that has several anatomical and physiological specializations hypothesized to increase aerobic swimming performance. A large swim-tunnel respirometer was used to measure oxygen consumption (MO2) in juvenile mako sharks (swimming under controlled temperature and flow conditions) to test the hypothesis that the mako shark has an elevated maintenance metabolism when compared to other sharks of similar size swimming at the same water temperature. Specimen collections were conducted off the coast of southern California, USA (32.94°N and 117.37°W) in 2001-2002 at sea-surface temperatures of 16.0–21.0°C. Swimming MO2 and tail beat frequency (TBF) were measured for nine mako sharks [77–107 cm in total length (TL) and 4.4 to 9.5 kg body mass] at speeds from 28 to 54 cm s−1 (0.27–0.65 TL s−1) and water temperatures of 16.5–19.5°C. Standard metabolic rate (SMR) was estimated from the extrapolation to 0-velocity of the linear regression through the LogMO2 and swimming speed data. The estimated LogSMR (±SE) for the pooled data was 2.0937 ± 0.058 or 124 mg O2 kg−1 h−1. The routine metabolic rate (RMR) calculated from seventeen MO2 measurements from all specimens, at all test speeds was (mean ± SE) 344 ± 22 mg O2 kg−1h−1 at 0.44 ± 0.03 TL s−1. The maximum metabolic rate (MMR) measured for any one shark in this study was 541 mg O2 kg−1h−1 at 54 cm s−1 (0.65 TL s−1). The mean (±SE) TBF for 39 observations of steady swimming at all test speeds was 1.00 ± 0.01 Hz, which agrees with field observations of 1.03 ± 0.03 Hz in four undisturbed free-swimming mako sharks observed during the same time period. These findings suggest that the estimate of SMR for juvenile makos is comparable to that recorded for other similar-sized, ram-ventilating shark species (when corrected for differences in experimental temperature). However, the mako RMR and MMR are apparently among the highest measured for any shark species.

Temperature- and body mass-related variation in cyclic gas exchange characteristics and metabolic rate of seven weevil species: Broader implications

The influence of temperature on metabolic rate and characteristics of the gas exchange patterns of flightless, sub-Antarctic Ectemnorhinus-group species from Heard and Marion islands was investigated. All of the species showed cyclic gas exchange with no Flutter period, indicating that these species are not characterized by discontinuous gas exchange cycles. Metabolic rate estimates were substantially lower in this study than in a previous one of a subset of the species, demonstrating that open-system respirometry methods provide more representative estimates of standard metabolic rate than do many closed-system methods. We recommend that the latter, and especially constant-pressure methods, either be abandoned for estimates of standard metabolic rate in insects, or have their outputs subject to careful scrutiny, given the wide availability of the former. V˙CO 2 increase with an increase in temperature (range: 0–15 °C) was modulated by an increase in cycle frequency, but typically not by an increase in burst volume. Previous investigations of temperature-related changes in cyclic gas exchange (both cyclic and discontinuous) in several other insect species were therefore substantiated. Interspecific mass-scaling of metabolic rate (ca. 0.466–0.573, excluding and including phylogenetic non-independence, respectively) produced an exponent lower than 0.75 (but not distinguishable from it or from 0.67). The increase of metabolic rate with mass was modulated by an increase in burst volume and not by a change in cycle frequency, in keeping with investigations of species showing discontinuous gas exchange. These findings are discussed in the context of the emerging macrophysiological metabolic theory of ecology.

Increased metabolic cost of swimming and consequent alterations to circadian activity in rainbow trout (Oncorhynchus mykiss) exposed to dietary copper

This study tests the hypothesis that rainbow trout (Oncorhynchus mykiss) compensate for the metabolic cost of dietary Cu exposure by reducing swimming activity at particular times during the diel cycle. Fish were exposed to excess dietary Cu for three months (726 mg Cu·kg–1dry weight) and simultaneously oxygen consumption (MO2) and spontaneous swimming activity were measured. Rhythmicity in swimming activity was examined by videorecording fish behaviours for 48 h. Standard metabolic rate estimates (RS) of 7.2 and 8.7 mmol O2·kg–1·h–1(15°C) were measured for control and Cu-exposed fish, respectively. MO2was higher in Cu-exposed fish at any chosen speed compared with control Cu-exposed trout, which decreased activity (mean speed) by at least 75%, spent more time at lower speeds, and lost circadian periodicity in these parameters compared with controls. Mean growth rates were normal, although Cu-exposed fish showed a narrower range of body weights and fewer mortalities than control groups, suggesting a suppression in social behaviour in Cu-exposed fish. Overall, the increased metabolic cost of swimming in Cu-exposed fish was fully compensated by a reduction in activity, particularly at night and dawn. However, this behavioural strategy suggests that spatial and temporal aspects of ecologically important social behaviours may be compromised in Cu-exposed fish.

Metabolic rates of juvenile scalloped hammerhead sharks (Sphyrna lewini)

Oxygen consumption of juvenile scalloped hammerhead sharks, Sphyrna lewini, was measured in a Brett-type flume (volume=635 l) to quantify metabolic rates over a range of aerobic swimming speeds and water temperatures. Oxygen consumption (log transformed) increased at a linear rate with increases in tailbeat frequency and swimming speed. Estimates of standard metabolic rate ranged between 161 mg O2 kg–1 h–1 at 21°C and 203 mg O2 kg–1 h–1 at 29°C (mean±SD: 189±15 mg O2 kg–1 h–1 at 26°C). Total metabolic rates ranged from 275 mg O2 kg–1 h–1 at swimming speeds of 0.5 body lengths per second (L s–1) to a maximum aerobic metabolic rate of 501 mg O2 kg–1 h–1 at 1.4 L s–1. Net cost of transport was highest at slower swimming speeds (0.5–0.6 L s–1) and was lowest between 0.75 and 0.9 L s–1. Therefore, these sharks are most energy efficient at swimming speeds between 0.75 and 0.9 L s–1. These data indicate that tailbeat frequency and swimming speed can be used as predictors of metabolic rate of free-swimming juvenile hammerhead sharks.

Metabolic rates in an anadromous clupeid, the American shad ( Alosa sapidissima )

To assess the energetics of migration in an anadromous fish, adult American shad (Alosa sapidissima) were swum in a large respirometer at a range of speeds (1.0–2.3 body lengths (BL) s−1, 13–24 °C). Metabolic rate (MO2) was logarithmically related to swimming speed (Bl s−1; r 2 = 0.41, slope = 0.23 ± 0.037) and tailbeat frequency (beats × min−1; r 2 = 0.52, slope = 0.003 ± 0.0003). Temperature had a significant effect on metabolic rate (r 2 = 0.41) with a Q10 of 2.2. Standard metabolic rate (SMR), determined directly after immobilization with the neuroblocker gallamine triethiodide, ranged from 2.2–6.2 mmolO2 kg−1 h−1 and scaled with mass (W) such that SMR = 4.0 (±0.03)W0.695(±0.15). Comparison of directly determined and extrapolated SMR suggests that swimming respirometry provides a good estimate of SMR in this species, given the differences in basal activity monitored by the two methods. Overall, American shad metabolic rates (MO2 and SMR) were intermediate between salmonids and fast-swimming perciforms, including tunas, and may be a result of evolutionary adaptation to their active pelagic, schooling life history. This study demonstrates variability in metabolic strategy among anadromous fishes that may be important to understanding the relative success of different migratory species under varying environmental conditions.

An estimate of the cost of free existence in the sandy-beach whelk Bullia digitalis (Dillwyn) on the west coast of South Africa

Data obtained previously on the energy expenditure of Bullia digitalis (Dillwyn) during its various activities have been applied to field records of the length of time spent in each activity. From the resulting figures an average cost of free existence of 52 cal · day −1 has been calculated for a whelk of 750 mg dry tissue wt. This is only 1.14 times the best estimate of standard metabolic rate. The animal can, at a single meal, ingest food containing 18 times the calories needed for 24 h of free existence.

The Influence of Temperature on Scope for Activity in Cutthroat Trout, Salmo clarki

Abstract One hundred eleven active and 71 standard metabolic rate estimates were made on 90-g cutthroat trout Salmo clarki at five temperatures. Active metabolism was lowest at 5 C (363 mg O2kg-h) and highest at 15 C (597 mg O2kg-h). At 20 C and 24 C it was 559 and 491 mg/kg-h, respectively. Scope for activity ranged from a low of 316 mg O2kg-h at 5 C to a high of 486 mg O2kg-h at 15 C then down to 374 mg O2kg-h at 24 C. Standard metabolisms at 5, 10, 15, 20, and 24 C were 47, 73, 111, 129, and 117 mg O2kg-h respectively.