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In situ chemical oxidation (ISCO) is a popular remediation technique for hydrocarbon-contaminated soil and groundwater. A range of oxidising agents and activators are available for ISCO; however, selection is usually based on contaminant destruction which is time-consuming and impacted by sample heterogeneity based on 1–10 g sample contaminant analysis. In this paper, we demonstrate the use of an automated respirometer, measuring CO2 production, as a rapid and reliable approach for activator type and concentration selection. The approach is demonstrated based on tests in matrices of different types (loam soil and sand). In both matrices, CO2 production was significantly increased following sodium persulphate (SPS) oxidation with iron activation in a concentration-dependant manner. Alkaline activation led to no increased CO2 production compared to SPS addition without activation. The approach will provide greater confidence in treatability testing and reagent efficiency in ISCO projects.

This analysis shows good intentions in the selection of valid and precise oxygen uptake ( M˙ O2 ) measurements by retaining only slopes of declining dissolved oxygen level in a respirometer that have very high values of the coefficient of determination, r2 , are not always successful at excluding nonlinear slopes. Much worse, by potentially removing linear slopes that have low r2 only because of a low signal-to-noise ratio, this procedure can overestimate the calculation of standard metabolic rate (SMR) of the fish. To remedy this possibility, a few simple diagnostic tools are demonstrated to assess the appropriateness of a given minimum acceptable r2 , such as calculating the proportion of rejected M˙ O2 determinations, producing a histogram of the r2 values and a plot of r2 as a function of M˙ O2 . The authors offer solutions for cases when many linear slopes have low r2 . The least satisfactory but easiest to implement is lowering the minimum acceptable r2 . More satisfactory solutions involve processing (smoothing) the raw signal of dissolved oxygen as a function of time to improve the signal-to-noise ratio and the r2 s.

[Purpose] We examined the inter-rater reliability of the Wright respirometer between therapists who assessed the vital capacity of patients with neuromuscular disorders. [Participants and Methods] We examined 18 patients with neuromuscular disorders. We performed a test-retest method after measuring their vital capacities. Two physical therapists experienced in the use of the Wright respirometer, specifically, therapist A with six years of clinical experience and therapist B with one, each took one measurement of the vital capacity of the same patients. The measurements between the therapists were taken at intervals of 3–7 days. We made a manual to standardize the measurements between the therapists. [Results] The vital capacities were 905 ± 490 mL for therapist A and 897 ± 483 mL for therapist B. The inter-rater reliability of ICC2,1 was 0.96 (95% CI: 0.89–0.98). Bland-Altman analyses revealed neither a fixed nor proportional bias. [Conclusion] These results demonstrated good to excellent inter-rater reliability of the Wright respirometer for patients with neuromuscular disorders using a manual and instructions.

International audience; Oxygen uptake, heart rate and contraction frequencies of slow oxidative (SO) and fast glycolytic (FG) muscle were measured simultaneously in gilthead seabream Sparus aurata submitted to stepwise increases in current speed in a swimming respirometer. Variation in oxygen uptake was closely related to variation in heart rate, over initial steps these rose in concert with an increase in contraction frequency of SO muscle. There was an asymptote in oxygen uptake and heart rate at high speeds that reflected a transition from exclusive use of aerobic SO muscle to a combination of SO and anaerobic FG muscle, and which preceded fatigue.

This study hypothesized that oxygen uptake (ṀO2 ) measured with a novel protocol of chasing rainbow trout Oncorhynchus mykiss to exhaustion inside a static respirometer while simultaneously monitoring ṀO2 (ṀO2chase ) would generate the same and repeatable peak value as when peak active ṀO2 (ṀO2active ) is measured in a critical swimming speed protocol. To reliably determine peak ṀO2chase , and compare to the peak during recovery of ṀO2 after a conventional chase protocol outside the respirometer (ṀO2rec ), this study applied an iterative algorithm and a minimum sampling window duration (i.e., 1 min based on an analysis of the variance in background and exercise ṀO2 ) to account for ṀO2 dynamics. In support of this hypothesis, peak ṀO2active (707 ± 33 mg O2 h-1 kg-1 ) and peak ṀO2chase (663 ± 43 mg O2 h-1 kg-1 ) were similar (P = 0.49) and repeatable (Pearson's and Spearman's correlation test; r ≥ 0.77; P < 0.05) when measured in the same fish. Therefore, estimates of ṀO2max can be independent of whether a fish is exhaustively chased inside a respirometer or swum to fatigue in a swim tunnel, provided ṀO2 is analysed with an iterative algorithm and a minimum but reliable sampling window. The importance of using this analytical approach was illustrated by peak ṀO2chase being 23% higher (P < 0.05) when compared with a conventional sequential interval regression analysis, whereas using the conventional chase protocol (1-min window) outside the respirometer increased this difference to 31% (P < 0.01). Moreover, because peak ṀO2chase was 18% higher (P < 0.05) than peak ṀO2rec , chasing a fish inside a static respirometer may be a better protocol for obtaining maximum ṀO2 .

Respirometric techniques were applied to estimate the toxic effect of several heavy metals (chromium(III), lead, nickel, mercury and zinc) on the activity of the heterotrophic bacteria present in activated sludge and to ascertain how the presence of these pollutants can affect biological treatment. For the assays, activated sludge was collected from the biological reactor (oxidation ditch) of a sewage treatment plant that also receives industrial wastewater. The tests were performed in a batch respirometer operating in dynamic mode, and the corresponding respirograms were obtained. The values obtained (between 0.47 and 0.71) for the specific growth yield coefficient in the different activated sludge samples pointed to the adequate performance of the biological treatment applied. The experimental data obtained showed that inhibition percentage is a logarithmic function of metal concentration, the toxicity of the heavy metals following the order: Hg ≫ Zn > Cr > Pb > Ni.

This study developed a portable, low-cost field respirometer for measuring oxygen consumption rates of large-bodied fishes. The respirometer performed well in laboratory tests and was used to measure the oxygen consumption rates ( M ˙ O2 ) of bull sharks Carcharhinus leucas (mean: 249.21 ± 58.10 mg O2 kg-1 h-1 at 27.05°C). Interspecific comparisons and assessments of oxygen degradation curves indicated that the respirometer provided reliable measurements of M ˙ O2 . This system presents a field-based alternative to laboratory respirometers, opening opportunities for studies on species in remote localities, increasing the ability to validate physiological field studies.

Goal of the work was to compare the respiration activities, as measured via oxygen consumption with three different organic waste stability methods so that to propose the optimal one. The novelty of the work is that there exists no comparison of solid-phase with liquid-phase stability assessment techniques in the literature. The respiration activities were assessed using two solid-phase methods and a manometric liquid-phase method (MANLIQ) performed on twenty-seven organic substrates. The methods rely on measuring oxygen consumption (uptake) via pressure drops (liquid-phase test, static solid-phase test) or via direct O2 measurements on the gaseous phases at the inlet and outlet of the respirometer (solid-phase dynamic test). A positive statistically significant correlation was calculated between the MANLIQ and the static solid-phase indices. The maximum rate MANLIQ index for the raw substrates was 2900 mg O2 kg−1 VS h−1, while most of the processed substrates had cumulative MANLIQ indices below 160 g O2 kg−1 VS. The ratio of the liquid indices to the static solid-phase indices ranged from 1.6 to 2.7 and the ratio of the liquid indices to the dynamic solid-phase indices ranged from 0.2 to 0.4. The MANLIQ method failed to result in a good correlation of the processing time with the respiration indices. On the other hand, a correlation was more visible in the two solid-phase tests, despite the large variability of the types and sources of the substrates. Therefore, the solid-phase methods should be preferred over the liquid-phase method to assess stability for various organic substrates.

The predicted growth in plastic demand and the targets for global CO2 emission reductions require a transition to replace fossil-based feedstock for polymers and a transition to close-loop recyclable, and in some cases to, biodegradable polymers. The global crisis in terms of plastic littering will furthermore force a transition towards materials that will not linger in nature but will degrade over time in case they inadvertently end up in nature. Efficient systems for studying polymer (bio)degradation are therefore required. In this research, the Respicond parallel respirometer was applied to polyester degradation studies. Two poly(lactic-co-glycolic acid) copolyesters (PLGA12/88 and PLGA6/94) were tested and shown to mineralise faster than cellulose over 53 days at 25 °C in soil: 37% biodegradation for PLGA12/88, 53% for PLGA6/94, and 30% for cellulose. The corresponding monomers mineralised much faster than the polymers. The methodology presented in this article makes (bio)degradability studies as part of a materials development process economical and, at the same time, time-efficient and of high scientific quality. Additionally, PLGA12/88 and PLGA6/94 were shown to non-enzymatically hydrolyse in water at similar rates, which is relevant for both soil and marine (bio)degradability.

WOS:000681398200011; International audience; Gilthead seabream were equipped with intraperitoneal biologging tags to investigate cardiac responses to hypoxia and warming, comparing when fish were either swimming freely in a tank with conspecifics or confined to individual respirometers. After tag implantation under anaesthesia, heart rate (f(H)) required 60 h to recover to a stable value in a holding tank. Subsequently, when undisturbed under control conditions (normoxia, 21 degrees C), mean f(H) was always significantly lower in the tank than in the respirometers. In progressive hypoxia (100% to 15% oxygen saturation), mean f(H) in the tank was significantly lower than in the respirometers at oxygen levels down to 40%, with significant bradycardia in both holding conditions below this level. Simultaneous logging of tri-axial body acceleration revealed that spontaneous activity, inferred as the variance of external acceleration (VAR(m)), was low and invariant in hypoxia. Warming (21 to 31 degrees C) caused progressive tachycardia with no differences in f(H) between holding conditions. Mean VAR(m) was, however, significantly higher in the tank during warming, with a positive relationship between VAR(m) and f(H) across all temperatures. Therefore, spontaneous activity contributed to raising f(H) of fish in the tank during warming. Mean f(H) in respirometers had a highly significant linear relationship with mean rates of oxygen uptake, considering data from hypoxia and warming together. The high f(H) of confined seabream indicates that respirometry techniques may bias estimates of metabolic traits in some fishes, and that biologging on free-swimming fish will provide more reliable insight into cardiac and behavioural responses to environmental stressors by fish in their natural environment.

Temperature is one of the most important variables that influence aquatic organisms. This study aimed to test physiological and molecular differences in the thermal tolerance of two morphologically similar Marsupenaeus japonicus. The physiological parameter was the upper thermal limit, tested via the critical thermal maximum, and the molecular parameter was the relative messenger RNA expression of heat shock proteins (HSP40, HSP60, HSP70 and HSP90), quantified via real-time polymerase chain reaction. Oxygen consumption of shrimp was measured with a respirometer. M. japonicus variety II showed a higher critical thermal maxima and survival rate and lower oxygen consumption rate than variety I, suggesting that it had higher thermal tolerance and acclimatory plasticity. M. japonicus variety I showed significantly higher production of HSP70 and HSP90, suggesting that these shrimp may have experienced more thermal damage. By comparing the differences in the stress response between two morphologically similar M. japonicus, this study provides useful information for the aquaculture of M. japonicus.

Standard tests such as ISO 17556 (Plastics - determination of the ultimate aerobic biodegradability in soil by measuring the oxygen demand in a respirometer or the amount of carbon dioxide evolved. International Organization for Standardization, Geneva, Switzerland, 2019) or ASTM D5988 (Standard test method for determining aerobic biodegradation of plastic materials in soil. ASTM International, West Conshohocken, 2018) have been developed for measuring the biodegradation of polymers and assessing their biodegradability in soil. In several experiments performed according to these standard tests, the measured biodegradation of cellulose was reported unexpectedly between 80 and 85%. These results are difficult to justify since cellulose is a well-known biodegradable material. In the present study, this phenomenon is explained as the consequence of starvation occurring in a confined bioreactor. It is proposed that the favourable conditions applied to the small-size bioreactors accelerate the proliferation of the microorganisms which are responsible for the biodegradation. Such a dense microbial population may face starvation when cellulose is consumed. It is assumed that starvation causes the secretion of an inhibitory chemical signal, which can diffuse to neighbouring sites still containing food, and suppresses biodegradation. This hypothesis was supported by two experiments. First, it was shown that the final measured biodegradation increased when the microbial growth rate decreased by reducing temperature. In the second experiment, it was shown that the biodegradation proceeded slower when a new cellulose quantity was inserted into a previously used soil substrate. To confirm the hypothesis regarding the presence of an inhibitory starvation factor, which can suppress biodegradation, a Kinetic Monte Carlo (KMC) model was also developed. The KMC simulations reproduced qualitatively the experimental findings.

The objective of this research was to determine the effects of diel cycle and flow velocity on rheotaxis, measure the swimming performance of Perch-barbel (Percocypris pingi, Tchang, 1930) and use the results to recommend an appropriate fishway entrance velocity and fish lift operating schedule. PIT tagging was used to monitor fish rheotaxis for 48 h in four channels with differing flow characteristics. Swimming performance tests were conducted in a swimming respirometer and induced flow speed, critical swimming speed and critical burst speed were determined. The relationship between flow velocity and fish swimming behavior was analyzed to determine the optimal attraction flow velocity. There were three primary findings. (1) Test fish were active both day and night, but made more attempts, had longer retention times, and swam longer through-water distances in all channels during the day. (2) Entry, retention, and effort were maximum at a flow velocity of 0.2 m/s (26% of absolute critical swimming speed (m/s) and 29% of relative critical swimming speed (bl/s)). (3) Attempt number, retention time and through-water distance increased with body length in the channel with greatest activity. Collectively, these data suggest that passage of P. pingi will be optimized by fishways operating throughout the day and most of the night, although these conditions could lead to size-based selectivity in passage.

Fish physiology and behavior are affected by exposure to light of varying colors, but little is known about the effects on swimming performance and metabolism. The purpose of this study was to measure the effects of light color on the swimming performance of bighead carp (Aristichthys nobilis), a planktivorous fish species widely used in aquaculture. Stepped velocity testing was conducted in a modified Brett-type swim tunnel respirometer to determine critical swimming speed (Ucrit), oxygen consumption (MO2), and excess post-exercise oxygen consumption (EPOC) for juvenile bighead carp under red, yellow, blue, and green lights at 25 °C. Ucrit was significantly lower for fish swimming under yellow and green lights compared with red and blue light. Cost of transport (COT), a measure of swimming efficiency, also varied with color. The results, obtained under controlled conditions, add to our knowledge on the effects of artificial color light on fish physiology and behavior and inform decisions on the use of artificial color light in aquaculture and fishway design.

Bluefin tunas are highly specialized fish with unique hydrodynamic designs and physiological traits. In this study, we present results in a captive population that demonstrate strong effects of ambient temperature on the tail beat frequency and swimming speed of a pelagic fish in both pre- and post-prandial states. We measured the responses of a ram ventilator, the Pacific bluefin tuna (Thunnus orientalis), after digestion of a meal to explore the impacts of the metabolic costs of digestion on behavior and respiration. A combination of respirometry, physiological biologging of visceral temperatures, and activity monitoring with accelerometry were used to explore the metabolic costs of digestion and the impacts on ventilation and swimming speed. Experiments were conducted at temperatures that are within the metabolic optimum for Pacific bluefin tuna (17 °C), and at a second temperature corresponding to the upper distributional limit of the species in the California Current (24 °C). Warmer temperatures resulted in higher tail-beat frequency and greater elevation of body temperature in pre-prandial Pacific bluefin tuna. Specific dynamic action (SDA) events resulted in a significant postprandial increase in tail-beat frequency of ~0.2 Hz, compared to pre-prandial levels of 1.5 Hz (17 °C) and 1.75 Hz (24 °C), possibly resulting from ventilatory requirements. Data of fish exercised in a swim-tunnel respirometer suggest that the observed increase in tail-beat frequency comprise 5.5 and 6.8% of the oxygen demand during peak SDA at 24 °C and 17 °C respectively. The facultative increase in swimming speed might increase oxygen uptake at the gills to meet the increasing demand by visceral organs involved in the digestive process, potentially decreasing the available energy of each meal for other metabolic processes, such as growth, maturation, and reproduction. We hypothesize that these post-prandial behaviors allow tuna to evacuate their guts more quickly, ultimately permitting fish to feed more frequently when prey is available.

Monitoring respiration as rates of either O2 consumption or CO2 production is an important tool to optimise the design of packaging systems or to maintain optimal conditions inside storage systems for fruit and vegetables. Currently, respiration rates are mostly measured by gas chromatography or headspace gas analysers. Both these methods are manual and, for analysis, draw a considerable amount of gas from the system. Thus, they risk lowering the air pressure inside the storage and packaging volumes. In this study, a compact (free volume of 3.3 L) and modular respirometer based on a respiration measuring sphere (RMS88) was developed, which consisted of one O2 (0–25%) and two CO2 sensors (0–0.5% and 0–5%) for continuous real-time monitoring of gas concentrations and respiration rates of fresh produce. This system was tested under different conditions and respiration rates of strawberries were measured. At first, the system was tested without and with flushing of ambient air (every 6 h at 5 L/min) inside the respirometer at 10 °C. The system was further tested with strawberries stored under modified atmospheric conditions and flushing (every 5 h at 5 L/min) with stepwise reductions of O2 from 21% to 16%, 8%, 4%, 2%, and 1% O2 (balanced by nitrogen). Additionally, the developed system was tested under in-situ conditions for strawberries stored inside respirometer, kept in two separate controlled atmosphere (CA) metal chambers at 10 °C and 20 °C respectively. In addition, the respiratory quotient (RQ) of strawberries was calculated from the respective O2- and CO2-based respiration rates at all storage conditions. The modular respirometer proved to be a useful system for rapid, high accuracy and real-time measurement of respiration rates of fresh produce during time windows of several days.

Water temperature is known to be a particularly important environmental factor that affects fish swimming performance, but it is unknow how acute temperature changes affect the fish performance of Ptychobarbus kaznakovi. P. kaznakovi in the Lancang River have declined quickly in recent years, and this species was used to examine the effects of acute temperature changes on swimming abilities and oxygen consumption in a Brett‐type swimming tunnel respirometer. The standard metabolic rate (SMR) and routine metabolic rate (RMR) showed 216% and 134% increases, respectively, at 22°C (an acute increase from 17 to 22°C) compared to those at 12°C (an acute decrease from 17 to 12°C). Moreover, the RMR was approximately 1.7, 1.6 and 1.3 times the value of the SMR at 12°C, 17°C and 22°C, respectively. The critical swimming speed (Ucᵣᵢₜ) of P. kaznakovi at 22°C was 5.45 ± 0.45BL/S, which was 45% higher than that at 12°C (3.77 ± 0.92BL/S). The oxygen consumption rates (MO₂) reached their maximum values at swimming speeds near the Ucᵣᵢₜ for all the temperature treatments. The maximum metabolic rate (MMR) values at 12°C, 17°C and 22°C were 274.53 ± 142.60 (mgO₂ kg⁻¹ hr⁻¹), 412.85 ± 216.34 (mgO₂ kg⁻¹ hr⁻¹) and 1,095.73 ± 52.50 (mgO₂ kg⁻¹ hr⁻¹), respectively. Moreover, there was a narrow aerobic scope at 12°C compared to that at 17°C and 22°C. The effect of acute temperature changes on the swimming abilities and oxygen consumption of P. kaznakovi indicated that water temperature changes caused by dam construction could directly affect energy consumption during the upstream migration of fish.

© 2021 by the authors., On-growing juveniles of gilthead sea bream were acclimated for 45 days to mild-hypoxia (M-HYP, 40–60% O2 saturation), whereas normoxic fish (85–90% O2 saturation) constituted two different groups, depending on if they were fed to visual satiety (control fish) or pair-fed to M-HYP fish. Following the hypoxia conditioning period, all fish were maintained in normoxia and continued to be fed until visual satiation for 3 weeks. The time course of hypoxia-induced changes was assessed by changes in blood metabolic landmarks and muscle transcriptomics before and after exhaustive exercise in a swim tunnel respirometer. In M-HYP fish, our results highlighted a higher contribution of aerobic metabolism to whole energy supply, shifting towards a higher anaerobic fitness following normoxia restoration. Despite these changes in substrate preference, M-HYP fish shared a persistent improvement in swimming performance with a higher critical speed at exercise exhaustion. The machinery of muscle contraction and protein synthesis and breakdown was also largely altered by mild-hypoxia conditioning, contributing this metabolic re-adjustment to the positive regulation of locomotion and to the catch-up growth response during the normoxia recovery period. Altogether, these results reinforce the presence of large phenotypic plasticity in gilthead sea bream, and highlights mild-hypoxia as a promising prophylactic measure to prepare these fish for predictable stressful events., This work was financially supported by a grant from the European Commission of the European Union under the Horizon 2020 research infrastructure project AQUAEXCEL2020 (652831) to J.P-S. Additional funding was obtained by a Spanish MICINN project (Bream-AquaINTECH, RTI2018–094128-B-I00). J.A.M.-S. received a Postdoctoral Research Fellowship (Juan de la CiervaFormación, Reference FJCI-2014-20,161).

The quantitative measurement of environmental DNA (eDNA) from field-collected water samples is gaining importance for the monitoring of fish communities and populations. The interpretation of these signal strengths depends, among other factors, on the amount of target eDNA shed into the water. However, shedding rates are presumably associated with species-specific traits such as physiology and behavior. Although such differences between juvenile and adult fish have been previously detected, the general impact of movement and energy use in a resting state on eDNA release into the surrounding water remains hardly addressed. In an aquarium experiment, we compared eDNA shedding between seven fish species occurring in European freshwaters. The investigated salmonids, cyprinids, and sculpin exhibit distinct adaptions to microhabitats, diets, and either solitary or schooling behavior. The fish were housed in aquaria with constant water flow and their activity was measured by snapshots taken every 30 s. Water samples for eDNA analysis were taken every 3 h and energy use was determined in an intermittent flow respirometer. After controlling for the effect of fish mass, our results demonstrate a positive correlation between target eDNA quantities as measured with digital PCR, fish activity, and energy use, as well as species-specific differences. For cyprinids, the model based on data from individual fish was only partly transferable to groups, which showed lower activity and higher energy use. Our findings highlight the importance of fish physiology and behavior for the comparative interpretation of taxon-specific eDNA quantities. Species traits should therefore be incorporated into eDNA-based monitoring and conservation efforts.

Cardiac and behavioural responses to hypoxia and warming were investigated in free-swimming gilthead seabreamSparus aurataequipped with biologging tags in the peritoneal cavity. After suitable recovery in a holding tank, heart rate (fH) and the variance of tri-axial body acceleration (VARm) were logged during exposure to stepwise progressive hypoxia or warming, comparing when either swimming in a tank or confined to individual respirometer chambers. When undisturbed under control conditions (normoxia, 21 °C), meanfHwas significantly lower in tank than respirometers. In progressive hypoxia (100 - 15% oxygen saturation), meanfHin the tank was significantly lower than respirometers at oxygen levels until 40%, with significant bradycardia in both holding conditions below this. Mean VARmwas low and invariant in hypoxia. Warming (21 to 31 °C) caused progressive tachycardia with no differences infHbetween holding conditions. Mean VARmwas, however, significantly higher in the tank during warming, with a positive relationship between VARmandfHacross all temperatures. Therefore, spontaneous activity contributed to raisingfHof fish in the tank during warming. MeanfHin respirometers had a highly significant linear relationship with mean rates of oxygen uptake, considering data from hypoxia and warming together. The highfHof confinedS. aurataindicates that static respirometry techniques may bias estimates of metabolic traits in some fish species. Biologging on free-swimming fish revealed novel information about cardiac responses to environmental stressors, which may be closer to responses exhibited by fish in their natural environment.SUMMARY STATEMENTImplantable biologgers were used to provide the first measurements of cardiac responses to hypoxia and warming in a free-swimming fish, revealing that confinement in respirometer chambers raises heart rate, with consequences for estimates of metabolic rates.

Species-specific ecological traits in fishes are likely to vary between populations or stocks due to differences in regional oceanic conditions, such as latitudinal temperature. We examined potential intraspecific differences in the swimming performance and metabolism of Pacific chub mackerel (Scomber japonicus) from the Northwest and Northeast Pacific stocks, which are distributed on opposite sides of the North Pacific at similar latitudes, but where the temperature contrast is large. Swimming bioenergetics and metabolic data of Northwest stock mackerel were measured at 14, 18, and 24°C using variable-speed swim-tunnel respirometers, and then the resulting bioenergetic parameters were compared with previous findings from the Northeast stock. At a given size, the maximum sustainable swimming speed (Umax) of the Northwest stock showed no significant difference compared to the Northeast stock at 18 and 24°C, but was lower at 14°C. In addition, the oxygen consumption rate (MO2) of the Northwest stock showed lower mass dependence and different temperature dependence at a given swimming speed than in the Northeast stock. Combined with stock-specific data on growth and experienced temperatures in the wild, these bioenergetic differences indicate that the swimming performance and metabolism of the two stocks are specific to their local environment to maximize bioenergetic efficiency.

Synopsis Group living is widespread among animal species and yields both costs and benefits. Presence of conspecifics can restrict or enhance the expression of individual behavior, and the recent social environment is thought to affect behavioral responses in later contexts, even when individuals are alone. However, little is known about how social group size influences the expression of individual physiological traits, including metabolic rates. There is some evidence that shoaling can reduce fish metabolic rates but this variable may be affected by habitat conditions such as shelter availability via density-dependent processes. We investigated how social group size and shelter availability influence Eurasian minnow (Phoxinus phoxinus) metabolic rates estimated by respirometry. Respirometry trials were conducted on fish in isolation before and after they were housed for 3 weeks in a social treatment consisting in a specific group size (n = 4 or 8) and shelter availability (presence or absence of plant shelter in the experimental tank). Plant shelter was placed over respirometers for half of the duration of the respirometry trials, allowing estimation of minimum daytime and nighttime metabolic rates in both conditions (in the presence or absence of plant shelter). Standard metabolic rate (SMR), maximum metabolic rate (MMR), and aerobic scope were also estimated over the entire trial. Minimum daytime and nighttime metabolic rates estimated while in presence of plant shelter were lower than when estimated in absence of plant shelter, both before and after individuals were housed in their social treatment. After the social treatment, SMRs were higher for fish that were held in groups of 4 as compared with those of fish held in groups of 8, while MMR showed no difference. Plant shelter availability during the social treatments did not influence SMR or MMR. Our results suggest that social group size may directly influence energy demands of individuals, highlighting the importance of understanding the role of group size on variations in physiological traits associated with energy expenditure.