Metabolic Scope Research Articles

Effects of different predator stress on vulnerability to predation and the underlying physiological and behavioral mechanisms of this vulnerability in juvenile qingbo (Spinibarbus sinensis)

Differences in the early life history would have a profound influence on the survival of the animal during the later life stages. We aimed to examine the effect of predator stress on vulnerability to predation in fish and the possible underlying behavioral and physiological mechanisms of this vulnerability. For this, we selected juvenile qingbo (Spinibarbus sinensis) as the prey and its natural predator, the southern catfish (Silurus meridionalis), as the predator. The juvenile qingbo were reared together with free predators (lethal group), caged predators (non-lethal group), and without predators (control group) for 4weeks at 25±0.5°C. After predator acclimation, predation mortality was evaluated to understand the potential difference in vulnerability to predation among these treatments when prey fish from each treatment group was cultured together with the predator. To investigate the possible physiological and behavioral mechanisms of this vulnerability, we measured the following parameters under the same environmental conditions: metabolic response parameters such as routine metabolic rate (RMR), maximum metabolic rate (MMR), and metabolic scope (MS=MMR−MS); routine activity level determined by measuring the total movement distance, percentage of time spent moving or hiding, and average velocity while moving; fast-start escape performance determined by measuring the response latency, maximum swimming speed (Vmax), and maximum acceleration (Amax). Both the lethal and non-lethal group fish exhibited significantly lower predation mortality, greater boldness (as suggested by the percentage of time spent hiding), and shorter response latency of fast-start response compared to those of the control group. Furthermore, the lethal group exhibited higher activity level, as evidenced by the increased amount of time spent moving at higher average speed and higher RMR. However, neither the fast-start parameters (Vmax and Amax) nor the maximum metabolic capacity (MMR and MS) of the two predator-stress groups differed from those of the control group. These results suggest that the S. sinensis cultured under predation stress was less vulnerable to predators because of shorter response latency and more explorative routine activities. However, the increase in spontaneous activity and enhanced alertness resulted in further energy expenditure in qingbo. Thus, the plasticity in physiology and behavior in qingbo may be one of the main anti-predator strategies that can increase the survival rate of this fish species under predator stress conditions.

Optimal slopes and speeds in uphill ski mountaineering: a laboratory study.

The purpose of this study was to estimate the energy cost of linear (EC) and vertical displacement (ECvert), mechanical efficiency and main stride parameters during simulated ski mountaineering at different speeds and gradients, to identify an optimal speed and gradient that maximizes performance. 12 subjects roller skied on a treadmill at three different inclines (10, 17 and 24%) at three different speeds (approximately 70, 80 and 85% of estimated peak heart rate). Energy expenditure was calculated by indirect calorimetry, while biomechanical parameters were measured with an inertial sensor-based system. At 10% there was no significant change with speed in EC, ECvert and mechanical efficiency. At 17 and 24% the fastest speed was significantly more economical. There was a significant effect of gradient on EC, ECvert and mechanical efficiency. The most economical gradient was the steepest one. There was a significant increase of stride frequency with speed. At steep gradients only, relative thrust phase duration decreased significantly, while stride length increased significantly with speed. There was a significant effect of gradient on stride length (decrease with steepness) and relative thrust phase duration (increase with steepness). A combination of a decreased relative thrust phase duration with increased stride length and frequency decreases ECvert. To minimize the energy expenditure to reach the top of a mountain and to optimize performance, ski-mountaineers should choose a steep gradient (~24%) and, provided they possess sufficient metabolic scope, combine it with a fast speed (~6kmh(-1)).

Oxygen consumption and swimming behavior of juvenile Siberian sturgeon Acipenser baerii during stepped velocity tests

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 24:211-217 (2016) - DOI: https://doi.org/10.3354/ab00649 Oxygen consumption and swimming behavior of juvenile Siberian sturgeon Acipenser baerii during stepped velocity tests Xi Yuan1,2,3, Lu Cai3,4, David M. Johnson3,5, Zhiying Tu3, Yingping Huang3,* 1Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China 2University of Chinese Academy of Sciences, Beijing 100039, China 3Engineering Research Center of Eco-environment in Three Gorges Reservoir Region, Ministry of Education, China Three Gorges University, Hubei Yichang 443002, China 4Key Laboratory of Ecological Impacts of Hydraulic-Projects and Restoration of Aquatic Ecosystem of Ministry of Water Resources, Institute of Hydroecology, Ministry of Water Resources and Chinese Academy of Sciences, Wuhan 430079, China 5School of Natural Sciences and Mathematics, Ferrum College, Ferrum, VA 24088, USA *Corresponding author: chem_ctgu@126.com ABSTRACT: Oxygen consumption rate (MO2) and critical swimming speed (Ucrit) of juvenile Siberian sturgeon Acipenser baerii were measured at 24°C using a step-wise velocity test in a flume-type respirometer. Swimming behavior was video-recorded before and after the swimming experiment in a respirometer and an open tank. The relationship between MO2 and swimming speed (U) can be accurately described by a power function. The Ucrit of A. baerii was found to be 2.28 ± 0.09 body lengths (BL) s-1 or 0.51 ± 0.05 m s-1. The standard metabolic rate was calculated to be 149.24 mg O2 kg-1 h-1, and measured maximum metabolic rate (MMR) was 385.04 mg O2 kg-1 h-1. This is a relatively low MMR, resulting in a low metabolic scope, and is consistent with the low Ucrit of juvenile sturgeon. Excess post-exercise oxygen consumption, measured over a 60 min recovery period, was 65.20 mg O2 kg-1. Therefore, A. baerii possess high fatigue recovery capability. Tail beat frequencies increased significantly with U, but there was very little change in tail beat amplitude, and results differed between respirometer and open tank observations. Our results provide data on the physiology and behavior of A. baerii and will help to support conservation of this important species. KEY WORDS: Siberian sturgeon · Swimming capability · Swimming behavior · Oxygen consumption Full text in pdf format PreviousNextCite this article as: Yuan X, Cai L, Johnson DM, Tu Z, Huang Y (2016) Oxygen consumption and swimming behavior of juvenile Siberian sturgeon Acipenser baerii during stepped velocity tests. Aquat Biol 24:211-217. https://doi.org/10.3354/ab00649 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 24, No. 3. Online publication date: March 17, 2016 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2016 Inter-Research.

Allometric size-scaling of biometric growth parameters and metabolic and excretion rates. A comparative study of intertidal and subtidal populations of mussels (Mytilus galloprovincialis)

Allometric relationships between biometric parameters (i.e., soft body and shell weights and shell organic content vs. shell length) as well as for routine and standard metabolic and ammonia excretion rates related to flesh weight and shell length were estimated and compared for subtidal and intertidal populations of Mytilus galloprovincialis in Galicia (NW Spain). This is the first report on allometric size-scaling of excretion and metabolic (both routine and standard) rates in this species. No evidences of differences in size exponent were found between physiological rates or between both populations for any physiological rate. Intercepts of regression lines were significantly higher in subtidal than in intertidal mussels, indicating greater levels of energy expenditure in the former. However, metabolic scope for feeding and growth was about two-fold in intertidal mussels, pointing to a reduced growth efficiency compared with subtidal mussels. Evolution of biometric parameters of body components with size indicated that subtidal mussels allocated energy resources preferably into flesh growth, achieving higher condition indices, while intertidal mussels put more effort on shell calcification and thickening which resulted in heavier shells of reduced organic content. These differentiated growth “strategies” of both populations could be related to their differences in growth efficiencies.

Temperature dependence of fish performance in the wild: links with species biogeography and physiological thermal tolerance

Summary Temperature strongly regulates the distribution and fitness of ectotherms, and many studies have measured the temperature dependence of physiological performance in controlled laboratory settings. In contrast, little is known about how temperature influences ectotherm performance in the wild, so the ecological significance of physiological performance as measured in the laboratory is unclear. Our aim was to measure the temperature dependence of performance in the wild for several species of fishes and to explore how temperatures that maximize performance in the wild (ToptE) are related to species biogeographies. We gathered body activity and growth data from the wild for nine tropical and temperate fish species, and by fitting thermal performance curves to these data, compared ToptE to species‐specific warm range boundary temperatures (the average temperature of the warmest month at equatorward range limits). To explore the degree to which trends in the wild reflect trends in physiological performance measured in the laboratory, we also compiled published data on the temperature dependence of aerobic metabolic scope in fishes and compared these to our wild fish data. We found ToptE in the wild was strongly correlated with warm range boundary temperatures, and that the difference between these two temperatures (the ‘environmental heating tolerance’) was smaller for more‐tropical species. Comparison with laboratory data revealed that ToptE approaches warm boundary temperatures in the wild at the same rate that the optimal temperature for aerobic scope (ToptAS) approaches upper critical temperatures (upper Tcrit) for aerobic scope in the laboratory, meaning that environmental heating tolerances in wild fishes closely mirror physiological heating tolerance (i.e. upper Tcrit − ToptAS) in captive fishes. Our comparison of field‐ and laboratory‐derived data highlights the ecological significance of aerobic metabolic scope in fishes and suggests wild fish species tend to perform best near the highest temperatures encountered in their range while maintaining a safety margin from the deleterious effects of upper critical temperatures.

Partitioning the metabolic scope: the importance of anaerobic metabolism and implications for the oxygen- and capacity-limited thermal tolerance (OCLTT) hypothesis.

Ongoing climate change is predicted to affect the distribution and abundance of aquatic ectotherms owing to increasing constraints on organismal physiology, in particular involving the metabolic scope (MS) available for performance and fitness. The oxygen- and capacity-limited thermal tolerance (OCLTT) hypothesis prescribes MS as an overarching benchmark for fitness-related performance and assumes that any anaerobic contribution within the MS is insignificant. The MS is typically derived from respirometry by subtracting standard metabolic rate from the maximal metabolic rate; however, the methodology rarely accounts for anaerobic metabolism within the MS. Using gilthead sea bream (Sparus aurata) and Trinidadian guppy (Poecilia reticulata), this study tested for trade-offs (i) between aerobic and anaerobic components of locomotor performance; and (ii) between the corresponding components of the MS. Data collection involved measuring oxygen consumption rate at increasing swimming speeds, using the gait transition from steady to unsteady (burst-assisted) swimming to detect the onset of anaerobic metabolism. Results provided evidence of the locomotor performance trade-off, but only in S. aurata. In contrast, both species revealed significant negative correlations between aerobic and anaerobic components of the MS, indicating a trade-off where both components of the MS cannot be optimized simultaneously. Importantly, the fraction of the MS influenced by anaerobic metabolism was on average 24.3 and 26.1% in S. aurata and P. reticulata, respectively. These data highlight the importance of taking anaerobic metabolism into account when assessing effects of environmental variation on the MS, because the fraction where anaerobic metabolism occurs is a poor indicator of sustainable aerobic performance. Our results suggest that without accounting for anaerobic metabolism within the MS, studies involving the OCLTT hypothesis could overestimate the metabolic scope available for sustainable activities and the ability of individuals and species to cope with climate change.

Thyroid hormone influences muscle mechanics in carp (Cyprinus carpio) independently from SERCA activity

Thyroid hormone is a key regulator of metabolism, and in zebrafish, hypothyroidism decreases sustained and burst swimming performance. These effects are accompanied by decreases in both metabolic scope and the activity of sarco-endoplasmic reticulum ATPase (SERCA) in zebrafish. Our aim was to determine whether thyroid hormone affects skeletal muscle contractile function directly and whether these effects are mediated by influencing SERCA activity. We show that hypothyroidism reduces sustained locomotor performance but not sprint performance in carp (Cyprinus carpio). We accept our hypothesis that hypothyroidism reduces force production in isolated skeletal muscle, when compared with the thyroid hormone T2, but we reject the hypothesis that this effect is mediated by influencing SERCA activity. Blocking SERCA activity with thapsigargin reduced muscle fatigue resistance, but hypothyroidism had no effect on fatigue. Hence, thyroid hormone plays a role in determining isolated skeletal muscle mechanics, but its effects are more likely to be mediated by mechanisms other than affecting SERCA activity.

Trophic contamination by pyrolytic polycyclic aromatic hydrocarbons does not affect aerobic metabolic scope in zebrafish Danio rerio.

The effect of trophic exposure to pyrolitic polycyclic aromatic hydrocarbons (PAH) on aerobic metabolism of zebrafish Danio rerio was investigated. There were no significant differences in standard metabolic rate (SMR), active metabolic rate (AMR) or aerobic metabolic scope (AS) at any sublethal concentration of PAH in the diet of adult or juvenile fish. This suggests that under these experimental conditions, exposure to PAH in food did not influence aerobic metabolism of this species.

Measuring maximum and standard metabolic rates using intermittent-flow respirometry: a student laboratory investigation of aerobic metabolic scope and environmental hypoxia in aquatic breathers.

Metabolic rate is one of the most widely measured physiological traits in animals and may be influenced by both endogenous (e.g. body mass) and exogenous factors (e.g. oxygen availability and temperature). Standard metabolic rate (SMR) and maximum metabolic rate (MMR) are two fundamental physiological variables providing the floor and ceiling in aerobic energy metabolism. The total amount of energy available between these two variables constitutes the aerobic metabolic scope (AMS). A laboratory exercise aimed at an undergraduate level physiology class, which details the appropriate data acquisition methods and calculations to measure oxygen consumption rates in rainbow trout Oncorhynchus mykiss, is presented here. Specifically, the teaching exercise employs intermittent flow respirometry to measure SMR and MMR, derives AMS from the measurements and demonstrates how AMS is affected by environmental oxygen. Students' results typically reveal a decline in AMS in response to environmental hypoxia. The same techniques can be applied to investigate the influence of other key factors on metabolic rate (e.g. temperature and body mass). Discussion of the results develops students' understanding of the mechanisms underlying these fundamental physiological traits and the influence of exogenous factors. More generally, the teaching exercise outlines essential laboratory concepts in addition to metabolic rate calculations, data acquisition and unit conversions that enhance competency in quantitative analysis and reasoning. Finally, the described procedures are generally applicable to other fish species or aquatic breathers such as crustaceans (e.g. crayfish) and provide an alternative to using higher (or more derived) animals to investigate questions related to metabolic physiology.

Phenotypic variation in metabolism and morphology correlating with animal swimming activity in the wild: relevance for the OCLTT (oxygen- and capacity-limitation of thermal tolerance), allocation and performance models.

Ongoing climate change is affecting animal physiology in many parts of the world. Using metabolism, the oxygen- and capacity-limitation of thermal tolerance (OCLTT) hypothesis provides a tool to predict the responses of ectothermic animals to variation in temperature, oxygen availability and pH in the aquatic environment. The hypothesis remains controversial, however, and has been questioned in several studies. A positive relationship between aerobic metabolic scope and animal activity would be consistent with the OCLTT but has rarely been tested. Moreover, the performance model and the allocation model predict positive and negative relationships, respectively, between standard metabolic rate and activity. Finally, animal activity could be affected by individual morphology because of covariation with cost of transport. Therefore, we hypothesized that individual variation in activity is correlated with variation in metabolism and morphology. To test this prediction, we captured 23 wild European perch (Perca fluviatilis) in a lake, tagged them with telemetry transmitters, measured standard and maximal metabolic rates, aerobic metabolic scope and fineness ratio and returned the fish to the lake to quantify individual in situ activity levels. Metabolic rates were measured using intermittent flow respirometry, whereas the activity assay involved high-resolution telemetry providing positions every 30 s over 12 days. We found no correlation between individual metabolic traits and activity, whereas individual fineness ratio correlated with activity. Independent of body length, and consistent with physics theory, slender fish maintained faster mean and maximal swimming speeds, but this variation did not result in a larger area (in square metres) explored per 24 h. Testing assumptions and predictions of recent conceptual models, our study indicates that individual metabolism is not a strong determinant of animal activity, in contrast to individual morphology, which is correlated with in situ activity patterns.

Responses by fishes to environmental hypoxia: integration through Fry's concept of aerobic metabolic scope.

The problem of understanding the effect of the environment on fish activities and performance, in any generalized way, remains intractable. Solving this issue is, however, a key to addressing contemporary environmental concerns. As suggested 20 years ago by W. H. Neill, the authors returned to the drawing board, using as a background the conceptual scheme initially proposed by F. E. J. Fry. They revisited the effect of ambient oxygen availability upon fish metabolism and clarified the definitions of limiting, critical and incipient lethal oxygen (ILO) levels. The concepts of oxy-conformer and oxy-regulator are revisited, and P. W. Hochachka's idea of scope for survival is explored. Finally, how the cardiovascular system contributes to the capacity of fishes to respond to the reduced oxygen availability is considered. Various hands-on recommendations and software (R scripts) are provided for researchers interested in investigating these concepts.

Physiology-based modelling approaches to characterize fish habitat suitability: Their usefulness and limitations

Models are useful tools for predicting the impact of global change on species distribution and abundance. As ectotherms, fish are being challenged to adapt or track changes in their environment, either in time through a phenological shift or in space by a biogeographic shift. Past modelling efforts have largely been based on correlative Species Distribution Models, which use known occurrences of species across landscapes of interest to define sets of conditions under which species are likely to maintain populations. The practical advantages of this correlative approach are its simplicity and the flexibility in terms of data requirements. However, effective conservation management requires models that make projections beyond the range of available data. One way to deal with such an extrapolation is to use a mechanistic approach based on physiological processes underlying climate change effects on organisms. Here we illustrate two approaches for developing physiology-based models to characterize fish habitat suitability. (i) Aerobic Scope Models (ASM) are based on the relationship between environmental factors and aerobic scope (defined as the difference between maximum and standard (basal) metabolism). This approach is based on experimental data collected by using a number of treatments that allow a function to be derived to predict aerobic metabolic scope from the stressor/environmental factor(s). This function is then integrated with environmental (oceanographic) data of current and future scenarios. For any given species, this approach allows habitat suitability maps to be generated at various spatiotemporal scales. The strength of the ASM approach relies on the estimate of relative performance when comparing, for example, different locations or different species. (ii) Dynamic Energy Budget (DEB) models are based on first principles including the idea that metabolism is organised in the same way within all animals. The (standard) DEB model aims to describe empirical relationships which can be found consistently within physiological data across the animal kingdom. The advantages of the DEB models are that they make use of the generalities found in terms of animal physiology and can therefore be applied to species for which little data or empirical observations are available. In addition, the limitations as well as useful potential refinements of these and other physiology-based modelling approaches are discussed. Inclusion of the physiological response of various life stages and modelling the patterns of extreme events observed in nature are suggested for future work.

Disentangling environmental drivers of metabolic flexibility in birds: the importance of temperature extremes versus temperature variability

Examining physiological traits across large spatial scales can shed light on the environmental factors driving physiological variation. For endotherms, flexibility in aerobic metabolism is especially important for coping with thermally challenging environments and recent research has shown that aerobic metabolic scope [the difference between maximum thermogenic capacity (Msum) and basal metabolic rate (BMR)] increases with latitude in mammals. One explanation for this pattern is the climatic variability hypothesis, which predicts that flexibility in aerobic metabolism should increase as a function of local temperature variability. An alternative explanation is the cold adaptation hypothesis, which predicts that cold temperature extremes may also be an important driver of variation in metabolic scope. To determine the thermal drivers of aerobic metabolic flexibility in birds, we combined data on metabolic scope from 40 bird species sampled across a range of environments with several indices of local ambient temperature. Using phylogenetically‐informed analyses, we found that minimum winter temperature was the best predictor of variation in avian metabolic scope, outperforming all other thermal variables. Additionally, Msum was a better predictor of latitudinal patterns of metabolic scope than BMR, with species inhabiting colder environments exhibiting increased Msum over their counterparts in warmer environments. Taken together, these results suggest that cold temperature extremes drive latitudinal patterns of metabolic scope via selection for enhanced thermogenic performance in cold environments, supporting the cold adaptation hypothesis. Temperature extremes may therefore be an important selective pressure driving macrophysiological trends of aerobic performance in endotherms.

Kinematics and energetics of swimming performance during acute warming in brown trout Salmo trutta.

This study examined how acute warming of water temperature affects the mechanical efficiency of swimming and aerobic capabilities of the brown trout Salmo trutta. Swimming efficiency was assessed using the relationship between swimming kinematics and forward speed (U), which is thought to converge upon an optimum range of a dimensionless parameter, the Strouhal number (St ). Swim-tunnel intermittent stopped-flow respirometry was used to record kinematics and measure oxygen consumption (ṀO2) of S. trutta during warming and swimming challenges. Salmo trutta maintained St between 0·2 and 0·3 at any given U over a range of temperatures, irrespective of body size. The maintenance of St within the range for maximum efficiency for oscillatory propulsion was achieved through an increase in tail-beat frequency (ftail) and a decrease in tail-beat amplitude (A) as temperature increased. Maintenance of efficient steady-state swimming was fuelled by aerobic metabolism, which increased as temperature increased up to 18° C but declined above this temperature, decreasing the apparent metabolic scope. As St was maintained over the full range of temperatures whilst metabolic scope was not, the results may suggest energetic trade-offs at any given U at temperatures above thermal optima.

Diets supplemented with seaweed affect metabolic rate, innate immune, and antioxidant responses, but not individual growth rate in European seabass (Dicentrarchus labrax)

This study investigated the effects of seaweed dietary supplementation on measures of fish performance including aerobic metabolism, digestive enzymes activity, innate immune status, oxidative damage, and growth rate using European seabass (Dicentrarchus labrax). Fish were fed for 49 days with three different diets: a control diet (CTRL), a Gracilaria-supplemented diet (GR7.5), and a mixed diet (Mix) composed of Gracilaria, Fucus, and Ulva genera representatives. All diets were isoenergetic (22 kJ g−1 adjusted for dry matter (DM)), isoproteic (47 %DM), and isolipidic (18 %DM) and tested in triplicate groups of 20 fish (initial body weight 25.5 ± 4.1 g). Final results showed similar growth rates and digestive activities between diets. Maximum and standard metabolic rates and aerobic metabolic scope revealed comparable results for the three diets. In contrast, fish fed with GR7.5 exhibited elevated routine metabolic rate (190.7 mg O2 kg−1 h−1). Fish fed with the GR7.5 and Mix diets had lower alternative complement pathway (ACH50) (62.5 and 63 units mL−1 respectively) than CTRL (84 units mL−1) GR7.5 increased lipid peroxidation and cholinesterase levels, as well as glutathione s-transferase activity. Mix diet increased glutathione reductase activity when compared to CTRL. Collectively, our findings suggest that dietary seaweed supplementation may alter seabass metabolic rate, innate immune, and antioxidant responses without compromising growth parameters.

Individual variation in metabolism and swimming performance in juvenile black carp (Mylopharyngodon piceus) and the effects of hypoxia

We investigated inter-individual variation in metabolism, swimming performance and the relationship between metabolism and swimming performance under normoxic and hypoxic oxygen conditions ([O2]) in juvenile black carp (Mylopharyngodon piceus). We measured the standard metabolic rate (SMR), critical swimming speed (Ucrit), active metabolic rate (AMR) and aerobic scope (AS) of 40 fish (body weight, 9.7–11.0 g; body length, 8.4–8.8 cm) at 20 °C under normoxic (100% air saturation) and hypoxic (30% air saturation) conditions. Hypoxia resulted in a significant decrease in all the investigated parameters (p < 0.05). The SMR, Ucrit and AMR exhibited consistent individual differences (repeatability) (p ≤ 0.022), whereas the AS had no consistency across different water [O2] conditions (p = 0.088). The SMR was positively correlated with the Ucrit, AMR and AS (p ≤ 0.002) under normoxic conditions. The SMR was also positively correlated with the Ucrit and AMR under hypoxic conditions (p ≤ 0.003) but there was no correlation between the SMR and AS (p = 0.141). The slope of the correlation between the SMR and Ucrit was shallower under hypoxic conditions than under normoxic conditions (F1,76 = 13.844, p < 0.001), which indicated that the swimming performance decreased more profoundly under hypoxic conditions in individuals with a high SMR.

UV‐B radiation interacts with temperature to determine animal performance

Summary The interaction between UV‐B and temperature can modify the effects of climate variability on animal function because UV‐B and increasing temperatures may increase reactive oxygen species (ROS) production and thereby impair animal performance. However, antioxidant enzyme activities are also increased at higher temperatures, which could counteract negative effects of increased ROS. Conversely, UV‐B exposure at lower temperature can exacerbate the effects of ROS because of lower antioxidant enzyme activities. Phenotypes can be plastic to compensate for potentially negative environmental effects. Plasticity may be induced by conditions experienced during pre‐ or early post‐zygotic development, and it may occur reversibly within adult organisms (acclimation). Developmental plasticity and acclimation may interact to determine phenotypes in variable environments. Here, we tested the hypothesis that increased antioxidant enzyme activities are insufficient to alleviate the interactive effects of UV‐B and increased temperature on mosquitofish (Gambusia holbrooki). Additionally, we tested whether developmental conditions influenced the capacity for acclimation to UV‐B and temperature so that cohorts born in summer at high UV‐B and temperature conditions are better able to compensate for ROS damage compared to cohorts born in winter. We exposed mosquitofish to UV‐B and control (no‐UV‐B) at different acclimation temperatures (18, 28 and 32 °C), and measured responses acutely at 18, 28 and 32 °C in a fully factorial design. In fish born in summer, UV‐B had significant negative effects on swimming performance and resting metabolic rate at both low (18 °C) and high (32 °C) acclimation temperatures, which were accompanied by higher ROS‐induced damage. At their average temperature experienced naturally (28 °C), fish born in summer were not affected by UV‐B and showed lower damage and higher antioxidant enzyme activities compared to the other acclimation temperatures. In contrast, swimming performance of winter‐caught fish was negatively affected by UV‐B at all acclimation temperatures, which was paralleled by higher ROS‐induced damage and antioxidant enzyme activities that did not acclimate. However, metabolic scope was not reduced by UV‐B or temperature in any of the cohorts. Our results showed that developmental conditions modify the capacity for acclimation later in life, and that the interaction between developmental and acclimation conditions can increase the resilience of animals to environmental variability. These results have important implications for understanding the evolution of acclimation, and for predictions of how climate change affects animal performance.

Depletion of Essential Fatty Acids in the Food Source Affects Aerobic Capacities of the Golden Grey Mullet Liza aurata in a Warming Seawater Context.

The objective of this study was to evaluate the combined effects of thermal acclimation and n-3 highly unsaturated fatty acids (n-3 HUFA) content of the food source on the aerobic capacities of fish in a thermal changing environment. The model used was the golden grey mullet Liza aurata, a species of high ecological importance in temperate coastal areas. For four months, fish were exposed to two food sources with contrasting n-3 HUFA contents (4.8% ecosapentaenoic acid EPA + docosahexaenoic acid DHA on the dry matter DM basis vs. 0.2% EPA+DHA on DM) combined with two acclimation temperatures (12°C vs. 20°C). The four experimental conditions were LH12, LH20, HH12 and HH20. Each group was then submitted to a thermal challenge consisting of successive exposures to five temperatures (9°C, 12°C, 16°C, 20°C, 24°C). At each temperature, the maximal and minimal metabolic rates, metabolic scope, and the maximum swimming speed were measured. Results showed that the cost of maintenance of basal metabolic activities was particularly higher when n-3 HUFA food content was low. Moreover, fish exposed to high acclimation temperature combined with a low n-3 HUFA dietary level (LH20) exhibited a higher aerobic scope, as well as a greater expenditure of energy to reach the same maximum swimming speed as other groups. This suggested a reduction of the amount of energy available to perform other physiological functions. This study is the first to show that the impact of lowering n-3 HUFA food content is exacerbated for fish previously acclimated to a warmer environment. It raises the question of the consequences of longer and warmer summers that have already been recorded and are still expected in temperate areas, as well as the pertinence of the lowering n-3 HUFA availability in the food web expected with global change, as a factor affecting marine organisms and communities.

Increased gastrointestinal blood flow: An essential circulatory modification for euryhaline rainbow trout (Oncorhynchus mykiss) migrating to sea.

The large-scale migrations of anadromous fish species from freshwater to seawater have long been considered particularly enigmatic, as this life history necessitates potentially energetically costly changes in behaviour and physiology. A significant knowledge gap concerns the integral role of cardiovascular responses, which directly link many of the well-documented adaptations (i.e. through oxygen delivery, water and ion transport) allowing fish to maintain osmotic homeostasis in the sea. Using long-term recordings of cardiorespiratory variables and a novel method for examining drinking dynamics, we show that euryhaline rainbow trout (Oncorhynchus mykiss) initiate drinking long before the surrounding environment reaches full seawater salinity (30–33 ppt), suggesting the presence of an external osmo-sensing mechanism. Onset of drinking was followed by a delayed, yet substantial increase in gastrointestinal blood flow through increased pulse volume exclusively, as heart rate remained unchanged. While seawater entry did not affect whole animal energy expenditure, enhanced gastrointestinal perfusion represents a mechanism crucial for ion and water absorption, as well as possibly increasing local gastrointestinal oxygen supply. Collectively, these modifications are essential for anadromous fish to maintain homeostasis at sea, whilst conserving cardiac and metabolic scope for activities directly contributing to fitness and reproductive success.

Intraspecific variation in aerobic and anaerobic locomotion: gilthead sea bream (Sparus aurata) and Trinidadian guppy (Poecilia reticulata) do not exhibit a trade-off between maximum sustained swimming speed and minimum cost of transport.

Intraspecific variation and trade-off in aerobic and anaerobic traits remain poorly understood in aquatic locomotion. Using gilthead sea bream (Sparus aurata) and Trinidadian guppy (Poecilia reticulata), both axial swimmers, this study tested four hypotheses: (1) gait transition from steady to unsteady (i.e., burst-assisted) swimming is associated with anaerobic metabolism evidenced as excess post exercise oxygen consumption (EPOC); (2) variation in swimming performance (critical swimming speed; Ucrit) correlates with metabolic scope (MS) or anaerobic capacity (i.e., maximum EPOC); (3) there is a trade-off between maximum sustained swimming speed (Usus) and minimum cost of transport (COTmin); and (4) variation in Usus correlates positively with optimum swimming speed (Uopt; i.e., the speed that minimizes energy expenditure per unit of distance traveled). Data collection involved swimming respirometry and video analysis. Results showed that anaerobic swimming costs (i.e., EPOC) increase linearly with the number of bursts in S. aurata, with each burst corresponding to 0.53 mg O2 kg−1. Data are consistent with a previous study on striped surfperch (Embiotoca lateralis), a labriform swimmer, suggesting that the metabolic cost of burst swimming is similar across various types of locomotion. There was no correlation between Ucrit and MS or anaerobic capacity in S. aurata indicating that other factors, including morphological or biomechanical traits, influenced Ucrit. We found no evidence of a trade-off between Usus and COTmin. In fact, data revealed significant negative correlations between Usus and COTmin, suggesting that individuals with high Usus also exhibit low COTmin. Finally, there were positive correlations between Usus and Uopt. Our study demonstrates the energetic importance of anaerobic metabolism during unsteady swimming, and provides intraspecific evidence that superior maximum sustained swimming speed is associated with superior swimming economy and optimum speed.