Dietary lipid quality and mitochondrial membrane composition in trout: responses of membrane enzymes and oxidative capacities

Hypometabolic Responses to Chronic Hypoxia: A Potential Role for Membrane Lipids

Metabolic suppression is an essential strategy to cope with chronic hypoxia. This review examines the physiological processes used to survive in low oxygen environments. It proposes a novel mechanism-the remodeling of membrane lipids-to suppress ATP use and production. Temperature (homeoviscous adaptation), diet (natural doping in migrant birds) and body mass (membrane pacemaker of metabolism) have an impact on the lipid composition of membranes, which, in turn, modulates metabolic capacity. Vertebrate champions of hypoxia tolerance show extensive changes in membrane lipids upon in vivo exposure to low oxygen. These changes and those observed in hibernating mammals can promote the downregulation of ion pumps (major ATP consumers), ion channels, mitochondrial respiration capacity (state 3, proton leak, cytochrome c oxidase), and energy metabolism (β-oxidation and glycolysis). A common membrane signal regulating the joint inhibition of ion pumps and channels could be an exquisite way to preserve the balance between ATP supply and demand in hypometabolic states. Membrane remodeling together with more traditional mechanisms could work in concert to cause metabolic suppression.

The relationship between membrane fatty acid content and mitochondrial efficiency differs within- and between- omega-3 dietary treatments

An important, but underappreciated, consequence of climate change is the reduction in crucial nutrient production at the base of the marine food chain: the long-chain omega-3 highly unsaturated fatty acids (n-3 HUFA). This can have dramatic consequences on consumers, such as fish as they have limited capacity to synthesise n-3 HUFA de novo. The n-3 HUFA, such as docosahexaenoic acid (DHA, 22:6n-3) and eicosapentaenoic acid (EPA, 20:5n-3), are critical for the structure and function of all biological membranes. There is increasing evidence that fish will be badly affected by reductions in n-3 HUFA dietary availability, however the underlying mechanisms remain obscure. Hypotheses for how mitochondrial function should change with dietary n-3 HUFA availability have generally ignored ATP production, despite its importance to a cell's total energetics capacity, and in turn, whole-animal performance. Here we (i) quantified individual variation in mitochondrial efficiency (ATP/O ratio) of muscle and (ii) examined its relationship with content in EPA and DHA in muscle membrane of a primary consumer fish, the golden grey mullet Chelon auratus, receiving either a high or low n-3 HUFA diet. Mitochondria of fish fed on the low n-3 HUFA diet had higher ATP/O ratio than those of fish maintained on the high n-3 HUFA diet. Yet, mitochondrial efficiency varied up about 2-fold among individuals on the same dietary treatment, resulting in some fish consuming half the oxygen and energy substrate to produce the similar amount of ATP than conspecific on similar diet. This variation in mitochondrial efficiency among individuals from the same diet treatment was related to individual differences in fatty acid composition of the membranes: a high ATP/O ratio was associated with a high content in EPA and DHA in biological membranes. Our results highlight the existence of interindividual differences in mitochondrial efficiency and its potential importance in explaining intraspecific variation in response to food chain changes.

Impact of the replacement of dietary fish oil by animal fats and environmental salinity on the metabolic response of European Seabass (Dicentrarchus labrax)

The replacement of fish oil (FO) with other lipid sources (e.g. animal fats, AF) in aquafeeds improves the sustainability of aquaculture, even though alternatives have different fatty acid (FA) profiles. FO contains a higher proportion of long-chain polyunsaturated fatty acids (LC-PUFAs) than AF. LC-PUFAs have key physiological roles, despite limited biosynthetic capacity in marine fish. Therefore, replacing FO in feeds may limit physiological responses when fish face environmental challenges such as an acute change in salinity. To test this hypothesis, juvenile seabass (62.6 ± 1.6 g, 50 fish/ 500 L tank) were fed three different isoproteic and isolipidic diets in which the replacement levels of FO by AF varied (0%, 75% or 100% AF). Fish were fed the experimental diets at 2% their body weight (BW) daily for 85 days (20.0 ± 1.0 °C; 35‰). Thereafter, half of the fish were transferred to tanks at 15‰ or 35‰ salinity and sampled at 24 h and 72 h. Plasma osmolality, Na⁺, glucose, cholesterol and lactate levels were altered by the changing salinity, although cortisol remained unchanged. Standard metabolic rate was similar irrespective of the experimental factors. However, maximal metabolic rate decreased by 4-10% in fish subjected to a 15‰ salinity. Intestinal chymotrypsin activity was modified by the diet, with this digestive enzyme along with trypsin showing a two-fold increase in activity at 15‰ salinity. Hepatic lipid peroxidation (LPO) showed a ~1.4-fold increase at 15‰ salinity. Additionally, LPO and glutathione reductase activity were ~1.6-fold higher in fish fed the FO diet. Citrate synthase activity in gills was increased in fish fed the 100% AF diet. Therefore, both dietary replacement of FO by AF and environmental salinity have an impact on the metabolic response of seabass, although interactions between both factors (diet and salinity) are negligible in the metabolic parameters investigated. The results are relevant to the aquaculture industry considering the potential usage of AF to replace FO in aquafeeds and because of the variations in salinity experienced by fish cultured in transitional waters.

Ocean warming combined with lower omega-3 nutritional availability impairs the cardio-respiratory function of a marine fish

Highly unsaturated fatty acids of the omega-3 series (HUFA) are major constituents of cell membranes, yet are poorly synthesised de novo by consumers. Their production, mainly supported by aquatic microalgae, has been decreasing with global change. The consequences of such reductions may be profound for ectotherm consumers, as temperature tightly regulates the HUFA content in cell membranes, maintaining their functionality. Integrating individual, tissue and molecular approaches, we examined the consequences of the combined effects of temperature and HUFA depletion on the key cardio-respiratory functions of the golden grey mullet, an ectotherm grazer of high ecological importance. For 4 months, fish were exposed to two contrasting HUFA diets [4.8% eicosapentaenoic acid (EPA)+docosahexaenoic acid (DHA) on dry matter (DM) versus 0.2% EPA+DHA on DM] at 12 and 20°C. Ventricular force development coupled with gene expression profiles measured on cardiac muscle suggest that combining HUFA depletion with warmer temperatures leads to: (1) a proliferation of sarcolemmal and sarcoplasmic reticulum Ca²⁺ channels and (2) a higher force-generating ability by increasing extracellular Ca²⁺ influx via sarcolemmal channels when the heart has to sustain excessive effort due to stress and/or exercise. At the individual scale, these responses were associated with a greater aerobic scope, maximum metabolic rate and net cost of locomotion, suggesting the higher energy cost of this strategy. This impaired cardiac performance could have wider consequences for other physiological performance such as growth, reproduction or migration, all of which greatly depend on heart function.

Thermal tolerance and thermal sensitivity of heart mitochondria: Mitochondrial integrity and ROS production

Cardiac mitochondrial metabolism provides 90% of the ATP necessary for the contractile exertion of the heart muscle. Mitochondria are therefore assumed to play a pivotal role in heart failure (HF), cardiovascular disease and ageing. Heat stress increases energy metabolism and oxygen demand in tissues throughout the body and imposes a major challenge on the heart, which is suspected of being the first organ to fail during heat stress. The underlying mechanisms inducing heart failure are still unclear. To pinpoint the processes implicated in HF during heat stress, we measured mitochondrial respiration rates and hydrogen peroxide production of isolated Arctic char (Salvelinus alpinus) heart mitochondria at 4 temperatures: 10°C (acclimation), 15°C, 20°C and 25°C (just over critical maximum). We found that at temperature ranges causing the loss of an organism's general homeostasis (between 20°C and 25°C) and with a substrate combination close to physiological conditions, the heat-induced increase in mitochondrial oxygen consumption levels off. More importantly, at the same state, hydrogen peroxide efflux increased by almost 50%. In addition, we found that individuals with low mitochondrial respiration rates produced more hydrogen peroxide at 10°C, 15°C and 20°C. This could indicate that individuals with cardiac mitochondria having a low respiratory capacity, have a more fragile heart and will be more prone to oxidative stress and HF, and less tolerant to temperature changes and other stressors. Our results show that, at temperatures close to the thermal limit, mitochondrial capacity is compromised and ROS production rates increase. This could potentially alter the performance of the cardiac muscle and lead to heat-induced HF underlining the important role that mitochondria play in setting thermal tolerance limits.

The membrane pacemaker hypothesis: novel tests during the ontogeny of endothermy

The ‘membrane pacemaker’ hypothesis proposes a biochemical explanation for among-species variation in resting metabolism, based on the positive correlation between membrane docosahexaenoic acid (DHA) and metabolic rate. We tested this hypothesis using a novel model, altricial red-winged blackbird nestlings, predicting that the proportion of DHA in muscle and liver membranes should increase with the increasing metabolic rate of the nestling as it develops endothermy. We also used a dietary manipulation, supplementing the natural diet with fish oil (high DHA) or sunflower oil (high linoleic acid) to alter membrane composition and then assessed metabolic rate. In support of the membrane pacemaker hypothesis, DHA proportions increased in membranes from pectoralis muscle, muscle mitochondria, and liver during post-hatch development. By contrast, elevated dietary DHA had no effect on resting metabolic rate, despite causing significant changes to membrane lipid composition. During cold challenges, higher metabolic rates were achieved by birds that had lower DHA and higher linoleic acid in membrane phospholipids. Given the mixed support for this hypothesis, we conclude that correlations between membrane DHA and metabolic rate are likely spurious, and should be attributed to a still-unidentified confounding variable.

Dynamic changes in cardiac mitochondrial metabolism during warm acclimation in rainbow trout

Although the mitochondrial metabolism responses to warm acclimation have been widely studied in fish, the time course of this process is less understood. Here, we characterized the changes of rainbow trout (Oncorhynchus mykiss) cardiac mitochondrial metabolism during acute warming from 10 to 16°C, and during the subsequent warm acclimation for 39 days. We repeatedly measured mitochondrial oxygen consumption in cardiac permeabilized fibers and the functional integrity of mitochondria (i.e. mitochondrial coupling and cytochrome c effect) at two assay temperatures (10 and 16°C), as well as the activities of citrate synthase (CS) and lactate dehydrogenase (LDH) at room temperature. LDH and CS activities significantly increased between day 0 (10°C acclimated fish) and day 1 (acute warming to 16°C) while mitochondrial oxygen consumption measured at respective in vivo temperatures did not change. Enzymatic activities and mitochondrial oxygen consumption rates significantly decreased by day 2, and remained stable during warm acclimation (days 2-39). The decrease in rates of oxygen between day 0 and day 1 coincided with an increased cytochrome c effect and a decreased mitochondrial coupling, suggesting a structural/functional impairment of mitochondria during acute warming. We suggest that after 2 days of warm acclimation, a new homeostasis is reached, which may involve the removal of dysfunctional mitochondria. Interestingly, from day 2 onwards, there was a lack of differences in mitochondrial oxygen consumption rates between the assay temperatures, suggesting that warm acclimation reduces the acute thermal sensitivity of mitochondria. This study provides significant knowledge on the thermal sensitivity of cardiac mitochondria that is essential to delineate the contribution of cellular processes to warm acclimation.

Metabolic fuel kinetics in fish: swimming, hypoxia and muscle membranes

Muscle performance depends on the supply of metabolic fuels and disposal of end-products. Using circulating metabolite concentrations to infer changes in fluxes is highly unreliable because the relationship between these parameters varies greatly with physiological state. Quantifying fuel kinetics directly is therefore crucial to the understanding of muscle metabolism. This review focuses on how carbohydrates, lipids and amino acids are provided to fish muscles during hypoxia and swimming. Both stresses force white muscle to produce lactate at higher rates than it can be processed by aerobic tissues. However, lactate accumulation is minimized because disposal is also strongly stimulated. Exogenous supply shows that trout have a much higher capacity to metabolize lactate than observed during hypoxia or intense swimming. The low density of monocarboxylate transporters and their lack of upregulation with exercise explain the phenomenon of white muscle lactate retention. This tissue operates as a quasi-closed system, where glycogen stores act as an 'energy spring' that alternates between explosive power release during swimming and slow recoil from lactate in situ during recovery. To cope with exogenous glucose, trout can completely suppress hepatic production and boost glucose disposal. Without these responses, glycemia would increase four times faster and reach dangerous levels. The capacity of salmonids for glucoregulation is therefore much better than presently described in the literature. Instead of albumin-bound fatty acids, fish use lipoproteins to shuttle energy from adipose tissue to working muscles during prolonged exercise. Proteins may play an important role in fueling muscle work in fish, but their exact contribution is yet to be established. The membrane pacemaker theory of metabolism accurately predicts general properties of muscle membranes such as unsaturation, but it does not explain allometric patterns of specific fatty acids. Investigations of metabolic fuel kinetics carried out in fish to date have demonstrated that these ectotherms use several unique strategies to orchestrate energy supply to working muscles and to survive hypoxia.

Looking Beyond Structure: Membrane Phospholipids of Skeletal Muscle Mitochondria

Skeletal muscle mitochondria are highly dynamic and are capable of tremendous expansion to meet cellular energetic demands. Such proliferation in mitochondrial mass requires a synchronized supply of enzymes and structural phospholipids. While transcriptional regulation of mitochondrial enzymes has been extensively studied, there is limited information on how mitochondrial membrane lipids are generated in skeletal muscle. Herein we describe how each class of phospholipids that constitute mitochondrial membranes are synthesized and/or imported, and summarize genetic evidence indicating that membrane phospholipid composition represents a significant modulator of skeletal muscle mitochondrial respiratory function. We also discuss how skeletal muscle mitochondrial phospholipids may mediate the effect of diet and exercise on oxidative metabolism.

CELLULAR RESPONSES TO TRITIUM EXPOSURE IN RAINBOW TROUT: HTO- AND OBT-SPIKED FEED EXPOSURE EXPERIMENTS

Biological effects were evaluated in rainbow trout (Oncorhynchus mykiss) exposed to tritiated water (HTO) or food spiked with organically bound tritium (OBT). An HTO exposure study was conducted using a tritium activity concentration of 7000 Bq/L, and an OBT exposure study was conducted using a tritium activity concentration of 30 000 Bq/L. Following 140 days of in vivo HTO exposure, liver, heart, spleen, kidney, and brain cells did not show statistically significant differences in viability; kidney, liver, and spleen cells did not show significant differences in DNA double-strand break repair activity compared with control cells. Membrane fatty acid composition analysis was conducted on liver cells and no effects of HTO exposure could be detected. Following 140 days of in vivo OBT exposure, viability and DNA double-strand break repair activity were not statistically different from controls in liver, heart, spleen, kidney, and brain cells. Changes, however, were noted in the fatty acid composition of liver and muscle tissues.

For both studies, all measurements were performed on each tissue and on a fraction of the same tissue that was exposed to a gamma 4 Gy dose in vitro to test for adaptive responses, and no effects were observed except for fatty acid composition. The findings demonstrated that membrane fatty acid composition is a sensitive marker and that microscopic evaluation of gamma-H2AX foci is more sensitive than the flow cytometric approach. These studies are the first to correlate uptake and depuration with biological health indicators in edible fish for tritium exposures within worldwide drinking water guidelines.

Setting the pace of life: membrane composition of flight muscle varies with metabolic rate of hovering orchid bees

Patterns of metabolic rate variation have been documented extensively in animals, but their functional basis remains elusive. The membrane pacemaker hypothesis proposes that the relative abundance of polyunsaturated fatty acids in membrane phospholipids sets the metabolic rate of organisms. Using species of tropical orchid bees spanning a 16-fold range in body size, we show that the flight muscles of smaller bees have more linoleate (%18 : 3) and stearate (%18 : 0), but less oleate (%18 : 1). More importantly, flight metabolic rate (FlightMR) varies with the relative abundance of 18 : 3 according to the predictions of the membrane pacemaker hypothesis. Although this relationship was found across large differences in metabolic rate, a direct association could not be detected when taking phylogeny and body mass into account. Higher FlightMR, however, was related to lower %16 : 0, independent of phylogeny and body mass. Therefore, this study shows that flight muscle membrane composition plays a significant role in explaining diversity in FlightMR, but that body mass and phylogeny are other factors contributing to their variation. Multiple factors are at play to modulate metabolic capacity, and changing membrane composition can have gradual and stepwise effects to achieve a new range of metabolic rates. Orchid bees illustrate the correlated evolution between membrane composition and metabolic rate, supporting the functional link proposed in the membrane pacemaker hypothesis.

Effects of dietary fatty acids on mitochondrial phospholipid compositions, oxidative status and mitochondrial gene expression of zebrafish at different ages

Mitochondrial decay is generally associated with impairment in the organelle bioenergetics function and increased oxidative stress, and it appears that deterioration of mitochondrial inner membrane phospholipids (PL) and accumulation of mitochondrial DNA (mtDNA) mutations are among the main mechanisms involved in this process. In the present study, mitochondrial membrane PL compositions, oxidative status (TBARS content and SOD activity) and mtDNA gene expression of muscle and liver were analyzed in zebrafish fed two diets with lipid supplied either by rapeseed oil (RO) or a blend 60:40 of RO and DHA500 TG oil (DHA). Two feeding trials were performed using zebrafish from the same population of two ages (8 and 21 months). Dietary FA composition affected fish growth in 8-month-old animals, which could be related to an increase in stress promoted by diet composition. Lipid peroxidation was considerably higher in mitochondria of 8-month-old zebrafish fed the DHA diet than in animals fed the RO diet. This could indicate higher oxidative damage to mitochondrial lipids, very likely due to increased incorporation of DHA in PL of mitochondrial membranes. Lipids would be among the first molecules affected by mitochondrial reactive oxygen species, and lipid peroxidation could propagate oxidative reactions that would damage other molecules, including mtDNA. Mitochondrial lipid peroxidation and gene expression of 21-month-old fish showed lower responsiveness to diet composition than those of younger fish. Differences found in the effect of diet composition on mitochondrial lipids between the two age groups could be indicating age-related changes in the ability to maintain structural homeostasis of mitochondrial membranes.

Membranes as a possible pacemaker of metabolism in cypriniform fish: does phylogeny matter?

The 'membrane pacemaker theory of metabolism' proposes that membranes set metabolic rate by modulating protein activity, and thus purports to explain membrane fatty acid allometry. This relationship has never been tested across species in ectotherms. After accounting for phylogeny, recent analyses have failed to support this theory based on correlations between muscle membrane composition and body mass across mammals. Therefore, the goal of this study was to seek phylogenetically corrected correlations between membrane composition, body mass and calcium-ATPase activity, using 12 species of closely related cypriniform fish (4-5500 g) covering a much narrower genetic scale than in previous tests. The results show that fish membrane unsaturation decreases with mass, but through different mechanisms from those in endotherms: 16:0 replacing 22:6 in muscle and 18:0 replacing 16:1, 18:1 and 18:2 in liver. This shows that allometric patterns differ between endotherms and ectotherms as well as between tissues. After accounting for phylogeny, however, almost all these relationships lose significance except for overall unsaturation. No relationship between calcium-ATPase activity and mass or phospholipid composition was detected. This study shows that membrane unsaturation of cypriniforms decreases with mass, but that genetic cues unrelated to size account for differences in the relative abundance of individual fatty acids. The membrane pacemaker concept accurately predicts general membrane properties such as unsaturation, but fails to explain finer scale allometric patterns. Future examinations of the membrane pacemaker hypothesis will have to take into account that allometric patterns vary between endotherms and ectotherms and between tissues of the same animal class.

Dietary fatty acid composition and the homeostatic regulation of mitochondrial phospholipid classes in red muscle of rainbow trout (Oncorhynchus mykiss)

Although dietary lipid quality markedly affects fatty acid (FA) composition of mitochondrial membranes from rainbow trout red muscle (Oncorhynchus mykiss), mitochondrial processes are relatively unchanged. As certain classes of phospholipids interact more intimately with membrane proteins than others, we examined whether specific phospholipid classes from these muscle mitochondria were more affected by dietary FA composition than others. To test this hypothesis, we fed trout with two diets differing only in their FA composition: Diet 1 had higher levels of 18:1n-9 and 18:2n-6 than Diet 2, while 22:6n-3 and 22:5n-6 were virtually absent from Diet 1 and high in Diet 2. After 5 months, trout fed Diet 2 had higher proportions of phosphatidylcholine (PC) and less phosphatidylethanolamine (PE) in mitochondrial membranes than those fed Diet 1. The FA composition of PC, PE and cardiolipin (CL) showed clear evidence of regulated incorporation of dietary FA. For trout fed Diet 2, 22:6n-3 was the most abundant FA in PC, PE and CL. The n-6 FA were consistently higher in all phospholipid classes of trout fed Diet 1, with shorter n-6 FA being favoured in CL than in PC and PE. Despite these marked changes in individual FA levels with diet, general characteristics such as total polyunsaturated FA, total monounsaturated FA and total saturated FA were conserved in PE and CL, confirming differential regulation of the FA composition of PC, PE and CL. The regulated changes of phospholipid classes presumably maintain critical membrane characteristics despite varying nutritional quality. We postulate that these changes aim to protect mitochondrial function.

Dietary fatty acids affect mitochondrial phospholipid compositions and mitochondrial gene expression of rainbow trout liver at different ages

Mitochondria are among the first responders to various stressors that challenge the homeostasis of cells and organisms. Mitochondrial decay is generally associated with impairment in the organelle bioenergetics function and increased oxidative stress, and it appears that deterioration of mitochondrial inner membrane phospholipids (PL), particularly cardiolipin (CL), and accumulation of mitochondrial DNA (mtDNA) mutations are among the main mechanisms involved in this process. In the present study, liver mitochondrial membrane PL compositions, lipid peroxidation, and mtDNA gene expression were analyzed in rainbow trout fed three diets with the same base formulation but with lipid supplied either by fish oil (FO), rapeseed oil (RO), or high DHA oil (DHA) during 6 weeks. Specifically, two feeding trials were performed using fish from the same population of two ages (1 and 3 years), and PL class compositions of liver mitochondria, fatty acid composition of individual PL classes, TBARS content, and mtDNA expression were determined. Dietary fatty acid composition strongly affected mitochondrial membrane composition from trout liver but observed changes did not fully reflect the diet, particularly when it contained high DHA. The changes were PL specific, CL being particularly resistant to changes in DHA. Some significant differences observed in expression of mtDNA with diet may suggest long-term dietary effects in mitochondrial gene expression which could affect electron transport chain function. All the changes were influenced by fish age, which could be related to the different growth rates observed between 1- and 3-year-old trout but that could also indicate age-related changes in the ability to maintain structural homeostasis of mitochondrial membranes.

Holding our breath in our modern world: will mitochondria keep the pace with climate changes?

Changes in environmental temperature can pose considerable challenges to animals and shifts in thermal habitat have been shown to be a major force driving species’ adaptation. These adaptations have been the focus of major research efforts to determine the physiological or metabolic constraints related to temperature and to reveal the phenotypic characters that can or should adjust. Considering the current consensus on climate change, the focus of research will likely shift to questioning whether ectothermic organisms will be able to survive future modifications of their thermal niches. Organisms can adjust to temperature changes through physiological plasticity (e.g., acclimation), genetic adaptation, or via dispersal to more suitable thermal habitats. Thus, it is important to understand what genetic and phenotypic attributes—at the individual, population, and species levels—could improve survival success. These issues are particularly important for ectotherms, which are in thermal equilibrium with the surrounding environment. To start addressing these queries, we should consider what physiological or metabolic functions are responsible for the impact of temperature on organisms. Some recent developments indicate that mitochondria are key metabolic structures determining the thermal range that an organism can tolerate. The catalytic capacity of mitochondria is highly sensitive to thermal variation and therefore should partly dictate the temperature dependence of biological functions. Mitochondria contain a complex network of different enzymatic reaction pathways that interact synergistically. The precise regulation of both adenosine triphosphate (ATP) and reactive oxygen species (ROS) production depends on the integration of different enzymes and pathways. Here, we examine the temperature dependence of different parts of mitochondrial pathways and evaluate the evolutionary challenges that need to be overcome to ensure mitochondrial adaptations to new thermal environments.

Temperature during embryonic development has persistent effects on metabolic enzymes in the muscle of zebrafish

Global warming is intensifying interest in the physiological consequences of temperature change in ectotherms, but we still have a relatively poor understanding of the effects of temperature on early life stages. This study determined how embryonic temperature (TE) affects development and the activity of metabolic enzymes in the swimming muscle of zebrafish. Embryos developed successfully to hatching (survival ≥ 88%) from 22°C to 32°C, but suffered sharp increases in mortality outside of this range. Embryos that were incubated until hatching at a control TE (27°C) or near the extremes for successful development (22°C or 32°C) were next raised to adulthood under control conditions at 27°C. Growth trajectories after hatching were altered in the 22°C and 32°C TE groups compared to 27°C TE controls, but growth slowed after 3 months of age in all groups. Maximal enzyme activities of cytochrome c oxidase (COX), citrate synthase (CS), hydroxyacyl-coA dehydrogenase (HOAD), pyruvate kinase (PK), and lactate dehydrogenase (LDH) were measured across a range of assay temperatures (22°C, 27°C, 32°C, 36°C) in adults from each TE group that were acclimated to 27°C or 32°C. Substrate affinities (Km) were also determined for COX and LDH. In adult fish acclimated to 27°C, COX and PK activities were higher in 22°C and 32°C TE groups than in 27°C TE controls, and the temperature optimum for COX activity was higher in the 32°C TE group than in the 22°C TE group. Warm acclimation reduced COX, CS, and/or PK activities in the 22°C and 32°C TE groups, possibly to compensate for thermal effects on molecular activity. This response did not occur in the 27°C TE controls, which instead increased LDH and HOAD activities. Warm acclimation also increased thermal sensitivity (Q10) of HOAD to cool temperatures across all TE groups. We conclude that the temperature experienced during early development can have a persistent impact on energy metabolism pathways and acclimation capacity in later life.