Routine Oxygen Consumption Rates Research Articles

Lipopeptides from Bacillus tequilensis EA-CB0015 and cinnamon extract decrease the bioenergetic response of Fusarium oxysporum f. sp. cubense

AbstractLipopeptides (LPs) from B. tequilensis EA-CB0015 have antifungal activity against Fusarium species. Specifically, against F. oxysporum f. sp. cubense (Foc), the cause of Fusarium wilt of banana. Cinnamon (CN) extract is also known for its inhibitory activity against the Fusarium genus. The main goal of this research was to determine whether the effect of LPs and CN extract or their combination against a Foc isolate is related to an impairment of mitochondrial function. Our results show that biomass decreased by 74% (p < 0.0001) and 84% (p < 0.0001) when cultures were treated with 128 ppm LPs and 152.5 ppm CN extract, respectively. In parallel, we found a pronounced impairment of the bioenergetic response. That is, the routine oxygen consumption rate diminished by 55% (p = 0.0148) and 38% (p < 0.0001), respectively. Moreover, the ATP-linked respiratory rate decreased by 63% (p = 0.0461) and 44% (p = 0.0005), while the FCCP-simulated respiratory rate by 63% (p = 0.0255) and 45% (p = 0.0002). Therefore, our data suggest that the altered bioenergetic response observed in cultures of Foc treated with LPs or CN is mainly caused by an impairment of the activity of the respiratory complexes. On the other hand, biomass production was reduced by 80% (p < 0.0001) when cultures were treated with a mixture comprising only 10% LPs and 40% CN extract. Furthermore, ATP-linked and FCCP-stimulated respiratory rates decreased by 62% (p = 0.0024) and 68% (p < 0.0001), respectively under the same conditions. A potentially synergistic antifungal effect of cyclic LPs with a CN extract is suggested. Graphical Abstract

Growth, metabolism, and dissolved oxygen tolerance of juvenile burbot

The burbot, Lota lota, is being explored as a novel aquaculture species in North America due to its palatability and potential to be grown in areas that currently support rainbow trout, Oncorhynchus mykiss culture. Dissolved oxygen (DO) concentration is a primary limiting factor in fish survival and growth, with tolerance varying among species. We exposed juvenile burbot (19.5 ± 2.2 g) to five dissolved oxygen concentrations (5.0, 5.8, 6.6, 7.4, and 8.3 (control) mg·L −1) for 9 weeks at 15 °C. Size variability was high in all treatments, and food consumption, and growth rates did not differ among DO levels, although fish at 8.3 mg·L−1 grew ca. 29% larger than those at 5.0 mg·L−1. We also measured short-term hypoxia tolerance and resting routine oxygen consumption rates (MO2) of burbot that had been chronically acclimated to the same DO concentrations. Burbot acclimated to 8.3 mg·L−1 lost equilibrium (LOEcrit) at a significantly higher concentration (1.85 ± 0.33 mg·L −1) than that of the 7.4 and 6.6 mg·L −1 acclimated fish (1.50 ± 0.37 and 1.49 ± 0.27; respectively), while all other groups were intermediate (1.67 ± 0.28). The MO2s were not statistically distinguishable among acclimation groups (p-value = 0.25), but MO2 trended lower with decreasing DO concentrations. In summary, juvenile burbot are tolerant to DO concentrations down to 5.0 mg·L −1. We recommend rearing burbot at DO concentrations >7.0 mg·L −1 to optimize growth, especially with the presence of multiple stressors.

Cardiorespiratory adjustments to chronic environmental warming improve hypoxia tolerance in European perch (Perca fluviatilis).

Aquatic hypoxia will become increasingly prevalent in the future as a result of eutrophication combined with climate warming. While short-term warming typically constrains fish hypoxia tolerance, many fishes cope with warming by adjusting physiological traits through thermal acclimation. Yet, little is known about how such adjustments affect tolerance to hypoxia. We examined European perch (Perca fluviatilis) from the Biotest enclosure (23°C, Biotest population), a unique ∼1 km2 ecosystem artificially warmed by cooling water from a nuclear power plant, and an adjacent reference site (16-18°C, reference population). Specifically, we evaluated how acute and chronic warming affect routine oxygen consumption rate (ṀO2,routine) and cardiovascular performance in acute hypoxia, alongside assessment of the thermal acclimation of the aerobic contribution to hypoxia tolerance (critical O2 tension for ṀO2,routine: Pcrit) and absolute hypoxia tolerance (O2 tension at loss of equilibrium; PLOE). Chronic adjustments (possibly across lifetime or generations) alleviated energetic costs of warming in Biotest perch by depressing ṀO2,routine and cardiac output, and by increasing blood O2 carrying capacity relative to reference perch acutely warmed to 23°C. These adjustments were associated with improved maintenance of cardiovascular function and ṀO2,routine in hypoxia (i.e. reduced Pcrit). However, while Pcrit was only partially thermally compensated in Biotest perch, they had superior absolute hypoxia tolerance (i.e. lowest PLOE) relative to reference perch irrespective of temperature. We show that European perch can thermally adjust physiological traits to safeguard and even improve hypoxia tolerance during chronic environmental warming. This points to cautious optimism that eurythermal fish species may be resilient to the imposition of impaired hypoxia tolerance with climate warming.

Effects of temperature on hatching and growth performance of embryos and yolk-sac larvae of a threatened estuarine fish: Longfin smelt (Spirinchus thaleichthys)

The abundance of longfin smelt (Spirinchus thaleichthys) in the San Francisco Estuary (SFE) has declined to less than 1% of historic numbers, contributing to their listing as “threatened” under the California Endangered Species Act. To prevent local extirpation, a captive culture program is being developed for the longfin smelt at the Fish Conservation Culture Laboratory at UC Davis. To begin systematically addressing current issues with larviculture methods, we tested the effects of temperature on longfin smelt embryos from 7 clutches with different parentages. We reared embryos and newly hatched non-feeding yolk-sac larvae in freshwater at 9, 12, or 15 °C until the age when these fish underwent mass mortality (>90% mortality) during the experiment (3, 4, or 5 days post-hatch (dph), depending on rearing temperature). We measured hatch success, hatch morphometrics (notochord length, dry mass, yolk volume, and oil volume), length and dry mass growth rates, yolk and oil resorption rates, routine oxygen consumption rate, and locomotor activity (percent of time spent moving, total distance travelled, and average swimming velocity). Embryos and larvae reared at 15 °C performed poorly, experiencing reduced hatch success, hatch notochord lengths, growth rates, and earlier mass mortality. Embryos reared at 9 and 12 °C had similar hatch success but at hatch, larvae were longer at 9 compared to 12 °C. However, larvae grew faster in 12 compared to 9 °C resulting in both temperature groups having similar lengths prior to mass mortality (4 dph for 12 °C and 5 dph for 9 °C). Temperature had no effect on routine oxygen consumption rate among temperature groups but locomotor activity was elevated at 9 and 15 °C groups compared to 12 °C, suggesting that locomotor activity consumed a higher proportion of the energy budget, leaving a smaller fraction for growth. Finally, larval swimming speeds, one day prior to each temperature's respective day of mass mortality, were higher at 12 °C (3 dph) compared to 9 (4 dph) and 15 °C (2 dph), which could lead to higher foraging success. Interclutch variation was high, however, suggesting that parentage effects may result in brood-specific variation in the responses of larvae to water temperature. Taken together, these data suggest that rearing longfin smelt at 15 °C would have detrimental effects and we suggest that cooler temperatures such as 9 or 12 °C may improve the culturing of the earliest life stages of longfin smelt.

Age-related fatigue is associated with reduced mitochondrial function in peripheral blood mononuclear cells.

Fatigue is a complex syndrome associated with exhaustion not relieved by sleep. It occurs frequently in older adults in the context of chronic disease and is associated with decreased physical capacity. Whether a mitochondrial dysfunction and therefore an impaired energy production might contribute to the development of fatigue during aging is yet unknown. The aim of this study was to evaluate mitochondrial respiration of peripheral blood mononuclear cells (PBMCs) in older patients with and without fatigue. Fatigue was determined according to the Brief Fatigue Inventory. Mitochondrial respiration of freshly isolated PBMCs was investigated by high-resolution respirometry using the Oroboros Oxygraph-O2k. Functional impairment and depressive symptoms were assessed using questionnaires. 23 geriatric patients (77.8±4.9years; 43.5% female) with fatigue and 22 without fatigue (75.4±5.4years; 45.5% female) were analyzed. Patients with fatigue exhibited more functional limitations and more depressive symptoms. High-resolution respirometry of intact PBMCs revealed a lower routine (4.82±1.14pmol/s versus 5.89±1.90pmol/s, p=0.041) and maximum (6.55±1.51pmol/s versus 8.43±3.67pmol/s, p=0.013) oxygen consumption rate, resulting in a reduced ATP-linked respiration (4.26±1.00pmol/s versus 5.09±1.53pmol/s, p=0.035) of PBMCs from geriatric patients with fatigue compared to controls without. This short report shows that in this group of older patients, fatigue is associated with lower PBMC mitochondrial respiration. Whether the impaired mitochondrial respiration is accompanied by a reduced mitochondrial activity in other organs (e.g. muscle) remains to be elucidated.

Interspecific Differences in the Metabolic Rate, Gill Dimension and Hematology of Fish in an Amazonian Floodplain Lake

It has been hypothesized that respiratory physiology in fish is closely associated with ecological traits. Therefore, data on gill morphometrics (lamellae frequency, gill surface area and barrier thickness), metabolic rate (oxygen consumption) and blood oxygen capacity (hematology) were analyzed in several fish, including benthic, bentho-pelagic and pelagic species collected in an Amazon floodplain lake. Similar to other teleostean species, the 2nd and 3rd gill arches have numerous large filaments in both pelagic and benthic species, as these characteristics tend to increase the gill surface area. A large gill area (4 to 7 cm2 g-1, mass-specific) is associated with a high (100 to 300 mg O2 h-1 kg-1) routine oxygen consumption rate and has been observed in active pelagic swimmers, such as Cichla monoculus and Pygocentrus nattereri. Benthic dwelling fish (e.g., Pterygoplichthys pardalis and Sorubim lima) have low metabolic rates (20 to 50 mg O2 h-1 kg-1), small gill dimensions (2 to 3 cm2 g-1, mass-specific), low hemoglobin levels (3 to 5 g dL-1), reduced numbers of circulating red blood cells (1 to 2 Í106 mm-3) and low hematocrit values (25 to 35%) compared to pelagic species. These results demonstrated that pelagic fish have high routine oxygen consumption rates compatible with their large gill surface area and high blood oxygen capacity, whereas benthic species have low metabolic rates, small gill dimensions and reduced blood oxygen capacity.

Temperature and oxygen related ecophysiological traits of snow trout (Schizothorax richardsonii) are sensitive to seasonal changes in a Himalayan stream environment.

In this study, we investigated the seasonal changes in key eco-physiological traits of a wild population of snow trout, Schizothorax richardsonii from river Gola in the Indian Himalayan region over one year. Live specimens (5.8-31.4 g) were electro-fished from their natural habitat during representative months of four seasons with notable differences in water temperature, oxygen concentration and saturation. After 24-72 h of captive-acclimation, the fishes were examined for upper and lower critical thermal limits (CTmax and CTmin), incipient lethal oxygen thresholds (ILOC and ILOS), apparent routine and maximum oxygen consumption rates (MO2rout and MO2max), and blood haemoglobin-haematocrit. Across the seasons, mean CTmin and CTmax values ranged from ∼0 to 34.6 °C, suggesting a relatively wide acute thermal tolerance range for this predominantly cold-water fish. Changes in the habitat's thermal condition during winter to summer was reflected in the CTmin (∼0-2.4 °C) and CTmax (31.7-34.4 °C) estimates, while the highest thermal scope (CTmax-CTmin; 33.2 °C) was recorded in autumn. Concurrently, the incipient lethal hypoxia threshold observed in autumn (ILOS-2.6% and ILOC-0.19 mgO2/L) was significantly lower than the other three seasons, possibly linked to warm-acclimation. The reduction in blood haemoglobin-haematocrit levels during winter could limit the oxygen carrying capacity, with possible reciprocations in thermal tolerance and aerobic metabolism. Concerning body mass corrected oxygen consumption, the apparent MO2rout was found to increase in a temperature-dependent manner from 150.3 mgO2/kg/h at 12 °C to 315.2 mgO2/kg/h at 26 °C, with Q10 ranging from 1.6 to 2.2. Whereas, changes in MO2max was not temperature sensitive (Q10 of 0.7-1.3), except during spring-summer (Q10-2), with lowest and highest measurements in spring and autumn (934 and 1514 mgO2/kg/h), respectively. Collectively, these data form the first information report on the seasonal plasticity in thermal and respiratory physiology of a Schizothoracine fish species, bearing significance for their conservation, aquaculture and habitat monitoring.

Does hypoxia or different rates of re-oxygenation after hypoxia induce an oxidative stress response in Cyphocharax abramoides (Kner 1858), a Characid fish of the Rio Negro?

We examined whether oxidative damage and antioxidant responses are more likely to occur during hypoxia or re-oxygenation in hypoxia-tolerant fish, and whether there is an influence of the rate of re-oxygenation. An hypoxia/re-oxygenation experiment using wild-caught Cyphocharax abramoides (Rio Negro, Brazil), was designed to answer these questions. Lipid peroxidation (MDA), a measure of oxidative damage, and antioxidant activities (superoxide dismutase (SOD), glutathione peroxidase (GPx), antioxidant capacity against peroxyl radicals (ACAP)), were measured in brain, gill and liver tissues after normoxia, 3-h hypoxia (2.7 kPa), and 3-h hypoxia followed by 1-h or 3-h re-oxygenation, implemented either immediately or slowly (3.0 kPa·h−1). Critical oxygen tension of routine oxygen consumption rate (Pcrit) (4.1 kPa) and the PO2 at loss of equilibrium (LOE) (1.7 kPa) were determined to set the experimental hypoxia exposure. The Regulation Index, a measure of oxyregulation with declining PO2, was 0.32. Oxidative damage occurred during hypoxia: no additional damage was observed during re-oxygenation. Tissues responded differentially. GPx and MDA rose in the brain and gills, and SOD (and likely GPx) in the liver during hypoxia. Antioxidants increased further at LOE. Rate of oxygen increase during re-oxygenation did not affect antioxidant responses. In brain and gills, GPx and MDA decreased or recovered after 1-h re-oxygenation. In liver, SOD remained high and GPx increased. In summary, C. abramoides incurred oxidative damage during hypoxic exposure with no additional damage inflicted during re-oxygenation: the rate of re-oxygenation was inconsequential. Literature data support conclusion of greater damage during hypoxia than during re-oxygenation in hypoxia-tolerant fish.

The effect of temperature on the resting and post-exercise metabolic rates and aerobic metabolic scope in shortnose sturgeon Acipenser brevirostrum.

The effects of acclimation temperature (15, 20, 25°C) on routine oxygen consumption and post-exercise maximal oxygen consumption rates (MO2) were measured in juvenile shortnose sturgeon (Acipenser brevirostrum LeSueur, 1818). The routine MO2 of shortnose sturgeon increased significantly from 126.75mg O2h-1kg-1 at 15°C to 253.13mg O2h-1kg-1 at 25°C. The temperature coefficient (Q 10) values of the routine metabolic rates ranged between 1.61 and 2.46, with the largest Q 10 values occurring between 15 and 20°C. The average post-exercise MO2 of all temperature groups increased to a peak value immediately following the exercise, with levels increasing about 2-fold among all temperature groups. The Q 10 values for post-exercise MO2 ranged from 1.21 to 2.12, with the highest difference occurring between 15 and 20°C. Post-exercise MO2 values of shortnose sturgeon in different temperature groups all decreased exponentially and statistically returned to pre-exercise (resting) levels by 30min at 15 and 20°C and by 60min at 25°C. The aerobic metabolic scope (post-exercise maximal MO2-routine MO2) increased to a maximum value ∼156mg O2h-1kg-1 at intermediate experimental temperatures (i.e., 20°C) and then decreased as the temperature increased to 25°C. However, this trend was not significant. The results suggest that juvenile shortnose sturgeon show flexibility in their ability to adapt to various temperature environments and in their responses to exhaustive exercise.

Metabolic response of Arctic pteropods to ocean acidification and warming during the polar night/twilight phase in Kongsfjord (Spitsbergen)

Thecosome pteropods are considered highly sensitive to ocean acidification. During the Arctic winter, increased solubility of CO2 in cold waters intensifies ocean acidification and food sources are limited. Ocean warming is also particularly pronounced in the Arctic. Here, we present the first data on metabolic rates of two pteropod species (Limacina helicina, Limacina retroversa) during the Arctic winter at 79°N (polar night/twilight phase). Routine oxygen consumption rates and the metabolic response [oxygen consumption (MO2), ammonia excretion (NH3), overall metabolic balance (O:N)] to elevated levels of pCO2 and temperature were examined. Our results suggest lower routine MO2 rates for both Limacina species in winter than in summer. In an 18-h experiment, both pCO2 and temperature affected MO2 of L. helicina and L. retroversa. After a 9-day experiment with L. helicina all three metabolic response variables were affected by the two factors with interactive effects in case of NH3 and O:N. The response resembled a “hormesis-type” pattern with up-regulation at intermediate pCO2 and the highest temperature level. For L. retroversa, NH3 excretion was affected by both factors and O:N only by temperature. No significant effects of pCO2 or temperature on MO2 were detected. Metabolic up-regulation will entail higher energetic costs that may not be covered during periods of food limitation such as the Arctic winter and compel pteropods to utilize storage compounds to a greater extent than usual. This may reduce the fitness and survival of overwintering pteropods and negatively impact their reproductive success in the following summer.

The oxygen threshold for maximal feed intake of Atlantic salmon post-smolts is highly temperature-dependent

In order to maximize the growth potential of Atlantic salmon (Salmo salar L.) in the on-growing phase in open sea cages, the dissolved oxygen (DO, % of air saturation) level must exceed the minimum DO required for maximal feed intake (DOmaxFI). The main aim of this study was to determine the effect of temperature on this important threshold DO, and secondly, to provide aquaculturists with a model that estimates feed intake as function of both temperature and DO. Quadruple tank groups of Atlantic salmon post-smolts (~0.3–0.5kg) were kept at 7, 11, 15 and 19°C, and subjected to seven DO levels per temperature, ranging from ≈32–92, 42–102, 52–112 and 62–122% O2, respectively, for 42days. DO levels were changed every second day, in random order. Fish were fed a known amount of feed in excess twice daily, waste feed was collected and daily feed intake (DFI, % of biomass, BM, per day) estimated. The routine oxygen consumption rate (MO2 rout, measured in partially fasted and active fish) and the DO below which MO2 rout started to decline (termed the routine limiting oxygen saturation, LOSrout) was determined in fasted fish at all four temperatures at the end of experimentation, and the latter was used to estimate the “zero feed intake DO” in the DFI model. The data demonstrate sustained appetite with decreasing DO until a threshold level (DOmaxFI) is reached, at which point appetite gradually decreases. Both the maximal level of feed intake (DFImax) and the DOmaxFI were highly dependent on temperature, increasing from 0.47 to 0.88% of BM/day, and from 42 to 76% O2, respectively, within the temperature range tested. The LOSrout ranged from 24 to 40% O2. The present study is the first to present the pronounced effect of temperature on DOmaxFI, and results suggest that the DO requirement of A. salmon has previously been considerably over-estimated, particularly at lower temperatures. Statement of relevanceThe study links growth performance to environmental temperature and oxygen.

The effect of temperature on postprandial metabolism of yellowfin tuna (Thunnus albacares)

Specific dynamic action (SDA), the increase in metabolic expenditure associated with consumption of a meal, represents a substantial portion of fish energy budgets and is highly influenced by ambient temperature. The effect of temperature on SDA has not been studied in yellowfin tuna (Thunnus albacares, Bonnaterre 1788), an active pelagic predator that occupies temperate and subtropical waters. The energetic cost and duration of SDA were calculated by comparing routine and post-prandial oxygen consumption rates. Mean routine metabolic rates in yellowfin tuna increased with temperature, from 136mgO2kg−1h−1 at 20°C to 211mgO2kg−1h at 24°C. The mean duration of SDA decreased from 40.2h at 20°C to 33.1h at 24°C, while mean SDA coefficient, the percentage of energy in a meal that is consumed during digestion, increased from 5.9% at 20°C to 12.7% at 24°C. Digestion in yellowfin tuna is faster at a higher temperature but requires additional oxidative energy. Enhanced characterization of the role of temperature in SDA of yellowfin tuna deepens our understanding of tuna physiology and can help improve management of aquaculture and fisheries.

Interactive effects of copper exposure and environmental hypercapnia on immune functions of marine bivalves Crassostrea virginica and Mercenaria mercenaria.

Estuarine organisms such as bivalves are commonly exposed to trace metals such as copper (Cu) and hypercapnia (elevated CO2 levels) in their habitats, which may affect their physiology and immune function. This study investigated the combined effects of elevated CO2 levels (∼800-2000μatm PCO2, such as predicted by the near-future scenarios of global climate change) and Cu (50μgl(-1)) on immune functions of the sediment dwelling hard clams Mercenaria mercenaria and an epifaunal bivalve, the eastern oyster Crassostrea virginica. Clams and oysters were exposed for 4 weeks to different CO2 and Cu levels, and tissue Cu burdens and immune parameters were assessed to test the hypothesis that hypercapnia will enhance Cu uptake due to the higher bioavailability of free Cu(2+) and increase the immunomodulatory effects of Cu. Exposure to Cu stimulated key immune parameters of clams and oysters leading to increased number of circulating hemocytes, higher phagocytosis and adhesion ability of hemocytes, as well as enhanced antiparasitic and antibacterial properties of the hemolymph reflected in higher activities of lysozyme and inhibitors of cysteine proteases. Lysozyme activation by Cu exposure was most prominent in normocapnia (∼400μatm PCO2) and an increase in the levels of the protease inhibitors was strongest in hypercapnia (∼800-2000μatm PCO2), but other immunostimulatory effects of Cu were evident in all PCO2 exposures. Metabolic activity of hemocytes of clams and oysters (measured as routine and mitochondrial oxygen consumption rates) was suppressed by Cu exposure likely reflecting lower rates of ATP synthesis and/or turnover. However, this metabolic suppression had no negative effects of the studied immune functions of hemocytes such as phagocytosis or adhesion capacity. Hypercapnia (∼800-2000μatm PCO2) slightly but significantly enhanced accumulation of Cu in hemocytes, consistent with higher Cu(2+) bioavailability in CO2-acidified water, but had little effect on cellular and humoral immune traits of clams and oysters. These findings indicate that low levels of Cu contamination may enhance immunity of estuarine bivalves while moderate hypercapnia (such as predicted by the near future scenarios of the global climate change) does not strongly affect their immune parameters.

Physiology and performance of wild and domestic strains of diploid and triploid rainbow trout (Oncorhynchus mykiss) in response to environmental challenges

To determine the factors that may contribute to the poor survival of triploid (3n) rainbow trout (Oncorhynchus mykiss) in lake stocking programs, we compared the physiology and responses to environmental challenges of four wild strains and one domestic strain of diploid (2n) and 3n juvenile rainbow trout. Over four successive years, wild trout were caught from nature, spawned, and progeny were reared in a hatchery along with hatchery-bred domestic trout. Offspring of each strain were raised for up to 12 months as both 2n and 3n, and growth rate, critical swimming speed, routine oxygen consumption rate, critical oxygen tensions, thermal tolerance, and hypoxia tolerance were assessed in a laboratory setting. Cohorts of the 2008, 2009, and 2010 wild strains were also stocked into two experimental lakes and recaptured as adults using traps and fyke nets in 2011 for laboratory analysis. In the juvenile trout, the only measure of performance to show a consistent difference between 2n and 3n individuals across all strains was hypoxia tolerance, where 3n trout had a shorter time to loss of equilibrium (LOE) at 16 Torr than their 2n counterparts, but this effect was not seen in adult, lake-reared trout. Strain had a significant effect on specific growth rate, critical swimming speed (Ucrit), and time to LOE in hypoxia, although the effects of strain on these variables was not consistent from year to year. Overall, this study suggests that poorer hypoxia tolerance in 3n trout compared with 2n trout may be a contributing factor to the higher lake stocking mortalities in 3n trout.

Temperature-dependent physiological and biochemical responses of the marine medaka Oryzias melastigma with consideration of both low and high thermal extremes

This study aimed to investigate temperature effect on physiological and biochemical responses of the marine medaka Oryzias melastigma larvae. The fish were subjected to a stepwise temperature change at a rate of 1°C/h increasing or decreasing from 25°C (the control) to six target temperatures (12, 13, 15, 20, 28 and 32°C) respectively, followed by a 7-day thermal acclimation at each target temperature. The fish were fed ad libitum during the experiment. The results showed that cumulative mortalities were significantly increased at low temperatures (12 and 13°C) and at the highest temperature (32°C). For the survivors, their growth profile closely followed the left-skewed ‘thermal performance curve’. Routine oxygen consumption rates of fish larvae were significantly elevated at 32°C but suppressed at 13 and 15°C (due to a high mortality, larvae from 12°C were not examined). Levels of heat shock proteins and activities of malate dehydrogenase and lactate dehydrogenase were also measured in fish larvae exposed at 15, 25 and 32°C. The activities of both enzymes were significantly increased at both 15 and 32°C, where the fish larvae probably suffered from thermal discomfort and increased anaerobic components so as to compensate the mismatch of energy demand and supply at these thermal extremes. Coincidently, heat shock proteins were also up-regulated at both 15 and 32°C, enabling cellular protection. Moreover, the critical thermal maxima and minima of fish larvae increased significantly with increasing acclimation temperature, implying that the fish could develop some degrees of thermal tolerance through temperature acclimation.

Climate change and the performance of larval coral reef fishes: the interaction between temperature and food availability.

Climate-change models predict that tropical ocean temperatures will increase by 2-3°C this century and affect plankton communities that are food for marine fish larvae. Both temperature and food supply can influence development time, growth, and metabolism of marine fishes, particularly during larval stages. However, little is known of the relative importance and potential interacting effects of ocean warming and changes to food supply on the performance of larval fishes. We tested this for larvae of the coral reef anemonefish, Amphiprion percula, in an orthogonal experiment comprising three temperatures and three feeding schedules. Temperatures were chosen to represent present-day summer averages (29.2°C) and end-of-century climate change projections of +1.5°C (30.7°C) and +3°C (32.2°C). Feeding schedules were chosen to represent a reduction in access to food (fed daily, every 2 days, or every 3 days). Overall, larvae took longer to settle at higher temperatures and with less frequent feeding, and there was a significant interaction between these factors. Time to metamorphosis was fastest in the 30.7(o)C and high food availability treatment (10.5 ± 0.2 days) and slowest in the 32.2(o)C and low food availability treatment (15.6 ± 0.5 days; i.e. 50% faster). Fish from the lower feeding regimens had a lower body condition and decreased survivorship to metamorphosis. Routine oxygen consumption rates were highest for fish raised at 32.2°C and fed every third day (162 ± 107 mg O2 kg(-1) h(-1)) and lowest for fish raised at 29.2°C and fed daily (122 ± 101 mg O2 kg(-1) h(-1); i.e. 35% lower). The elevated routine oxygen consumption rate, and therefore greater energy use at higher temperatures, may leave less energy available for growth and development, resulting in the longer time to metamorphosis. Overall, these results suggest that larval fishes will be severely impacted by climate-change scenarios that predict both elevated temperatures and reduced food supply.

Hypoxia tolerance thresholds for post-smolt Atlantic salmon: Dependency of temperature and hypoxia acclimation

Atlantic salmon (Salmo salar L.) experience periodic drops in dissolved oxygen (O2) inside aquaculture sea cages. In order to evaluate whether fish function or welfare is compromised during such drops in O2 (termed hypoxia), it is necessary to establish the limit for acceptable O2 reductions; the hypoxia tolerance threshold. In the present study, effects of temperature (6, 12 and 18°C) and hypoxia acclimation (33days of hypoxic periods down to 50% O2 occurring every 6h at 16°C) on the routine oxygen consumption rate (ṀO2) and the limiting oxygen saturation (LOS, defined as the hypoxia tolerance threshold) were investigated in undisturbed, fed fish kept in groups with the aim of resembling commercial aquaculture conditions. ṀO2 was measured using open respirometry where a progressive decline in O2 was caused by fish O2 consumption during a period of low water turnover. LOS was defined as the O2 below which fish were no longer able to uphold routine ṀO2. Both ṀO2 and LOS were found to increase exponentially with temperature (Q10=2.7 for ṀO2 and 1.8 for LOS), but no effect of hypoxia acclimation was found. The mean (±SE) LOS at 6, 12, 16 and 18°C was 30±1, 39±1, 47±1 and 55±2% of air saturation respectively. The variation in LOS within and across temperatures was to a large extent explained by variation in ṀO2 (R2=0.93), suggesting that LOS increases with any factor that raises the metabolic rate of Atlantic salmon. This study provides aquaculturists and legislators with a lower limit for acceptable drops in O2 at temperatures relevant for the on-growing phase in Atlantic salmon aquaculture, and discusses the variation in LOS that can be expected at a given temperature.

The physiology of rainbow trout in social hierarchies: two ways of looking at the same data

Salmonids form dominance hierarchies in environments, where space or food are limiting. Our first objective was to investigate the physiology of individual rainbow trout in 4-fish hierarchies. Our second was to compare conclusions drawn from grouping physiological data on the basis of social rank with those based on relating individual physiology to individual aggressive behavior. To create a social hierarchy, groups of 4 juvenile trout were fed (1% ration) using a darkened feeding container, twice daily (morning and evening). Each morning feeding was videotaped to record aggressive behavior, thereby facilitating the assignment of a social status rank to each fish. On days 5 and 10-11, physiological parameters were measured in fish fasted for 24h. Social hierarchies formed in all tested groups. One fish would become dominant, whereas the three subordinate individuals would each assume a stable social rank. When classified according to this social rank, the three subordinate individuals all displayed similar physiology, different from the physiology of the dominant fish. The latter included higher ammonia excretion rate, greater protein utilization in aerobic metabolism, greater feeding, higher specific growth rate, greater increase in condition factor, and lower routine oxygen consumption rate. However, when individual aggression was taken into account, a continuous gradient was observed between aggression and physiology for most parameters, regardless of social status. These relationships could be improved by normalizing the aggression score to the overall level of aggression in each hierarchy. We argue that individual behavior should be considered instead of just social rank when studying the physiology of trout in social hierarchies.

Interactions between hypoxia tolerance and food deprivation in Amazonian oscars, Astronotus ocellatus (Agassiz)

Oscars are often subjected to a combination of low levels of oxygen and fasting during nest-guarding on Amazonian floodplains. We questioned whether this anorexia would aggravate the osmo-respiratory compromise. We compared fed and fasted oscars (10-14 days) in both normoxia and hypoxia (10-20 Torr, 4 h). Routine oxygen consumption rates (O2) were increased by 75% in fasted fish, reflecting behavioural differences, whereas fasting improved hypoxia resistance and critical oxygen tensions (Pcrit) lowered from 54 Torr in fed fish to 34 Torr when fasting. In fed fish, hypoxia reduced liver lipid stores by approximately 50% and total liver energy content by 30%. Fasted fish had a 50% lower hepatosomatic index, resulting in lower total liver protein, glycogen and lipid energy stores under normoxia. Compared with hypoxic fed fish, hypoxic fasted fish only showed reduced liver protein levels and even gained glycogen (+50%) on a per gram basis. This confirms the hypothesis that hypoxia-tolerant fish protect their glycogen stores as much as possible as a safeguard for more prolonged hypoxic events. In general, fasted fish showed lower hydroxyacylCoA dehydrogenase activities compared with fed fish, although this effect was only significant in hypoxic fasted fish. Energy stores and activities of enzymes related to energy metabolism in muscle or gills were not affected. Branchial Na(+) uptake rates were more than two times lower in fed fish, whereas Na(+) efflux was similar. Fed and fasted fish quickly reduced Na(+) uptake and efflux during hypoxia, with fasting fish responding more rapidly. Ammonia excretion and K(+) efflux were reduced under hypoxia, indicating decreased transcellular permeability. Fasted fish had more mitochondria-rich cells (MRC), with larger crypts, indicating the increased importance of the branchial uptake route when feeding is limited. Gill MRC density and surface area were greatly reduced under hypoxia, possibly to reduce ion uptake and efflux rates. Density of mucous cells of normoxic fasted fish was approximately fourfold of that in fed fish. Overall, a 10-14 day fasting period had no negative effects on hypoxia tolerance in oscars, as fasted fish were able to respond more quickly to lower oxygen levels, and reduced branchial permeability effectively.

Effect of body mass, temperature and food deprivation on oxygen consumption rate of common cuttlefish Sepia officinalis

Predictions of short and long term changes in Sepia officinalis metabolism are useful, since this species is both economically important for aquaculture and also is an ideal experimental laboratory organism. In this study standard and routine oxygen consumption rates of newly hatched and juvenile laboratory raised cuttlefish S. officinalis ranging between 0.04 and 18.48 g dry body mass (Dm), were measured over a range of temperatures (10, 15, 20 and 25°C). The mass exponent (b) ranged between 0.706 and 0.992 for standard oxygen consumption and between 0.694 and 0.990 for routine oxygen consumption. Oxygen consumption scaled allometrically (b = 0.7) with body mass for cuttlefish 2 g, MO2 = 0.076Dm0.9831.091T for standard oxygen consumption; cuttlefish 2 g, MO2 = 0.225Dm0.9621.081T for routine oxygen consumption. Using these equations it was estimated that a cuttlefish of 1 g Dm held at 20°C, eating 5% Dm day−1 and undergoing standard and routine metabolism consumes 21.3 and 35.4%, respectively of its total daily energy intake. Juvenile cuttlefish (3.32–5.08 g Dm) held at 15°C and deprived of food for 27 days maintained a stable standard oxygen consumption rate for the first 6 days following starvation. By the 18th day without food, oxygen consumption rate had declined by 53% and further declined to 65% below the standard oxygen consumption rate on the 27th day. Upon resumption of feeding, the respiration rate returned immediately to the initial level prior to food deprivation. The present study defines the basic energy requirements and general physiological state of young cuttlefish at temperatures of 10–25°C with and without food.