The effect of chronic heat stress on cortisol levels in the antarctic fishPagothenia borchgrevinki

Effect of heat stress on the antioxidant defense system and erythrocyte morphology of Antarctic fishes

This study analyzed the effect of thermal stress on erythrocytes of Notothenia rossii and Notothenia coriiceps, abundant notothenioids in Admiralty Bay, Antarctic Peninsula. In both species, the antioxidant defense system enzymes, superoxide dismutase, catalase, glutathione peroxidase, glutathione-S transferase, glutathione reductase were punctually altered (8°C for 1, 3 and 6 days) in erythrocytes, indicating that these markers are not ideal for termal stress. However, under the influence of thermal stress, morphological changes in Notothenia coriiceps erythrocytes were observed at all exposure times (1, 3 and 6 days at 8°C), and in Notothenia rossii occurred in 6 days. These results suggest that Notothenia corriceps presents a lower tolerance to thermal stress at 8°C for up to 6 days, since the cellular and nuclear alterations recorded are pathological and may be deleterious to the cells. Among the morphological markers analyzed in this work, we believe that the shape change and nuclear bubble formation may be good stress biomarkers in erythrocytes of Notothenia rossii and Notothenia coriiceps.

Temperature increase and its effects on fish stress physiology in the context of global warming

The capacity of fishes to cope with environmental variation is considered to be a main determinant of their fitness and is partly determined by their stress physiology. By 2100, global ocean temperature is expected to rise by 1-4°C, with potential consequences for stress physiology. Global warming is affecting animal populations worldwide through chronic temperature increases and an increase in the frequency of extreme heatwave events. As ectotherms, fishes are expected to be particularly vulnerable to global warming. Although little information is available about the effects of global warming on stress physiology in nature, multiple studies describe the consequences of temperature increases on stress physiology in controlled laboratory conditions, providing insight into what can be expected in the wild. Chronic temperature increase constitutes a physiological load that can alter the ability of fishes to cope with additional stressors, which might compromise their fitness. In addition, rapid temperature increases are known to induce acute stress responses in fishes and might be of ecological relevance in particular situations. This review summarizes knowledge about effects of temperature increases on the stress physiology of fishes and discusses these in the context of global warming.

Characterization of Myostain (MSTN) and Myogenic Differentiation Antigen (MyoD) and the Effect of Dexamethasone on Their Expression in Large-Scale Loach Paramisgurnus dabryanus

Myostatin (MSTN) and myogenic differentiation antigen (MyoD) play an essential role in specification and differentiation of skeletal muscle. However, the role of stress in the regulation of MyoD and MSTN has not been fully revealed and more evidence should be provided. Here, we reported the cloning and expressional analyses of MSTN and MyoD in Large-scale Loach Paramisgurnus dabryanus (hereafter PdMSTN and PdMyoD). Injecting individuals with 0, 60, 600, and 1,200 μg/kg dexamethasone (DXM) for five consecutive days resulted in a dose-dependent change of PdMSTN and PdMyoD expression. The expression of PdMSTN was upregulated with increasing DXM concentrations, while PdMyoD expression was downregulated. The changes in the expression of these genes at different time points for 10 consecutive days were studied after individuals were treated with 600 μg/kg DXM. Compared with the control group, PdMSTN expression decreased and PdMyoD expression increased before 12 h, and both PdMSTN and PdMyoD expression levels increased at 24 h, which was significantly higher than those in control group. At a prolonged treatment of 5-10 d, expression levels of PdMSTN and PdMyoD had significantly reduced. The results indicate that both PdMyoD and PdMSTN are involved in DXM-induced stress in Large-scale Loach.

An acute increase in water temperature can increase free amino acid concentrations in the blood, brain, liver, and muscle in goldfish (Carassius auratus)

Water temperature directly affects the body temperature in fish, so increasing water temperatures in oceans and rivers will lead to increases in fish body temperatures. Whilst a range of responses of fish to increases in water temperature have been measured, amino acid metabolism in a fish under high water temperature (HT) conditions has not been investigated. The aim of this study was to determine the effects of an acute increase in water temperature on oxygen consumption, plasma cortisol concentrations, and free amino acid concentrations in plasma and several tissues in goldfish (Carassius auratus). Oxygen consumption and plasma cortisol concentrations were increased in goldfish exposed to HT (30 ± 1 °C) for 200 min compared with goldfish at a control water temperature (CT 17 ± 1 °C). Oxygen consumption and plasma cortisol concentrations in both groups of fish combined were positively correlated. When goldfish were exposed to HT for 300 min oxygen consumption and plasma concentrations of 15 free amino acids were increased compared with goldish at CT. Concentrations of several free amino acids were increased to varying extents in the brain, liver, and muscle tissues. In conclusion, an acute increase in water temperature affected amino acid metabolism differently in the brain, liver, and muscle tissues. Goldfish will be a useful species for further studies of the possible roles of various amino acids in the brain, muscle, and liver during acute increases in water temperature in fish.

Metabolic responses in Antarctic Nototheniidae brains subjected to thermal stress

Antarctic Nototheniidae is an attractive group for studying metabolic and physiological responses at high temperatures. The present work investigated the metabolic responses of the carbohydrate metabolism and antioxidant system to thermal stress at 8 °C (for 2-144 h) in the brains of Notothenia rossii and Notothenia coriiceps. In N. coriiceps, glycogenolysis was essential in the first hours of exposure (2 h) at 8 °C and, in addition to inhibiting glucose-6-phosphatase activity, was important for activating the pentose phosphate pathway. In N. rossii, anaerobic metabolism was reduced in the first hours of exposure (2 and 6 h) at 8 °C, followed by reduced hexokinase activity, suggesting energy regulation between neurons and astrocytes. The antioxidant system results indicated the importance of the actions of the glutathione-dependent antioxidant enzymes glutathione-S-transferase and glutathione peroxidase as well as those of catalase in N. coriiceps and the action of glutathione-S-transferase, glutathione peroxidase and glutathione reductase in N. rossii, especially during the first 12 h of thermal stress exposure. These results indicate tissue-specific patterns and species-specific responses to this stress.

Survival Rate and Hematological Responses with Temperature Changes of Red Spotted Grouper, Epinephelus akaara in South Korea

The effect of sudden changes of water temperature (WT) on the survival rate and physiological responses of the red spotted grouper (Epinephelus akaara) were examined by manipulating WT control system for 9 days. Experimental condition was divided in two different regimes at low (from 10°C to 4°C, decreased 1℃/d) and high (from 28°C to 34°C, increased 1°C/d) WT. Survival rate of experimental fishes were observed, and determined the changes of hematological characteristics by analyzing plasma levels of cortisol, glucose, total protein, and electrolytes (Na(+), Cl-, K(+)). No mortality was observed until low WT 6°C (144 h) and high WT 32°C (96 h), and 100% mortality was observed at low WT 4°C (216 h) and high WT 35°C (171 h). Plasma levels of cortisol and glucose increased rapidly as decreasing WT, and the loss of swimming ability and respiration response was observed at low WT 7°C and high WT 34°C conditions.

Effects of water temperature on perchlorate toxicity to the thyroid and reproductive system of Oryzias latipes

Water temperature is expected to increase in many parts of the world due to global climate change. The change in water temperature may affect ecosystems through alterations of the chemical properties or by affecting the susceptibility of organisms. Perchlorate can disrupt thyroid function of an organism by inhibiting iodide uptake. In the present study, the effect of water temperature on perchlorate toxicity was evaluated using Japanese medaka (Oryzias latipes). Pairs of adult medaka fish were exposed to a sublethal concentration of sodium perchlorate (100mg/L) and a control, at a 'low' (26°C), 'medium' (29°C) or 'high' water temperature (33°C) for seven days. The effects of the water temperature on reproduction, thyroid hormones and cortisol concentrations were determined. Transcription of several genes related to thyroid function and stress were also investigated. Significant down-regulation of thyroid hormone receptor alpha (THR-α) and beta (THR-β) transcripts and up-regulation of deiodinase 2 (DIO2) transcripts were observed in the fish exposed to perchlorate. Thyroxine (T4) concentrations were decreased, while triiodothyronine (T3) levels remained constant following exposure to perchlorate, and this effect became more pronounced under the high water temperature conditions (33°C). Up-regulation of the DIO2 gene may explain these observations. The total number of spawned eggs decreased slightly as the water temperature increased, and this reduction became significant when fish were exposed to perchlorate. Our observations indicate that exposure to perchlorate could affect thyroid function and overall reproductive fitness, and these effects could be aggravated under high water temperatures.

Interaction of warm acclimation, low salinity, and trophic fluoride on plasmatic constituents of the Antarctic fish Notothenia rossii Richardson, 1844

The adaptive evolution of the Notothenia rossii occurred under the selective pressure of stable and low temperatures. It is an opportunistic feeder of Antarctic krill and the fluoride in the krill carapace is apparently not toxic. We investigated the interactive effect of fluoride, elevated temperatures, and low salinity on the plasmatic constituents of this Antarctic fish. The experiments were conducted at the Brazilian Antarctic Station Comandante Ferraz (EACF), located on King George Island. The Antarctic fish N. rossii was acclimatized to eight thermo-saline-trophic conditions, combining two temperatures (0 and 4 °C), two salinities (35 and 20), and two trophic conditions (with/without fluoride) for an 11-day period. Trophic fluoride was not able to alter the plasmatic levels of glucose, cholesterol, plasmatic protein, Cl⁻, Mg²⁺, Ca²⁺, and inorganic phosphate, but induced an acute elevation of triglycerides at 0 °C and salinity of 35. At low salinity, hyperglycemia, hypertriglyceridemia, and hypocalcemia were observed. The thermo-saline interaction at 4 °C was able to minimize the effects of fluoride and low salinity on the plasmatic constituents levels.

Dexamethasone modulates expression of genes involved in the innate immune system, growth and stress and increases susceptibility to bacterial disease in Senegalese sole (Solea senegalensis Kaup, 1858)

Cortisol, the main glucocorticoid in fish, undertakes pleiotropic biological effects in response to stressors to maintain homeostasis. It can exert several actions on the immune system, growth and cellular metabolism, establishing a fine-tune regulation stress response and cross-talk interactions with other regulatory pathways. In this study, we investigated a causal relationship between high levels of glucocorticoids and susceptibility to pathogens and modification of gene expression profiles in Senegalese sole. For this purpose, we carried out two experiments using post-metamorphic individuals (21 days after hatching) that were exposed to dexamethasone (DXM), a potent glucocorticoid, in order to mimic cortisol effects. We quantified transcript levels of a wide set of genes involved in innate immune system (g-type lysozyme and hepcidin (hamp1)), HPI axis (crf, crfbp, pomcα, pomcβ, gr1 and gr2), HPT axis (tgb), cellular stress defense system (hsp70 and hsp90aa), GH/IGF axis (igf-I and igf-Ir) and the neuropeptide trh. Short-term exposure to 0.1, 1 and 10 ppm DXM provoked a reduction of pomcβ transcripts and an increase of crfbp mRNAs in a dose-dependent manner at 48 and 72 h after treatment. Moreover, g-type lysozyme transcript levels decreased significantly at 72 h whereas hamp1 mRNA levels increased at 48 h after exposure. Long-term DXM treatment (10 ppm DXM) affected negatively weight of soles (~20% lower than controls). Moreover, reduced mRNA levels were observed for pomcβ after 1 week and igf-I and hamp1 after 2 weeks. In contrast, crfbp and crf increased mRNA levels after 2 weeks. hsp70 exhibited a dual response increasing transcript levels at 1 week after treatment and reducing thereafter. No significant changes in gene expression were observed at any time during this study for tgb, trh, hsp90aa, pomcα, gr1 and gr2. Finally, a challenge experiment using the pathogen Photobacterium damselae subsp piscicida confirmed earlier and higher mortalities in DXM-treated animals. Taken together, these data indicate that a prolonged exposure to DXM increases the susceptibility to pathogens and reduces growth. Moreover, DXM can trigger a wide cellular response modulating the expression of genes involved in the innate immune system, HPI and GH/IGF axes as well as cellular stress defense. These results are highly valuable to evaluate responses associated to aquaculture stressful conditions and discriminate specific glucocorticoid-mediated effects.

The endocrinology of stress in fish: an environmental perspective

Much of the understanding of the endocrine basis of stress in fish comes from studies of cultured stocks of teleosts; there is comparatively little information on stress responses in wild stock, and less still on chondrosteans and elasmobranchs. This understanding is being refined through increasing understanding of molecular processes underlying endocrine events, with molecular tools offering ready examination of parts of the endocrine pathway that have been resistant to easy measurement of hormone products. An assessment of the timecourse of activation of the hypothalamic-pituitary-interrenal axis shows generally strong independence of temperature, with most teleosts showing measurable increase in plasma cortisol within 10 min of stress. Chondrostean and elasmobranch responses are less well described, but in chondrosteans at least, the response pattern appears to be similar to teleosts. The short latency for increases in corticosteroids following exposure to a stressor means that sampling of wild fish needs to occur rapidly after encounter. Several techniques including underwater sampling and rapid line capture are suitable for this, as is measurement of steroid release to the water by undisturbed fish, albeit possibly with a reduced range of applications. Basal cortisol values in wild teleosts are typically <10 ng mL(-1), but a number of species show values orders of magnitude higher in unstressed fish. Variability in corticosteroid levels arises from a range of factors in addition to stress including, sex and maturity, time of day or since feeding, and season. These factors need to be understood for the sensible assessment of stress responses in wild fish. Studies on free-living birds suggest that environmental stress resides mainly around unpredictable change, and the limited data available for fish support this view. The effect of unpredictable event such as floods or storms are difficult to assess in wild fish due to the difficulty in sampling at these times, and would be predicted to impose environmental stress as in terrestrial systems; however, this has yet to be demonstrated. There is scope for use of stress responses to be used as a measure of environmental quality but only if the basic response to environmental stress is well understood first. Development of this understanding remains a priority for this field of research.

Effects of elevated temperature and nickel pollution on the immune status of Japanese medaka

Changes in a host's environment (i.e. physical or chemical) can alter normal immune function. In aquatic organisms, exposure to stress can result in significant changes in innate immunity. In the natural environment, fish are exposed to multiple stressors simultaneously. Temperature change and/or chemical exposure as individual environmental stressors have been shown in various fish species to alter all aspects of the immune response. These same stressors have also been shown to alter plasma steroid levels in exposed fish. For this study, the effects of elevated temperature and nickel pollution on specific immune parameters of Japanese medaka (Oryzias latipes) were determined. Fish were exposed for 1, 7 or 14d to either: waterborne nickel (Ni) at the nominal concentration of 125ppb; a 5 degrees C (+/-0.5 degrees C) rapid increase in water temperature; or, both potential stressors in combination. Medaka maintained at room temperature (25 degrees C+/-1 degrees C) served as the controls. Altered function of the innate and adaptive arms of the immune response was evaluated by assessing kidney macrophage-mediated superoxide (O(2)(-)) production and splenic T-cell proliferation, respectively. Plasma cortisol levels were analysed in the same fish as a marker of the physiological stress response. While kidney cell number was unaffected by exposure of fish to either stressor alone or both factors in combination, spleen cellularity was decreased (compared to control fish) in medaka exposed for 1d to thermal stress in combination with Ni, and to a lesser extent to thermal stress alone. T-lymphocyte proliferation by medaka splenocytes was not affected by any exposure paradigm. Unstimulated intracellular O(2)(-) production by kidney phagocytes was significantly elevated (compared to control) in medaka exposed for 1d to either thermal stress alone or temperature change in combination with Ni; by 7d, only the stressor combination significantly increased baseline O(2)(-) production. Resting levels of extracellular O(2)(-) production was significantly reduced in fish maintained for 1d at the elevated temperature. Effects on phorbol 12-myristate 13 acetate (PMA)-stimulated intracellular and extracellular O(2)(-) production were less dramatic than those observed for resting phagocytes. Exposure of medaka to elevated temperature for 14d tended (p<0.06) to reduce PMA-stimulated intracellular O(2)(-) production (compared to the time-matched control). Although exposure of fish for 14d to elevated temperature only slightly reduced stimulated extracellular O(2)(-) production, exposure for the same duration to Ni alone significantly depressed oxyradical production by kidney phagocytes (compared to the time-matched controls). Decreased plasma cortisol levels were observed in fish exposed for 7d to either an elevated water temperature or Ni (compared to the time-matched control); by 14d of exposure, no significant treatment-induced effects on cortisol levels were observed. These findings add to the growing body of literature seeking to determine what effects, if any, exposure to multiple aquatic pollution-induced effects have upon fish health and the health of impacted ecosystems.

Environment affects stress in exercised turbot

We investigated the interaction of water temperature (10, 18 and 22 degrees C) and salinity (33.5 and 15 per thousand ) on the stress response of juvenile turbot. At each temperature/salinity combination, fish were subjected to 10 min enforced exercise. This induced a moderate stress response, which differed at the various temperature and salinity combinations. High temperatures caused more rapid increases in plasma cortisol and glucose, larger and more rapid increases in plasma lactate levels, which were also influenced by body weight, and a faster recovery in plasma Na(+) and Cl(-). Low salinity ameliorated cortisol responses at low but not at high temperatures. The magnitude of ionic disturbance was reduced at 15 per thousand. Plasma K(+) did not change at any temperature or salinity. The stress response involved activation of the brain-pituitary-interrenal axis, as indicated by the cortisol elevations. The low magnitude of glucose responses, the mild Na(+) and Cl(-) disturbances, and the lacking K(+)-responses indicated mild activation of the brain-sympathetic-chromaffin cell axis, and hence a low release of catecholamines, which seemed though to occur to a higher extent at higher temperatures. The relatively low catecholaminergic response of turbot may be linked to their inactive sedentary lifestyle. The higher responsiveness at higher water temperatures may reflect a higher overall adaptive capacity.

Physiological disturbances at critically high temperatures: a comparison between stenothermal antarctic and eurythermal temperate eelpouts (Zoarcidae)

The effect of gradually increased water temperature on the metabolism of temperate eelpout from the North Sea (Zoarces viviparus) and Antarctic eelpout (Pachycara brachycephalum) was investigated. Standard metabolic rate (SMR) was similar in cold-adapted P. brachycephalum and cold-acclimated Z. viviparus in the low temperature range. This indicates that Antarctic eelpout show no metabolic cold adaptation (as originally defined by Wohlschlag); however, they do show a compensatory increase of oxygen consumption compared to warm-acclimated eelpout. SMR increased more strongly with rising temperature in P. brachycephalum than in Z. viviparus, which is reflected in a higher Arrhenius activation energy for oxygen consumption (99+/−5 kJ mol(−)(1), versus 55+/−3 kJ mol(−)(1) for cold-acclimated Z. viviparus; means +/− s.d.). The intracellular pH in the white musculature of Z. viviparus follows alphastat regulation over the whole investigated temperature range and dropped at a rate of −0.016 pH units per degrees C between 3 degrees C and 24 degrees C. In Antarctic eelpout white muscle pH declined at a rate of −0.015 pH units per degrees C between 0 degrees C and 3 degrees C, but deviated from alphastat at higher temperatures, indicating that thermal stress leads to acid-base disturbances in this species. The upper critical temperature limit (Tc(II); characterised by a transition to anaerobic metabolism) was found to be between 21 degrees C and 24 degrees C for Z. viviparus and around 9 degrees C for P. brachycephalum. In both species a rise of succinate concentration in the liver tissue turned out to be the most useful indicator of Tc(II). Obviously, liver is more sensitive to heat stress than is white muscle. Accordingly, the energy status of white muscle is not diminished at Tc(II). Heat-induced hyperglycaemia was observed in Antarctic eelpout (at 9 degrees C and 10 degrees C), but not in common eelpout. Based on our results and on literature data, impaired respiration in combination with circulatory failure is suggested as the final cause of heat death. Our data suggest that the southern distribution limit of Zoarces viviparus is correlated with the limit of thermal tolerance. Therefore, it can be anticipated that global warming would cause a shift in the distribution of this species.