Effects of thermal stress on the expression of glucocorticoid receptor complex linked genes in Senegalese sole (Solea senegalensis): Acute and adaptive stress responses

Characterising the Physiological Responses of Chinook Salmon (Oncorhynchus tshawytscha) Subjected to Heat and Oxygen Stress

In New Zealand, during the hottest periods of the year, some salmon farms in the Marlborough Sounds reach water temperatures above the optimal range for Chinook salmon. High levels of mortality are recorded during these periods, emphasising the importance of understanding thermal stress in this species. In this study, the responses of Chinook salmon (Oncorhynchus tshawytscha) to chronic, long-term changes in temperature and dissolved oxygen were investigated. This is a unique investigation due to the duration of the stress events the fish were exposed to. Health and haematological parameters were analysed alongside gene expression results to determine the effects of thermal stress on Chinook salmon. Six copies of heat shock protein 90 (HSP90) were discovered and characterised: HSP90AA1.1a, HSP90AA1.2a, HSP90AA1.1b, HSP90AA1.2b, HSP90AB1a and HSP90AB1b, as well as two copies of SOD1, named SOD1a and SOD1b. The amino acid sequences contained features similar to those found in other vertebrate HSP90 and SOD1 sequences, and the phylogenetic tree and synteny analysis provided conclusive evidence of their relationship to other vertebrate HSP90 and SOD1 genes. Primers were designed for qPCR to enable the expression of all copies of HSP90 and SOD1 to be analysed. The expression studies showed that HSP90 and SOD1 were downregulated in the liver and spleen in response to longer term exposure to high temperatures and lower dissolved oxygen. HSP90 was also downregulated in the gill; however, the results for SOD1 expression in the gill were not conclusive. This study provides important insights into the physiological and genetic responses of Chinook salmon to temperature and oxygen stress, which are critical for developing sustainable fish aquaculture in an era of changing global climates.

Impact of different levels of handling on Solea senegalensis culture: effects on growth and molecular markers of stress

Aquaculture routine practices may cause stress induction on the fish and compromise their welfare affecting the production. This experiment aimed to evaluate the potential links between handling during culture with stress responses and growth on Senegalese sole (Solea senegalensis). We worked with two fish cohorts in terms of initial body weight and culture stage: Trial 1 included specimens in the fattening stage (226 ± 4.96 g) and Trial 2 animals in the pre-fattening stage (27.20 ± 0.44 g). The tested culture protocol, which lasted 6 and 4 months for Trial 1 and 2, respectively, mainly reduced handling-derived stressors in the experimental tanks via lowering routine samplings to a minimum. This decrease of the handling-derived stress was reflected in both trials with lower concentration of circulating cortisol in blood plasma from the experimental fish when compared to controls. Moreover, the proposed protocol promoted higher growth in the fish cultured in the less disturbing protocol in Trial 2. Higher specific growth rates and mean body weight and length were reported. In order to further explore the potential beneficial effects of our protocol, we studied the musculoskeletal from Trial 2 gene expression of key genes regulating glucocorticoid signaling pathway and apoptosis: glucocorticoid receptors 1 and 2 (gr1, gr2), heat shock protein 90 AA (hsp90aa), and caspase 6 (casp6). In line with the cortisol reduced level in this trial, gr1, hsp90aa, and casp6 genes showed lower expression in the samples coming from the experimental group. The findings of this study provide valuable information to the aquaculture industry for the management of Solea senegalensis stress and welfare.

Environmental co-exposure of high temperature and Cu induce hormonal disturbance of cortisol signaling and altered responses of cellular defense genes in zebrafish

Global warming is causing a continuous increase in environmental temperatures, which simultaneously activates toxic environmental stresses, such as heavy metal exposure, in aquatic ecosystems. The present study aimed at evaluating the effects of Cu toxicity along with increased temperature during zebrafish embryogenesis. Decreased survival rates were observed following combined exposure to high temperature and Cu. Heart rates of zebrafish embryos were significantly increased only during heat stress. An abnormal morphology with curved body shape was induced by exposure to a combination of Cu and heat stress. Furthermore, heat stress also triggered Cu-induced intracellular reactive oxygen species (ROS) production, with upregulation of superoxide dismutase (SOD) and glutathione s-transferase (GST) expression, and cell death with modified expression of p53 and B-cell lymphoma-2 (Bcl-2) in zebrafish embryos. Finally, increased cortisol levels and altered expression of cortisol-signaling genes were observed following exposure to Cu and high temperatures. These results highlight that realistic exposure to combined stressors induces developmental disturbances via stress-induced responses involving oxidative stress and cell death as well as transcriptional alterations leading to cortisol signaling in fish.

Aquaponics as a Promising Strategy to Mitigate Impacts of Climate Change on Rainbow Trout Culture

Simple Summary

Climate change and overexploitation of natural resources drive the need for innovative food production within a sustainability corridor. Aquaponics, combining the technology of recirculation aquaculture systems (RAS) and hydroponics in a closed-loop network, could contribute to addressing these problems. Aquaponic systems have lower freshwater demands than agriculture, greater land use efficiency, and decreased environmental impact combined with higher fish productivity. Rainbow trout is one of the major freshwater fish cultured worldwide, which, however, has not yet been commercially developed in aquaponics. Nevertheless, research conducted so far indicates that the trout species represents a good candidate for aquaponics.

Abstract

The impact of climate change on both terrestrial and aquatic ecosystems tends to become more progressively pronounced and devastating over the years. The sector of aquaculture is severely affected by natural abiotic factors, on account of climate change, that lead to various undesirable phenomena, including aquatic species mortalities and decreased productivity owing to oxidative and thermal stress of the reared organisms. Novel innovative technologies, such as aquaponics that are based on the co-cultivation of freshwater fish with plants in a sustainable manner under the context of controlled abiotic factors, represent a promising tool for mitigating the effect of climate change on reared fish. The rainbow trout (Oncorhynchus mykiss) constitutes one of the major freshwater-reared fish species, contributing to the national economies of numerous countries, and more specifically, to regional development, supporting mountainous areas of low productivity. However, it is highly vulnerable to climate change effects, mainly due to the concrete raceways, in which it is reared, that are constructed on the flow-through of rivers and are, therefore, dependent on water’s physical properties. The current review study evaluates the suitability, progress, and challenges of developing innovative and sustainable aquaponic systems to rear rainbow trout in combination with the cultivation of plants. Although not commercially developed to a great extent yet, research has shown that the rainbow trout is a valuable experimental model for aquaponics that may be also commercially exploited in the future. In particular, abiotic factors required in rainbow trout farming along, with the high protein proportion required in the ratios due to the strict carnivorous feeding behavior, result in high nitrate production that can be utilized by plants as a source of nitrogen in an aquaponic system. Intensive farming of rainbow trout in aquaponic systems can be controlled using digital monitoring of the system parameters, mitigating the obstacles originating from extreme temperature fluctuations.

Maternal effect and dietary supplementation of estradiol-17β on female zebrafish (Danio rerio) affects the swimming behavior and stress-coping styles of its offspring

Extrinsic estradiol-17β (E2) is an environmental hormone. Female fish exposure to waterborne E2 might affect the development of craniofacial cartilage of its offspring. The present study investigates the effects of maternal E2 on larval craniofacial cartilage development by administering oral feed containing E2 (F-E2) to female zebrafish, and examines whether the swimming behavior and their stress coping style are influenced by maternal E2. The results showed that E2 contents responded to dosage and time in male fish after being fed with a diet containing E2. In addition, the E2 contents in female ovaries showed a significant increase after 250 mg of E2/kg treatment for 14 d. On the other hand, the fecundity rate of F-E2 group was lower around 2 folds than FC (female fed 0 mg of E2/kg) group. Craniofacial chondrogenesis on 72 hpf (hours of post fertilization) of F-E2 larvae were abnormalities, and a recovery to a normal developmental pattern was observed at the 96 hpf stage. The swimming speed was slower for F-E2 larvae compared to the FC larvae; and the F-E2 juvenile seems to be less responsive to cortisol (LRC) after cold stress. According to the results, we suggested that F-E2 larvae might have worse environmental adaptability than FC larvae.

Characterization of the glucocorticoid receptor of large yellow croaker (Larimichthys crocea) and its expression in response to salinity and immune stressors

Glucocorticoids are steroidal hormones critical to stress responses in vertebrates. To gain further insight into the role of the glucocorticoid receptor (GR) in acute stress responses in teleost fish, the relevant cDNA of large yellow croaker (Larimichthys crocea; LcGR) was cloned using the rapid amplification of cDNA ends (RACE) technique. Multiple alignment of the amino acids (aa) of LcGR and the GR of other teleosts indicated LcGR contained four commonly conserved domains and lacked the 9-aa insert seen in GR1. Phylogenetic analysis of the amino acid sequence revealed that LcGR grouped most closely with the GR2 of other teleosts and can therefore be considered a GR2 subtype. In healthy L. crocea, Lcgr mRNA was found to be expressed at high levels in the gill, brain, and muscle tissue, expressed at intermediate levels in heart and stomach tissue, and expressed at low levels in the kidney, intestine, head kidney, liver, and spleen tissue. The response of L. crocea to acute low-salinity stress was tested, with a significant increase in plasma cortisol concentration after 3 h, peaking after 6 h, and gradually returning to base levels. Regarding changes of Lcgr expression in different body tissues under the stress, there was up-regulation of the Lcgr transcript in the brain, liver, and gill tissues, but not in muscle tissue. Responses to pathogen mimics were also tested. Injection with lipopolysaccharide resulted in Lcgr expression, with an increase-decrease-increase trend in the head kidney. In contrast, a down-regulation of Lcgr expression in the head kidney was observed throughout the experimental period upon injection of polyinosinic:polycytidylic acid, revealing different roles of Lcgr for different types of pathogens. The results offer novel insights about the effects of different stressors on GR gene expression in L. crocea, and can facilitate further investigations into stress responses in other mariculture fish species.

The stress response in Atlantic salmon (Salmo salar L.): identification and functional characterization of the corticotropin-releasing factor (crf) paralogs

Corticotropin-Releasing Factor (CRF) is one of the main mediators of the Hypothalamic-Pituitary-Interrenal (HPI) axis to stress response. In Atlantic salmon, a comparative understanding of the crf1 paralogs role in the stress response is still incomplete. Our database searches have identified four crf1 genes in Atlantic salmon, named crf1a1, crf1a2, crf1b1 and crf1b2. Brain distribution analysis revealed that the four crf1 paralogs were widely distributed, and particularly abundant in the telencephalon, midbrain, and hypothalamus of Atlantic salmon post-smolts. To increase the knowledge on crf1-mediated response to stress, Atlantic salmon post-smolts were exposed to either repeated chasing, hypoxia or a combination of chasing and hypoxia for eight days, followed by a novel-acute stressor, confinement. Cortisol, glucose, lactate, and creatinine levels were used as markers for the stress response. The crf1 paralogs mRNA abundance showed to be dependent on the stress exposure regime. Both crf1 mRNA levels in the telencephalon and crf1a1 mRNA levels in the hypothalamus showed similar response profiles to the serum cortisol levels, i.e., increasing levels during the first 24 h after stress exposure followed by a decline during the eight-day exposure. The similar trend between crf1 and cortisol disappeared once exposed to the novel-acute stressor. There was a minor response to stress for both crf1b1 and crf1b2 in the hypothalamus, while no changes at mRNA level were observed in the hypothalamic crf1a2 under the different stress conditions. No or weak relationship was found between the crf1 paralogs mRNA expression and the other serum stress-indicators analysed. In summary, our data provide novel insights on the dynamic of the HPI axis activation in Atlantic salmon, and thus underline the involvement of the crf1 paralogs as additional factors in the regulation of the stress response in this species. Likewise, the data highlight the importance of analysing all crf1 paralogues response to a stress-condition, in particular in this premature knowledge stage of their functionality. Further analysis and a more detailed time-point series will help to elucidate the response of the HPI axis and the link of crf1 paralogs in the stress response mechanism.

Biomarkers of exposure and effect in the armoured catfish Hoplosternum littorale during a rice production cycle

Fish cultivation in rice fields is a valuable resource in some rural areas of the world. Fish is a source of protein and an additional source of income for local farmers. However, the use of pesticides may impact fish and consumer health. The aim of this study was to evaluate exposure and effect biomarkers in native fish inhabiting a rice field during a production cycle. Samples of fish, water and sediment from a rice field in Santa Fe, Argentina were collected during a cultivation season (at the beginning: November 2017, in the middle: December 2017 and at the end: February 2018). At each sampling period, fish biomarkers of effect (biometric indices, hematological parameters, energy reserves, oxidative stress and neurotoxicity) were assessed together with pesticide screening in water, sediment, and fish samples. Only herbicides were present in water and sediment samples in agreement with land treatment before rice sowing stage, where only herbicides were applied. In general, the greatest water concentrations of bentazone, glyphosate and aminomethylphosphonic acid (AMPA), and the lowest sediment glyphosate and AMPA levels were observed at the beginning of the farming cycle. Fish bioaccumulated AMPA residues at all sampling periods and showed biological responses to cope with a stressful environment. Alterations in hematological parameters, mobilization of energetic reserves and activation of the antioxidant system were detected. However, no oxidative damage nor neurotoxic effects were present along the production cycle. Under a real exposure scenario, the present work demonstrates that biological changes are induced in fish to cope with stressors present in a rice field. Fish-rice coculture is an efficient and ecologically sustainable approach to increase food supplies, and a better understanding of the effect of this particular environment on fish would allow a greater and safer development of this promising productive activity in South American rice producing countries.

Effects of warming rates on physiological and molecular components of response to CTMax heat stress in the Antarctic fish Harpagifer antarcticus

Maximum and minimum Critical thermal limits (CTMax and CTMin) have been studied extensively to assess thermal tolerance in ectotherms by means of ramping assays. Notothenioid fish have been proposed as particularly sensitive to temperature increases related to global climate change. However, there are large gaps in our understanding of the thermal responses of these extreme cold-adapted fish in assays with heating rates. We evaluated the effects of two commonly used heating rates (0.3 and 1 °C/min) on the cellular stress responses in the intertidal Antarctic fish Harpagifer antarcticus immediately after CTMax was reached, and at 2 and 4 h of recovery time in ambient water. We compared CTMax values, the relative transcript expression of genes relvant to heat shock response (Hsc70, Hsp70, Grp78), hypoxia (Hif1-α, LDHa, GR), ubiquitination (Ube2), and apoptosis (SMAC/DIABLO), and five plasma parameters - glucose, lactate, total protein, osmolality and cortisol. CTMax values between the two heating rates are not significantly different, and both rates elicited a similar stress response at molecular and physiological levels. We found a lack of up-regulated response of heat shock proteins, consistent with other Antarctic notothenioids. The general transcriptional pattern trended to downregulation, which was more evident in the slower 0.3 °C/min rate, and instances of upregulation were mainly related to ubiquitination. The faster 1 °C/min rate, rarely used for Antarctic fish, can be suitable for studying cold-adapted stenothermic fish without overestimating thermal tolerance or inducing damage from longer heat exposure.

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.

Rearing temperature conditions (constant vs. thermocycle) affect daily rhythms of thermal tolerance and sensing in zebrafish

In the wild, the environment does not remain constant, but periodically oscillates so that temperature rises in the daytime and drops at night, which generates a daily thermocycle. The effects of thermocycles on thermal tolerance have been previously described in fish. However, the impact of thermocycles on daytime-dependent thermal responses and daily rhythms of temperature tolerance and sensing expression mechanisms remain poorly understood. This study investigates the effects of two rearing conditions: constant (26 °C, C) versus a daily thermocycle (28 °C in the daytime; 24 °C at night, T) on the thermal tolerance response in zebrafish. Thermal tolerance (mortality) was assessed in 4dpf (days post fertilization) zebrafish larvae after acute heat shock (39 °C for 1 h) at two time points: middle of the light phase (ML) or middle of the dark phase (MD). Thermal stress responses were evaluated in adult zebrafish after a 37 °C challenge for 1 h at ML or MD to examine the expression of the heat-shock protein (HSP) (hsp70, hsp90ab1, grp94, hsp90aa1, hspb1, hsp47, cirbp) and transient receptor potential (TRP) channels (trpv4, trpm4a, trpm2, trpa1b) in the brain. Finally, the daily rhythms of gene expression of HSPs and TRPs were measured every 4 h for 24 h. The results revealed the larval mortality rates and the expression induction of most HSPs in adult zebrafish brain reached the highest values in fish reared under constant temperature and subjected to thermal shock at MD. The expression of most HSPs and TRPs was mainly synchronized to the light/dark (LD) cycle, regardless of the temperature regime. Most HSPs involved in hyperthermic challenges displayed diurnal rhythms with their acrophases in phase with warm-sensing thermoTRPs acrophases. The cold-sensing trpa1b peaked in the second half of the light period and slightly shifted toward the dark phase anticipating the acrophase of cirpb, which is involved in hypothermic challenges. These findings indicated that: a) thermal shocks are best tolerated in the daytime; b) the implementation of daily thermocycles during larval development reduces mortality and stress-cellular expression of HSPs to an acute thermal stress at MD; c) daily rhythms need to be considered when discussing physiological responses of thermal sensing and thermotolerance in zebrafish.

Dynamic Responses of the Caudal Neurosecretory System (CNSS) Under Thermal Stress in Olive Flounder (Paralichthys olivaceus)

Temperature is a critical environmental factor that affect most biological and physiological processes in fish. The caudal neurosecretory system (CNSS) is unique to fish and is proved to maintain homeostasis during seasonal alterations. However, the dynamic expression and secretion pattern of its major hormones, corticotrophin-releasing hormone (CRH), urotensin I (UI), and urotensin II (UII), and their response to thermal stress has not been studied. CRH, UII and cortisol in plasma, gene expression levels of CRH, UI, and UII in the CNSS of olive flounder (Paralichthys olivaceus) were therefore characterized. UI- and UII-positive Dahlgren cells, as well as cell proliferation in the CNSS, were also quantified. The results showed that plasma cortisol and CRH were increased in both low temperature (LT) and high temperature (HT) groups. However, there was no difference in plasma UI and UII during thermal stress. In CNSS, CRH, UI, and UII mRNA levels were all significantly elevated in response to acute hypothermal stress and recovered back to the control (normal) level after 8 days of adaptation. During hyperthermal challenge, gene expression of CRH and UI only significantly increased after 8-days of transfer but no change in UII was observed. We also demonstrated an increasing percent of UI-positive Dahlgren cells in the CNSS of 8-days hyperthermal stressed fish. However, no BrdU-labeled Dahlgren cells were found among the three treatment groups. Collectively, our results demonstrate that the CNSS is subjected to dynamic responses under thermal stress and expands upon the role of the CNSS in thermoregulation. The dynamic responses of hormone levels and the gene expression of CRH, UI and UII in CNSS are all involved in the process of hyper- or hypo-thermal stress and adaptation.

Effect of time and temperature on stability of progestagens, testosterone and cortisol in Asian elephant blood stored with and without anticoagulant

The value of biological samples collected in the field is compromised if storage conditions result in analyte degradation, especially in warmer climates like Thailand. We evaluated the effects of time and temperature on immunoactive steroid hormone stability in Asian elephant (Elephas maximus) blood stored with and without an anti-coagulant before centrifugation. For each elephant (5 male, 5 female), whole blood was aliquoted (n = 2 ml each) into 13 red top (without anticoagulant) or purple top (with anticoagulant) tubes. One tube from each treatment was centrifuged immediately and the serum or plasma frozen at -20°C (Time 0, T0). The remaining 12 aliquots were divided into stored temperature groups: 4°C, room temperature (RT, ~22°C), and 37°C, and centrifuged after 6, 24, 48 and 62 h of storage. Serum and plasma concentrations of progestagens in females, testosterone in males and cortisol in both sexes were quantified by validated enzyme immunoassays. Steroid concentration differences from T0 were determined by a randomized complete block ANOVA and Dunnett's tests. The only evidence of hormone degradation was cortisol and testosterone concentrations in serum stored at 37°C. Testosterone concentrations declined by 34% at 48 h and 52% at 62 h, cortisol was decreased by 19% after 48 h and 27% after 62 h at 37°C, respectively. None of the other aliquots displayed significant changes over time at any temperature. In conclusion, steroids appear to be stable in blood for nearly 3 days at room or refrigeration temperatures before centrifugation; steroids in samples with ethylenediaminetetraacetic acid were particularly stable. However, warmer temperatures may negatively affect steroids stored without anti-coagulant, perhaps due to red blood cell metabolism. Thus, under field conditions with no access to cold or freezer temperatures, collection of plasma is a better choice for elephants up to at least 62 h before centrifugation.

Cortisol responses of goldfish (Carassius auratus) to air exposure, chasing, and increased water temperature

Fish can respond to stimuli from the internal or external environment with activation of the hypothalamo-pituitary-interrenal (HPI) axis and the secretion of cortisol. Stimuli that activate the HPI axis of fish include short term air exposure and increases in water temperature. The present study was conducted to determine how quickly cortisol concentrations increase in goldfish subjected to an increase in water temperature, and to compare the response to an increase in water temperature with responses to other stimuli. Plasma cortisol concentrations varied widely between individual goldfish, with concentrations ranging from 9.1 to 516.0 ng/mL in goldfish on the day of arrival from the supplier. Mean cortisol concentrations in undisturbed goldfish were low (4.5 ± 1.0 ng/mL). Mean cortisol concentrations in fish exposed to air for 3 min and in fish that experienced chasing for 10 min were markedly elevated 15 min after the beginning of the stimuli (132.6 ± 31.0 and 121.1 ± 23.9 ng/mL respectively). Mean cortisol concentrations in fish that experienced an increase in water temperature rose to 22.2 ± 7.6 ng/mL after 15 min, declined to <10 ng/mL at 30 and 60 min then increased and were elevated (79.0 ± 10.8 ng/mL) at 240 min. Cortisol measurements can be used to indicate the responsiveness of fish to changes in water temperature and goldfish will be a convenient study species for the development of studies of plasticity in responses of fish to increases in water temperature that are happening due to climate change.

Influence of vegetable diets on physiological and immune responses to thermal stress in Senegalese sole (Solea senegalensis)

The substitution of fish resources as ingredients for aquafeeds by those based on vegetable sources is needed to ensure aquaculture sustainability in the future. It is known that Senegalese sole (Solea senegalensis) accepts high dietary content of plant ingredients without altering growth or flesh quality parameters. However, scarce information is available regarding the long-term impact of vegetable diets (combining the inclusion of both vegetable protein and oils) on the stress response and immunity of this fish species. This study aims to evaluate the concomitant effect of the extended use of vegetable protein-based diets with fish oil (FO) replacement (0, 50 or 100%) by vegetable oils (VO), on the response to acute (10 min) or prolonged (4 days) stress, induced by thermal shock. Plasma levels of cortisol, glucose and lactate as well as hepatic levels of glucose, glycogen and lactate were evaluated as primary and secondary responses to stress, 6 and 18 months after feeding the experimental diets (6 and 18 MAF). The brain monoaminergic activity in telencephalon and hypothalamus, and non-specific immune parameters were also evaluated. As expected, thermal shock induced an increase in values of plasma parameters related to stress, which was more evident in acute than in prolonged stress. Stress also affected lactate levels in the liver and the values of the alternative complement pathway-ACH50 in the plasma. Dietary substitution of FO induced an effect per se on some parameters such as decreased hepatic glucose and glycogen levels and peroxidase activity in plasma as well enhanced serotonergic activity in brain of non-stressed fish. The results obtained in some parameters indicate that there is an interaction between the use of vegetable diets with the physiological response to thermal stress, as is the case of the hepatic lactate, serotonergic neurotransmission in brain, and the activity of ACH50 in plasma. These results suggest that the inclusion of VO in plant protein based diets point to a slightly inhibited stress response, more evident for an acute than a prolonged stress.