Cortisol and glucose responses after acute stress by net handling in the sparid red porgy previously subjected to crowding stress

Immunomodulatory effects of Isochrysis galbana incorporated diet on Oreochromis sp. (red hybrid tilapia) via Sera-1H NMR metabolomics study

Tilapia is one of the most common fish species that is intensively produced all over the world. However, significant measures at improving aquaculture health must be taken since disease outbreaks are often encountered in the rapidly developing aquaculture industry. Therefore, the objective of the study was designed to evaluate the metabolite changes in tilapia' sera through ¹H NMR metabolomics in identifying the potential biomarkers responsible for immunomodulatory effect by the indigenous species of Malaysian microalgae Isochrysis galbana (IG). The results showed that IG-incorporated diet mainly at 5.0% has improved the immune response of innate immunity as observed in serum bactericidal activity (SBA) and serum lysozyme activity (SLA). The orthogonal partial least squares (OPLS) analysis indicated 5 important metabolites significantly upregulated namely as ethanol, lipoprotein, lipid, α-glucose and unsaturated fatty acid (UFA) in the 5.0% IG-incorporated diet compared to control. In conclusion, this study had successfully determined IG in improving aquaculture health through its potential use as an immune modulator. This work also demonstrated the effective use of metabolomics approach in the development of alternative nutritious diet from microalgae species to boost fish health in fulfilling the aquaculture's long-term goals.

Lactobacillus casei (IBRC-M 10,711) ameliorates the growth retardation, oxidative stress, and immunosuppression induced by malathion toxicity in goldfish (Carassius auratus)

Probiotics can functionality improve fish wellbeing and are suggested as antioxidative agents to protect fish from xenobiotics toxicity. Herein, dietary Lactobacillus casei (IBRC-M 10,711) was included in the diets of goldfish (Carassius auratus) to protect against malathion toxicity. Fish (12.47 ± 0.06 g) were randomly allocated to six groups (triplicates), as follows: T1) control; T2) fish exposed to 50% of malathion 96 h LC50; T3) L. casei at 106 CFU/g diet; T4) L. casei at 107 CFU/g diet; T5) fish exposed to 50% of malathion 96 h LC50 + L. casei at 106 CFU/g diet; T6) fish exposed to 50% of malathion 96 h LC50 + L. casei at 107 CFU/g diet. After 60 days, goldfish fed T4 had the highest final body weight (FBW), weight gain (WG), and specific growth rate (SGR), and the lowest feed conversion ratio (FCR) among the groups (P < 0.05). However, the T2 group showed lower FBW, WG, and SGR and higher FCR than fish in T1 (P < 0.05). Fish in the T4 group had the highest blood total proteins, albumin, and globulin, while fish in T2 had the lowest levels (P < 0.05). Fish in the group T2 had the highest triglycerides, cholesterol, cortisol, lactate dehydrogenase (LDH), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP) levels in the blood, while fish fed T4 had the lowest values (P < 0.05). The superoxide dismutase (SOD) and catalase (CAT) showed the highest activities in T3 and T4 groups, and the lowest SOD was seen in the T2 group, whereas the lowest CAT was seen in the T2, T5, and T6 groups (P < 0.05). Fish in the T5 and T6 groups had higher glutathione peroxidase (GSH-Px) activities than fish in T1 and T2 groups but T3 and T4 groups showed the highest values (P < 0.05). T2 group had the highest malondialdehyde (MDA) level, while T3 and T4 groups had the lowest MDA level (P < 0.05). Blood immunoglobulin (Ig) and lysozyme activity were significantly higher in T3 and T4 groups and lower in the T2 group than in the control (P < 0.05). The alternative complement pathway (ACH50) was significantly higher in T2, T3, T4, T5, and T6 groups than in the T1 group (P < 0.05). Skin mucus Ig was significantly higher in T3 and T4 groups and lower in the T2 group than in the control (P < 0.05). The highest lysozyme activity, protease, and ACH50 in the skin mucus samples were in the T4 group, while the lowest values were in the T2 group (P < 0.05). In conclusion, dietary L. casei protects goldfish from malathion-induced growth retardation, oxidative stress, and immunosuppression.

Blood Will Tell: What Hematological Analyses Can Reveal About Fish Welfare

Blood analyses provide substantial information about the physiological aspects of animal welfare assessment, including the activation status of the neuroendocrine and immune system, acute and long-term impacts due to adverse husbandry conditions, potential diseases, and genetic predispositions. However, fish blood is still not routinely analyzed in research or aquaculture for the assessment of health and/or welfare. Over the years, the investigative techniques have evolved from antibody-based or PCR-based single-parameter analyses to now include transcriptomic, metabolomic, and proteomic approaches and from hematological observations to fluorescence-activated blood cell sorting in high-throughput modes. The range of testing techniques established for blood is now broader than for any other biogenic test material. Evaluation of the particular characteristics of fish blood, such as its cell composition, the nucleation of distinct blood cells, or the multiple isoforms of certain immune factors, requires adapted protocols and careful attention to the experimental designs and interpretation of the data. Analyses of fish blood can provide an integrated picture of the endocrine, immunological, reproductive, and genetic functions under defined environmental conditions and treatments. Therefore, the scarcity of high-throughput approaches using fish blood as a test material for fish physiology studies is surprising. This review summarizes the wide range of techniques that allow monitoring of informative fish blood parameters that are modulated by different stressors, conditions, and/or treatments. We provide a compact overview of several simple plasma tests and of multiparametric analyses of fish blood, and we discuss their potential use in the assessment of fish welfare and pathologies.

Effects of Fouling Management and Net Coating Strategies on Reared Gilthead Sea Bream Juveniles

Simple Summary

Fish farming strives to cover the increasing demand for aquatic food sources as a result of global population growth. As a primary sector industry, aquaculture profit margins are narrow. Fouling management is an issue and represents a significant part of the operational cost of this activity. Over the last 30 years, this problem has been approached from different perspectives and the use of copper dioxide to control fouling production has been the most successful strategy. However, far beyond being the definite solution, the use of copper involves several concerns, and so the aquaculture industry has been continuously trying to find a reliable alternative. Coating the nets and cleaning on-site was adopted by the industry as a realistic alternative around 2015. This work contrasts these two fouling management strategies, simulating real working conditions by analysing the results from different perspectives. The conclusions from this work suggest a combination of both as a promising future alternative.

Abstract

In aquaculture, biofouling management is a difficult and expensive issue. Cuprous oxide has been commonly used to prevent fouling formation. To cheapen net management and reduce the use of copper, the industry has proposed several alternatives. Currently, polyurethane coatings are being explored and commercially implemented. With this alternative, net cleaning is done in situ, reducing the number of nets necessary to raise a batch, thus ideally reducing operational costs. This pilot study compared this new strategy to the use of cuprous oxide. The results show that nets treated with antifouling perform better and bioaccumulation of copper in fish tissues do not pose health risks to fish. Alternatives involving on-site cleaning need to improve efficiency. Although the conditions of this work are not completely comparable to commercial aquaculture conditions, the results might indicate the strengths and constrains of the solutions tested in real life.

Koi (Cyprinus rubrofuscus) Seek Out Tactile Interaction with Humans: General Patterns and Individual Differences

The study of human-animal interactions has provided insights into the welfare of many species. To date, however, research has largely focused on human relationships with captive mammals, with relatively little exploration of interactions between humans and other vertebrates, despite non-mammals constituting the vast majority of animals currently living under human management. With this study, we aimed to address this gap in knowledge by investigating human-fish interactions at a community garden/aquaponics learning-center that is home to approximately 150 goldfish (Carassius auratus) and seven adult and two juvenile koi (Cyprinus rubrofuscus). After a habituation period (July-September 2019) during which time the fish were regularly provided with the opportunity to engage with the researcher's submerged hand, but were not forced to interact with the researcher, we collected video data on 10 non-consecutive study days during the month of October. This procedure produced 18~20-min interaction sessions, 10 during T1 (when the experimenter first arrived and the fish had not been fed) and eight during T2 (20-30 min after the fish had been fed to satiation; two sessions of which were lost due equipment malfunction). Interactions between the researcher and the seven adult koi were coded from video based on location (within reach, on the periphery, or out of reach from the researcher) and instances of physical, tactile interaction. Analyses revealed that overall, koi spent more time than expected within reach of the researcher during both T1 (p < 0.02) and T2 (p < 0.03). There were also substantial differences between individuals' overall propensity for being within-reach and engaging in physical interaction. These results show that koi will voluntarily interact with humans and that individual koi display unique and consistent patterns of interaction. By providing quantitative data to support anecdotal claims that such relationships exist around the world, this research contributes to the ongoing discoveries highlighting the profound dissonance between how humans think about and treat fish and who fish actually are, thereby emphasizing the necessity of stronger moral and legal protections for fishes.

Full Spectrum Lighting Induces Behavioral Changes and Increases Cortisol Immunoreactivity in Captive Arachnids

The use of full spectrum illumination, including ultraviolet (UV), during captive husbandry of arachnids is common practice. The effect of this on captive arachnids has not been previously investigated. Comparison of key behavioral changes and hemolymph cortisol immunoreactivity was undertaken with and without full spectrum lighting. King baboon spiders, Pelinobius muticus and Indian giant scorpions, Heterometrus swammerdami were selected for the study. Both organisms spent all their time hidden when exposed to full spectrum light compared to low-level ambient light except for one instance. There was no significant difference in burrowing and webbing in P. muticus when exposed to full spectrum lighting. There was a decrease in the number of behaviors or postures expressed in full spectrum lighting compared to ambient light for both species. Cortisol immunoactivity of both species were significantly elevated after exposure to full spectrum lighting. This study provides the first evidence of detectable cortisol immunoactivity in arachnid hemolymph. These levels changed in response to full spectrum illumination and were linked to behavioral changes. This suggests that a common husbandry practice may be detrimental to arachnids.

Impact of Ringer's Solution Challenge Stress to Immunostimulatory Experiment, Insights From Japanese Flounder

Ringer's or phosphate buffer saline (PBS) solution buffer usually was used as dilution butter in intraperitoneal injection. Stress could activate immune response, inflammatory response and glycogen metabolic process. The impact of solution buffer as a stressor to immune system was ignored in immunostimulatory experiment. In this report, we tested the hypothesis that the innate immune response and glycogen metabolic process were altered when it were challenged with Ringer's in Japanese flounder (Paralichthys olivaceus). RNA-seq was performed after challenge with Ringer's at 8 h and 48 h. The data revealed that the expression profiles of blood, gill, and kidney were significantly changed. Differentially expressed genes (DEGs) were identified, and energy metabolic and immune-related genes were up-regulated or down-regulated obviously. GO and KEGG analyses showed that DEGs were mainly enriched in innate immune terms and pathways. Weighted gene co-expression networks analysis (WGCNA) also indicated the highest association module with stress. A total of 16 genes were detected in the gray module, which were immune-related and metabolic-related genes. These results provided fundamental information on intraperitoneal injection with solution buffer. It offered useful clues to further explore the functional mechanism of stress and immunity.

Acute Stress and an Electrolyte- Imbalanced Diet, but Not Chronic Hypoxia, Increase Oxidative Stress and Hamper Innate Immune Status in a Rainbow Trout (Oncorhynchus mykiss) Isogenic Line

In aquaculture, fish may be exposed to sub-optimal rearing conditions, which generate a stress response if full adaptation is not displayed. However, our current knowledge of several coexisting factors that may give rise to a stress response is limited, in particular when both chronic and acute stressors are involved. This study investigated changes in metabolic parameters, oxidative stress and innate immune markers in a rainbow trout (Oncorhynchus mykiss) isogenic line exposed to a combination of dietary (electrolyte-imbalanced diet, DEB 700 mEq Kg-1) and environmental (hypoxia, 4.5 mg O2 L-1) challenges and their respective controls (electrolyte-balanced diet, DEB 200 mEq Kg-1 and normoxia, 7.9 or mg O2 L-1) for 49 days. At the end of this period, fish were sampled or subjected to an acute stressor (2 min of handling/confinement) and then sampled. Feeding trout an electrolyte-imbalanced diet produced a reduction in blood pH, as well as increases in cortisol levels, hepato-somatic index (HSI) and total energy content in the liver. The ratio between the lactate dehydrogenase (LDH) and isocitrate dehydrogenase (IDH) activities decreased in the liver of trout fed the DEB 700 diet, but increased in the heart, suggesting a different modulation of metabolic capacity by the dietary challenge. Several markers of oxidative stress in the liver of trout, mainly related to the glutathione antioxidant system, were altered when fed the electrolyte-imbalanced diet. The dietary challenge was also associated with a decrease in the alternative complement pathway activity (ACH50) in plasma, suggesting an impaired innate immune status in that group. Trout subjected to the acute stressor displayed reduced blood pH values, higher plasma cortisol levels as well as increased levels of metabolic markers associated with oxidative stress in the liver. An interaction between diet and acute stressor was detected for oxidative stress markers in the liver of trout, showing that the chronic electrolyte-imbalance impairs the response of rainbow trout to handling/confinement. However, trout reared under chronic hypoxia only displayed changes in parameters related to energy use in both liver and heart. Taken together, these results suggest that trout displays an adaptative response to chronic hypoxia. Conversely, the dietary challenge profoundly affected fish homeostasis, resulting in an impaired physiological response leading to stress, which then placed constraints on a subsequent acute challenge.

Real-time fish stress visualization came true：A novel multi-stage color-switching wireless biosensor system

An optical communication type biosensor system has been developed which can measure blood glucose concentration, which is a stress indicator of fish, in real-time while fish swimming freely. However, this system is hard to make instant acknowledgment of fish stress level which has to contain an unavoidable delay in the judgment. In this research, we aimed to develop a novel stress visualization system which can quickly judge the levels for fish stress response instantly based on a color changeable LED while another LED was designed to send data. The present system is based on the principle of converting the output current value measured by the glucose biosensor corresponding to the stress response into a voltage value. Then, the color and stress switching points of the LED (Red, Yellow, Green) were decided based on the voltage value gained from the biosensor which mentioned above. Furthermore, we attempted to use our biosensor system to make real-time monitoring of fish stress in vivo. As results, the proposed sensor can make real-time measurement of glucose and shows a great response to those of actual fish sample in the range from 35.36 to 300 mg dl^-1 (R = 0.9899). When the glucose concentration in the collected sample was switched to the concentration pre-sett, it was successful to switch the LED color according to the gained voltage value both in vitro and in vivo. Furthermore, when monitoring the stress responses of the fish in vivo, color switching corresponding to the sensor output current value was observed successfully.

Influence of bacteriophages cocktail on European eel (Anguilla anguilla) immunity and survival after experimental challenge

Inland fishery belongs to those branches of animal production that use very large amounts of chemotherapeutics, in particular antibiotics. The accumulation of chemotherapeutic agents in bottom sediments is a direct threat to the aquatic environment and directly affects the condition and health of the fish. Finding a preparation that could be used both prophylactically to increase the resistance of fish and therapeutically in case of infection with pathogenic bacteria, without side effects for fish and aquatic environment could be a great solution to this problem. Our aim was to determine influence of BAFADOR^® the new bacteriophage-based preparation on European eel immunity and survival after experimental challenge. Application of BAFADOR^® increased total protein level, immunoglobulin level, lysozyme activity and ceruloplasmin level in European eel serum. Potential killing activity and metabolic activity of spleen phagocytes as well as pronephros lymphocyte proliferation of was higher compared to control. The preparation also reduced mortality after experimental infections with the pathogenic bacteria Aeromonas hydrophila and Pseudomonas fluorescens. Our results showed that preparation BAFADOR^® is well tolerated by the fish organism causing stimulation of cellular and humoral immunity parameters and reduces the mortality of the European eel after experimental challenge.

Transcriptomic and cortisol analysis reveals differences in stress alleviation by different methods of anesthesia in Crucian carp (Carassius auratus)

Stress response has negative effect on fish in aquaculture and research, which can be alleviated with anesthetic. To determine the optimal anesthetic, we investigated the physiological response of crucian carp (Carassius auratus) treated with three different anti-stress treatments: MS-222, eugenol and percussive stunning. Stress responses were evaluated by analyzing serum cortisol level and gene expression in blood. We determined the optimal concentrations of MS-222 (100 mg L^-1) and eugenol (20 mg L^-1) by dose selection. We found that the control group had significantly higher cortisol levels (172.78 ± 19.95 ng mL^-1) compared to the MS-222 treated group (46.85 ± 3.22 ng mL^-1), the eugenol treated group (72.78 ± 9.07 ng mL^-1), and the stunning treatment group (82.78 ± 8.16 ng mL^-1). Transcriptome analysis revealed 1572 differentially expressed genes (DEGs), including 155 DEGs related to the stress response, mainly involved in oxidative-stress response, heat shock proteins, and cold shock domain-containing protein. The heat shock protein genes were the primary DEGs in response to stress. RT-qPCR analysis confirmed differential expression of Hsps. We analyzed the function of the DEGs, which were enriched in genes involved in cellular response to stress and antigen processing and presentation. Combining the results from biochemical, transcriptome, and gene expression analysis, our data suggest that eugenol is more effective than MS-222 and percussive stunning in alleviating stress in crucian carp.

Effects of repeated anaesthesia on gill and general health of Atlantic salmon, Salmo salar

Fish are the second most widely utilized vertebrate group used for scientific procedures in the United Kingdom, but the development and application of 3Rs (the principles of replacement, reduction, and refinement) in aquaculture disease research lags behind methodologies in place for mammalian studies. With a need for individual monitoring and non-lethal sampling, the effect of repeat anaesthesia on experimental fish needs to be better understood. This study analyses the effect of repeat anaesthesia with MS-222, metomidate and AQUI-S upon the gill and general health of post-smolt Atlantic salmon Salmo salar. A single, lethal dose of anaesthetic was compared with seven anaesthetizing time points over 28 days, terminating in a lethal dose. No anaesthetic showed significant differences in accumulation in the muscle tissue, or changes in plasma glucose after repeated or single dosing. Fish repeatedly anaesthetized with MS-222 or AQUI-S exhibited upregulation of osmoregulatory genes in the gill and AQUI-S-treated individuals showed, histologically, epithelial lifting from the lamellae capillary irrespective of whether they had a single or repeated dose history. No significant changes were seen in inflammatory or stress genes in the head kidney of fish repeatedly anaesthetized with AQUI-S or metomidate, however MS-222 treatment resulted in upregulation of tnfα3. Repeated anaesthesia with MS-222 and metomidate gave a significant decrease and increase in peripheral blood neutrophils, respectively. This study concludes that no increase in cumulative stress or inflammation is induced by the repeated anaesthetization of S. salar with any of the tested anaesthetics, however gill osmotic regulation and blood parameters may be affected.

Rapid acclimation of the cortisol stress response in adult turquoise killifish Nothobranchius furzeri

The turquoise killifish Nothobranchius furzeri is an increasingly popular model species for comparative vertebrate research, and the basic physiology including responses to stressful stimuli are of primary interest. We exposed adult killifish to a single or repeated periods of acute confinement followed by analysis of tissue cortisol and plasma cortisol concentrations. Individuals were also sampled for messenger RNA (mRNA) expression of corticotropin-releasing hormone (CRH), mineralocorticoid receptor (MR), and glucocorticoid receptor (GR) in the brain to examine the effects of repeated stress events on constitutive expression of these important stress axis components. Following a single 30-minute confinement stress, male plasma cortisol significantly differed from baseline (p = 0.04). Both male and female whole-body cortisol were significantly increased (p = 0.004 and p = 0.04, respectively) at 15 and 30 minutes poststress. Despite obvious dimorphic behavior and morphology, cortisol concentrations did not differ between the sexes. Exposure to daily repeated confinement for one week altered the cortisol response in both sexes. Time 0, 15, and 60 minutes poststress cortisol concentrations were depressed in repeatedly stressed males (p ≤ 0.05), and times 0, 30 and 120 minutes poststress cortisol concentrations were depressed in repeatedly stressed females (p ≤ 0.05). Constitutive expression of CRH, MR, and GR mRNA in the brain following one week of repeated stress events did not differ among treatments or sexes. This study introduces the first description of hypothalamic-pituitary-interrenal axis activity in this important model species. Reduced cortisol production in repeatedly stressed adult killifish suggests acclimation to repeated stressors. Furthermore, acclimation was rapid, and plasma cortisol concentrations altered significantly in as little as one week.

Impact of Air Exposure on Vasotocinergic and Isotocinergic Systems in Gilthead Sea Bream (Sparus aurata): New Insights on Fish Stress Response

The hypothalamus-pituitary-interrenal (HPI) and hypothalamus-sympathetic-chromaffin cell (HSC) axes are involved in the regulation of the stress response in teleost. In this regard, the activation of a complex network of endocrine players is needed, including corticotrophin-releasing hormone (Crh), Crh binding protein (Crhbp), proopiomelanocortin (Pomc), thyrotropin-releasing hormone (Trh), arginine vasotocin (Avt), and isotocin (It) to finally produce pleiotropic functions. We aimed to investigate, using the gilthead sea bream (Sparus aurata) as a biological model, the transcriptomic response of different endocrine factors (crh, crhbp, pomcs, trh), neuropeptides (avt and it), and their specific receptors (avtrv1a, avtrv2, and itr) in four important target tissues (hypothalamus, pituitary, kidney and liver), after an acute stress situation. We also investigated several stress hormones (catecholamines and cortisol). The stress condition was induced by air exposure for 3 min, and hormonal, metabolic and transcriptomic parameters were analyzed in a time course response (15 and 30 min, and 1, 2, 4, and 8 h post-stress) in a total of 64 fish (n = 8 fish per experimental group; p = 0.05; statistical power = 95%). Our results showed that plasma noradrenaline, adrenaline and cortisol values increased few minutes after stress exposure. At hypothalamic and hypophyseal levels, acute stress affected mRNA expression of all measured precursors and hormonal factors, as well as their receptors (avtrs and itr), showing the activation, at central level, of HPI, HSC, and Avt/It axes in the acute stress response. In addition, stress response also affected mRNA levels of avtrs and itr in the head kidney, as well as the steroidogenic acute regulatory protein (star) and tyrosine hydroxylase (th) expression, suggesting their participation in the HPI and HSC axes activation. Moreover, the pattern of changes in hepatic avtrs and itr gene expression also highlights an important role of vasotocinergic and isotocinergic pathways in liver metabolic organization after acute stress events. Our results demonstrate, both at transcriptional and circulating levels of several hormones, the existence of a complex activation of different endocrine pathways in S. aurata related to the stress pathways, where vasotocinergic and isotocinergic systems can also be considered key players of the acute stress response orchestration.

Effects of acute handling stress on short-term central expression of orexigenic/anorexigenic genes in zebrafish

Physiological mechanisms driving stress response in vertebrates are evolutionarily conserved. These mechanisms involve the activation of both the hypothalamic-sympathetic-chromaffin cell (HSC) and the hypothalamic-pituitary-adrenal (HPA) axes. In fish, the reduction of food intake levels is a common feature of the behavioral response to stress but the central mechanisms coordinating the energetic response are not well understood yet. In this work, we explore the effects of acute stress on key central systems regulating food intake in fish as well as on total body cortisol and glucose levels. We show that acute stress induced a rapid increase in total body cortisol with no changes in body glucose, at the same time promoting a prompt central response by activating neuronal pathways. All three orexigenic peptides examined, i.e., neuropeptide y (npy), agouti-related protein (agrp), and ghrelin, increased their central expression level suggesting that these neuronal systems are not involved in the short-term feeding inhibitory effects of acute stress. By contrast, the anorexigenic precursors tested, i.e., cart peptides and pomc, exhibited increased expression after acute stress, suggesting their involvement in the anorexigenic effects.

Hippocampal and cerebellar histological changes and their behavioural repercussions caused by brain ischaemic hypoxia experimentally induced by sodium nitrite

INTRODUCTION

Brain ischaemic hypoxia can produce severe neurological damage that leads to behavioural disorders. This research analysed the hippocampal and cerebellar histological alterations caused by brain ischaemic hypoxia experimentally induced by sodium nitrite (NaNO₂) and possible direct repercussions of this hypoxia on behaviour.

METHODOLOGY

An experimental study was carried out by administering 60mg/kg NaNO₂ to 10 Wistar rats at 3 months of age for 15 consecutive days. Ten control rats did not receive NaNO₂. To assess behavioural repercussions, the animals were evaluated in Open Field, Elevated Plus-Maze (EPM), and Forced Swim tests before and after injury to evaluate locomotion, anxiety, and depression, respectively. Markers of stress were evaluated by measuring the blood levels of cortisol, glucose, cholesterol, and lactate. The presence of hippocampal lesions was verified by histologically studying the CA1-CA4 areas. Sections of the cerebellum were also evaluated because Purkinje cells are highly sensitive to ischaemic hypoxia and may serve as markers for this process.

RESULTS

The number of neurons with lesions was significantly higher in animals exposed to NaNO₂ in the hippocampus areas CA2, CA3, and CA4. The cerebellum was also very vulnerable to hypoxia, presenting extensive lesion áreas. These results are correlated with the parameters of the anxiety and depression tests.

CONCLUSION

NaNO₂ promoted brain damage due to ischaemic hypoxia in rats. Intoxicated animals showed decreased brain weights; damage in hippocampus and cerebellum; and anxiogenic and depressive behaviour.

Linking cortisol response with gene expression in fish exposed to gold nanoparticles

Fish exposure to environmental stressors (e.g. chemicals, hypoxia, temperature) induce responses enabling them to cope with alterations in their environment. A stress response involves a wide array of changes, from molecular to physiological and behavioural, set to counteract the effect of the stressor and recover homeostatic equilibrium. Among other processes, there is activation of the hypothalamus-pituitary-interrenal (HPI) axis, resulting in stimulation of the steroidogenic pathway and release of cortisol, important mediator of the adaptive response to stress. The purpose of this study was to evaluate if exposure of a marine teleost (gilthead sea bream) to gold nanoparticles (AuNP) could interfere with the HPI axis eliciting an acute stress response and how this response would be linked with alterations in the mRNA levels of target genes in the head kidney, important centre of endocrine response in fish. Fish were exposed via water, for 96h, to four concentrations (0, as control, 4, 80 and 1600μg⋅L^-1) of 40nm spherical AuNP, covered with two different types of coatings (citrate and PVP). At the end of the exposure, fish were anesthetized and blood and the head kidney sampled. Results showed that exposure to 1600μg⋅L^-1 AuNP-citrate and 80μg⋅L^-1 AuNP-PVP increased plasma cortisol levels, compared to controls, but caused no change in glucose levels. AuNP modulated the expression of target genes related to oxidative stress, cell-tissue repair, immune function and apoptosis in the head kidney of fish. The patterns of response were distinct for the two coatings tested. Unlike AuNP-citrate, AuNP-PVP elicited an inverted U-shaped response. Present findings demonstrated that AuNP were able to activate the fish HPI axis and alter a battery of related molecular markers in the head kidney.

New approach for monitoring fish stress: A novel enzyme-functionalized label-free immunosensor system for detecting cortisol levels in fish

Fishes display a wide variation in their physiological responses to stress, which is clearly evident in the plasma corticosteroid changes, chiefly cortisol levels in fish. As a well-known indicator of fish stress, a simple and rapid method for detecting cortisol changes especially sudden increases is desired. In this study, we describe an enzyme-functionalized label-free immunosensor system for detecting fish cortisol levels. Detection of cortisol using amperometry was achieved by immobilizing both anti-cortisol antibody (selective detection of cortisol) and glucose oxidase (signal amplification and non-toxic measurement) on an Au electrode surface with a self-assembled monolayer. This system is based on the maximum glucose oxidation output current change induced by the generation of a non-conductive antigen-antibody complex, which depends on the levels of cortisol in the sample. The immunosensor responded to cortisol levels with a linear decrease in the current in the range of 1.25-200ngml^-1 (R=0.964). Since the dynamic range of the sensor can cover the normal range of plasma cortisol in fish, the samples obtained from the fish did not need to be diluted. Further, electrochemical measurement of one sample required only ~30min. The sensor system was applied to determine the cortisol levels in plasma sampled from Nile tilapia (Oreochromis niloticus), which were then compared with levels of the same samples determined using the conventional method (ELISA). Values determined using both methods were well correlated. These findings suggest that the proposed label-free immunosensor could be useful for rapid and convenient analysis of cortisol levels in fish without sample dilution. We also believe that the proposed system could be integrated in a miniaturized potentiostat for point-of-care cortisol detection and useful as a portable diagnostic in fish farms in the future.

Are coping styles consistent in the teleost fish Sparus aurata through sexual maturation and sex reversal?

Individual differences in behaviour and physiological responses to stress are associated with evolutionary adaptive variation and thus raw material for evolution. In farmed animals, the interest in consistent trait associations, i.e. coping styles, has increased dramatically over the last years. However, one of limitations of the available knowledge, regarding the temporal consistency, is that it refers always to short-term consistency (usually few weeks). The present study used an escape response during a net restraining test, previously shown to be an indicative of coping styles in seabream, to investigate long-term consistency of coping styles both over time and during different life history stages. Results showed both short-term (14 days) consistency and long-term (8 months) consistency of escape response. However, we did not found consistency in the same behaviour after sexual maturation when the restraining test was repeated 16, 22 and 23 months after the first test was performed. In conclusion, this study showed consistent behaviour traits in seabream when juveniles, and a loss of this behavioural traits when adults. Therefore, these results underline that adding a life story approach to data interpretation as an essential step forward towards coping styles foreground. Furthermore, a fine-tuning of aquaculture rearing strategies to adapt to different coping strategies may need to be adjusted differently at early stages of development and adults to improve the welfare of farmed fish.

Routine handling methods affect behaviour of three-spined sticklebacks in a novel test of anxiety

Fish are increasingly popular subjects in behavioural and neurobiological research. It is therefore important that they are housed and handled appropriately to ensure good welfare and reliable scientific findings, and that species-appropriate behavioural tests (e.g. of cognitive/affective states) are developed. Routine handling of captive animals may cause physiological stress responses that lead to anxiety-like states (e.g. increased perception of danger). In fish, these may be particularly pronounced when handling during tank-to-tank transfer involves removal from water into air. Here we develop and use a new combined scototaxis (preference for dark over light areas) and novel-tank-diving test, alongside conventional open-field and novel-object tests, to measure the effects of transferring three-spined sticklebacks (Gasterosteus aculeatus) between tanks using a box or net (in and out of water respectively). Preference tests for dark over light areas confirmed the presence of scototaxis in this species. Open-field and novel-object tests failed to detect any significant differences between net and box-handled fish. However, the combined diving and scototaxis detected consistent differences between the treatments. Net-handled fish spent less time on the dark side of the tank, less time in the bottom third, and kept a greater distance from the 'safe' bottom dark area than box-handled fish. Possible explanations for this reduction in anxiety-like behaviour in net-handled fish are discussed. The combined diving and scototaxis test may be a sensitive and taxon-appropriate method for measuring anxiety-like states in fish.

Acoustic stress responses in juvenile sea bass Dicentrarchus labrax induced by offshore pile driving

Underwater sound generated by pile driving during construction of offshore wind farms is a major concern in many countries. This paper reports on the acoustic stress responses in young European sea bass Dicentrarchus labrax (68 and 115 days old), based on four in situ experiments as close as 45 m from a pile driving activity. As a primary stress response, whole-body cortisol seemed to be too sensitive to 'handling' bias. On the other hand, measured secondary stress responses to pile driving showed significant reductions in oxygen consumption rate and low whole-body lactate concentrations. Furthermore, repeated exposure to impulsive sound significantly affected both primary and secondary stress responses. Under laboratory conditions, no tertiary stress responses (no changes in specific growth rate or Fulton's condition factor) were noted in young sea bass 30 days after the treatment. Still, the demonstrated acute stress responses and potentially repeated exposure to impulsive sound in the field will inevitably lead to less fit fish in the wild.

Effects of acute handling stress on cerebral monoaminergic neurotransmitters in juvenile Senegalese sole Solea senegalensis

Juvenile Senegalese sole Solea senegalensis were subjected for short periods to two different types of handling-related stress: air exposure stress and net handling stress. The S. senegalensis were sacrificed 2 and 24 h after the stress events and the levels of serotonin (5-HT), noradrenaline (NA), dopamine (DA) and their respective major metabolites, 5-hydroxyindoleacetic acid (5-HIAA), 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylacetic acid (DOPAC), were measured in three brain regions (telencephalon, hypothalamus and optic tectum) and compared with those in control, non-stressed S. senegalensis. Neither type of stress caused any significant alteration of serotoninergic activity (5-HIAA:5-HT ratio) or NA levels. Dopaminergic activity (DOPAC:DA ratio) was lower in stressed fish in all of the brain regions studied. For both air exposure stress and net handling stress, DA levels were significantly higher (P < 0.05) than in the control S. senegalensis. In addition, the higher DA levels after net handling stress were always significantly higher (P < 0.05) than those observed after acute air exposure stress, except in the telencephalon after 24 h. The significantly lower DOPAC:DA ratio (P < 0.05) in all of the brain regions studied was only observed in response to net handling stress.

HIFs genes expression and hematology indices responses to different oxygen treatments in an ovoviviparous teleost species Sebastes schlegelii

Hypoxia-inducible factors (HIFs) are transcription factors considered as a respond factor to oxygen tension. By using quantitative real-time PCR, expression files of HIF-1α and HIF-2α mRNA were detected in the Korean rockfish ovary, liver, gill and spleen after 30 min and 60 min acute hypoxia exposure. Meanwhile, the cortisol levels, white blood cells and several serum biochemical values of Korean rockfish under different oxygen concentration treatments were also detected. All the results might be helpful for further understanding of the potential effect of hypoxia in ovoviviparous fish.

Variation in glucocorticoid levels in relation to direct and third-party interactions in a social cichlid fish

In complex animal societies, direct interactions between group members can influence the behavior and glucocorticoid levels of individuals involved. Recently, it has become apparent that third-party group members can influence dyadic interactions, and vice versa. Thus, glucocorticoid levels may vary depending on interactions of other members of the social group. Using the social cichlid fish Neolamprologus pulcher, we examined the relationship between levels of the glucocorticoid hormone cortisol in subordinate females and 1) direct interactions with dominant group members, as well as 2) dyadic interactions between the dominant male and female, in which the subordinate female was not directly involved. Subordinate females that frequently engaged in non-aggressive interactions with dominant females had lower cortisol levels. There was no relationship between subordinate female cortisol and agonistic interactions between the subordinate female and either dominant. Subordinate females had higher cortisol levels when in groups in which the dominant breeding pair behaved agonistically towards each other and performed fewer courtship behaviors. For subordinate females in this species, variation in cortisol levels is associated with their own affiliative behavior, but also can be explained by the broader social context of interactions between dominant members of the group.

A putative corticosteroid hormone in Pacific lamprey, Entosphenus tridentatus

Great efforts have been put forth to elucidate the mechanisms of the stress response in vertebrates and demonstrate the conserved response across different vertebrate groups, ranging from similarities in the activation of the hypothalamic-pituitary-adrenal axis to the release and role of corticosteroids. There is however, still very little known about stress physiology in the Pacific lamprey (Entosphenus tridentatus), descendants of the earliest vertebrate lineage, the agnathans. In this paper we demonstrate that 11-deoxycortisol, a steroid precursor to cortisol in the steroidogenic pathway, may be a functional corticosteroid in Pacific lamprey. We identified the putative hormone in Pacific lamprey plasma by employing an array of methods such as RIA, HPLC and mass spectrometry analysis. We demonstrated that plasma levels of 11-deoxycortisol significantly increased in Pacific lamprey 0.5 and 1 h after stress exposure and that lamprey corticotropin releasing hormone injections increased circulating levels of 11-deoxycortisol, suggesting that the stress response is under the control of the HPA/I axis as it is in higher vertebrates. A comprehensive understanding of vertebrate stress physiology may help shed light on the evolution of the corticosteroid signaling system within the vertebrate lineage.

Changes in digestive enzyme activities of red porgy Pagrus pagrus during a fasting-refeeding experiment

An experiment was carried out in red porgy, Pagrus pagrus (Teleostei, Sparidae), to assess the effects of a 14-day fasting period, followed by refeeding to apparent satiation, on the contents of digestive enzymes (total proteases, and particularly pepsin, trypsin, chymotrypsin, carboxypeptidases A and B; amylase and lipase). Two fish groups were considered: one (indicated as fasted/refed group) was fasted for 14 days and then refed during further 7 and 15 days, and the other was fed throughout the study and was taken as a control group. The measured enzymatic values showed that fasting resulted in a generalized, not significant decrease, of the activity of digestive enzymes. Refeeding caused a significant increase for most of the assayed enzymes: total proteases both in the middle and distal intestine, pepsin in the stomach, trypsin in the middle intestine, and amylase and lipase in the proximal intestine. Nevertheless, the detection in the fasted/refed fish of enzymatic values still lower than those measured in the control fish suggested that fish experiencing short-term fasting were partially impaired in their digestive capacity.

Dietary administration of Bacillus subtilis on hematology and non-specific immunity of Nile tilapia Oreochromis niloticus raised at different stocking densities

An 84-day feeding trial was conducted to evaluate the effect of the dietary administration of Bacillus subtilis on the growth performance, body composition, intestinal probiotic recovery, hematology, and non-specific immunity of Nile tilapia (Oreochromis niloticus) raised at two stocking densities. Five hundred twenty male Nile tilapias (32.63 ± 1.25 g) were distributed in 16,800-L tanks. The experimental design was completely randomized using four replications and a 2 × 2 factorial scheme with two stocking densities (18.75 fish m(-3) 62.50 fish m(-3)) and two diets (control and with probiotic). The probiotic-supplemented diet included 5 × 10(6) CFU g feed(-1). There were no significant differences (P > 0.05) in the growth performance, body composition, and levels of cortisol and glucose between the animals fed with the control diet and the animals fed with the probiotic-supplemented diet. Differences in the growth performance were observed between the fish reared at different stocking densities; in particular, the fish raised at the high stocking density exhibited reduced weight gain, feed intake, and specific growth rate compared with those raised at the low stocking density. The B. subtilis remained viable after its inclusion in the feed, storage, and passage through the stomach, which demonstrations the feasibility of using this bacteria as a probiotic. Higher values (P < 0.05) in the plasma lysozyme levels and phagocytic activity were observed in the fish that received the probiotic-supplemented diet and reared at the high stocking density, but this difference was not observed in the fish raised at the low stocking density and fed the different diets. The administration of the probiotic caused decreases in the number of erythrocytes and the hematocrit level in the fish reared at the high stocking density, but these erythrocytes showed higher values of mean corpuscular hemoglobin. The stocking density was shown to be a stressor agent that causes a lower fish growth rate. The fish fed the control diet and raised at the high stocking density had lower lysozyme levels than the fish subjected to the other treatments. The inclusion of the probiotic bacteria B. subtilis at a concentration of 5 × 10(6) CFU g feed(-1) benefited the innate immune system of Nile tilapia by decreasing the stress associated with exposure to a high stocking density, increasing the mean corpuscular hemoglobin, and improving the innate immune system (lysozyme and phagocytic activities of macrophages).

Diel changes in plasma cortisol and effects of size and stress duration on the cortisol response in European sea bass (Dicentrarchus labrax)

European sea bass (Dicentrarchus labrax), one of the most economically important fish in Mediterranean mariculture, shows high basal cortisol concentrations compared with other teleosts. The present study aims (a) to identify cortisol diel variation in fish held under a 12L:12D cycle and minimum handling stress, and (b) to establish the effect of fish size and stressor duration on the cortisol response. The results indicate high intrapopulation variability in plasma cortisol and a significant diel fluctuation with a peak value at dusk (18 h). Stressors of different intensity and/or duration affected the cortisol stress response in a differential manner according to fish size (and/or age). Maximum cortisol values in small-size fish were found at 1 and 2 h post-stress, depending on the duration of the stressor, while at 0.5 h post-stress in large fish regardless stress duration.

Physiological responses in wild broodstocks of the Caspian Kutum (Rutilus frisii kutum) subjected to transportation stress

Caspian Kutum (Rutilus frisii kutum) broodstocks in the wild were subjected to 2 different densities (100 and 300 kg m(-3)) for 2 hr of transport, and their physiological responses were examined. Fifteen fish were placed into the plastic container for each replicate and blood was taken at 0, 10, 30, 60, and 120 min after transportation in different densities. Mean levels of cortisol and glucose as primary and secondary responses to the stress were significantly different between densities. Significant differences in both densities were observed in cortisol for all times and glucose levels at 30 and 120 min after transportation, and the highest values were found in both densities at 120 min. Testosterone concentrations declined considerably in the first 10 min, and then they showed a gradual decrease with a significant difference between 2 densities at 10 and 30 min after transportation. Serum estradiol reached the lowest level at 120 min after transportation, and differences were significant between the 2 densities after 30 min. Based on the results, it was concluded that Kutum broodstocks are sensitive to transport, especially at high density. Therefore, welfare during transport should be considered.

The adaptive significance of population differentiation in offspring size of the least killifish, Heterandria formosa

We tested the hypothesis that density-dependent competition influences the evolution of offspring size. We studied two populations of the least killifish (Heterandria formosa) that differ dramatically in population density; these populations are genetically differentiated for offspring size, and females from both populations produce larger offspring when they experience higher social densities. To look at the influences of population of origin and relative body size on competitive ability, we held females from the high-density population at two different densities to create large and small offspring with the same genetic background. We measured the competitive ability of those offspring in mesocosms that contained either pure or mixed population treatments at either high or low density. High density increased competition, which was most evident in greatly reduced individual growth rates. Larger offspring from the high-density population significantly delayed the onset of maturity of fish from the low-density population. From our results, we infer that competitive conditions in nature have contributed to the evolution of genetically based interpopulation differences in offspring size as well as plasticity in offspring size in response to conspecific density.

Profile of cortisol, glycaemia, and blood parameters of American Bullfrog tadpoles Lithobates catesbeianus exposed to density and hypoxia stressors

The aim of this study was to evaluate alterations to the physiological profile (cortisol, glycaemia, and blood parameters) of Lithobates catesbeianus caused by the stressors density and hypoxia. The organisms were in the prometamorphosis stage and exposed to different tadpole densities: 1 tadpole/L (T1), 5 tadpoles/L (T2), and 10 tadpoles/L (T3) for 12 days. The blood was collected through the rupture of the caudal blood vessel and collected under normoxia (immediate collection) and hypoxia (after 15 minutes of air exposure) conditions. Cortisol levels rose on the fourth and eighth days of treatment and returned to basal levels by the end of the experiment. The stressor mechanisms tested did not affect glycaemia. White blood cells (total number of lymphocytes, neutrophils, and eosinophils) showed a significant difference at the twelfth day of the experiment when compared with the start of the experiment. We concluded that, under controlled conditions, a density of up to 10 tadpoles/L and air exposure for 15 minutes did not cause harmful physiological alterations during the experimental period. The answer to these stressors maybe was in another hormonal level (corticosterone).

Short fasting and refeeding in red porgy (Pagrus pagrus, Linnaeus 1758): response of some haematological, biochemical and non specific immune parameters

A short fasting-refeeding experience was applied to specimens of red porgy, Pagrus pagrus (Teleostei, Sparidae) to assess its effects on some physiological parameters. Haematological (haematocrit), biochemical (serum cortisol and glucose) and immunological (lysozyme, haemolytic and haemagglutinating activities) parameters were measured. For this study, two fish groups were considered: one was fasted for 14 days and then refed to satiation during further 7 and 15 days (indicated as fasted/refed group), the other was fed throughout the study and was taken as a control group. Significantly lower values were recorded for the condition index, the hepato-somatic index and viscero-somatic index in the fasted/refed group compared to the fed one. Fasting did not affect significantly the examined parameters, except for cortisol; refeeding for 7 days induced a significant increase in the haemoagglutinating titre and the spontaneous haemolytic activity, but when refeeding was extended to 14 days haemagglutinating and haemolytic values remained lower than those measured in fed fish.

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.

Cortisol and finfish welfare

Previous reviews of stress, and the stress hormone cortisol, in fish have focussed on physiology, due to interest in impacts on aquaculture production. Here, we discuss cortisol in relation to fish welfare. Cortisol is a readily measured component of the primary (neuroendocrine) stress response and is relevant to fish welfare as it affects physiological and brain functions and modifies behaviour. However, we argue that cortisol has little value if welfare is viewed purely from a functional (or behavioural) perspective-the cortisol response itself is a natural, adaptive response and is not predictive of coping as downstream impacts on function and behaviour are dose-, time- and context-dependent and not predictable. Nevertheless, we argue that welfare should be considered in terms of mental health and feelings, and that stress in relation to welfare should be viewed as psychological, rather than physiological. We contend that cortisol can be used (with caution) as a tractable indicator of how fish perceive (and feel about) their environment, psychological stress and feelings in fish. Cortisol responses are directly triggered by the brain and fish studies do indicate cortisol responses to psychological stressors, i.e., those with no direct physicochemical action. We discuss the practicalities of using cortisol to ask the fish themselves how they feel about husbandry practices and the culture environment. Single time point measurements of cortisol are of little value in assessing the stress level of fish as studies need to account for diurnal and seasonal variations, and environmental and genetic factors. Areas in need of greater clarity for the use of cortisol as an indicator of fish feelings are the separation of (physiological) stress from (psychological) distress, the separation of chronic stress from acclimation, and the interactions between feelings, cortisol, mood and behaviour.

The effects of insulin, glucagon, glutamate, and glucose infusion on blood glutamate and plasma glucose levels in naive rats

BACKGROUND

Elevated levels of glutamate in brain fluids, in the context of several neurodegenerative conditions, are associated with a worsened neurological outcome. Because there is a clear relationship between brain glutamate levels and glutamate levels in the blood, and an association of the latter with stress, the purpose of this study was to investigate the effects of glucose, insulin, and glucagon on rat blood glutamate levels.

METHODS

Rats received either 1 mL/100 g of rat body weight (BW) intravenous isotonic saline (control), 150 mg/1 mL/100 g BW intravenous glucose, 75 mg/1 mL/100 g BW intravenous glutamate, 50 g/100 g BW intraparitoneal glucagon, or 0.2 UI/100 g BW intraparitoneal insulin. Blood samples were subsequently drawn at 0, 30, 60, 90, and 120 minutes for determination of blood glutamate and glucose levels.

RESULTS

We observed a significant decrease in blood glutamate levels at 30 minutes after injection of glucose (P<0.05), at 30 and 60 minutes after injection of insulin (P<0.05), and at 90 and 120 minutes after injection of glucagon. Plasma glucose levels were elevated after infusion of glutamate and glucose but were decreased after injection of insulin.

CONCLUSIONS

The results of this study demonstrate that glucose, insulin, and glucagon significantly reduce blood glutamate levels. The effect of insulin is immediate and transient, whereas the effect of glucagon is delayed but longer lasting, suggesting that the sensitivity of pancreatic glucagon and insulin-secreting cells to glutamate is dependent on glucose concentration. The results of this study provide insight into blood glutamate homeostasis and may assist in the implementation of new therapies for brain neuroprotection from excess glutamate.

Stress and immune modulation in fish

Stress is an event that most animals experience and that induces a number of responses involving all three regulatory systems, neural, endocrine and immune. When the stressor is acute and short-term, the response pattern is stimulatory and the fish immune response shows an activating phase that specially enhances innate responses. If the stressor is chronic the immune response shows suppressive effects and therefore the chances of an infection may be enhanced. In addition, coping with the stressor imposes an allostatic cost that may interfere with the needs of the immune response. In this paper the mechanisms behind these immunoregulatory changes are reviewed and the role of the main neuroendocrine mechanisms directly affecting the building of the immune response and their consequences are considered.

Changes of glycogen metabolism in the gills and hepatic tissue of tilapia (Oreochromis mossambicus) during short-term Cd exposure

The aim of the study was to test the hypothesis that the mechanism of glycogen metabolism has taken place in gills rather than in liver during Cd exposure. Male tilapia were exposed to 44.45 μM ambient Cd for 12h, and we found blood glucose significantly increased, however, lactate levels showed no significant changes. The glycogen phosphorylase (GP) activity increased immediately after 0.75 to 3h of Cd exposure in the gills, and after 1 to 6h in the liver, respectively. In addition, the glycogen level depleted faster in the gills than in the liver. Plasma cortisol level increased from 0.25 to 1h and recovered after 3h, while the glucagon did not significantly change during Cd exposure. Glucocorticoid receptor (GR) mRNA expression decreased after 0.75 h in the gills, while it significantly increased after 6h in the liver. Ca(2+), Na(+), Cl(-), and K(+) significantly decreased upon Cd exposure within 6h following Cd-induced toxic stress. We suggested that the cortisol is the spontaneous stimulation of glycogen metabolism in the gills, and it triggers a subsequent energy supply later in the liver. Taken together, the profile of glycogen metabolism between gills and liver during Cd-exposure stress provide good support to our hypothesis.

Whole body cortisol and expression of HSP70, IGF-I and MSTN in early development of sea bass subjected to heat shock

Whole body cortisol levels were determined during early larval developmental stages of sea bass (Dicentrarchus labrax) subjected to a heat shock with the aim to investigate the correlation between the stress event and the activation of the hypothalamic-pituitary-interrenal axis. Moreover, the mRNA expression of inducible heat shock protein 70 (HSP70), insulin-like growth factor I (IGF-I) and myostatin (MSTN) was also detected. Whole body cortisol was determined by a radio-immunoassay (RIA) technique whereas the expression of HSP70, IGF-I and MSTN mRNAs was quantified by Real-Time PCR. Cortisol was detectable in all the larvae from hatching but its level increased significantly in larvae submitted to heat shock from 2-day post hatching onwards. An effect of the sole transfer on cortisol levels was detectable at day 10, indicating an increase of the hypothalamic-pituitary-interrenal axis sensitivity from this stage of sea bass development. In animals exposed to heat shock, the expression of inducible HSP70 resulted in a marked increase of mRNA levels already at hatching. This increase was significantly higher from 6 days onwards if compared to controls. Moreover, heat shock resulted in a decrease (although not significant) in IGF-I mRNA expression of stressed larvae if compared to controls. On the contrary, heat shock did not influence the expression of MSTN mRNA in all groups. The results indicate a very early activation of the hypothalamic-pituitary-interrenal axis and in general of the stress response during the development of European sea bass. Moreover, these results suggest the importance of cortisol and inducible HSP70 as bioindicators of stress in aquaculture and confirm the role of IGF-I and MSTN as regulatory factors during development and growth of fish.

Annual variations of the plasmatic levels of glucose and amino acid and daily changes under different natural conditions of temperature and photoperiod in Gilthead Sea bream (Sparus aurata, L.)

Daily and annual changes in the plasmatic glucose and amino acid concentration have been determined in Sparus aurata L. Fish (average weight 330 g) were kept in cages under natural conditions of temperature and photoperiod and fed with a commercial diet. The months studied were chosen to establish whether there is any influence on the plasmatic glucose and amino acid concentration due to the change in temperature and photoperiod (equal photoperiod and different temperature, March and October; different photoperiod and equal temperature, May and November; and different photoperiod and temperature, June and January). To study the daily profile of glucose and amino acids concentrations, blood was extracted from six fish every 3 h during 24 h. Annual changes were determined as the average of the samples obtained during 1 day. Results show an annual rhythm with acrophase in June with a positive correlation with photoperiod for glucose and amino acids and with temperature only for amino acids. Daily profiles are rhythmical with a period of 24 h except in November with a period of 8 h for amino acids.

Chronic and acute stress responses in Senegalese sole (Solea senegalensis): the involvement of cortisol, CRH and CRH-BP

The hypothalamus-pituitary-interrenal (HPI) axis is pivotal in the endocrine stress response of fish. Hypothalamic corticotropin-releasing hormone (CRH) initiates the endocrine stress response and stimulates the release of adrenocorticotropic hormone (ACTH) from the pituitary pars distalis, which in turn activates cortisol production and release by the interrenal cells of the head kidney. CRH activity depends on the levels of a specific CRH binding protein (CRH-BP). We have characterized the cDNAs coding for CRH and CRH-BP in Senegalese sole (Solea senegalensis) and investigated their mRNA expression in juveniles that were submitted to a protocol that involved exposure to a chronic stressor (viz. increased cultivation densities) followed by an acute stressor (viz. transfer to increased ambient salinity). Juveniles were cultivated at three densities (1.9, 4.7 and 9.8 kg/m(2)) for 33 days, and then exposed to an osmotic challenge that involved transfer from seawater (39‰ salinity, SW) to hypersaline seawater (55‰, HSW). The highest density imposed stress as indicated by elevated cortisol levels and CRH mRNA expression compared to fish stocked at low density. Fish kept at high density differentially responded to a posterior transfer to HSW; no cortisol or CRH response was seen, but osmoregulatory and metabolic parameters were affected. No differences in CRH-BP mRNA expression levels were found at different stocking densities; transfer to HSW enhanced expression in both low and high density stocked animals, suggesting that CRH-BP acts as a modulator of the acute stress response, not so of the chronic stress response. We conclude that stocking of Senegalese sole at high density is a stressful condition that may compromise the capacity to cope with subsequent stressors.

Unpredictable chronic stress model in zebrafish (Danio rerio): behavioral and physiological responses

Zebrafish (Danio rerio) have emerged as a promising model organism to study development, toxicology, pharmacology, and neuroscience, among other areas. Despite the increasing number of studies using zebrafish, behavioral studies with this species are still elementary when compared to rodents. The aim of this study was to develop a model of unpredictable chronic stress (UCS) in zebrafish. We evaluated the effects of UCS protocol during 7 or 14 days on behavioral and physiological parameters. The effects of stress were evaluated in relation to anxiety and exploratory behavior, memory, expression of corticotrophin-releasing factor (CRF) and glucocorticoid receptor (GR), and cortisol levels. As expected, UCS protocol increased the anxiety levels, impaired cognitive function, and increased CRF while decreased GR expression. Moreover, zebrafish submitted to 7 or 14 days of UCS protocol presented increased cortisol levels. The protocol developed here is a complementary model for studying the neurobiology and the effects of chronic stress in behavioral and physiological parameters. In addition, this protocol is less time consuming than standard rodent models commonly used to study chronic stress. These results confirm UCS in zebrafish as an adequate model to preclinical studies of stress, although further studies are warranted to determine its predictive validity.