Effects of high doses of cortisol on innate cellular immune response of seabream (Sparus aurata L.)

Implications of ammonia stress for the pathogenicity of Shewanella spp. in Oreochromis niloticus: effects on hematological, biochemical, immunological, and histopathological parameters

Environmental stressors (such as ammonia) in aquaculture could increase the risk of pathogenicity, posing a more severe threat to farmed fish. The aim of this study was to investigate the effects of ammonia stress on the pathogenicity of Shewanella spp. in Oreochromis niloticus. First, a 96-hour static test was used to determine the median lethal concentration (LC50) of unionized ammonia to Nile tilapia. After 96 h of exposure, the Un-ionized ammonia (UIA) LC50 was estimated to be 4.26 mg/L. Second, an experiment was conducted to test the effect of unionized ammonia stress on the pathogenicity of Shewanella spp. in O. niloticus for 30 days. A study involved 180 fish divided into six groups, with the first group serving as a control. The second group (AMN1/10) and the third group (AMN1/20) were not challenged and were exposed to 1/10 (0.42 mg/L) and 1/20 (0.21 mg/L) of the 96-hour LC50 of UIA, respectively. Then 0.2 mL (0.14 × 105) of Shewanella spp. was intraperitoneally injected into the fourth (SH), fifth (SH + AMN1/10), and sixth (SH + AMN1/20) groups, which were subjected to 0, 1/10 (0.42 mg/L), and 1/20 (0.21 mg/L) of the 96-hour LC50 of UIA, respectively. The survival rate, hematological indices, immunological parameters, and antioxidant activity of the fish significantly decreased when they were exposed to ammonia and Shewanella infection separately or together. Histopathological changes were also observed in the kidney and liver. Furthermore, both individual and combined exposures significantly altered renal and hepatic function, with notable increases in glucose and cortisol levels, as well as in the expression of proinflammatory cytokine genes (TNF-α and IL-1ß). However, the detrimental effects of co-exposure to ammonia stress and Shewanella infection were greater than those of separate exposures. As a result, we may say that increased ammonia concentrations enhance the infection of Shewanella spp. These findings could contribute to a better understanding of Shewanella infection in Nile tilapia.

Infection dynamics of Shewanella spp. in Nile tilapia under varied water temperatures: A hematological, biochemical, antioxidant-immune analysis, and histopathological alterations

In aquaculture, fluctuating water temperatures can act as a potent stressor, influencing the virulence and transmission dynamics of pathogenic bacteria, potentially triggering outbreaks and impacting fish health. The purpose of this work was to examine the impact of Shewanella spp. infection on hematological, biochemical, and antioxidant-immune parameters of Nile tilapia (Oreochromis niloticus) under different water temperatures. For this purpose, 180 fish were divided into 6 groups in triplicate (30 fish per group; 10 fish per replicate). Group 1 (G1), G2, and G3 were reared at varying water temperatures (22 °C, 28 °C, and 31 °C, respectively) without infection. While G4, G5, and G6 were IP-injected with 0.2 mL of Shewanella spp. (0.14 × 105) and reared at 22 °C, 28 °C, and 31 °C, respectively. Shewanella spp. infection induced significant lowering (p < 0.05) in hematological parameters (red and white blood cells, hemoglobin, and packed cell volume%) and immune-antioxidant responses (phagocytic activity%, phagocytic index, lysozyme, nitric oxide), total antioxidant capacity, catalase, and reduced glutathione, especially at 22 °C. Moreover, a significant increase (p < 0.05) in the hepato-renal function indicators (alanine aminotransferase, aspartate aminotransferase, urea, and creatinine), stress biomarkers (glucose and cortisol), malondialdehyde, and pro-inflammatory cytokines (interleukin-1β and tumor necrosis factor-α) were the consequences of the Shewanella spp. infection, especially at 22 °C. The Shewanella spp. infection exhibited marked histopathological changes in the hepatic and renal tissues. Worthily, Shewanella spp. can cause detrimental alterations in Nile tilapia's hematological, biochemical, and antioxidant-immune parameters at various water temperatures, but the major detrimental changes were observed at a water temperature of 22 °C. Consequently, we can conclude that the infection dynamics of Shewanella spp. are exaggerated at 22 °C. These outcomes could help in understanding the nature of such an infection in Nile tilapia.

Mitigating multiple stresses in Pangasianodon hypophthalmus with a novel dietary mixture of selenium nanoparticles and Omega-3-fatty acid

Effects of a novel dietary mixture of selenium nanoparticles (Se-NPs) and omega-3-fatty acids i.e., Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on mitigating arsenic pollution, high-temperature stress and bacterial infection were investigated in Pangasianodon hypophthalmus. To aim this, four isocaloric and iso-nitrogenous diets were prepared: control feed (no supplementation), Se-NPs at 0.2 mg kg^-1 diet with EPA + DHA at 0.2, 0.4 and 0.6% as supplemented diets. Fish were reared under normal condition or concurrent exposure to arsenic (2.65 mg L^-1), and temperature (34 °C) (As + T) stress for 105 days. The experiment was conducted with eight treatments in triplicates. Response to various stresses i.e., primary (cortisol), secondary (oxidative stress, immunity, and stress biomarkers) and tertiary stress response (growth performance, bioaccumulation and mortality due to bacterial infection) were determined. Supplementation of dietary Se-NPs at 0.2 mg kg^-1 diet and EPA + DHA at 0.2 and 0.4% reduced the primary stress level. Exposure to arsenic and temperature (As + T) and fed with control diet and EPA + DHA at 0.6% aggravated the cortisol level. Anti-oxidative enzymes (Catalase, superoxide dismutase, glutathione peroxidase and glutathione-s-transferase) and immunity (Nitroblue tetrazolium, total protein, albumin, globulin, A:G ratio, total immunoglobulin and myeloperoxidase) of the fish were augmented by supplementation of Se-NPs and EPA + DHA at 0.2 and 0.4%. Neurotransmitter enzyme, HSP 70, Vitamin C were significantly enhanced (p < 0.01) with supplementation of Se-NPs at 0.2 mg kg^-1 and EPA + DHA at 0.2 and 0.4%. Whereas total lipid, cholesterol, phospholipid, triglyceride and very low-density lipoprotein (VLDL) were reduced (p < 0.01) with the supplementation of Se-NPs at 0.2 mg kg^-1 diet and EPA + DHA at 0.2 and 0.4%. Tertiary stress response viz. growth performance was also significantly enhanced with supplementation of Se-NPs at 0.2 mg kg^-1 and EPA + DHA at 0.2 and 0.4% reared under As + T. Whereas arsenic bioaccumulation in fish tissues was significantly reduced with dietary supplementation of Se-NPs and EPA + DHA. Cumulative mortality and relative percentage survival were reduced with Se-NPs at 0.2 mg kg^-1 and EPA + DHA at 0.2 and 0.4%. The investigation revealed that a novel combination of Se-NPs at 0.2 mg kg^-1 and EPA + DHA at 0.4% followed by 0.2% has the potential to alleviate temperature stress, bacterial infection and arsenic pollution. Whereas diet containing Se-NPs at 0.2 mg kg^-1 diet and EPA + DHA at 0.6% was noticeably enhanced the stress in P. hypophthalmus.

Modulation of immunity and hepatic antioxidant defense by corticosteroids in pacu (Piaractus mesopotamicus)

We investigated the impact of both the oral administration of hydrocortisone (HC) and an acute stressor on stress, innate immune responses and antioxidant system/oxidative stress responses of juvenile Piaractus mesopotamicus. Fish were either 1) given a commercial feed (C), 2) given a feed supplemented with 400 mg/kg HC, or 3) fed a commercial feed, chased for 2 min and exposed to air for 4 min (S). After initial sampling, fish C and HC were fed and sampled 1, 3, 6, 24 and 72 h post-feeding. Fish S were fed at the same time as the other groups, exposed to a stressor, and sampled 1, 3, 6, 24 and 72 h after. Exposure to the stressor increased circulating glucose and cortisol levels (at 1 and 3 h, respectively), while oral HC increased circulating cortisol at 1 h and glucose at 3 h. The stressor activated respiratory activity of leukocytes (RAL) at 3 h and reduced it at 6 h. HC did not activate RAL, but it did impair it at 6 h. The serum hemolytic activity of the complement system (HAC₅₀) was impaired by the stressor at 1 and 3 h and by HC at 1 h. Regarding the antioxidant system, exposure to the stressor reduced glutathione peroxidase (GPx) and catalase (CAT) activity and decreased concentrations of reduced glutathione (GSH) in the liver up to 6 h. HC only impaired GPx. Additionally, stress induced the accumulation of melano-macrophage (MM) and melano-macrophage centers (MMC), which are biomarkers of oxidative stress, in the spleen. Differences in biomarkers in fish given cortisol and exposed to stress indicate that exogenous hormone was unable to precisely reproduce stress responses.

Ex vivo approach supports both direct and indirect actions of melatonin on immunity in pike-perch Sander lucioperca

The melatonin hormone, which is a multifunctional molecule in vertebrates, has been shown to exert complex actions on the immune system of mammals. In teleosts, the immunomodulatory capacity of this hormone has seldom been investigated. In the present experiment, we exposed ex vivo spleen and head kidney tissues of pike-perch to melatonin (Mel) and cortisol (Cort). We applied three concentrations of both hormones, alone and in combination, namely (1) Mel (10, 100 or 1000 pg mL^-1) (2) Cort (50, 500 or 5000 ng mL^-1) (3) Mel + Cort (10 + 50, 100 + 500 or 1000 pg mL^-1+5000 ng mL^-1). Pure medium without Mel or Cort served as control. After 15 h of incubation, we assessed the expression of a set of immunity-related genes, including genes encoding for pro-inflammatory proteins (il-1β, cxcl8 and tnf-α), acute-phase proteins (fgl2, fth1, hepc, hp and saa1) and key factors of the adaptive immune system (fκbp4 and tcrg). Both Mel and Cort, when used alone or combined at physiological concentrations, significantly influenced immune gene expressions that may lead to a global immune stimulation. Our results support both, an indirect action of the Mel hormone on the immune system through the regulation of intermediates such as Cort, as well as a direct action on immune targets through specific receptors.

Influence of chronic stress on the mechanism of the cytotoxic system in common carp (Cyprinus carpio)

Aquaculture conditions expose fish to internal and environmental stressors that increase their susceptibility to morbidity and mortality. The brain accumulates stress signals and processes them according to the intensity, frequency duration and type of stress, recruiting several brain functions to activate the autonomic or limbic system. Triggering the autonomic system causes the rapid release of catecholamines, such as adrenaline and noradrenaline, into circulation from chromaffin cells in the head kidney. Catecholamines trigger blood cells to release proinflammatory and regulatory cytokines to cope with acute stress. Activation of the limbic axis stimulates the dorsolateral and dorsomedial pallium to process emotions, memory, behaviour and the activation of preoptic nucleus‐pituitary gland‐interrenal cells in the head kidney, releasing glucocorticoids, such as cortisol to the bloodstream. Glucocorticoids cause downregulation of various immune system functions depending on the duration, intensity and type of chronic stress. As stress persists, most immune functions, with the exception of cytotoxic functions, overcome these effects and return to homeostasis. The deterioration of cytotoxic functions during chronic stress appears to be responsible for increased morbidity and mortality.

Fish Pathology Research and Diagnosis in Aquaculture of Farmed Fish; a Proteomics Perspective

One of the main constraints in aquaculture production is farmed fish vulnerability to diseases due to husbandry practices or external factors like pollution, climate changes, or even the alterations in the dynamic of product transactions in this industry. It is though important to better understand and characterize the intervenients in the process of a disease outbreak as these lead to huge economical losses in aquaculture industries. High-throughput technologies like proteomics can be an important characterization tool especially in pathogen identification and the virulence mechanisms related to host-pathogen interactions on disease research and diagnostics that will help to control, prevent, and treat diseases in farmed fish. Proteomics important role is also maximized by its holistic approach to understanding pathogenesis processes and fish responses to external factors like stress or temperature making it one of the most promising tools for fish pathology research.

Understanding neurobehavioral effects of acute and chronic stress in zebrafish

Stress is a common cause of neuropsychiatric disorders, evoking multiple behavioral, endocrine and neuro-immune deficits. Animal models have been extensively used to understand the mechanisms of stress-related disorders and to develop novel strategies for their treatment. Complementing rodent and clinical studies, the zebrafish (Danio rerio) is one of the most important model organisms in biomedicine. Rapidly becoming a popular model species in stress neuroscience research, zebrafish are highly sensitive to both acute and chronic stress, and show robust, well-defined behavioral and physiological stress responses. Here, we critically evaluate the utility of zebrafish-based models for studying acute and chronic stress-related CNS pathogenesis, assess the advantages and limitations of these aquatic models, and emphasize their relevance for the development of novel anti-stress therapies. Overall, the zebrafish emerges as a powerful and sensitive model organism for stress research. Although these fish generally display evolutionarily conserved behavioral and physiological responses to stress, zebrafish-specific aspects of neurogenesis, neuroprotection and neuro-immune responses may be particularly interesting to explore further, as they may offer additional insights into stress pathogenesis that complement (rather than merely replicate) rodent findings. Compared to mammals, zebrafish models are also characterized by increased availability of gene-editing tools and higher throughput of drug screening, thus being able to uniquely empower translational research of genetic determinants of stress and resilience, as well as to foster innovative CNS drug discovery and the development of novel anti-stress therapies.

Prolactin peptide (pPRL) induces anti-prolactin antibodies, ROS and cortisol but suppresses specific immune responses in rainbow trout

Prolactin has several immune functions in fish however, the effects on innate and specific components of rainbow trout immunity are currently unknown. Therefore in this study, prolactin peptide (pPRL) injection in rainbow trout generated anti-PRL antibodies that were confirmed through Western blot assays of fish brain tissue extract. At the same time, this group of fish was immunized with a viral antigen (VP2) and the specific antibody titer generated by the rainbow trout was subsequently determined, as well as the sero-neutralizing capacity of the antibodies. Interestingly, this group of fish (pPRL-VP2) generated approximately 150% less antibodies compared with fish immunized only with the viral antigen (VP2), and pPRL-VP2 fish increased their cortisol level by 4 times compared to the control. Additionally, through qPCR assay, we determined that the pPRL-VP2 fish group decreased pro-inflammatory transcript expression, and the serum of these (pPRL-VP2) fish stimulated ROS production in untreated fish leukocytes, a phenomenon that was blocked by the pharmacological cortisol receptor inhibitor (RU486). Collectively, this is the first report that indicates that pPRL could modulate both components of immunity in rainbow trout.

β-Glucan enhances respiratory activity of leukocytes suppressed by stress and modulates blood glucose levels in pacu (Piaractus mesopotamicus)

We evaluated the immune response of pacu fed with a β-glucan diet (0.5%) for 10 days. After the feeding period, fish were subjected to handling and 3 h after, inoculated with Aeromonas hydrophila. Fish were sampled before handling (baseline condition), 3, 6, and 24 h and 1 week after inoculation. A higher level of blood glucose was found in fish treated with β-glucan in baseline conditions. Handling and bacterial inoculation increased the circulating levels of cortisol and glucose and promoted the acute inflammatory response (lymphopenia and neutrophilia). β-Glucan prevented the decrease in the respiratory activity of leukocytes observed in the control group at 3 h sampling. β-Glucan did not affect the complement and lysozyme, which were activated 24 h after the bacterial challenge in control fish. A reduction in the number of leukocytes was found in fish treated with β-glucan 1 week after the challenge. We suggest two plausible hypotheses for this event: (1) it could be attributed to a depletion of the immune responses or (2) it could be due to a mobilization of the leukocytes to the spleen for antigen presenting/processing. In general, β-glucan avoided the reduction of the activity of leukocytes after stress and the bacterial challenge and increased the baseline glucose levels. Our findings confirm the immunomodulatory action of glucan and add evidence showing that glucan can have a role in stress response.

Are cortisol and melatonin involved in the immune modulation by the light environment in pike perch Sander lucioperca?

The pineal gland is the main organ involved in the transduction process converting environmental light information into a melatonin response. Since light environment was described as an important factor that could affect physiology of teleosts, and because melatonin is a crucial hormone regulating numerous physiological processes, we hypothesized that environmental light may act on both stress and circadian axes which in turn could influence the immune status of pike perch. Therefore, we investigated the effects of two light spectra (red and white) and two light intensities (10 and 100 lx) with a constant photoperiod 12L_(8:00-20:00) /12D on pike perch physiological and immune responses. Samples were collected at 04:00 and 16:00 at days 1 and 30 of the experiment. Stress markers, plasma melatonin levels, humoral innate immune markers, and expression of key immune genes in the head kidney were assessed. Light intensity clearly affected pike perch physiology. This included negative growth performances, increase in stress status, decrease in plasma melatonin levels, and immune depression. Light spectrum had only little influences. These results demonstrate that high stress status may have impacted melatonin production and secretion by the pineal organ. The drop in circulating melatonin and the increase in stress status may both be involved in the immune suppression.

The palliative role of Eruca sativa leaves dietary supplementation against oxidative stress, immunosuppression, and growth retardation in temperature-stressed Oreochromis niloticus

This study was conducted to investigate the effects of dietary dried Rocket Leaves meal (DRLM) supplementation on growth performance, immune response, and antioxidant capacity of Oreochromis niloticus reared under different water temperature. For this purpose, five hundred and forty apparently healthy O. niloticus were allocated into nine groups fed three DRLM-supplemented diets (0,1, and 3%) and reared at three water temperature (18, 24, and 32°C) in a 3 × 3 total randomized factorial design. The results revealed that exposure of fish to low (18°C) or high (32°C) temperatures for 30 days evoked significant growth retardation, depleted antioxidant enzymes activities (Catalase; CAT and super oxide dismutase; SOD), lipid peroxidation (malondialdehyde; MDA), immunosuppression, altered cortisol level compared to those reared at 24°C. Moreover, a marked down-regulation of oxidative stress related genes with up-regulation of interleukin 1β gene were apparent. In contrast, DRLM incorporation, particularly at 3%, in heat or cold stressed fish diets significantly enhanced growth, restored IgM and lysozymes levels, and SOD and CAT activities. Also, both the MDA and cortisol levels were significantly depressed. Furthermore, both antioxidant and immune-related genes expression were significantly corrected. Conclusively, 3% DRLM dietary supplementation in tilapia diet could be a promising strategy to alleviate the temperature stress-induced negative impacts on fish health and performance.

Immunosuppression-induced alterations in fish gut microbiota may increase the susceptibility to pathogens

Intestinal bacteria play an important role in the health and provide a variety of beneficial effects to host. Immunosuppressant can reduce the immunity of host and increase the susceptibility to pathogens. But it is not clear whether the increased susceptibility caused by immunosuppressant is related to changes of gut microbiota. In this study, we used crucian carp administrated with dexamethasone to explore the effects of immunosuppressants on gut microbial communities and further evaluate the potential association between changes in gut microbiota and susceptibility to pathogens. The results of MANOVA based on the top 10 PCoA axis scores from unweighed/weighted UniFrac distances showed that administration of dexamethasone (P = 0.021) and the administration time (P = 0.027) had a significant impact on the gut microbial composition, regardless of pathogens infection status (P = 0.35). After administration with dexamethasone, the fish had higher abundance of Cetobacterium and lower abundance of Bacillus and Lactococcus, and the abundance of genus Bacillus, Pseudomonas and Lactococcus decreased along with prolong administration time of dexamethasone. The results may help us understand the correlation between the host susceptibility to pathogenic bacteria and gut microbial community shift, and extend our knowledge regarding the role of gut microbiota in keeping the balance between pathogenic and symbiotic bacteria.

Modulation of stress and innate immune response by corticosteroids in pacu (Piaractus mesopotamicus)

Understanding how stress and corticosteroid modulates the innate immune response is one of the keys to improving productivity and reducing losses in intensive aquaculture. Thus, we investigated the effects of dietary corticosteroids (7 days; long-term exposure) and transport (4 h; short-term stress) on stress and innate immune response in pacu. For this end, fish were fed with diets containing dexamethasone (100 mg kg^-1) or hydrocortisone (200 mg kg^-1), followed by transport, and then were intraperitoneally inoculated with heat-killed Aeromonas hydrophila or PBS (sham-inoculation). Fish were sampled after a 7-day feeding period, immediately post-transport and 24 h post-transport and inoculation. The dietary treatment of corticosteroids decreased resting cortisol levels by inhibiting the production of cortisol on the hypothalamus pituitary interrenal-axis. Further, both corticosteroids reduced hematocrit, red blood cells, haemoglobin and hemolytic activity of the complement, while they increased glucose levels and serum lysozyme concentrations. The transport increased cortisol and glucose levels and reduced the humoral immune defenses such as serum lysozyme concentration and hemolytic activity of the complement system. Interestingly, the hemolytic activity of the complement system increased sharply in fish fed with corticosteroids immediately post-transport, when they had their HPI-axis partially suppressed by the corticosteroids. This finding suggests a stimulatory effect of the catecholamines released during the transport on the activity of the complement system. Our results are highly valuable to understanding the stress and innate immune responses to long-term exposure to corticosteroids and short-term stress in fish and may provide insights into how corticosteroids modulate the innate immune system.

Orange-spotted grouper Epinephelus coioides that have encountered low salinity stress have decreased cellular and humoral immune reactions and increased susceptibility to Vibrio alginolyticus

Orange-spotted grouper Epinephelus coioides reared at 34‰ and 27 °C were abruptly transferred to 6‰, 20‰ and 34‰ (control) and examined for innate cellular and humoral parameters after 3-96 h. Total leucocyte count (TLC), respiratory burst (RB), phagocytic activity (PA), alternative complement pathway (ACP) and lysozyme activity were significantly decreased 3-6 h, 3-6 h, 3-96 h, 3-96 h and 3-96 h, respectively after transferal into 6‰ salinity. TLC, RB and PA significantly increased after 3-48 h, 3-96 h and 3-24 h, respectively, with recovery of TLC and PA after 96 h and 48-96 h, whereas ACP and lysozyme activity significantly decreased 3-96 h after being transferred to 20‰. In another experiment, grouper reared at 34‰ and 27 °C were injected with Vibrio alginolyticus grown in tryptic soy broth (TSB) at 2.3 × 10⁹ colony-forming units (cfu) fish^-1 and then transferred to 6‰, 20‰ and 34‰ (control). The cumulative mortalities of V. alginolyticus-injected fish held in 6‰ were significantly higher than in injected fish held at 20‰ and 34‰. It was concluded that grouper E. coioides encountering a 34‰-6‰ salinity drop stress exhibited a depression in immunity as evidenced by decreased cellular and humoral parameters and increased susceptibility to V. alginolyticus. Grouper encountering a salinity stress drop from 34‰ to 20‰, however, exhibited decreased humoral immune parameters but also increased TLC and cellular immune parameters, indicating immunomodulation.

Physiological and proteomic responses to corticosteroid treatments in Eurasian perch, Perca fluviatilis: Investigation of immune-related parameters

The comparative effects of cortisol and 11-deoxycorticosterone (DOC), two major corticosteroids in fish, have yet received little attention in teleosts. We evaluated the proteomic and immune responses of Eurasian perch to chronic corticosteroid treatments. We implanted immature perch with cortisol (80mg/kg) or DOC (4mg/kg) and measured the proportions of blood leucocytes, immune indices in the plasma, spleen and liver (complement and lysozyme activity, total immunoglobulin and immune gene expression in the tissues) and differential proteome expression (corticosteroid versus control) in the liver and the spleen on days 2, 4 and 14 post-treatment. Implantation of cortisol decreased the ratio of blood leucocytes and depressed Ig levels in both organs while DOC modulated the proportion of leucocyte sub-populations (increase in lymphocytes and decrease in granulocytes). In contrast, the innate humoral immunity was not strongly influenced by any of corticosteroid implants. The only immune parameter that was significantly affected was lysozyme, after DOC treatment. A number of proteins were differentially regulated by these hormones and some were identified in the liver (21 for cortisol and 8 for DOC) and in the spleen (10 for cortisol and 10 for DOC). None of the proteins was directly linked to immunity, except the natural killer enhancing factor, which was repressed by cortisol in the spleen. Our results also confirm that the proteins involved in energetic and glucose metabolism are affected by corticosteroids. Furthermore, these corticosteroids differently regulate immune status in Eurasian perch and they primarily impact leucocytes, as opposed to innate immune function.

Dietary administration of sodium alginate ameliorated stress and promoted immune resistance of grouper Epinephelus coioides under cold stress

Grouper, Epinephelus coioides, fed a diet containing sodium alginate at 0 (control, named C) and 1.0 g kg^-1 (named S) at a temperature of 28 °C for 12 days, were then further individually transferred to 28 (two groups named C-28 and S-28) or 20 °C (two groups named C-20 and S-20), and immune parameters and stress indexes were measured at the beginning and after 6, 12, 24 and 48 h of exposure. Examination of immune parameters revealed that the alternative complement activity (ACH₅₀), lysozyme activity, phagocytic activity, superoxide dismutase, and respiratory bursts significantly increased in groupers fed the sodium alginate-containing diet for 12 days, and were higher in the S-28 than those of the C-28 and S-20 groups, which were higher than those of the C-20 group from 6 to 48 h except for ACH₅₀ at 48 h, respiratory bursts at 48 h, and lysozymes at 6 h. For the assessment of stress indicators, cortisol, glucose, and lactate levels of serum significantly decreased in grouper fed the sodium alginate-containing diet for 12 days, and were higher in the C-20 group than those of the C-28 and S-20 groups, which were higher than those of the S-20 group at 6-48 h. In another experiment, grouper fed the test diet for 12 days at a temperature of 28 °C were challenged with Photobacterium damselae subsp. piscicida at a dose of 5 × 10³ colony-forming units (cfu) (g fish)^-1, and then individually transferred to 28 or 20 °C. The survival rate of challenged fish of the C-28 group was significantly lower than those of challenged fish of the C-20 and S-28 groups, which were significantly lower than that of challenged fish of the S-20 group. All challenged fish of the S-20 group survived. Survival rates over 144 h were 30.0%, 70.0%, and 56.7% for the C-28, C-20, and S-28 groups, respectively. Our results indicated that dietary sodium alginate administration downregulated stress response indicators, enhanced immune responses, and prevented impacts of physiologic stress responses, immunosuppression, and susceptibility to P. damselae subsp. piscicida in grouper subjected to cold stress. Grouper cultured at 28 °C were more susceptible to P. damselae subsp. piscicida infection.

Levamisole enhances the innate immune response and prevents increased cortisol levels in stressed pacu (Piaractus mesopotamicus)

We analyzed the effects of levamisole on stress and the innate immune responses of pacu (Piaractus mesopotamicus). A total of 300 fish (180 ± 1.27 g) were fed a diet containing levamisole hydrochloride (LHC) for 15 days, then distributed into the following groups: T0 (control group); T1 (100), T2 (150), T3 (300) and T4 (500) mg kg^-1 LHC (15 fish per group and four replicates per treatment). After this, fish (n = 8 per treatment) were exposed to air for three minutes to simulate stress conditions and were then challenged with the bacterium Aeromonas hydrophila to stimulate the immune system. Fish were sampled at 1, 3 and 24 h after bacterial inoculation to measure plasma cortisol and glucose concentrations, the leukocyte respiratory burst (LRB), hemolytic activity of the complement system (HAC₅₀) and serum lysozyme activity (SLA). LHC attenuated the increase in plasma cortisol at 1 h (500 mg kg^-1) and 3 h (300 mg kg^-1) after air exposure and bacterial inoculation compared to control fish. The highest glucose concentrations were observed at 1 and 3 h after stress, which then returned to initial levels after 24 h, without any effect of LHC. The LHC 100 mg kg^-1 dose increased LRB 1 h after inoculation and activated the HAC₅₀ 3 h later. At 24 h, all LHC concentrations increased the HAC₅₀. SLA was reduced after inoculation, throughout the experimental period, without an effect of levamisole. Our results indicate that the oral administration of levamisole for 15 days modulated circulating cortisol levels during the stress response and improved the innate immune response against A. hydrophila infection in pacu.

Assessment of immune status of yellowfin seabream (Acanthopagrus latus) during short term exposure to phenanthrene

The aim of the present investigation was to assess the immune status in yellowfin seabream (Acanthopagrus latus) exposed to different concentrations of phenanthrene (Phe) for 14days. In addition, the Phe accumulation in the fish muscle was measured during the experiment. Fish were injected with different concentrations (0, 2, 20 and 40mg/kg) of Phe and samples were taken from tissue and blood of fish 1, 4, 7 and 14days after injection. Exposure of fish to Phe caused a significant decrease in white blood cells, C3 and C4 levels, lysosomal membrane stability, lysozyme activity after 4days and antibacterial activity after 7days of the experiment. In contrast, cortisol level significantly increased after 4days. The concentration of Phe in fish muscle increased rapidly after 4days. The main tissue changes observed in the head kidney including increase in melanomacrophage centers (MMCs), empty spaces between cells and hemorrhage. The degree of tissue changes ranged from normal to moderate in Phe-treated fish. The size and number of MMCs in treated fish were significantly higher than control. In conclusion, Phe toxicity in yellowfin seabream can induce increased cortisol level, tissue changes and immune suppression.

Preliminary study on the relationship between dexamethasone and pathogen susceptibility on crucian carp (Carassius auratus)

Dexamethasone, a known immunosuppressant, can inhibit the immune response and increase the amount of pathogen in body, but the role of dexamethasone affecting susceptibility of crucian carp (Carassius auratus) to pathogen is unclear. The effects of dexamethasone on susceptibility of crucian carp to Aeromonas hydrophila were investigated in this study. The fish were divided into four groups randomly and injected intraperitoneally by dexamethasone for 0 day (group D), 3 days (group C), 6 days (group B), and 9 days (group A), respectively. The serum lysozyme activity was significantly declined in group A, B and C. Relative immune gene expression such as il-1β, cxcl-8, tnfα and crp in kidney were down-regulation compared to group D. After that crucian carp were infected with A. hydrophila, crucian carp treated by dexamethasone had higher mortality (group A 95%, group B 76%, group C 31%) when compared to group D (4% mortality); the amount of pathogen in was significantly increased (P < 0.05) in liver, kidney and spleen of fish in group A-C compared to group D. These results implicated that higher susceptibility caused by dexamethasone may be induced by the decrease of lysozyme activity and the down-regulation of some immune genes.

Stress-induced adaptation of neutrophilic granulocyte activity in K and R3 carp lines

Both in mammals and fish, stress induces remarkable changes in the immune response. We focused on stress-induced changes in the activity of neutrophilic granulocytes in the R3 and K lines of common carp, which showed differential stress responses. Our study clearly demonstrates that a prolonged restraint stress differentially affects the activity of K and R3 carp neutrophils. In the K line, stress decreased the respiratory burst, while in the R3 line it reduced the release of extracellular DNA. Surprisingly, the stress-induced changes in ROS production and NET formation did not correlate with changes in gene expression of the inflammatory mediators and GR receptors. In neutrophilic granulocytes from K carp, gene expression of the stress-sensitive cortisol GR1 receptor was significantly higher than in neutrophils from R3 fish, which will make these cells more sensitive to high levels of cortisol. Moreover, upon stress, neutrophilic granulocytes of K carp up-regulated gene expression of the anti-inflammatory cytokine IL-10 while this was not observed in neutrophilic granulocytes of R3 carp. Therefore, we can hypothesize that, in contrast to R3 neutrophils, the more cortisol sensitive neutrophils from K carp respond to stress with up-regulation of IL-10 and consequently reduction of ROS production. Most probably the ROS-independent NET formation in K carp is not regulated by this anti-inflammatory cytokine. These data may indicate a predominantly ROS-independent formation of NETs by carp neutrophilic granulocytes. Moreover, they underline the important role of IL-10 in stress-induced immunoregulation.

Effects of repeated handling and air exposure on the immune response and the disease resistance of gibel carp (Carassius auratus gibelio) over winter

High mortalities and suppressed immune functions of farmed fish over winter are the universal problems in aquaculture. It is necessary to improve the immune response and disease resistance in the overwintering fish. A recent study suggested that repeated handling increased innate immune mechanisms and disease resistance in Senegalese sole. Therefore, the present study evaluated the hypothesis that appropriate repeated handling could compromise the immune depression and increase the disease resistance in gibel carp over winter. The experiment was executed in field net cages (2 m × 2 m × 2 m) from Dec. 4, 2012 to Apr. 2, 2013. Three cages with 50 fish per cage were randomly designed as the control group and did not receive any interfere over winter. The other three cages received repeated handling with an air exposure for 5 min every week during the experiment. Fish were not fed over winter. At the end of the trial, fish were challenged with Aeromonas hydrophila at a dose of 1.5 × 10(8) CFU ml(-1). The results showed that no significant difference of final body weight was found between groups. The spleen and kidney somatic index increased in the control fish after bacterial challenge and showed a rising trend but not a statistical change in repeated handled fish. Plasma cortisol levels significantly increased in the control fish at 6 h post bacterial challenge and then declined. However, repeated handled fish did not show any significant change in plasma cortisol levels after challenge. The reduced inducement of heat shock protein 70 (HSP70) expressions by repeated handling was found in gibel carp post bacterial challenge. After overwintering, the repeated handled fish exhibited increased catalase (CAT) and superoxide dismutase (SOD) activities. Enhanced plasma CAT activities and reduced plasma malondialdehyde (MDA) contents were found in repeated handled fish over time against invading bacteria. Up-regulation of myeloid differentiation primary response gene 88 (MyD88) and interleukin 11 (IL11) was observed in repeated handled fish over time after bacterial challenge. The overexpression of IL11 was significantly reduced by repeated handling against invading bacteria compared to the control group. The present results implied that a MyD88-dependent signaling pathway was involved in the innate immune responses of gibel carp by repeated handling over winter against invading bacteria.

Repeated handling compromises the immune suppression and improves the disease resistance in overwintering channel catfish (Ictalurus punctatus)

In winter, fish have suppressed immune functions and are susceptible to bacteria or virus which may lead to a high mortality. It is necessary to improve the immune response and disease resistance for overwintering fish. A recent study suggested that repeated handling increased the innate immune mechanisms and disease resistance in Senegalese sole. Therefore, the present study tested the hypothesis that appropriate repeated handling could compromise the immune depression and increase the disease resistance in channel catfish over winter. The experiment was carried out in field cages from Nov. 2012 to April 2013. Before the experiment, 35 fish with an average weight of 188.4 g were randomly assigned to one of six cages (2 m × 2 m × 2 m). Three cages were designed as the control group and did not receive any interfere. Fish in the other three cages received a weekly repeated handling of an air exposure for 5 min. Fish were not fed over winter. At the end of the trial, fish were challenged with Aeromonas hydrophila at a dose of 5.6 × 10(8) CFU ml(-1). The results showed that final body weight was not changed between groups. The spleen somatic index increased while the head kidney somatic index decreased in the unhandled fish after bacterial challenge, but these indices were not significantly changed in the repeated handled fish. Plasma cortisol levels in the control fish were induced at 6 h post challenge and then declined to the normal levels. However, plasma cortisol levels in the repeated handled fish did not show any significant change after bacteria challenge. The reduced inducement of heat shock protein 70 (HSP70) expression by repeated handling was observed in fish post bacterial challenge. After overwintering, repeated handled fish exhibited increased catalase (CAT) activities and reduced malondialdehyde (MDA) contents. Plasma total antioxidant capacity (TAOC), CAT and superoxide dismutase (SOD) activities of channel catfish were enhanced by repeated handling post bacterial challenge. The enhanced up-regulation of Interleukin 8 (IL8), IL1β-a, IL1β-b together with the immune related genes of Toll-like receptor 2 (TLR2), TLR3, nucleotide-binding oligomerization domain 1 (NOD1) and NOD2 by repeated handling was found in catfish after bacterial challenge. The present results indicated that a combination of signaling pathways through TLRs and NODs was involved in the innate immune response of the overwintering repeated handled channel catfish against invading bacteria.

Dietary tryptophan and methionine as modulators of European seabass (Dicentrarchus labrax) immune status and inflammatory response

Amino acids regulate key metabolic pathways important to immune responses and their nutritional supply may increase synthesis of immune-related proteins. The present study aimed to evaluate the effects of dietary supplementation of tryptophan and methionine on European seabass (Dicentrarchus labrax) cellular and humoral status. The immunomodulatory effects of tryptophan and methionine during an inflammatory insult was also evaluated after intraperitoneal injection with inactivated Photobacterium damselae subsp. piscicida (Phdp). A practical isonitrogenous (45% crude protein) and isolipidic (16% crude fat) diets was formulated to include fish meal and a blend of plant feedstuffs as protein sources and fish oil as the main lipid source (CRL diet). Two other diets were formulated similar to the control but including L-tryptophan or L-methionine at ×2 the requirement level (diets TRP and MET, respectively). European seabass weighing 275 g were fed the experimental diets for a period of 15 days before being sampled (trial 1). Then, fish were subjected to a peritoneal inflammation by intraperitoneally injecting UV killed Phdp (10(6) colony forming units ml(-1)) and sampled following 4 and 24 h post-injection (trial 2). Fish injected with a saline solution served as control. The haematological profile, peripheral cell dynamics and several plasma immune parameters were determined in trials 1 and 2, whereas cell migration to the inflammatory focus was also determined in trial 2. MET positively affected European seabass immune status by improving the peripheral leucocyte response, complement activity and bactericidal capacity, a stronger cellular recruitment to the inflammatory focus, and higher plasma peroxidase and bactericidal activities. TRP also seemed to improve immunostimulation, as there was a trend to augment both cell-mediated immunity and humoral capacity. However, TRP failed to improve an inflammatory response, verified by a decrease in blood phagocyte numbers and lack of immune cells recruitment. In summary, it is confirmed that MET has a pronounced influence on the innate immune response to inflammation, which is more evident than TRP, and raises its potential to incorporate in functional feeds to be used in prophylactic strategies against predictable unfavourable events.

Neuroendocrine mechanisms for immune system regulation during stress in fish

In the last years, the aquaculture crops have experienced an explosive and intensive growth, because of the high demand for protein. This growth has increased fish susceptibility to diseases and subsequent death. The constant biotic and abiotic changes experienced by fish species in culture are challenges that induce physiological, endocrine and immunological responses. These changes mitigate stress effects at the cellular level to maintain homeostasis. The effects of stress on the immune system have been studied for many years. While acute stress can have beneficial effects, chronic stress inhibits the immune response in mammals and teleost fish. In response to stress, a signaling cascade is triggered by the activation of neural circuits in the central nervous system because the hypothalamus is the central modulator of stress. This leads to the production of catecholamines, corticosteroid-releasing hormone, adrenocorticotropic hormone and glucocorticoids, which are the essential neuroendocrine mediators for this activation. Because stress situations are energetically demanding, the neuroendocrine signals are involved in metabolic support and will suppress the "less important" immune function. Understanding the cellular mechanisms of the neuroendocrine regulation of immunity in fish will allow the development of new pharmaceutical strategies and therapeutics for the prevention and treatment of diseases triggered by stress at all stages of fish cultures for commercial production.

Neuroendocrine modulation of the inflammatory response in common carp: adrenaline regulates leukocyte profile and activity

Inflammatory responses have to be carefully controlled, as high concentrations and/or prolonged action of inflammation-related molecules (e.g. reactive oxygen species, nitric oxide and pro-inflammatory cytokines) can be detrimental to host tissue and organs. One of the potential regulators of the inflammatory process are stress mediators including adrenaline. In vivo effects of adrenaline were studied during zymosan-induced (Z) peritoneal inflammation in the common carp Cyprinus carpio L. Adrenaline injected together with zymosan (ZA) did not change the number of inflammatory leukocytes in the peritoneal cavity, however at 24h post-injection it significantly reduced the percentage of monocytes/macrophages. Moreover, compared to cells retrieved from fish treated with PBS or zymosan only, adrenaline increased the percentage of apoptotic leukocytes in the focus of inflammation. Furthermore, adrenaline significantly reduced the expression of chemokine CXCL8_L1 (a functional homolog of mammalian IL-8) and its receptors (CXCR1 and CXCR2), indicating changes in leukocyte recruitment after stress. We conclude that adrenaline may contribute to a coordinated reaction by influencing the inflammatory response via direct regulation of leukocyte migration and/or apoptosis.

The interaction between maternal stress and the ontogeny of the innate immune system during teleost embryogenesis: implications for aquaculture practice

The barrier defences and acellular innate immune proteins play critical roles during the early-stage fish embryos prior to the development of functional organ systems. The innate immune proteins in the yolk of embryos are of maternal origin. Maternal stress affects the maternal-to-embryo transfer of these proteins and, therefore, environmental stressors may change the course of embryo development, including embryonic immunocompetency, via their deleterious effect on maternal physiology. This review focuses on the associations that exist between maternal stress, maternal endocrine disturbance and the responses of the acellular innate immune proteins of early-stage fish embryos. Early-stage teleostean embryos are dependent upon the adult female for the formation of the zona pellucida as an essential barrier defence, for their supply of nutrients, and for the innate immunity proteins and antibodies that are transferred from the maternal circulation to the oocytes; maternally derived hormones are also transferred, some of which (such as cortisol) are known to exert a suppressive action on some aspects of the immune defences. This review summarizes what is known about the effects of oocyte cortisol content on the immune system components in early embryos. The review also examines recent evidence that embryonic cells during early cleavage have the capacity to respond to increased maternal cortisol transfer; this emphasizes the importance of maternal and early immune competence on the later life of fishes, both in the wild and in intensive culture.

Physiological and proteomic responses to single and repeated hypoxia in juvenile Eurasian perch under domestication--clues to physiological acclimation and humoral immune modulations

We evaluated the physiological and humoral immune responses of Eurasian perch submitted to 4-h hypoxia in either single or repeated way. Two generations (F1 and F5) were tested to study the potential changes in these responses with domestication. In both generations, single and repeated hypoxia resulted in hyperglycemia and spleen somatic index reduction. Glucose elevation and lysozyme activity decreased following repeated hypoxia. Complement hemolytic activity was unchanged regardless of hypoxic stress or domestication level. A 2D-DIGE proteomic analysis showed that some C3 components were positively modulated by single hypoxia while C3 up- and down-regulations and over-expression of transferrin were observed following repeated hypoxia. Domestication was associated with a low divergence in stress and immune responses to hypoxia but was accompanied by various changes in the abundance of serum proteins related to innate/specific immunity and acute phase response. Thus, it appeared that the humoral immune system was modulated following single and repeated hypoxia (independently of generational level) or during domestication and that Eurasian perch may display physiological acclimation to frequent hypoxic disturbances.

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.

Health of farmed fish: its relation to fish welfare and its utility as welfare indicator

This brief review focuses on health and biological function as cornerstones of fish welfare. From the function-based point of view, good welfare is reflected in the ability of the animal to cope with infectious and non-infectious stressors, thereby maintaining homeostasis and good health, whereas stressful husbandry conditions and protracted suffering will lead to the loss of the coping ability and, thus, to impaired health. In the first part of the review, the physiological processes through which stressful husbandry conditions modulate health of farmed fish are examined. If fish are subjected to unfavourable husbandry conditions, the resulting disruption of internal homeostasis necessitates energy-demanding physiological adjustments (allostasis/acclimation). The ensuing energy drain leads to trade-offs with other energy-demanding processes such as the functioning of the primary epithelial barriers (gut, skin, gills) and the immune system. Understanding of the relation between husbandry conditions, allostatic responses and fish health provides the basis for the second theme developed in this review, the potential use of biological function and health parameters as operational welfare indicators (OWIs). Advantages of function- and health-related parameters are that they are relatively straightforward to recognize and to measure and are routinely monitored in most aquaculture units, thereby providing feasible tools to assess fish welfare under practical farming conditions. As the efforts to improve fish welfare and environmental sustainability lead to increasingly diverse solutions, in particular integrated production, it is imperative that we have objective OWIs to compare with other production forms, such as high-density aquaculture. However, to receive the necessary acceptance for legislation, more robust scientific backing of the health- and function-related OWIs is urgently needed.

Elevated cortisol modulates Hsp70 and Hsp90 gene expression and protein in sea bass head kidney and isolated leukocytes

In fish, interactions between Hsps and cortisol are involved in stress modulated physiological processes including innate immune responses. Cortisol exerts a role in the regulation of Hsps synthesis. Fish head kidney is a lymphomieloid and endocrine organ releasing cortisol, and it is the central organ for immune-endocrine interactions. In sea bass, cortisol intraperitoneal injection and in vitro treatment of head kidney cells show that inducible Hsp70 and Hsp90 are modulated by this hormone. However, an inverse relationship between mRNA expression (real-time PCR) and Hsp70 and Hsp90 protein levels (densitometric band analysis) was found. Time-course assays indicate a cortisol-mediated regulation. Furthermore, Hsp70 gene modulation appears to be more susceptible to the cortisol action and the mRNA was transcribed within 3h post-injection. The restoration of the homeostatic conditions was observed at a week p.i., when plasma cortisol baseline was reached. Although fish manipulation and injection exerted stressing effects as indicated by serological parameters, differences between cortisol treated specimens compared to untreated or sham fish are statistically significant. Similar results were found by examining in vitro total cells and isolated leukocytes from head kidney cultured for 3h with increasing cortisol concentration. Finally, MTT test and DNA fragmentation experiments showed that the apoptotic effect expected in cortisol-treated cells could be counteracted by high Hsp70 intracellular levels.

Dietary arginine and repeated handling increase disease resistance and modulate innate immune mechanisms of Senegalese sole (Solea senegalensis Kaup, 1858)

Stress is known to impair immune function and disease resistance in fish. In the present study, repeated handling was employed as a chronic stressor in order to verify whether its attributed immunosuppressive effects could be minimized by dietary arginine supplementation. Therefore, Senegalese sole (Solea senegalensis) were air exposed daily for 3 min during 14 days (handling) or left undisturbed (control). In addition, both control and handled specimens were fed 3 diets with graded levels of arginine (Arg 4.4, Arg 5.7 and Arg 6.9 g 16 g(-1) N). Following the 14 days stress challenge and feeding on those diets, fish were infected with Photobacterium damselae subsp. piscicida (strain PC566.1; LD(50) 5 × 10(3) cfu mL(-1)) and fed the same experimental diets. Respiratory burst activity and nitric oxide production of head-kidney leucocytes increased parallel to dietary arginine supplementation. HIF-1, HAMP-1, MIP1-alpha and gLYS expression values and some humoral parameters augmented in control specimens fed the Arg 5.7 and Arg 6.9 diets. Interestingly, repeated acute stress increased both disease resistance and some innate immune mechanisms in handled fish. The role of dietary arginine and repeated handling on Senegalese sole innate immunity and disease resistance are discussed.

Physiological and proteomic evidences that domestication process differentially modulates the immune status of juvenile Eurasian perch (Perca fluviatilis) under chronic confinement stress

The current study aimed to evaluate the influence of domestication process on the stress response and subsequent immune modulation in Eurasian perch juveniles (Perca fluviatilis) submitted to chronic confinement. Briefly, F1 and F4 generations were confined into small-size tanks and sampled 7 and 55 days after stocking. Cortisol and glucose levels as well as lysozyme activity and immunoglobulin level were evaluated in the serum. Spleen Somatic Index and spleen ROS production were also measured. A proteomic analysis was performed on serum sampled on day 7. Finally, both generations were genetically characterized using a microsatellite approach. Globally, results revealed that chronic confinement did not elicit a typical stress response but resulted in a prolonged immune stimulation. Proteomic results suggested that domestication process influenced the immune status of perch submitted to chronic confinement as the F1 confined fish displayed lower abundance of C3 complement component, transferrin and Apolipoprotein E. Microsatellite data showed a strong genetic drift as well as reduced genetic diversity, allelic number and heterozygosity along with domestication process. The present work is the first to report that fish under domestication can develop an immune response, assessed by a combined approach, following recurrent challenges imposed by captive environment despite a reduced genetic variation.

The influence of oocyte cortisol on the early ontogeny of intelectin and TLR-5, and changes in lysozyme activity in rainbow trout (Oncorhynchus mykiss) embryos

The ontogeny of lysozyme activity, intelectin, TLR-5M and TLR-5S gene expression and intelectin localization was examined in rainbow trout (Oncorhynchus mykiss) reared from oocytes immersed for 3h prior to fertilization in either ovarian fluid alone (CC) or cortisol-enriched ovarian fluid at either 100 ng mL(-1) (C1) or 1000 ng mL(-1) (C2) [final oocyte cortisol concentrations were ~3, ~5, and ~7.5 ng oocyte(-1) for the CC, C1 and C2 treatment groups, respectively]. Lysozyme activity was elevated in the cortisol-treated groups from the zygote until 13-days post fertilization (dpf), but was not affected at 21-dpf. Intelectin levels were elevated in both cortisol treatment groups at 12-hpf (2-cell stage) and then suppressed between 36- and 48-hpf. Intelectin mRNA transcript levels were elevated in both cortisol treatment groups in oocytes; there were no differences among treatment groups at 1- and 5-dpf, and suppressed in the C2 treatment group in 13-dpf and 26-dpf. TLR-5 mRNA transcripts were higher in cortisol-treated oocytes prior to fertilization; TLR-5S mRNA was more abundant than TLR-5M mRNA. The ontogeny of the gene expression patterns, and the gene, lectin and lysozyme responses to oocyte cortisol adjustments suggest an important role of innate immune systems in the early cleavage stages of embryonic cells.

The effects of estrogenic and androgenic endocrine disruptors on the immune system of fish: a review

During the last decade, a number of studies have shown that, in addition to their classically described reproductive function, estrogens and androgens also regulate the immune system in teleosts. Today, several molecules are known to interfere with the sex-steroid signaling. These chemicals are often referred to as endocrine disrupting contaminants (EDCs). We review the growing evidence that these compounds interfere with the fish immune system. These studies encompass a broad range of approaches from field studies to those at the molecular level. This integrative overview improves our understanding of the various endocrine-disrupting processes triggered by these chemicals. Furthermore, the research also explains why fish that have been exposed to EDCs are more sensitive to pathogens during gametogenesis. In this review, we first discuss the primary actions of sex-steroid-like endocrine disruptors in fish and the specificity of the fish immune system in comparison to mammals. Then, we review the known interactions between the immune system and EDCs and interpret the primary effects of sex steroids (estrogens and androgens) and their related endocrine disruptors on immune modulation. The recent literature suggests that immune parameters may be used as biomarkers of contamination by EDCs. However, caution should be used in the assessment of such immunotoxicity. In particular, more attention should be paid to the specificity of these biomarkers, the external/internal factors influencing the response, and the transduction pathways induced by these molecules in fish. The use of the well-known mammalian models provides a useful guide for future research in fish.

Effects of temperature change on the innate cellular and humoral immune responses of orange-spotted grouper Epinephelus coioides and its susceptibility to Vibrio alginolyticus

Orange-spotted grouper Epinephelus coioides held at 27 degrees C were then further cultured at 19, 27 (control), and 35 degrees C, and were examined for innate cellular and humoral responses after 3-96 h. The total leucocyte count, respiratory burst, and phagocytic activity significantly decreased 3, 48, and 96 h after fish were transferred to 19 and 35 degrees C. Both the alternative complement pathway (ACH(50)) and the lysozyme activity significantly decreased at 3-96 h after fish were transferred to 19 and 35 degrees C. In another experiment, groupers reared at 27 degrees C at 34 per thousand salinity were injected with Vibrio alginolyticus grown in tryptic soy broth (TSB) at a dose of 2.3 x 10(9) colony-forming units (cfu) fish(-1), and then further reared in water temperatures of 19, 27 (control), and 35 degrees C. The cumulative mortalities of V. alginolyticus-injected fish held in 19 and 35 degrees C were significantly higher than that of injected fish held in 27 degrees C. Resistance had decreased after 12 h for the challenged grouper held at 35 degrees C. All injected fish held in 19 degrees C had died after 72 h. It was concluded that at 12 h after transfer of grouper from 27 to 19 and 35 degrees C, immunity was suppressed and resistance against V. alginolyticus had decreased.

In vivo actions of melatonin on the innate immune parameters in the teleost fish gilthead seabream

Melatonin, a molecule produced in the pineal gland and retina of vertebrates, plays a major role in day-night circadian rhythms and other physiological processes, including the immune responses. Because little is known in this respect in fish, we have evaluated the in vivo role of melatonin in the main innate immune activities and the expression of immune-relevant genes in a teleost fish, the gilthead seabream (Sparus aurata L.). An intraperitoneal injection of 1 or 10 mg melatonin/kg of body weight produced a dose-time dependent increase in circulating melatonin serum levels. Several innate immune responses such as peroxidase, phagocytic, reactive oxygen intermediates and cell-mediated cytotoxic activities were significantly enhanced by the administration of melatonin at different sampling times. The expression of immune-relevant genes such as interleukin-1beta, major histocompatibility complex, virus-related response (interferon-regulatory factor-1 and Mx) and lymphocyte markers (immunoglobulin M and T-cell receptor for B and T lymphocytes, respectively), as analysed by semi-quantitative reverse transcription-polymerase chain reaction, was up-regulated in the head-kidney of melatonin-injected fish 1 and 3 days postinjection and decreased after 7 days. These data, together with our previous observations describing how photoperiod and in vitro melatonin treatment may affect seabream and sea bass immunology, confirm melatonin as a regulator of fish immunology. However, further studies are still needed to reveal the mechanisms underlying the direct or indirect interactions of melatonin with the fish immune system.

Immunological alterations in juvenile Pacific herring, Clupea pallasi, exposed to aqueous hydrocarbons derived from crude oil

The effects of acute and subchronic aqueous hydrocarbon exposures in the ppb range (0.2-127microg/L total PAH) on the immune system in Pacific herring (Clupea pallasi) were examined through specific immunocompetency assays and a host resistance model using Listonella anguillarum. Short-term hydrocarbon exposure at the highest concentration significantly enhanced respiratory burst activity (RBA) in macrophages and decreased plasma lysozyme concentrations, however, subchronic exposure (4-57d) reduced RBA. Fish in the high exposure group were also less susceptible to the pathogen L. anguillarum following acute hydrocarbon exposure; however, this group was the most susceptible following subchronic exposures. These results are explained by a measured transient physiological stress response and long-term effects on ionoregulation. This study illustrates that hydrocarbon-elicited effects are dynamic and that toxic outcomes with respect to the teleost immune system depend on chemical concentrations and composition, exposure durations and the specific pathogen challenge.

Expression of a glucocorticoid receptor (DlGR1) in several tissues of the teleost fish Dicentrarchus labrax

Since glucocorticoids have a role in maintaining the homeostatic status in fish, in the present paper mRNA expression (in situ hybridization) and tissue immunohistochemical localization of a glucocorticoid receptor (DlGR1) in several Dicentrarchus labrax organs are reported. Riboprobe and specific antibodies were prepared by using the DlGR1 that has been previously cloned and sequenced from peritoneal cavity leukocytes. Both mRNA and receptor were identified in head kidney, spleen, gills, intestine, heart and liver tissues. The functional roles of DlGR1 localization are discussed.

The immune response of tilapia Oreochromis mossambicus and its susceptibility to Streptococcus iniae under stress in low and high temperatures

Mozambique tilapia Oreochromis mossambicus acclimated to 27 degrees C were then held at 19, 23, 27 (control), 31 and 35 degrees C, and were examined for non-specific cellular and humoral responses after 12-96 h. Total leucocyte count decreased significantly when fish were transferred to 19 and 23 degrees C after 48 and 96 h, and when transferred to 35 degrees C over 12-96 h, respectively. Respiratory burst decreased significantly when fish were transferred to 19, 31 and 35 degrees C over 24-96 h, whereas phagocytic activity and phagocytic index decreased significantly when fish were transferred to low temperatures (19 and 23 degrees C) and high temperatures (31 and 35 degrees C) over 12-96 h. Lysozyme activity decreased significantly when fish were transferred to 19 degrees C after 12-96 h, but increased significantly when transferred to 31 and 35 degrees C over 48-96 h. Alternative complement pathway (ACH(50)) also decreased significantly when transferred to 19 and 23 degrees C after 12h, but increased significantly when transferred to 31 and 35 degrees C after 24h. In another experiment, tilapia reared at 27 degrees C were injected intraperitoneally with Streptococcus iniae at a dose of 1 x 10(7)colony-forming units (cfu)fish(-1), and then reared onward at water temperatures of 19, 23, 27 (control), 31 and 35 degrees C. Over 48-168 h, the cumulative mortality of S. iniae-injected fish held in 19 and 35 degrees C was significantly higher than that of injected-fish held in 23, 27 and 31 degrees C. It is concluded that transfer of tilapia O. mossambicus from 27 degrees C to low temperatures (19 and 23 degrees C) after 12h, and transfer of fish from 27 degrees C to high temperatures (31 and 35 degrees C) reduced their immune capability. Moreover, tilapia under temperature stress at 19 and 35 degrees C from 27 degrees C decreased its resistance against S. iniae.

Peritoneal cavity phagocytes from the teleost sea bass express a glucocorticoid receptor (cloned and sequenced) involved in genomic modulation of the in vitro chemiluminescence response to zymosan

To gain further insight into the role of cortisol in fish innate immune responses, we cloned and sequenced a 2592bp cDNA from sea bass (Dicentrarchus labrax) peritoneal leukocytes (PCLs) encoding a glucocorticoid receptor (DlGR1). The deduced aminoacid sequence displayed that DlGR1 belong to a multigenic family of steroid hormone receptors, and exhibited high homology (80%) to the Burton's mouth breeder (Haplochromis burtoni) HbGR1. The DlGR1 functional domains presented homologies with those of several vertebrate species. In situ hybridization assay revealed that DlGR1 was expressed in macrophages and neutrophils from the peritoneal cavity. Since in a previous paper, sea bass PCL chemiluminescence response (CL) has been related to increased respiratory burst of phagocytes stimulated with zymosan, PCLs, pre-incubated in vitro with cortisol at various concentrations, were assayed for their CL response. Dose-dependent cortisol inhibitory effects, and significant competitive activity of a low concentration of mifepristone (RU486), a glucocorticoid-receptor blocker, supported that cortisol-GR interaction was involved in modulating CL response via a genomic pathway. Results also indicated that cortisol could be effective through an additional not-genomic way, and showed that high doses of RU486 exerted an inhibitory effect on PCL chemiluminescence activity.

Effect of the pineal hormone melatonin on teleost fish phagocyte innate immune responses after in vitro treatment

Although neuroendocrine-immune system interaction has been shown in teleost fish, no study has evaluated the role of melatonin (Mel) on fish immune response even considering that it is affected by the photoperiod. Gilthead seabream (Sparus aurata L.) and sea bass (Dicentrarchus labrax L.) head-kidney leucocytes were incubated with Mel (0-control-, 20 pM-400 microM) and leucocyte viability and main innate cellular immune parameters were evaluated. Overall, seabream and sea bass head-kidney leucocytes incubated with low (similar to physiological) doses of Mel unchanged the innate immune response, whereas very high (pharmacological) dosages did. Phagocytosis was not affected by any Mel treatment while the peroxidase activity was significantly inhibited with the highest Mel concentration. In contrast, the sea bass respiratory burst activity was increased in a dose-dependent manner with 400 nM Mel or higher. Further studies are needed to clarify whether there are interactions between the fish pineal gland, and its hormone Mel, and the fish immune system.

Husbandry stress during early life stages affects the stress response and health status of juvenile sea bass, Dicentrarchus labrax

In aquaculture management it is important to establish objective criteria to assess health and welfare of the fish. Here we show that European sea bass (Dicentrarchus labrax) confronted with husbandry-associated stress (tank cleaning, i.e. scrubbing, and water temperature variation) during early life stages show poorer survival and disease resistance as juveniles. We evaluated several parameters for stress (plasma cortisol, glucose and lactate, hydromineral status), growth performance, the immune response (plasma IgM levels) and the effects of a nodavirus challenge. Principal component analysis allowed the establishment of a stress panel including plasma cortisol, osmolality, IgM levels and weight. Sea bass juveniles reared during early life in high and constant temperature perform best in terms of stress-related parameters assessed by principle component analysis. Variable water temperature triggers dramatic changes in plasma cortisol, osmolality, IgM levels, body weight and susceptibility to nodavirus that suggest a strong and prolonged activation of the HPI axis. Scrubbing induces some disturbances typical for mild short-term, acute stress, viz. increased plasma osmolality and decreased IgM levels, but does not affect plasma cortisol, growth or susceptibility to nodavirus of sea bass. Our data fit well with the concept of allostasis. We discuss the relevance of our work for sea bass aquaculture.