Hormonal status and phagocytic activity in sea bream infected with vibriosis

Isolation and Characterization of Bacteria Colonizing Acartia tonsa Copepod Eggs and Displaying Antagonist Effects against Vibrio anguillarum, Vibrio alginolyticus and Other Pathogenic Strains

Copepods represent a major source of food for many aquatic species of commercial interest for aquaculture such as mysis shrimp and early stages of fishes. For the purpose of this study, the culturable mesophilic bacterial flora colonizing Acartia tonsa copepod eggs was isolated and identified. A total of 175 isolates were characterized based on their morphological and biochemical traits. The majority of these isolates (70%) were Gram-negative bacteria. Matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) was used for rapid identification of bacterial isolates. Here, 58% of isolates were successfully identified at the genus level and among them, 54% were identified at the species level. These isolates belong to 12 different genera and 29 species. Five strains, identified as Bacillus pumilus, named 18 COPS, 35A COPS, 35R COPS, 38 COPS, and 40A COPS, showed strong antagonisms against several potential fish pathogens including Vibrio alginolyticus, V. anguillarum, Listeria monocytogenes, and Staphylococcus aureus. Furthermore, using a differential approach, we show that the antimicrobial activity of the 35R COPS strain is linked primarily to the production of antimicrobial compounds of the amicoumacin family, as demonstrated by the specific UV-absorbance and the MS/MS fragmentation patterns of these compounds.

Pituitary-thyroid axis development during the larval-juvenile transition in the pejerrey Odontesthes bonariensis

The morphological development of the thyroid gland of pejerrey Odontesthes bonariensis during larval-juvenile transition was studied and related to whole-body concentrations of thyroxine (T₄ ) and tri-iodothyronine (T₃ ). A complementary (c)DNA fragment of the thyroid-stimulating hormone β-subunit (tshb) was sequenced and transcript levels quantified during this period. Follicles with eosinophilic and T₄ -immunoreactive colloids were detected at hatching together with tshb transcript levels and whole-body concentrations of T₄ and T₃ hormones. Thyroid follicles were located in the subpharyngeal region associated with the ventral aorta below the hyoid bone. Follicle structure switched from the rounded form at hatching to oval in juveniles. Significant increase of follicle number per larva, mean colloidal area and total colloidal area was observed throughout development with maximum values at the end of the larval-juvenile transition. A significant decrease of tshb expression together with a significant increase in T₄ and T₃ whole-body concentrations was observed prior to achieving the juvenile phenotype. These results are in accordance with a negative feedback regulation of tshb expression by thyroid hormones and a possible association between thyroid hormone levels and the acceleration of metabolic processes necessary to complete metamorphosis.

Differential effects of exposure to parasites and bacteria on stress response in turbot Scophthalmus maximus simultaneously stressed by low water depth

The stress response of turbot Scophthalmus maximus was evaluated in fish maintained 8 days under different water depths, normal (NWD, 30 cm depth, total water volume 40 l) or low (LWD, 5 cm depth, total water volume 10 l), in the additional presence of infection-infestation of two pathogens of this species. This was caused by intraperitoneal injection of sublethal doses of the bacterium Aeromonas salmonicida subsp. salmonicida or the parasite Philasterides dicentrarchi (Ciliophora:Scuticociliatida). The LWD conditions were stressful for fish, causing increased levels of cortisol in plasma, decreased levels of glycogen in liver and nicotinamide adenine dinucleotide phosphate (NADP) and increased activities of G6Pase and GSase. The presence of bacteria or parasites in fish under NWD resulted in increased cortisol levels in plasma whereas in liver, changes were of minor importance including decreased levels of lactate and GSase activity. The simultaneous presence of bacteria and parasites in fish under NWD resulted a sharp increase in the levels of cortisol in plasma and decreased levels of glucose. Decreased levels of glycogen and lactate and activities of GSase and glutathione reductase (GR), as well as increased activities of glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH) and levels of nicotinamide adenine dinucleotide phosphate (NADPH) occurred in the same fish in liver. Finally, the presence of pathogens in S. maximus under stressful conditions elicited by LWD resulted in synergistic actions of both type of stressors in cortisol levels. In liver, the presence of bacteria or parasites induced a synergistic action on several variables such as decreased activities of G6Pase and GSase as well as increased levels of NADP and NADPH and increased activities of GPase, G6PDH and 6PGDH.

The immunomodulatory role of the hypothalamus-pituitary-gonad axis: Proximate mechanism for reproduction-immune trade offs?

The present review discusses the communication between the hypothalamic-pituitary-gonad (HPG) axis and the immune system of vertebrates, attempting to situate the HPG-immune interaction into the context of life history trade-offs between reproductive and immune functions. More specifically, (i) we review molecular and cellular interactions between hormones of the HPG axis, and, as far as known, the involved mechanisms on immune functions, (ii) we evaluate whether the HPG-immune crosstalk serves as proximate mechanism mediating reproductive-immune trade-offs, and (iii) we ask whether the nature of the HPG-immune interaction is conserved throughout vertebrate evolution, despite the changes in immune functions, reproductive modes, and life histories. In all vertebrate classes studied so far, HPG hormones have immunomodulatory functions, and indications exist that they contribute to reproduction-immunity resource trade-offs, although the very limited information available for most non-mammalian vertebrates makes it difficult to judge how comparable or different the interactions are. There is good evidence that the HPG-immune crosstalk is part of the proximate mechanisms underlying the reproductive-immune trade-offs of vertebrates, but it is only one factor in a complex network of factors and processes. The fact that the HPG-immune interaction is flexible and can adapt to the functional and physiological requirements of specific life histories. Moreover, the assumption of a relatively fixed pattern of HPG influence on immune functions, with, for example, androgens always leading to immunosuppression and estrogens always being immunoprotective, is probably oversimplified, but the HPG-immune interaction can vary depending on the physiological and envoironmental context. Finally, the HPG-immune interaction is not only driven by resource trade-offs, but additional factors such as, for instance, the evolution of viviparity shape this neuroendocrine-immune relationship.

Stress and Humoral Innate Immune Response of Gilthead Seabream Sparus aurata Cultured in Sea Cages

Innate and acquired immune responses of Gilthead Seabream Sparus aurata was studied under normal culture and short-term stressful conditions for 18 months in offshore sea cages in Alghero Bay, Italy. Every 45 d, 50 fish were sampled and divided into two groups: fish in the first group (normal culture conditions) were bled after harvesting; fish in the second group were put into a tank under stressful conditions (crowding and confinement) and bled after 2 h. Innate humoral immunity, such as complement-like, hemagglutination, and lysozyme activities, was determined in the sera of both groups. Pathogen challenge was not performed, but the specific humoral immune response was assessed against the most common pathogens affecting cultured fish in Sardinia. Stressed fish, compared with the control, showed a lower lysozyme activity against Vibrio (Listonella) anguillarum, which was not clearly correlated with temperatures. Complement-like activity differed between the first and second half of the study and, at the end of the trial, a slightly higher activity was recorded in the controls than in the stressed fish. Hemagglutination activity was mainly higher in the stressed fish than in control fish. Confinement, crowding, and cold water temperature caused decreased lysozyme activity in short-term stressed Gilthead Seabream compared with those reared normally. The specific humoral immune response, against V. anguillarum, Tenacibaculum mesophilum, Enterococcus Seriolicida, and Aeromonas sobria, fluctuated during the rearing period, particularly during the first year of culture. Received October 12, 2015; accepted March 24, 2016.

The effect of hyperthermia on liver histology, oxidative stress and disease resistance of the Wuchang bream, Megalobrama amblycephala

This study aimed to investigate the effects of hyperthermia on serum hormones, hepatic oxidization indices, hepatic heat shock protein (HSP60, 70, and 90) mRNA expression levels and liver cell ultrastructure in Megalobrama amblycephala before and after high temperature stress. Fish were exposed to the optimal temperature (25 ± 1 °C) or high temperature (32 ± 1 °C) and then challenged with Aeromonas hydrophila. The results showed that hyperthermic stress significantly increased serum adrenocorticotropic hormone (ACTH) at 0.5 and 2 d, serum cortisol (COR) at 0.5, 14, and 21 d and serum 3,5,3'-triiodothyronine (T3) at 1, 14, and 21 d after stress. Additionally, hyperthermia led to oxidative stress, as evidenced by a significant decrease in the hepatic anti-superoxide anion free radical concentration (ASAFER) at 1, 2, 7, and 21 d and in hepatic superoxide dismutase (SOD) activity at 1, 2, 14 and 21 d after stress; however, hepatic malondialdehyde content (MDA) increased at 1, 2, and 7 d after stress. Moreover, the expression of HSP60 at 1 d, HSP70 at 1 and 2 d, and HSP90 at 0.25, 0.5, 1 and 2 d after stress was higher in the stress group compared with the control group. The histological results clearly showed that hyperthermia resulted in fat and glycogen accumulation and structural alterations of the hepatocytes, mitochondria, and nuclei. The cumulative mortality increased in the high temperature stress group at 1 d after acute stress and at 2 and 7 d after chronic stress compared with the control group. Overall, 1 d or 2 d after hyperthermia stress damaged the hepatic ultrastructure and impaired mitochondrial bioenergetics. Dysfunction of the mitochondria subsequently mediated oxidative stress and improved HSP expression modulated the cellular anti-stress response, which in turn led to reduced efficacy of the immune system and increased mortality from Aeromonas hydrophila infection in Megalobrama amblycephala.

Vaccination of Silver Sea Bream (Sparus sarba) against Vibrio alginolyticus: Protective Evaluation of Different Vaccinating Modalities

In order to develop more effective immunological strategies to prevent vibriosis of farmed marine fish in Hong Kong and southern China, various vaccine preparations including formalin-, phenol-, chloroform- and heat-killed whole cell bacterins and subcellular lipopolysaccharides (LPS), as well as different administration routes, were investigated. Fish immunized with the subcellular LPS exhibited the best protection [Relative Percent of Survival (RPS) = 100], while fish immunized with whole cell bacterins displayed varying degrees of protection (RPS ranged from 28 to 80), in descending order: formalin-killed > phenol-killed > heat-killed > chloroform-killed bacterins. Regarding various administration routes, fish immunized with two intraperitoneal (i.p.) injections exhibited the best protection, and the RPS values were 100 or 85 upon higher or lower doses of pathogenic V. alginolyticus challenges. Both oral vaccination and a combination of injection/immersion trial were also effective, which achieved relatively high protection (the RPS values ranged from 45 to 64.3). However, two hyperosmotic immersions could not confer satisfactory protection, especially when fish were exposed to the severe pathogenic bacteria challenge. Marked elevations of serum agglutinating antibody titer were detected in all immunized fish. Macrophage phagocytosis was enhanced significantly, especially in the fish immunized by formalin- and phenol-killed bacterins through various administration routes. Both adaptive (specific antibody) and innate (phagocytic activity) immunity elicited by different immunization strategies were in parallel with the degree of protection offered by each of them. Although all vaccination trials had no significant effect on the serum hematocrit and hemoglobin levels, the circulating lymphocyte counts were significantly elevated in the fish immunized with LPS, formalin- and phenol-killed bacterins. Serum cortisol levels appeared to be reduced in all immunized fish except the trial of hyperosmotic immersion, which indicated the stressful impact on vaccinated fish.

Nodavirus Colonizes and Replicates in the Testis of Gilthead Seabream and European Sea Bass Modulating Its Immune and Reproductive Functions

Viruses are threatening pathogens for fish aquaculture. Some of them are transmitted through gonad fluids or gametes as occurs with nervous necrosis virus (NNV). In order to be transmitted through the gonad, the virus should colonize and replicate inside some cell types of this tissue and avoid the subsequent immune response locally. However, whether NNV colonizes the gonad, the cell types that are infected, and how the immune response in the gonad is regulated has never been studied. We have demonstrated for the first time the presence and localization of NNV into the testis after an experimental infection in the European sea bass (Dicentrarchus labrax), and in the gilthead seabream (Sparus aurata), a very susceptible and an asymptomatic host fish species, respectively. Thus, we localized in the testis viral RNA in both species using in situ PCR and viral proteins in gilthead seabream by immunohistochemistry, suggesting that males might also transmit the virus. In addition, we were able to isolate infective particles from the testis of both species demonstrating that NNV colonizes and replicates into the testis of both species. Blood contamination of the tissues sampled was discarded by completely fish bleeding, furthermore the in situ PCR and immunocytochemistry techniques never showed staining in blood vessels or cells. Moreover, we also determined how the immune and reproductive functions are affected comparing the effects in the testis with those found in the brain, the main target tissue of the virus. Interestingly, NNV triggered the immune response in the European sea bass but not in the gilthead seabream testis. Regarding reproductive functions, NNV infection alters 17β-estradiol and 11-ketotestosterone production and the potential sensitivity of brain and testis to these hormones, whereas there is no disruption of testicular functions according to several reproductive parameters. Moreover, we have also studied the NNV infection of the testis in vitro to assess local responses. Our in vitro results show that the changes observed on the expression of immune and reproductive genes in the testis of both species are different to those observed upon in vivo infections in most of the cases.

Antimicrobial response is increased in the testis of European sea bass, but not in gilthead seabream, upon nodavirus infection

Antimicrobial peptides (AMPs) have a crucial role in the fish innate immune response, being considered a fundamental component of the first line of defence against pathogens. Moreover, AMPs have not been studied in the fish gonad since this is used by some pathogens as a vehicle or a reservoir to be transmitted to the progeny, as occurs with nodavirus (VNNV), which shows vertical transmission through the gonad and/or gonadal fluids, but no study has looked into the gonad of infected fish. In this framework, we have characterized the antimicrobial response triggered by VNNV in the testis of European sea bass, a very susceptible species of the virus, and in the gilthead seabream, which acts as a reservoir, both in vivo and in vitro, and compared with that present in the serum and brain (target tissue of VNNV). First, our data show a great antiviral response in the brain of gilthead seabream and in the gonad of European sea bass. In addition, for the first time, our results demonstrate that the antimicrobial activities (complement, lysozyme and bactericidal) and the expression of AMP genes such as complement factor 3 (c3), lysozyme (lyz), hepcidin (hamp), dicentracin (dic), piscidin (pis) or β-defensin (bdef) in the gonad of both species are very different, but generally activated in the European sea bass, probably related with the differences of susceptibility upon VNNV infection, and even differs to the brain response. Furthermore, the in vitro data suggest that some AMPs are locally regulated playing a local immune response in the gonad, while others are more dependent of the systemic immune system. Data are discussed in the light to ascertain their potential role in viral clearance by the gonad to avoid vertical transmission.

Effects of aluminium and bacterial lipopolysaccharide on oxidative stress and immune parameters in roach, Rutilus rutilus L

Aluminium is used in diverse anthropogenic processes at the origin of pollution events in aquatic ecosystems. In the Champagne region (France), high concentrations of aluminium (Al) are detected due to vine-growing practices. In fish, little is known about the possible immune-related effects at relevant environmental concentrations. The present study analyzes the simultaneous effects of aluminium and bacterial lipopolysaccharide (LPS), alone and in combination, on toxicological biomarkers in the freshwater fish species Rutilus rutilus. For this purpose, roach treated or not with LPS were exposed to environmental concentrations of aluminium (100 μg/L) under laboratory-controlled conditions for 2, 7, 14 and 21 days. After each exposure time, we assessed hepatic lipoperoxidation, catalase activity, glutathione reductase activity and total glutathione content. We also analyzed cellular components related to the LPS-induced inflammatory response in possible target tissues, i.e. head kidney and spleen. Our results revealed a significant prooxidant effect in the liver cells and head kidney leukocytes of roach exposed to 100 μg of Al/L for 2 days. In liver, we observed more lipoperoxidation products and lower endogenous antioxidant activity levels such as glutathione reductase activity and total glutathione content. These prooxidant effects were associated with a higher oxidative burst in head kidney leukocytes, and they were all the more important in fish stimulated by LPS injection. These findings demonstrate that environmental concentrations of Al induce oxidative and immunotoxic effects in fish and are associated to an immunomodulatory process related to the inflammatory response.

Nitrite-induced alterations in sex steroids and thyroid hormones of Labeo rohita juveniles: effects of dietary vitamin E and L-tryptophan

An experiment was conducted to study the effect of sub-lethal nitrite exposure on sex steroids (testosterone and estradiol), cortisol and thyroid hormones (T3 and T4) of Labeo rohita juveniles. Fishes previously fed with normal or elevated levels of vitamin E (VE) and tryptophan for 60 days were exposed to sub-lethal nitrite for another 45 days with same feeding regime. There were nine treatment groups, viz. VE0TRP0-N, VE0TRP0+N, VE100TRP0-N, VE100TRP0+N, VE100TRP0.75+N, VE100TRP1.5+N, VE150TRP0+N, VE300TRP0+N and VE200TRP1+N. Except the groups VE0TRP0-N and VE100TRP0-N, all other groups were exposed to nitrite. At the end of the 45 days of nitrite exposure, serum samples were assayed for sex steroids, cortisol and thyroid hormones. The serum T3 and T4 levels decreased to the extent of 84.5 and 94.06%, respectively, upon nitrite exposure. Dietary supplementation with additional amounts of VE and tryptophan appears to reduce the decline of the production of T4. The serum testosterone and estradiol decreased 97.31 and 92.86%, respectively, upon nitrite exposure. Supplementation with additional amounts of VE was found to reverse nitrite-induced inhibition of testosterone and estradiol production. Serum cortisol increased upon nitrite exposure and unexposed (VE100-N) group showed lower levels, which were comparable to groups fed with elevated levels of VE. The overall results of the present study revealed that environmental nitrites have a negative impact on steroidogenesis, which can be overcome by dietary supplementation of elevated amounts of VE (minimum of 150 mg VE Kg diet(-1)) and to a lesser extent by tryptophan (only at the level of 1.5% of the diet).

Effects of mannan oligosaccharide on the physiological responses, HSP70 gene expression and disease resistance of Allogynogenetic crucian carp (Carassius auratus gibelio) under Aeromonas hydrophila infection

We evaluated the effect of dietary supplementation with mannan oligosaccharide (MOS) on the resistance to Aeromonas hydrophi1a infection in Allogynogenetic crucian carp. The fish were randomly divided into five groups: a control group was fed with basal diet, and four treatment groups fed with basal diet supplemented with 60, 120, 240, 480 mg/kg MOS for 10 weeks, respectively. We then challenged the fish with A. hydrophi1a and recorded the mortality and the changes in serum cortisol, T3, T4, lysozyme, alkaline phosphatase (ALP), globin and hepatic total anti-oxidative capacity, superoxide dismutase (SOD), malondialdehyde (MDA) and the relative expression of heat shock protein 70 (HSP70) mRNA for a period of 7 d. Supplementation with 240 mg/kg MOS significantly increased serum ALP activity before infection, 1d and 2d after infection, serum globin concentration prior to infection, 1d and 7d after infection, serum lysozyme activity at 2d after infection, T3 concentration at 2d after infection, hepatic total anti-oxidative capacity prior to infection, hepatic SOD activity at 7d after infection and reduced serum cortisol concentration at 2d after infection, hepatic malondialdehyde content at 1d and 2d after infection. Supplementation with 480 mg/kg MOS significantly increased serum ALP activity before infection, 1d and 2d after infection, T3 content 1d after infection, T4 content prior infection and 7d after infection, serum globin concentration prior to infection, 1d and 7d after infection, serum lysozyme activity prior infection and 1d after infection, serum total anti-oxidative capacity prior to infection and 7d after infection, hepatic SOD activity at 7d after infection and the relative level of hepatic HSP70 mRNA at 2d and 7d after infection, had decreased levels of serum cortisol concentration before the infection, at 2d after infection, T4 concentration at 1d and 2d after infection, hepatic malondialdehyde content at 1d and 2d after infection. Mortality was significantly lower in the group of 240 and 480 mg/kg MOS than the control. Our results suggest that ingestion of a basal diet supplemented with 240-480 mg/kg MOS can enhance resistance against pathogenic infections in Allogynogenetic crucian carp.

Rapid decreases in salinity, but not increases, lead to immune dysregulation in Nile tilapia, Oreochromis niloticus (L.)

Rapid changes in salinity, as with other environmental stressors, can have detrimental effects on fish and may trigger increased susceptibility to disease. However, the precise mechanisms of these effects are not well understood. We examined the effects of sudden increases or decreases in salinity on teleost immune function using Nile tilapia, Oreochromis niloticus (L.), as the fish model in a battery of bioassays of increasing immune system specificity. Two different salinity experiments were performed: one of increasing salinity (0 to 5, 10 and 20 g L(-1) ) and one of decreasing salinity (20 to 15, 10 and 5 g L(-1) ). Histopathology of anterior kidney, gills, gonads, intestines and liver of exposed fish was performed, but no remarkable lesions were found that were attributable to the salinity treatment regimes. The spleen was removed from each fish for analysis of cytokine expression, and peripheral blood was used for haematology, cortisol and phagocytosis assays. In the increasing salinity experiments, no significant changes were observed in any immune system assays. However, in the decreasing salinity experiments, lymphopenia, neutrophilia and monocytosis were observed in the peripheral blood without modification of the packed cell volume, plasma protein or plasma cortisol levels. Phagocytosis was increased in response to decreases in salinity from 20 g L(-1) to 15 g L(-1) , 10 g L(-1) and 5 g L(-1) , whereas phagocytic index was not significantly altered. Transforming growth factor-β (TGF-β) transcription increased during the same decreases in salinity. However, the TGF-β value at 5 g L(-1) was less than those in the 15 and 10 g L(-1) salinity treatments. Interleukin-1β (IL-1β) transcription did not significantly respond to either salinity regime. In total, acute salinity changes appeared to trigger reactive dysregulation of the immune response in tilapia, a situation which, when combined with additional co-occurring stressors such as sudden changes in temperature and/or dissolved oxygen, could make fish more susceptible to infectious diseases. Accordingly, these findings may help to explain how sudden environmental changes may initiate disease outbreaks and lead to critical declines in cultured or wild fish populations.

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.

Direct actions of cortisol, thyroxine and growth hormone on IGF-I mRNA expression in sea bream hepatocytes

The present study aims to investigate potential regulatory effect of different growth-related hormones including growth hormone (GH), human insulin-like growth factor-I (hIGF-I), thyroxine (T(4)), triiodothyronine (T(3)) and cortisol, on insulin-like growth factor-I (IGF-I) mRNA expression of hepatocytes isolated from silver sea bream. By using real-time PCR, IGF-I mRNA expression profiles of hepatocytes in response to individual hormones were determined in vitro. Hepatocytes incubated with GH at concentrations of 10-1000 ng/mL showed significantly higher IGF-I expression, but the elevation was attenuated at high concentration of GH (1000 ng/mL). IGF-I expression remained unchanged in hepatocytes after incubation with hIGF-I. Hepatocytes incubated with T(4) at concentration of 1000 ng/mL exhibited a significant elevation in IGF-I expression, whereas no difference in IGF-I expression was demonstrated in hepatocytes after incubation with T(3). Upon incubation with cortisol (1-1000 ng/mL), IGF-I expression was significantly decreased in hepatocytes in a dose-dependent manner. Our study demonstrated that GH, T(4), and cortisol had direct modulatory effects on IGF-I expression in fish hepatocytes in vitro.

Effect of sex-steroid hormones, testosterone and estradiol, on humoral immune parameters of gilthead seabream

The role of sex-steroid hormones, testosterone (T) and 17beta-estradiol (E2), on the humoral immune parameters of the teleost gilthead seabream Sparus aurata was studied attempting to deepen on the knowledge of the immune-reproductive system interactions. Fish were injected intraperitoneally with coconut oil containing different dosages of T (0, 2, or 5 microg g(-1) body weight [bw]) or E2 (0, 1, or 2 microg g(-1) bw) and sampled 1, 3, and 7 days later. Hormonal levels and immune parameters (complement, peroxidase and antiprotease activities and IgM levels) were determined in plasma. Plasma hormone levels peaked at 1 day post-injection decreasing thereafter. Treatment with T significantly increased both complement and peroxidase activities after 3 days of injection but antiprotease activity and IgM levels remained unchanged. Treatment with E2 enhanced complement activity 1 day post-injection while decreased it after 3 and 7 days. However, peroxidase activity increased at 3 and 7 days post-injection while total IgM levels decreased. Implications of T and E2 in the immune-reproductive system interactions were discussed.

Effects of mitogenic hormones on HSP70 expression in a silver sea bream fibroblast cell line and a primary macrophage preparation

This study was performed in order to elucidate the role and importance of three mitogenic hormones [growth hormone (GH), insulin-like growth factor-I (IGF-1) and prolactin (PRL)] on heat shock protein 70 (HSP70) expression in a silver sea bream fibroblast cell line and a primary macrophage preparation. Fibroblasts and macrophages that were exposed to GH at concentrations of 1-1000ng/ml did not exhibit modulated HSP70 expression, whereas GH at an exposure concentration of 10ng/ml lowered HSP70 levels in macrophages. Upon exposure to IGF-1 it was found that HSP70 expression remained unchanged in fibroblasts but was significantly decreased in macrophages at exposure concentrations of 1-10ng/ml. Finally, and using a preparation of ovine PRL it was found that HSP70 expression decreased in fibroblasts at exposure concentrations of 1-1000ng/ml and also decreased in macrophages at exposure concentrations of 1-100ng/ml.

Cortisol can be pro- or anti-apoptotic in sea bream cells: potential role of HSP70 induction for cytoprotection

Cortisol, and heat shock protein 70 (HSP70) are known to perform key roles as part of the fish stress response. In the present study, two in vitro systems were used to investigate a possible cortisol-HSP70-apoptosis regulatory relationship. Using a developed silver sea bream fibroblast cell line (SSF), cortisol was found to induce HSP70 synthesis with a concomitant protection against camptothecin induced apoptosis. The induction of HSP70 synthesis using azetidine was also found to protect SSF against apoptosis. A primary culture of silver sea bream macrophages (SSM) displayed reduced HSP70, underwent apoptosis and displayed reduced phagocytic activity upon exposure to cortisol. The effect of cortisol on HSP70 expression in both SSF and SSM were blocked by the glucocorticoid antagonist, RU486. Treatment of SSM with azetidine protected against apoptosis and also enhanced phagocytic activity. The data from this study demonstrates for the first time that cortisol can be either anti- apoptotic or pro-apoptotic in different fish cells and such actions can be mediated via HSP70 induction or suppression respectively.

Differential status of the renin-angiotensin system of silver sea bream (Sparus sarba) in different salinities

Silver sea bream (Sparus sarba) is extremely euryhaline and can survive in a wide range of salinities (0-70 per thousand). The status of the renin-angiotensin system (RAS) in sea bream adapted to different salinities was studied. As indicated by plasma Ang II levels, a suppressed status of the RAS was found to occur under brackish water conditions; while under hypersaline conditions, an activated RAS prevailed, especially in fish adapted to double strength seawater (70 per thousand). Captopril successfully blocked the conversion of Ang I to Ang II, causing a dramatic drop in plasma Ang II levels, and such decrease was accompanied by lowered plasma cortisol levels. The pattern of changes in branchial Na-K-ATPase activity in different salinities was similar to those of plasma Ang II and cortisol, suggesting a causal regulatory role of Ang II on branchial Na-K-ATPase activity. Intraperitoneal injection of Ang II elicited a dose-dependent increase in branchial Na-K-ATPase activity in both 33- and 6 per thousand-adapted sea bream, but a relatively more intense stimulation of enzyme activity occurred in hyposmotic-adapted fish. Abrupt hyposmotic transfer rapidly lowered plasma Ang II level but elevated branchial Na-K-ATPase and transiently elevated plasma cortisol, indicating that these parameters are not solely controlled by Ang II but are also influenced by other hormonal factors that change during salinity transfer. Blood volumes of both 33- and 6 per thousand-adapted sea bream exhibited high stability during short-term salinity transfers and after long-term salinity adaptation. Captopril significantly reduced resting blood pressure in both 33- and 6 per thousand-adapted sea bream, indicating that the RAS was involved in maintenance of resting blood pressure in both hyperosmotic and hyposmotic environments. Blood pressure was highly stable during abrupt salinity transfer and captopril blockade did not alter such stability. The vasopressive effect of angiotensins was more potent in 6 per thousand-adapted sea bream. These results showed that the RAS is involved in the maintenance of fluid and pressure homeostasis in sea bream and hyposmotic-adapted sea bream has an abated RAS status.

Modulation of juvenile brook trout (Salvelinus fontinalis) cellular immune system after Aeromonas salmonicida challenge

In fish, the first line of defence against infectious microorganisms is based on non-specific cellular immune mechanisms (innate immunity). In this study, we measured the non-specific immune parameters (natural cytotoxic cells (NCC) activity, lymphoproliferation, percentage of phagocytosis and phagocytic activity) in brook trout (Salvelinus fontinalis) infected by a virulent strain of Aeromonas salmonicida. Eight days post-infection, the mortality of infected fish reached 70%. A transient immunostimulation of the NCC activity was noticed 24h post-infection, but there was no significant difference at 48 h. Then, infection of brook trout with A. salmonicida induced a biphasic immune response. At 24h post-infection, lymphoproliferation was drastically depressed but returned to control level at 96 h. A slight increase in the percentage of phagocytosis and the phagocytic activity was noticed throughout the experiment. Conversely the cell mortality was significantly higher in infected fish compared to control. The modulation of immunological parameters might reveal important clues on how innate immunity might protect fish from bacterial infections.

Molecular cloning of growth hormone from silver sea bream: effects of abiotic and biotic stress on transcriptional and translational expression

The pituitary growth hormone (GH) gene of silver sea bream (Sparus sarba) was cloned and characterized and found to be 615 base pairs encoding a protein of 204 amino acids. Using a bacterial expression system, recombinant protein was prepared and rabbit polyclonal antibody was raised. Transcript and protein amounts of GH were measured in fish that were adapted to a range of salinities, acclimated to different temperatures, or undergoing a natural time course of Vibrio alginolyticus infection. Isoosmotic salinity (12 ppt) adaptation resulted in increased GH transcript and protein in comparison to freshwater (0 ppt) and seawater (33 ppt) adapted fish. It was also found that cold temperature (12 degrees C) acclimated sea bream had higher amounts of pituitary GH transcript and protein when compared to warm temperature (25 degrees C) acclimated fish. Finally, the amounts of GH transcript and protein were found to be rapidly downregulated from an early stage of disease. The results from the present study demonstrate how GH can be modulated during both abiotic and biotic stress in fish.

Modulation of beta-actin, insulin-like growth factor 1 and glucose-6-phosphate dehydrogenase gene expression during vibriosis of sea bream, Sparus (=Rhabdosargus) sarba Forsskål

Gene expression changes, related to growth regulation, were investigated in silver sea bream, Sparus (=Rhabdosargus) sarba, subjected to vibriosis. Using reverse transcriptase polymerase chain reaction assays, transcript levels of beta-actin, insulin-like growth factor 1 (IGF-1) and glucose-6-phosphate dehydrogenase (G6PDH) were analysed. A tissue-specific response for beta-actin was found, as transcript levels in the kidney increased during early- and mid-stage vibriosis, but remained unchanged in liver tissue. The gene transcript levels of IGF-1 were found to decrease in both liver and kidney from an early stage of vibriosis. The gene transcript levels of G6PDH increased at early and mid stages of vibriosis in liver and kidney before decreasing during the late stage of vibriosis. Further studies on G6PDH demonstrated that chemical inhibition of G6PDH in silver sea bream fibroblasts resulted in increased cell death upon exposure to hydrogen peroxide. The results from the present study demonstrate the complexity of growth-related gene expression events that occur in fish tissues during disease.

Cloning and characterization of sea bream Na+-K+-ATPase alpha and beta subunit genes: in vitro effects of hormones on transcriptional and translational expression

The full length genes encoding the catalytic alpha and glycosylated beta subunits of the sodium pump (Na+-K+-ATPase) were cloned and characterized from silver sea bream gill. Using in vitro preparations of gill tissue it was found that growth hormone (10 and 100 ng/ml) caused an increase in subunit transcription, translation, and Na+-K+-ATPase enzyme activity. Similarly, insulin-like growth factor 1 (10 and 100 ng/ml) also caused an increase in Na+-K+-ATPase subunit amounts and enzyme activity. Cortisol (10 and 100 ng/ml) increased alpha subunit transcript and protein but did not modulate beta subunit expression or enzyme activity. Ovine prolactin did not cause any changes in Na+-K+-ATPase subunit transcription, translation or enzyme activity. This study is the first to describe how both Na+-K+-ATPase alpha and beta subunits are modulated at transcriptional and translational levels in fish osmoregulatory tissue upon exposure to hormones.

Cloning and characterization of the hsp70 multigene family from silver sea bream: Modulated gene expression between warm and cold temperature acclimation

The genes encoding heat shock cognate 70 (hsc70) and inducible heat shock protein 70 (hsp70) were cloned and characterized from silver sea bream liver. Upon acute heat shock (+7 degrees C), the transcript abundance of hsc70 was increased 1.7-fold whereas the transcript abundance of hsp70 increased 6.7-fold. The chronic acclimation of sea bream to cold temperature (12 degrees C) resulted in a downregulation of hsc70 and an upregulation of hsp70 in comparison to levels in sea bream kept at a warmer temperature (25 degrees C). The expression of heat shock transcription factor I was also increased during cold temperature acclimation. Increased amounts of hepatic insulin-like growth factor 1 transcript, serum thyroxine (T4), and triiodothyronine (T3) were also found during cold temperature acclimation whereas serum cortisol remained unchanged. The results from this study demonstrate how temperature acclimation, in fish, can affect the regulation of the hsp70 multigene family and hormonal factors that are associated with anabolism.

Evidence for disruption of Na(+)-K(+)-ATPase and hsp70 during vibriosis of sea bream, Sparus (=Rhabdosargus) sarba Forsskål

Osmoregulation via the sodium pump (Na(+)-K(+)-ATPase) and cytoprotection via expression of different families of heat shock protein (hsp) were studied at transcriptional/translational levels during progressive vibriosis in silver sea bream, Sparus (=Rhabdosargus) sarba Measurements of Na(+)-K(+)-ATPase activity showed that an early and drastic decline occurred in the kidney of infected fish. This reduction in Na(+)-K(+)-ATPase activity was not caused by transcriptional downregulation of genes coding for either the Na(+)-K(+)-ATPase alpha or beta subunits. Using specific antibodies, data from immunoassays showed that the decreased sodium pump activity was caused by the specific loss of the translated glycosylated Na(+)-K(+)-ATPase beta subunit. Data from immunoassays of different hsp families demonstrated that the expression of hsp90 and hsp60 remained unchanged throughout vibriosis whereas expression of the hsp70 family decreased in kidney and liver tissues. As hsp70 is a multigene family, the expression of the constitutive (hsc70) and inducible (hsp70) members of the hsp70 family were studied and it was found that hsp70 and hsc70 expression decreased from an early stage of infection in the kidney and the liver respectively. Reverse transcriptase-polymerase chain reaction analysis of the hsp70 transcription-inducing factor, hsf1, demonstrated that loss of cytoprotective function during vibriosis was mediated by a downregulation of hsf1 transcription.

Differential effects of thyroxine on metabolic enzymes and other macromolecules in a freshwater teleost

The effects of thyroxine (T(4)) on citrate synthase (CS), glucose 6-phosphate dehydrogenase (G6-PDH), lactate dehydrogenase (LDH), DNA, RNA, and protein of various tissues were studied to elucidate the hormonal control of metabolism in a freshwater catfish, Clarias batrachus. T(4) did not produce any significant effect on DNA content of the fish. The CS, RNA, and protein contents of brain, liver, and skeletal muscle of the fish exposed to thiourea for 28 days decreased approximately 50-58% as compared to their levels in control individuals. Injection of T(4) to thiourea-exposed fish produced about three-fold increases in CS, RNA, and protein. These macromolecular inductions by T(4) were blocked by actinomycin D or cycloheximide. This suggests T(4)-induced de novo synthesis of macromolecules and stimulation of aerobic capacity. However, the activities of G6-PDH and LDH of brain, liver, and skeletal muscle of the fish exposed to thiourea increased two times that of the activities in control individuals. Administration of T(4) to thiourea-exposed fish reduced LDH and G6-PDH activities by about 64-74%, which reflects T(4)-dependent inhibition in anaerobic power and selective anabolic activities of the HMP pathway. These differential effects of T(4) on some metabolic enzymes and other important macromolecules may be to meet the other T(4)-induced responses in the freshwater catfish.

Aquatic hypoxia is an disrupter and impairs fish reproduction

There is increasing concern that certain chemicals in the aquatic environment can disrupt endocrine systems, leading to reproductive impairment and threatening survival of wild populations of invertebrates, fish, bird, reptiles, and wildlife. For the first time, we report that hypoxia is also an endocrine disruptor and poses a significant threat to the reproduction and hence sustainability of fish populations. Serum levels of testosterone, estradiol, and triiodothyronine significantly decreased in carp (Cyprinus carpio) upon chronic exposure to hypoxia. These hormonal changes were associated with retarded gonadal development in both male and female carp, reduced spawning success, sperm motility, fertilization success, hatching rate, and larval survival, indicating that adverse effects of hypoxia on reproductive performance resulted from endocrine disruption. Since aquatic hypoxia commonly occurs over thousands of square kilometers in aquatic systems worldwide, our results imply that endocrine disruption and reproductive impairment in fish may be a widespread environmental problem.

Ontogeny of thyroid hormones, cortisol, hsp70 and hsp90 during silver sea bream larval development

We studied the profiles of silver sea bream (Sparus sarba) thyroxine (T(4)), triiodothyronine (T(3)), cortisol and the heat shock protein (hsp) families hsp70 and hsp90 during larval development. Eggs from sexually mature female sea bream were fertilized and larvae were collected at incremental time intervals between 1-46 days post hatch (dph). Both T(4) and T(3) were detected in 1 dph larvae and it was found that both increased as development progressed with a distinct surge in amounts between 21-35 dph, a time associated with direct development of larvae to juveniles. Cortisol increased from 1 dph reaching a maximum and constant level from 35 dph onwards. Using RT-PCR coupled with radioisotope hybridization of immobilized cDNA we assessed the transcript levels of hsp70 and it was found that transcript remained unaltered between 1-14 dph before progressively increasing. Immunoblotting was used to study the larval concentrations of hsp70 and hsp90 and it was found that hsp70 was not significantly changed between 1-14 dph whereas hsp90 increased from 1 dph onwards. These findings suggest an important role for hsp90 in the corticosteroid receptor complex during silver sea bream larval development.