The effect of cortisol administration on blood plasma immunoglobulin M (IgM) concentrations in masu salmon (Oncorhynchus masou)

Effects of Stocking Density on Stress, Hematological Responses, and Growth of Black Rockfish Sebastes schlegelii

The objective of the current study was to evaluate the effect of stocking density on juvenile Black Rockfish Sebastes schlegelii (average weight = 12 g) in terms of stress, hematological responses, and growth performance during a 4-month growth trial in a flow-through system. The initial stocking densities were 1.3 kg/m³ (low), 1.8 kg/m³ (medium), and 2.3 kg/m³ (high), and the final densities were 4.9 kg/m³ (low), 5.6 kg/m³ (medium), and 6.3 kg/m³ (high). At the end of the trial, the high stocking density significantly affected growth characteristics, levels of growth hormone and insulin-like growth factor 1, and hematological indices (hematocrit, red blood cell count, and hemoglobin level) compared to the medium and low stocking densities. The plasma cortisol and immunoglobulin-M levels were significantly higher at the high density than at the other two densities. Taken together, while the low and medium stocking densities (final densities of up to 5.6 kg/m³ ) did not affect stress and hematological indices or growth, the high stocking density (final density of 6.3 kg/m³ ) significantly impacted those variables, which suggests an allostatic load at that density. Thus, the use of a final stocking density less than 6.3 kg/m³ should be considered to avoid compromising the stress and health condition and growth of Black Rockfish at this size and temperature range.

Effect of Feed Containing Hermetia illucens Larvae Immunized by Lactobacillus plantarum Injection on the Growth and Immunity of Rainbow Trout (Oncorhynchus mykiss)

Simple Summary

In this study, we evaluated the effect on the growth and immunity of rainbow trout of a feed formulated using Hermetia illucens with increased antimicrobial peptides expression by Lactobacillus plantarum infection (ImHIL). As a result, growth and immunological indicators improved, and therefore, ImHIL is expected to become a good feed source for rainbow trout aquaculture.

Abstract

We investigated the effects of a feed containing Hermetia illucens larvae injected with bacteria on the growth and immunity of Oncorhynchus mykiss. The feed was prepared by replacing fishmeal in feed with 25 and 50% nonimmunized (HIL25, HIL50) or immunized HIL (ImHIL25, ImHIL50), and its protein:fat:carbohydrate ratio was 45:15:18. ImHIL extracts showed inhibitory activity against fish pathogenic bacteria. Both red blood cell count and insulin-like growth factor-1 as the growth indicator were the highest among the groups at week 6 after feeding in the ImHIL50 group. As immune indicators, blood aspartate aminotransferase levels were lower in the ImHIL25 and ImHIL50 groups than in that of other groups at week 6 after feeding, and lysozyme content was significantly higher in ImHIL25 and ImHIL50. The above results demonstrate that ImHIL has a beneficial effect on the improvement of growth and immunity. Accordingly, we suggest that ImHIL has the potential to be a good feed source in aquaculture.

Production and characterization of a mouse monoclonal antibody against smallmouth bass (Micropterus dolomieu) IgM

A murine monoclonal antibody (mAb, IgG2a) was produced for the detection of smallmouth bass (Micropterus dolomieu) immunoglobulin (IgM). The antibody is specific for IgM heavy chain and was shown to also recognize the Ig heavy chain of largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus) using Western Blot analysis of plasma from 9 teleost taxa. When applied to the analysis of smallmouth bass total plasma IgM using ELISA, the mAb was found to be effective when used in an inhibition kinetic assay.

Optimal α-lipoic acid strengthen immunity of young grass carp (Ctenopharyngodon idella) by enhancing immune function of head kidney, spleen and skin

This study was for the first time to investigate the effects of α-lipoic acid (LA) on growth and immune function of head kidney, spleen and skin in young grass carp (Ctenopharyngodon idella). A total of 540 healthy grass carp (with initial body weight at 216.59 ± 0.33 g) were randomly divided into six groups and fed six separate diets with graded dietary levels of LA for 70 days. Un-supplemented group did not find LA and its concentrations in the other five diets were 203.25, 403.82, 591.42, 781.25 and 953.18 mg kg^-1, respectively. After the growth trial, fish were challenged with A. hydrophila for 14 days. The results showed that, compared with the un-supplemented group, optimal LA improved lysozyme (LZ) and acid phosphatase (ACP) activities, enhanced complement 3 (C3), C4 and immunoglobulin (Ig) M contents and up-regulated hepcidin, liver expressed antimicrobial peptide (LEAP)-2A, LEAP-2B and β-defensin-1 mRNA levels in the head kidney, spleen and skin of young grass carp; meanwhile, optimal LA up-regulated anti-inflammatory cytokines transforming growth factor (TGF)-β1, TGF-β2, interleukin (IL)-4/13A (not IL-4/13B), IL-10 and IL-11 mRNA levels partly related to target of rapamycin (TOR) signaling and down-regulated pro-inflammatory cytokines tumor necrosis factor (TNF)-α, interferon (IFN)-γ2, IL-1β, IL-6, IL-8, IL-12p40 (not IL-12p35), IL-15 (not in the skin) and IL-17D mRNA levels partially associated with nuclear factor-kappa B (NF-κB) signaling in the head kidney, spleen and skin of young grass carp. Above results indicated that optimal LA enhanced the immune function of head kidney, spleen and skin in fish. Interestingly, excessive LA decreased the growth and impaired the immune function of head kidney, spleen and skin in fish. Finally, on the basis of the percent weight gain (PWG), the ability against skin hemorrhage and lesion, the IgM content in the head kidney and the LZ activity in the spleen, the optimal dietary LA levels were estimated to be 315.37, 382.33, 353.19 and 318.26 mg kg^-1 diet, respectively.

Using cell apoptosis, micronuclei and immune alternations as biomarkers of phenanthrene exposure in yellowfin seabream (Acanthopagrus latus)

In the present study, the apoptosis and tissue changes in the spleen, as well as humoral immune-related parameters, micronuclei (MN) induction in blood cells and Ethoxyresorufin-O-deethylase (EROD) activity were investigated in yellowfin seabream (Acanthopagrus latus) after short-term exposure to phenanthrene (Phe). The fish were intraperitoneally injected with different concentrations (2, 20 and 40 mg kg^-1) of Phe and tissue and blood samples were collected 1, 4, 7 and 14 days after injection. The concentrations of Phe in the fish liver increased 4 days after the experiment. EROD activity showed a pattern consistent with Phe concentration in the liver. Apoptotic index in the spleen increased dose dependently in Phe-exposed fish. Exposure to Phe caused significant decrease in the plasma level of immunoglobulin M, phagocytic and respiratory burst activity after 4 days of exposure. The frequency of MN in the erythrocytes of the treated fish was significantly higher than control. The main pathological alterations in the spleen included the increase in melanomacrophage centers (MMCs), destroyed red blood cell and hemorrhage. The degree of tissue changes in the spleen of the exposed fish ranged from slight to moderate damage. The size and number of MMCs in the spleen were significantly higher in Phe-treated fish compared to the control. Our results showed that Phe could suppress immune responses in fish, induce cell apoptosis, histological changes in the spleen and MN formation. This may suggest those parameters consider as useful biomarkers for monitoring of the health status of fish during exposure to Phe.

Increased stocking density causes changes in expression of selected stress- and immune-related genes, humoral innate immune parameters and stress responses of rainbow trout (Oncorhynchus mykiss)

The present study investigated the effects of various stocking densities on the health status (stress and immune responses) of rainbow trout (Onchorhynchus mykiss). Juvenile rainbow trout were acclimated, placed in circular tanks under stocking densities of 10, 40 and 80 kg m(-3) and reared for 30 days. The relative expression of genes involved in stress and immunity such as HSP70, LyzII, TNF-1α, IL-1β, IL-8 and IFN-γ1 in the head kidney was determined. Serum cortisol, ACTH, total antioxidant capacity, osmolality and lactate were measured after 30 days of culture at different stocking densities (D1:10 kg m(-3), D2: 40 kg m(-3) and D3: 80 kg m(-3)) as indices of stress responses. In addition, the effects of stocking densities on serum complement, bactericidal activity, agglutinating antibody titers, serum IgM, anti-protease activity, serum total protein and alkaline phosphatase of the fish were measured. HSP70 gene expression was significantly density-dependent upregulated in D2 and D3 densities compared to D1 (P < 0.05). Also, there was significant downregulation in expression of LyzII, TNF-1α, IL-1β, IL-8 and IFN-γ1 in fish reared at density of either D2 or D3 (P < 0.05). In terms of stress responses, serum ACTH, cortisol and lactate level showed significant density-dependent increase (P < 0.05) while serum osmolality and total antioxidant capacity showed significant decline (P < 0.05) in fish reared at higher densities (D2 and D3) compared to fish reared at lower density (D1) (P < 0.05). Concordant with the expression of the immune-related genes, the serum complement and bactericidal activity as well as specific antibody titer against Aeromonas hydrophila, IgM and anti-protease activity decreased along with elevation of stocking density from D1 to D3 (P < 0.05). However, different stocking densities had no significant effect on serum total protein level and alkaline phosphatase activity. These results suggested that elevation of stocking densities and crowding resulted in the increase in HSP70 gene expression and the levels of selected stress responses in the serum. However, there was down-regulation of immune genes expression and decreased innate immune responses in the fish. The mRNA expression of the genes and immune parameters that were measured in this study could be helpful in monitoring the health status and welfare of the fish in aquaculture systems particularly in relation to increased stocking densities.

Combined effects of high stocking density and Piscirickettsia salmonis treatment on the immune system, metabolism and osmoregulatory responses of the Sub-Antarctic Notothenioid fish Eleginops maclovinus

The aim of this study was to evaluate immunological, metabolic and osmoregulatory secondary stress responses in Eleginops maclovinus specimens submitted to three different stocking densities: i) low (3.1 kg m(-3)), medium (15 kg m(-3)) and high (60 kg m(-3)) during 10 days, alone or in combination with a previous treatment of a protein extract of the pathogen Piscirickettsia salmonis (0.5 μg g weight body(-1)). Plasma, liver, gill and kidney samples were obtained at the end of both experiments. Plasma cortisol and amino acid levels increased, while plasma glucose, triglyceride and lactate levels decreased at higher stocking densities. However, no effects were observed on serum Immunoglobulin type M (IgM anti P. salmonis level) values. Gill Na(+), K(+)-ATPase activity enhanced under these experimental conditions, suggesting an osmotic imbalance. Energy metabolism changes, assessed by metabolite concentrations and enzyme activities, indicated a reallocation of energetic substrates at higher stocking densities. Specimens inoculated with a protein extract of P. salmonis and maintained at different stocking densities showed primary stress response, as all groups enhanced plasma cortisol concentrations. Serum IgM levels increased after treatment with P. salmonis extract but a negative influence of high stocking density on IgM production was observed when immune system was activated. Furthermore, treatment with P. salmonis protein extract evoked deep changes in the metabolite stores in all tissues tested, indicating a mobilization of energy substrates in response to infection. The results show that stocking density induced immunological, metabolic and osmoregulatory secondary stress responses in E. maclovinus specimens and that previous treatment with P. salmonis compromise these changes.

Effects of cortisol on the intestinal mucosal immune response during cohabitant challenge with IPNV in Atlantic salmon (Salmo salar)

Infectious pancreatic necrosis virus (IPNV) causes high incidence of disease in salmonids during the first period after SW transfer. During this period as well as during periods of stress, cortisol levels increase and indications of a relationship between IPNV susceptibility and cortisol have been suggested. The intestine is an entry route and a target tissue for IPNV displaying severe enteritis and sloughing of the mucosa in infected fish. The mechanisms behind effects of the virus on the intestinal tissue and the impact of cortisol on the effect remain unclear. In the present study, Atlantic salmon post smolts treated with or without slow release cortisol implants were subjected to a cohabitant IPNV challenge. Analysis of genes and proteins related to the innate and acquired immune responses against virus was performed 6 days post-challenge using qPCR and immunohistochemistry. An increased mRNA expression of anti-viral cytokine interferon type I was observed in the proximal intestine and head kidney as a response to the viral challenge and this effect was suppressed by cortisol. No effect was seen in the distal intestine. T-cell marker CD3 as well as MHC-I in both intestinal regions and in the head kidney was down regulated at the mRNA level. Number of CD8α lymphocytes decreased in the proximal intestine in response to cortisol. On the other hand, mRNA expression of Mx and IL-1β increased in the proximal intestine and head kidney in IPNV challenged fish in the presence of cortisol suggesting that the immune activation shifts in timing and response pathway during simulated stress. The present study clearly demonstrates that IPNV infection results in a differentiated epithelial immune response in the different intestinal regions of the Atlantic salmon. It also reveals that the epithelial immune response differs from the systemic, but that both are modulated by the stress hormone cortisol.

Development and validation of a sensitive enzyme immunoassay (EIA) for blood plasma cortisol in female cattle, buffaloes, and goats

A highly sensitive enzyme immunoassay (EIA) that used the second antibody coating technique and the cortisol-horseradish peroxidase conjugate as a label for determination of free and total cortisol in blood plasma of dairy animals (cows, buffaloes, and goats) was developed. For biological validation of the EIA, blood samples were collected from the animals at 48 and 24 h before and 0, 12, 24, 36, 48, 60, 72, 84, 96, 108, 120, and 132 h after dexamethasone administration. The EIA was performed directly with 20 μL of fresh plasma (for free cortisol) and also with 20 μL of heat-treated plasma (for total cortisol) after 1:5 dilutions with PBS. Cortisol standards ranging from 0.39 to 200 pg/well/20 μL were used, and the sensitivity of the EIA procedure was found to be 0.39 pg/well/20 μL, which corresponded to 0.02 ng/mL. In comparison with RIA the EIA was at least 4 times more sensitive and required 5 times less cortisol antiserum. In female cattle, buffaloes, and goats, the total, free, and bound plasma cortisol before dexamethasone administration was significantly (P < 0.05) higher than the total, free, and bound cortisol after dexamethasone administration. It can be concluded from these studies that the direct, sensitive EIA validated for estimating the free and total cortisol concentrations was sufficiently reliable and quick for studying the dynamics of cortisol distribution in blood plasma of dairy animals.

Immune protection of Mozambique tilapia (Oreochromis mossambicus) exposed to different infectious doses of ectoparasite (Cryptocaryon irritans)

The objectives of the present study were to standardize a reproducible infection procedure with Cryptocaryon irritans and to examine the effects of infectious dose level on the immune protection in Mozambique tilapia (Oreochromis mossambicus). This study demonstrated that direct enumeration of trophonts on the pectoral fin was useful to quantitatively assess immune protection against C. irritans. The number of trophonts on a pectoral fin was positively correlated with infectious dose of live theronts. Fish immunized by direct exposure under controlled laboratory conditions allowed for in depth examination of the effects of the degree of infectious dose on immune response. There was no significant positive correlation between the initial infectious dose and degree of immune responses. Mozambique tilapia initiated a strong immune protection by direct exposure with even a small number of parasites (e.g. 300 theronts per fish). Moreover, as the result of the protein analysis, we identified 28 kD proteins that could be responsible for the immobilizing antigen.

Role of maternally derived immunity in fish

Maternal immunity is of paramount importance for protection of young ones at early stage of life since the immune factors of an immunocompetent female are transferred transplacentally or through colostrum, milk or yolk to an immunologically naive neonate. Both innate and adaptive type of immunity are transferred of from mother to offspring in fishes. These factors include immunoglobulin (Ig)/antibody, complement factors, lysozymes, protease inhibitors like alpha macroglobulin, different types of lectins and serine proteases like molecules. Among different types of Ig viz. IgM, IgD, IgT/IgZ and IgM-IgZ chimera types, IgM is present in most of the teleostean fishes. In teleosts, IgM either as a reduced/breakdown product or monomeric form is usually transferred to the offsprings. The maternally derived IgM usually persists for a limited duration, exhausts within the completion of yolk absorption process, and completely disappears thereafter during larval stages. Maternal transfer of immunity which provides defense to embryo and larvae depends upon the health as well as the immune status of brood fish. The overall health status of brood fish can affect breeding performances, quality seed production and protection of offsprings. However, factors such as age, maturation, reproductive behaviour and nutrition (micro and macro-nutrients) may affect the immunity in brood fishes. Besides these, seasonal changes such as photoperiods, temperature, adverse environmental conditions, and stress conditions like handling, crowding, and water pollution/contamination can also affect the immunity of brood fishes. The maintenance of the brood stock immunity at high level during vitellogenesis and oogenesis, is utmost important for reducing mortalities at larval/post larval stages through maximum/optimum transfer of maternal immunity. Brood stock immunization prior to breeding as well as selective breeding among the disease resistant families might be the ideal criteria for producing quality seed.

Application of sensitive enzymeimmunoassay for determination of cortisol in blood plasma of yaks (Poephagus grunniens L.)

As an alternative to radioimmunoassays, a simple, highly sensitive and quick enzymeimmunoassay (EIA) for determination of cortisol in blood plasma of yaks on microtiterplates using second antibody coating technique and cortisol-horseradish peroxidase as a label has been developed. The wells of the microtiterplate were coated with affinity-purified goat IgG (antirabbit IgG) that binds the hormone specific antibody. The EIA was carried out directly in 20 microl of heat treated plasma after 1:5 dilution with PBS. The cortisol standard curve, with doses ranged from 0.4 to 100 pg/well. The sensitivity of the assay was 20 pg/ml. Cortisol standard curve in buffer showed parallelism with serially diluted yak plasma containing high endogenous cortisol. Intra- and inter-assay coefficients of variation (CV) determined using pooled plasma was found 6.58 and 11.35%, respectively. Recovery of known concentrations of added cortisol in charcoal stripped plasma was linear (r = 0.98). For biological validation of cortisol enzymeimmunoassay, the blood samples were collected from yak cows at -48 and -24h before and 0, 12, 24, 36, 48, 60, 72, 84 and 96 h after dexamethasone administration. The plasma cortisol before dexamethasone administration was significantly (P < 0.05) higher than after dexamethasone administration. The developed EIA was further validated biologically by estimating cortisol in peri-parturient cows beginning day 10 prior to calving till day 10 post-calving; the concentrations were along with the expected lines as reported in bovine. In conclusion, the EIA developed in this study is simple, highly sensitive, valid and sufficiently reliable method for estimation of cortisol directly in bovine plasma.

Antibody repertoire development in teleosts--a review with emphasis on salmonids and Gadus morhua L

The group of teleosts is highly diverse, comprising more than 23000 extant species. Studies of the teleost antibody repertoire have been conducted in many different species within different orders, though some species and families have been better characterised than others. The Atlantic cod (Gadus morhua L.) and several species within the Salmoninae (e.g. Salmo salar and Oncorynchus mykiss) are among the best-studied teleosts in terms of the antibody repertoire. The estimated size of the repertoire, the organisation of immunoglobulin (IG) gene segments, the expressed IG repertoire, the IgM serum concentration, and the serum antibody responses reveal some fundamental differences between these species. The serum IgM concentration of G. morhua is some ten times higher than that of S. salar, though G. morhua is characterised as a 'low' (or 'non') responder in terms of specific antibody production. In contrast, an antibody response is readily induced in S. salar, although the response is strongly regulated by antigen induced suppression. The IGHD gene of G. morhua has a unique structure, while the IGHM and IGHD genes of S. salar have a characteristic genomic organisation in two parallel loci. In addition, salmonids, express a broad repertoire of IGH and IGI V-region gene segments, while a single V gene family dominates the expressed heavy and light chain repertoire of G. morhua. Little is known about the developing antibody repertoire during ontogeny, in different stages of B-cell maturation, or in separate B-cell subsets. Information on the establishment of the preimmune repertoire, and the possible role of environmental antigens is also sparse.

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.

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

The effects of high doses of cortisol, biologically the most active corticosteroid in the circulating blood of teleost fish, on gilthead seabream (Sparus aurata L.) leucocytes were determined. Leucocytes isolated from the head-kidney (the principal haemopoietic organ of this fish species) were incubated with five different concentrations (ranging from 0 to 10(-1) mM) of cortisol for 30, 120, 240, 360, and 480 min and their effects on leucocyte viability and some of the main innate cellular immune responses were evaluated. The viability and the cytotoxic activity of leucocytes against tumor cells were not significantly affected by in vitro incubation with cortisol, at any of the assayed concentration or incubation times. With cortisol concentrations of 10(-9), 10(-7) or 10(-5) mM, the respiratory burst activity of head-kidney leucocytes were significantly depressed after 30 min of incubation. On the other hand, with cortisol concentrations of 10(-1) mM, the phagocytosis of yeast cells and the total peroxidase content of leucocytes were significantly depressed at incubation times longer than 240 min. To corroborate that the observed effects were due to the cortisol treatment, assays were developed using both cortisol and cycloheximide, which blocked the inhibitory effects of cortisol. The present results demonstrate that cortisol plays an important role in the down-regulation of phagocytic but not of cytotoxic activity in seabream leucocytes.

Interaction between endocrine and immune systems in fish

Diseases in fish are serious problems for the development of aquaculture. The outbreak of fish disease is largely dependent on environmental and endogenous factors resulting in opportunistic infection. Recent studies, particularly on stress response, have revealed that bidirectional communication between the endocrine and immune systems via hormones and cytokines exists at the level of teleost fish. Recently information on such messengers and receptors has accumulated in fish research particularly at the molecular level. Furthermore, it has become apparent in fish that cells of the immune system produce or express hormones and their receptors and vice versa to exchange information between the two systems. This review summarizes and updates the knowledge on endocrine-immune interactions in fish with special emphasis on the roles of such mediators or receptors for their interactions.

Cold-stress induced the modulation of catecholamines, cortisol, immunoglobulin M, and leukocyte phagocytosis in tilapia

The concentrations of norepinephrine in hypothalamus and norepinephrine and epinephrine in head kidney were significantly decreased in treated tilapia (Oreochromis aureus) during the time course of cold exposure (12 degrees) as compared to the control (25 degrees). The elevation of norepinephrine and epinephrine in plasma was detected earlier than that of cortisol in cold-treated tilapia. Phagocytic activity of leukocytes and the levels of plasma immunoglobulin M (IgM) were depressed in cold-treated tilapia as compared to the control group. Handling stress in the control (25 degrees) also resulted in increased plasma cortisol and decreased plasma IgM levels but not phagocytic activity. In vitro cortisol suppressed leukocyte phagocytosis in a dose (10(-12) to 10(-4) M)-dependent manner. Adrenergic agonist (phenylephrine and isoproterenol) had a significant suppression of phagocytosis only at the highest dose (10(-4) M). No effect on phagocytosis was detected in the treatment with norepinephrine and epinephrine. A combination of cortisol and isoproterenol (0.1 mM) had an additive effect in the suppression of phagocytosis. It is concluded that the cold stress modulated the changes of catecholamines and cortisol and further depressed phagocytic activity and antibody levels in tilapia. Cortisol could play a main and important role in the down-regulation of phagocytic activity. Adrenergic agonists also could interact with cortisol to further suppress immunity in tilapia.

Modulation of the fish immune system by hormones

Immune-neuroendocrine interactions in fish, as in mammals, have become a focus of considerable interest, with the modulation of immune responses by hormones receiving particular attention. Cortisol, growth hormone (GH), prolactin (PRL), reproductive hormones, melanin-concentrating hormone (MCH) and proopiomelanocortin (POMC)-derived peptides have all been shown to influence immune functions in a number of fish species. This review summarises the known effects of these hormones on the fish immune system, as well as the often complex interactions between different hormones. The possible implications for fish health, with respect to aquaculture and the changes in immunocompetence that take place during different stages in the fish life cycle are also discussed.

Pituitary proopiomelanocortin-derived peptides and hypothalamus-pituitary-interrenal axis activity in gilthead sea bream (Sparus aurata) during prolonged crowding stress: differential regulation of adrenocorticotropin hormone and alpha-melanocyte-stimulating hormone release by corticotropin-releasing hormone and thyrotropin-releasing hormone

Plasma levels of cortisol, growth hormone (GH), adrenocorticotropin hormone (ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH), N-acetyl-beta-endorphin, in vitro ACTH-stimulated cortisol secretion, and in vitro corticotropin-releasing hormone (CRH)- and thyrotropin-releasing hormone (TRH)-stimulated ACTH and alpha-MSH secretion were investigated in gilthead sea bream exposed to high stocking density (30 kg m(-3)) for 23 days. Within 3 days after the onset of crowding, plasma levels of cortisol, ACTH, alpha-MSH, and N-acetyl-beta-endorphin were above control values. After 7 days, plasma parameters had returned to control levels, but at 23 days, cortisol, alpha-MSH, and N-acetyl-beta-endorphin levels were again elevated over controls, indicating a long-term activation of the melanotrope cells. In contrast, crowding stress elicited a prolonged reduction in plasma GH levels concomitant with the increased hypothalamus-pituitary-interrenal axis (HPI) activation. Crowding stress enhanced cortisol secretory activity of the unstimulated interrenal cells. However, interrenal tissue from crowded fish in vitro displayed an attenuated response to ACTH stimulation compared with tissue from control fish, indicating a desensitization of these cells to ACTH during crowding. The involvement of pituitary proopiomelanocortin-derived peptides in the HPI axis of sea bream is indicated by the observed modulation of the CRH and TRH responsiveness of the corticotropes and melanotropes in crowded fish. At day 1, when there were crowding-induced plasma increases in ACTH and alpha-MSH, there was an attenuated CRH-stimulated but not TRH-stimulated, ACTH release. However, at that time, CRH- and TRH-induced responses of alpha-MSH secretion, and the unstimulated secretory activity of the MSH cells, were enhanced in crowded sea bream. These data provide evidence for stimulatory roles of multiple hypothalamic (CRH and TRH) and pituitary (ACTH and alpha-MSH) peptides in the activation of the hypothalamus-pituitary-interrenal axis under crowding conditions in sea bream.

Effects of prolactin and growth hormone on plasma immunoglobulin M levels of hypophysectomized rainbow trout, Oncorhynchus mykiss

Immunoglobulin M (IgM) is a major component of the humoral immune system of teleosts. This study examines the effects of hypophysectomy and subsequent replacement with prolactin (PRL) or growth hormone (GH) upon the plasma IgM levels of the rainbow trout (Oncorhynchus mykiss). Plasma IgM levels of the hypophysectomized fish were decreased to 30% of those in sham-operated fish 1 or 4 weeks after operation. Implantation of a cholesterol pellet containing salmon PRL or GH restored plasma IgM levels of the hypophysectomized fish, suggesting important roles for PRL and GH in the regulation of circulating IgM level in trout.