Cortisol and its effects on plasma thyroid hormone and electrolyte concentrations in fresh water and during seawater acclimation in yearling coho salmon, Oncorhynchus kisutch

Gut microbiome composition associates with corticosteroid treatment, morbidity, and senescence in Chinook salmon (Oncorhynchus tshawytscha)

Pacific salmon experience prolonged elevation in corticosteroid hormones during important life history events including migration, reproduction, and senescence. These periods of elevated corticosteroids correspond with changes to immunity and energy metabolism; therefore, fish may be particularly vulnerable to mortality at these times. Recent studies found that stress-induced cortisol release associated with microbial community shifts in salmonids, raising the question of how longer-term corticosteroid dynamics that accompany life history transitions affect salmonid microbiomes. In this work, we experimentally evaluated the relationships between gut microbiome composition, chronically elevated corticosteroids, and mortality in juvenile Chinook salmon (Oncorhynchus tshawytscha). We found that treatment with slow-release implants of the corticosteroids cortisol or dexamethasone resulted in changes to the gut microbiome. Morbidity was also associated with microbiome composition, suggesting that the gut microbiome reflects individual differences in susceptibility to opportunistic pathogens. Additionally, we analyzed a small number of samples from adult fish at various stages of senescence. Results from these samples suggest that microbiome composition associated with gut integrity, and that the microbial communities of corticosteroid treated juveniles shift in composition toward those of senescent adults. Overall, findings from this work indicate that the gut microbiome correlates with mortality risk during periods of chronic corticosteroid elevation.

Effect of low-dose Piscirickettsia salmonis infection on haematological-biochemical blood parameters in Atlantic salmon (Salmo salar)

Piscirickettsia salmonis is the etiological agent of Piscirickettsiosis, a severe disease that affects Atlantic salmon (Salmo salar) farmed in Chile and many other areas (Norway, Scotland, Ireland, Canada and the USA). This study investigated the effects of low-dose P. salmonis infection (1 × 10²  CFU/ml) on Atlantic salmon. In this study, we challenged fish with an isolated representative of the EM-90 genogroup via intraperitoneal injection for 42 days. Infected fish displayed decreased haematocrit and haemoglobin levels at day 13 post-infection, indicating erythropenia, haemolysis and haemodilution. Conversely, their white blood cell counts increased on days 13 and 21 post-infection. Additionally, their iron levels decreased from day 2 post-infection, indicating iron deficiency and an inability to retrieve stored iron before infection. Their magnesium levels also decreased at day 28 post-infection, possibly due to osmoregulatory problems. Also, we observed an increase in lactate dehydrogenase activity on days 5, 21, and 28 post-infection, suggesting early symptoms of hepatotoxicity. Later analyses determined a decrease in plasma glucose levels from day 2 post-infection. This may be attributed to the hypoxic conditions caused by P. salmonis, leading to an excess utilization of stored carbohydrates. Our results suggest that the blood parameters we studied are useful for monitoring the physiological status of Atlantic salmon infected with P. salmonis.

Transport and Barrier Functions in Rainbow Trout Trunk Skin Are Regulated by Environmental Salinity

The mechanisms underpinning ionic transport and barrier function have been relatively well characterised in amphibians and fish. In teleost fish, these processes have mostly been characterised in the gill and intestine. In contrast, these processes remain much less clear for the trunk skin of fish. In this study, we measured barrier function and active transport in the trunk skin of the rainbow trout, using the Ussing chamber technique. The effects of epithelial damage, skin region, salinity, and pharmacological inhibition were tested. Skin barrier function decreased significantly after the infliction of a superficial wound through the removal of scales. Wound healing was already underway after 3 h and, after 24 h, there was no significant difference in barrier function towards ions between the wounded and control skin. In relation to salinity, skin permeability decreased drastically following exposure to freshwater, and increased following exposure to seawater. Changes in epithelial permeability were accompanied by salinity-dependent changes in transepithelial potential and short-circuit current. The results of this study support the idea that barrier function in rainbow trout trunk skin is regulated by tight junctions that rapidly respond to changes in salinity. The changes in transepithelial permeability and short circuit current also suggest the presence of an active transport component. Immunostaining and selective inhibition suggest that one active transport component is an apical V-ATPase. However, further research is required to determine the exact role of this transporter in the context of the trunk skin.

Salinity modulates biochemical and histopathological changes caused by silver nanoparticles in juvenile Persian sturgeon (Acipenser persicus)

The objective of this study was to evaluate the effect of salinity on the acute and sub-chronic toxicity of silver nanoparticles (AgNPs) in Persian sturgeon. This was evaluated by exposing Persian sturgeon to AgNPs in three salinities: freshwater (F: 0.4 ppt), brackish water 1 (B₁: 6 ± 0.2 ppt), and brackish water 2 (B₂: 12 ± 0.3 ppt) for 14 days, which was followed by analysis of alterations in plasma chemistry and histopathology of the gills, liver, and intestine. Values of 96-h median lethal concentration (LC₅₀) were calculated as 0.89 mg/L in F, 2.07 mg/L in B₁, and 1.59 mg/L in B₂. After sub-chronic exposures, plasma cortisol, glucose, potassium, and sodium levels illustrated no significant changes within each salinity level. In F, 0.2 mg/L AgNP caused the highest levels of alkaline phosphatase and osmolality levels. In B₁, 0.6 mg/L AgNP induced the highest level of alkaline phosphatase and elevated plasma osmolality was recorded in all AgNP-exposed treatments in comparison with the controls. The B₂ treatment combined with 0.6 mg/L AgNP significantly reduced plasma chloride level. The results showed elevating salinity significantly increased osmolality, chloride, sodium, and potassium levels of plasma in the fish exposed to AgNPs. The abundance of the tissue lesions was AgNP concentration-dependent, where the highest number of damages was observed in the gills, followed by liver and intestine, respectively. The histopathological study also confirmed alterations such as degeneration of lamella, lifting of lamellar epithelium, hepatic vacuolation, pyknotic nuclei, and cellular infiltration of the lamina propria elicited by AgNPs in the gills, liver, and intestine of Persian sturgeon. In conclusion, the stability of AgNPs in aquatic environments can be regulated by changing the salinity, noting that AgNPs are more stable in low salinity waters.

The physiology of saltwater acclimation in large juvenile Atlantic salmon Salmo salar

The present study investigated the effects of transferring freshwater (FW) acclimated S. salar (678 g) that had been maintained under a constant photoperiod and thermal regime, into FW (salinity 0) and salt water (SW; salinity 35) on growth and physiological responses over a 28 day period. There were no mortalities observed throughout the study and no significant differences in mass or fork length between FW and SW groups after 28 days. Compared with fish transferred to FW, plasma osmolality and plasma chloride levels increased significantly in fish in SW by day 1. In the SW group, plasma chloride and osmolality had decreased significantly at day 14 when compared with day 1. Na⁺ -K⁺ -ATPase activity was significantly higher in SW compared with the FW group from day 7 and thereafter, but continued to increase until day 22. No differences in plasma cortisol and thyroxine were observed between FW and SW groups throughout the study. Plasma glucose significantly increased from day 1 to day 2 in SW but not in the FW group and levels were significantly reduced in SW compared with the FW group at day 28. Plasma cholesterol and triglyceride levels were significantly higher in FW at day 22 and day 14 to day 22, respectively, when compared with the SW group. In the SW group, plasma cholesterol and triglyceride levels did not change significantly throughout the study. The findings of this study suggest that large S. salar retained in FW maintain a high level of SW tolerance in the absence of photoperiod and thermal regimes necessary for smoltification, as demonstrated by 100% survival, unaffected growth performance, increased Na⁺ -K⁺ -ATPase activity and a capacity to regulate plasma chloride and osmolality for 28 days in the SW group.

Salinity effects on plasma ion levels, cortisol, and osmolality in Chinook salmon following lethal sampling

Studies on hydromineral balance in fishes frequently employ measurements of electrolytes following euthanasia. We tested the effects of fresh- or salt-water euthanasia baths of tricaine mesylate (MS-222) on plasma magnesium (Mg(2+)) and sodium (Na(+)) ions, cortisol and osmolality in fish exposed to saltwater challenges, and the ion and steroid hormone fluctuations over time following euthanasia in juvenile spring Chinook salmon (Oncorhynchus tshawytscha). Salinity of the euthanasia bath affected plasma Mg(2+) and Na(+) concentrations as well as osmolality, with higher concentrations in fish euthanized in saltwater. Time spent in the bath positively affected plasma Mg(2+) and osmolality, negatively affected cortisol, and had no effect on Na(+) concentrations. The difference of temporal trends in plasma Mg(2+) and Na(+) suggests that Mg(2+) may be more sensitive to physiological changes and responds more rapidly than Na(+). When electrolytes and cortisol are measured as endpoints after euthanasia, care needs to be taken relative to time after death and the salinity of the euthanasia bath.

The effects of venting and decompression on Yellow Tang (Zebrasoma flavescens) in the marine ornamental aquarium fish trade

Each year, over 45 countries export 30 million fish from coral reefs as part of the global marine ornamental aquarium trade. This catch volume is partly influenced by collection methods that cause mortality. Barotrauma in fish resulting from forced ascent from depth can contribute to post-collection mortality. However, implementing decompression stops during ascent can prevent barotrauma. Conversely, venting (puncturing the swim bladder to release expanded internal gas) following ascent can mitigate some signs of barotrauma like positive buoyancy. Here, we evaluate how decompression and venting affect stress and mortality in the Yellow Tang (Zebrasoma flavescens). We examined the effects of three ascent treatments, each with decompression stops of varying frequency and duration, coupled with or without venting, on sublethal effects and mortality using histology and serum cortisol measurements. In fish subjected to ascent without decompression stops or venting, a mean post-collection mortality of 6.2% occurred within 24 h of capture. Common collection methods in the fishery, ascent without decompression stops coupled with venting, or one long decompression stop coupled with venting, resulted in no mortality. Histopathologic examination of heart, liver, head kidney, and swim bladder tissues in fish 0d and 21d post-collection revealed no significant barotrauma- or venting-related lesions in any treatment group. Ascent without decompression stops resulted in significantly higher serum cortisol than ascent with many stops, while venting alone did not affect cortisol. Future work should examine links in the supply chain following collection to determine if further handling and transport stressors affect survivorship and sublethal effects.

Physiologic implications of inter-hormonal interference in fish: lessons from the interaction of adrenaline with cortisol and thyroid hormones in climbing perch (Anabas testudineus Bloch)

Adrenaline and cortisol, the major stress hormones, are known for its direct control on stress response in fish. Likewise, as an important stress modifier hormone, thyroid hormone has also been implicated in stress response of fish. We tested whether the hypothesis on the phenomenon of inter-hormonal interference, a process that explains the hormonal interactions, operates in fish particularly between adrenaline, cortisol and thyroid hormones. To achieve this goal, indices of acid-base, osmotic and metabolic regulations were quantified after adrenaline challenge in propranolol pre-treated air-breathing fish (Anabas testudineus). Short-term adrenaline (10 ng g(-1)) injection for 30 min produced a rise in plasma cortisol without affecting plasma T(3) and T(4). On the contrary, blocking of adrenaline action with a non-selective blocker, propranolol (25 ng g(-1)) for 90 min reduced plasma cortisol along with plasma T(4) and that indicate a possible interference of these hormones in the absence of adrenaline challenge. Similarly, a reduction in plasma T(3) was found after adrenaline challenge in propranolol pre-treated fish and that suggests a functional synergistic interference of adrenaline with T(3). Adrenaline challenge in these fish, however, failed to abolish this propranolol effect. The remarkable systemic hypercapnia and acidosis by propranolol pre-treatment were reversed by adrenaline challenge, pointing to a direct action of adrenaline on acid-base indices probably by a mechanism which may not require β-adrenergic receptor systems. Interestingly, the prominent adrenaline-induced hyperglycemia, hyperlactemia and hyperuremea were not altered by propranolol treatment. Similarly, adrenaline challenge promoted and propranolol reduced the osmotic competencies of the gills, kidneys and liver of this fish as evident in the sodium and proton pump activities. The modified physiologic actions of adrenaline and its modified interaction with THs and cortisol in blocked fish indicate an interaction of adrenaline with cortisol and THs. Our physiologic evidences thus support the hypothesis of the phenomenon of inter-hormonal interference.

QTL affecting stress response to crowding in a rainbow trout broodstock population

Background

Genomic analyses have the potential to impact selective breeding programs by identifying markers that serve as proxies for traits which are expensive or difficult to measure. Also, identifying genes affecting traits of interest enhances our understanding of their underlying biochemical pathways. To this end we conducted genome scans of seven rainbow trout families from a single broodstock population to identify quantitative trait loci (QTL) having an effect on stress response to crowding as measured by plasma cortisol concentration. Our goal was to estimate the number of major genes having large effects on this trait in our broodstock population through the identification of QTL.

Results

A genome scan including 380 microsatellite markers representing 29 chromosomes resulted in the de novo construction of genetic maps which were in good agreement with the NCCCWA genetic map. Unique sets of QTL were detected for two traits which were defined after observing a low correlation between repeated measurements of plasma cortisol concentration in response to stress. A highly significant QTL was detected in three independent analyses on Omy16, many additional suggestive and significant QTL were also identified. With linkage-based methods of QTL analysis such as half-sib regression interval mapping and a variance component method, we determined that the significant and suggestive QTL explain about 40-43% and 13-27% of the phenotypic trait variation, respectively.

Conclusions

The cortisol response to crowding stress is a complex trait controlled in a sub-sample of our broodstock population by multiple QTL on at least 8 chromosomes. These QTL are largely different from others previously identified for a similar trait, documenting that population specific genetic variants independently affect cortisol response in ways that may result in different impacts on growth. Also, mapping QTL for multiple traits associated with stress response detected trait specific QTL which indicate the significance of the first plasma cortisol measurement in defining the trait. Fine mapping these QTL can lead towards the identification of genes affecting stress response and may influence approaches to selection for this economically important stress response trait.

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.

Effects of Capture by Trammel Net on Colorado River Native Fishes

Trammel nets are commonly used to sample rare fishes; however, little research has assessed delayed mortality associated with this capture technique. We conducted laboratory experiments to evaluate the effects of capture by trammel net on bonytail Gila elegans, razorback sucker Xyrauchen texanus, and roundtail chub Gila robusta, at 15, 20, and 25°C. Fish (139–288 mm total length) were entangled in a trammel net for 2 h or captured by seine net and then monitored for mortality for at least 14 d. Blood samples were collected immediately after capture, and plasma cortisol levels were quantified as an index of capture-related stress. The cortisol response varied by species, but mean cortisol levels were higher for fish captured by trammel netting (295.9 ng/mL) relative to fish captured by seine netting (215.8 ng/mL). Only one fish (of 550) died during capture and handling, but 42% of the trammel-netted fish and 11% of the seine-netted fish died within 14 d after capture. In general, mortality after capture by trammel net increased with increased water temperature and at 25°C was 88% for bonytail, 94% for razorback sucker, and 25% for roundtail chub. Delayed mortality of wild-caught fish captured by trammel net has the potential to be high, at least under some circumstances. We suggest that sampling frequency, timing of sampling (relative to reproductive cycles), and water temperature all be considered carefully when using trammel nets to sample diminished populations of imperiled native fishes.

Damage in brain development by morpholino knockdown of zebrafish dax1

DAX1 is an orphan nuclear receptor and involved in development of steroidogenic organs, which activates transcription of genes involved in steroidogenesis. In this study, we analyzed the function of the zebrafish dax1 during early development of central nervous systems to appear unidentified aspects of DAX1 and decrease confusions concerned with functions of DAX1 in early development of vertebrates. By whole-mount in situ hybridization of embryo at the 32 h post fertilization (hpf), expression of zebrafish dax1 was detected around the forebrain, midbrain, hindbrain, and the extending tail tip. Embryos injected with zebrafish dax1 morpholino antisense nucleotide (MO) exhibited delayed development. When the developmental stage of wild type embryos was at Prim-15 (32 hpf), zebrafish dax1MO injected embryos were at Prim-5 (24 hpf). Concurrently with developmental delay, the MO injected embryos showed high mortality. At 48 hpf, the MO injected embryos exhibited abnormal development in the central nervous systems. The enlarged tectum and the protruded rhombomeres were observed. Moreover, development of central nervous systems, especially midbrain-hindbrain boundary, became narrower. At 5 day post fertilization, the MO injected embryos formed edemas around head, pericardial sac and abdomen. Collectively, our results indicated that the zebrafish dax1 is important for brain development.

Recovery potential of black rockfish, Sebastes melanops Girard, recompressed following barotrauma

Overfished species of rockfish, Sebastes spp., from the Northeast Pacific experience high bycatch mortality because of 'barotrauma', a condition induced from the rapid change in pressure during capture. Field experiments show that it may be possible for rockfish to recover from barotrauma if quickly recompressed; however, no work has followed the physiological recovery of rockfish after recompression or determined whether it is possible for rockfish to survive barotrauma in the long term. Barotrauma was induced in adult black rockfish, Sebastes melanops Girard, from a simulated depth of 35 m, followed by recompression. Blood and selected tissues (eye, heart ventricle, head kidney, liver, rete mirabile and gonad) were sampled at days 3, 15 and 31 post-recompression to evaluate the tissue- and physiologic-level response during recovery. No mortality from barotrauma occurred during the experiments, and feeding resumed in 80% of both treatment and control fish. The primary injury in treatment fish was the presence of a ruptured swimbladder and/or a ruptured tunica externa (outer layer of swimbladder), which was slow to heal. Blood plasma was analysed for glucose, sodium, chloride, potassium, calcium, phosphorus, insulin-like growth factor-1 and cortisol. Plasma analyses indicated no strong effects because of barotrauma, suggesting overall handling stress outweighed any effect from barotrauma. Rockfish with ruptured swimbladders may face compromised competency in the wild; however, it appears the majority of black rockfish decompressed from 35 m have a high potential for recovery if recompressed immediately after capture. This research suggests recompression could be a valuable bycatch mortality reduction tool for rockfish in recreational fisheries.

Effect of dietary vitamin E on cortisol and glucose responses to handling stress in juvenile beluga Huso huso

An 8-week feeding experiment was conducted to investigate the effect of dietary vitamin E on the physiological response to handling stress in juvenile beluga Huso huso. Fish were fed six experimental diets supplemented with 0, 25, 50,100, 200, or 400 mg Dl-all-rac-alpha-tocopherol acetate/kg diet. At the end of the experiment, the fish in each tank were subjected to acute handling and air exposure stress. Cortisol and glucose were measured as the primary hormonal and secondary metabolic responses to the stressors, both before and 3 h after application of the stressors. The growth parameters and feed utilization rates were significantly lower in fish fed the diet not supplemented with vitamin E than in fish fed diets supplemented with vitamin E. Cortisol concentration was not affected by dietary treatment but glucose concentration was. Fish fed vitamin E at 0, 25, 100, and 400 mg/kg diet had higher concentrations of glucose than those fed vitamin E at 50 and 200 mg/kg. However, fish fed diets with 50 and 200 mg/kg exhibited higher growth rates. These results indicate that dietary vitamin E has some effect on plasma glucose but no effect on plasma cortisol. In general, when the stressors were applied to belugas, the glucose and cortisol responses were relatively low. This may be due to higher resistance and lower physiological responses to these types of stressors by this species or by chondrosteans in general.

The interruption of thyroid and interrenal and the inter-hormonal interference in fish: does it promote physiologic adaptation or maladaptation?

Endocrines, the chief components of chemical centers which produce hormones in tune with intrinsic and extrinsic clues, create a chemical bridge between the organism and the environment. In fishes also hormones integrate and modulate many physiologic functions and its synthesis, release, biological actions and metabolic clearance are well regulated. Consequently, thyroid hormones (THs) and cortisol, the products of thyroid and interrenal axes, have been identified for their common integrative actions on metabolic and osmotic functions in fish. On the other hand, many anthropogenic chemical substances, popularly known as endocrine disrupting chemicals, have been shown to disrupt the hormone-receptor signaling pathways in a number fish species. These chemicals which are known for their ability to induce endocrine disruption particularly on thyroid and interrenals can cause malfunction or maladaptation of many vital processes which are involved in the development, growth and reproduction in fish. On the contrary, evidence is presented that the endocrine interrupting agents (EIAs) can cause interruption of thyroid and interrenals, resulting in physiologic compensatory mechanisms which can be adaptive, though such hormonal interactions are less recognized in fishes. The EIAs of physical, chemical and biological origins can specifically interrupt and modify the hormonal interactions between THs and cortisol, resulting in specific patterns of inter-hormonal interference. The physiologic analysis of these inter-hormonal interruptions during acclimation and post-acclimation to intrinsic or extrinsic EIAs reveals that combinations of anti-hormonal, pro-hormonal or stati-hormonal interference may help the fish to fine-tune their metabolic and osmotic performances as part of physiologic adaptation. This novel hypothesis on the phenomenon of inter-hormonal interference and its consequent physiologic interference during thyroid and interrenal interruption thus forms the basis of physiologic acclimation. This interfering action of TH and cortisol during hormonal interruption may subsequently promote ecological adaptation in fish as these physiologic processes ultimately favor them to survive in their hostile environment.

Effects of chronic manipulation of adrenocorticotropic hormone levels in Chinook salmon on expression of interrenal steroidogenic acute regulatory protein and steroidogenic enzymes

The effects of chronic exposure to adrenocorticotropic hormone (ACTH) or the synthetic glucocorticoid dexamethasone (DEX) on the expression of genes involved in cortisol synthesis were examined using quantitative RT-PCR and immunohistochemistry. Juvenile Chinook salmon were treated with either ACTH via micro-osmotic pumps or with DEX via a lipid-based sustained release vehicle. Plasma cortisol levels were significantly elevated in ACTH-treated fish after 1 day, with a significant reduction in this effect with increasing treatment duration. ACTH also appeared to cause progressive hyperplasia of interrenal cells. Steroidogenic acute regulatory protein (StAR) and cytochrome P450 side chain cleavage enzyme (P450scc) transcripts but not 3β-hydroxysteroid dehydrogenase-isomerase (3β-HSD) or cytochrome P450 11β-hydroxylase (P45011β) transcripts in head kidneys significantly increased after 5 days of ACTH treatment. Significant linear relationships between plasma cortisol levels and transcript levels were identified at day 1 and day 5 for StAR, and day 5 for P450scc. Increased immunoreactivity for P450scc was observed in interrenal cells of ACTH-treated fish after 5 and 10 days. No effect of ACTH on 3β-HSD immunoreactivity was apparent at any time point. P45011β immunoreactivity was more intense after 5 days treatment with ACTH. DEX significantly reduced resting plasma cortisol levels and induced interrenal cell atrophy. Although no significant effect of treatment with DEX was found for any transcript, immunoreactivity for P450scc and P45011β appeared to be reduced. These results indicate that StAR and P450scc are subject to transcriptional regulation by chronic changes in ACTH levels.

Plasma cortisol and hypothalamic monoamine responses in yellow perch Perca flavescens after intraperitoneal injection of lipopolysaccharide

The concentrations of monoamines in the hypothalamus were determined in yellow perch Perca flavescens before and after injection with lipopolysaccharide (LPS; 3 mg kg⁻¹ fish weight) or saline to test for the presence of neurochemical changes potentially associated with changes in plasma cortisol characteristic of intraperitoneal (ip) challenge with LPS. In the first experiment, yellow perch were injected with saline or LPS and the hypothalamus removed and plasma sampled before and at 0.5, 1.5, 3.0, and 6 h after injection. Plasma cortisol was elevated in both saline- and LPS-injected fish through 1.5 h after injection and returned to levels resembling pre-injection by 3 h after injection. Significantly higher amounts of cortisol in plasma from LPS-injected relative to saline-injected fish were observed 6 h following injection. A significant decrease relative to levels observed 0.5-3 h after handling was observed in serotonin concentrations at 6 h following LPS and saline injection with a concomitant increase in the ratio of 5-hydroxyindoleacetic acid:serotonin. In the second experiment, hypothalamic monoamines were sampled before and at 3, 6, 9, 12, and 24 h after injection with LPS or saline. Significant increases from pre-injection levels were observed in the ratio 5-hydroxyindoleacetic acid:serotonin at 9, 12, and 24 h after injection, but no differences were detected between LPS- and saline-injected fish. These results support a model linking serotonergic system activation following handling stress, but no correlations with the sustained elevations of plasma cortisol associated with inflammatory challenge were observed.

Salinity-dependent in vitro effects of homologous natriuretic peptides on the pituitary-interrenal axis in eels

We examined the effects of atrial, B-type, ventricular and C-type natriuretic peptides (ANP, BNP, VNP and CNP1, 3, 4) on cortisol secretion from interrenal tissue in vitro in both freshwater (FW) and seawater (SW)-acclimated eels. We first localized the interrenal and chromaffin cells in the eel head kidney using cell specific markers (cholesterol side-chain cleavage enzyme (P450ssc) and tyrosine hydroxylase (TH), respectively) and established the in vitro incubation system for eel interrenal tissue. Unexpectedly, none of the NPs given alone to the interrenal tissue of FW and SW eels stimulated cortisol secretion. However, ANP and VNP, but not BNP and three CNPs, enhanced the steroidogenic action of ACTH in SW interrenal preparations, while CNP1 and CNP4, but not ANP, BNP, VNP and CNP3, potentiated the ACTH action in FW preparations. These salinity dependent effects of NPs are consistent with the previous in vivo study in the eel where endogenous ACTH can act with the injected NPs. 8-Br-cGMP also enhanced the ACTH action in both FW and SW eel preparations, suggesting that the NP actions were mediated by the guanylyl cyclase-coupled NP receptors (GC-A and B) that were localized in the eel interrenal. Further, ANP and CNP1 stimulated ACTH secretion from isolated pituitary glands of SW and/or FW eels. In summary, the present study revealed complex mechanisms of NP action on corticosteroidogenesis through the pituitary-interrenal axis in eels, thereby providing a deeper insight into the role of the NP family in the acclimation of this euryhaline teleost to diverse salinity environments.

The role of thyroid hormones in stress response of fish

Thyroxine (T(4)) and triiodothyronine (T(3)), the principal thyroid hormones (THs) secreted from the hypothalamic-pituitary-thyroid (HPT) axis, produce a plethora of physiologic actions in fish. The diverse actions of THs in fishes are primarily due to the sensitivity of thyroid axis to many physical, chemical and biological factors of both intrinsic and extrinsic origins. The regulation of THs homeostasis becomes more complex due to extrathyroidal deiodination pathways by which the delivery of biologically active T(3) to target cells has been controlled. As primary stress hormones and the end products of hypothalamic-pituitary-interrenal (HPI) and brain-sympathetic-chromaffin (BSC) axes, cortisol and adrenaline exert its actions on its target tissues where it promote and integrate osmotic and metabolic competence. Despite possessing specific osmoregulatory and metabolic actions at cellular and whole-body levels, THs may fine-tune these processes in accordance with the actions of hormones like cortisol and adrenaline. Evidences are presented that THs can modify the pattern and magnitude of stress response in fishes as it modifies either its own actions or the actions of stress hormones. In addition, multiple lines of evidence indicate that hypothalamic and pituitary hormones of thyroid and interrenal axes can interact with each other which in turn may regulate THs/cortisol-mediated actions. Even though it is hard to define these interactions, the magnitude of stress response in fish has been shown to be modified by the changes in the status of THs, pointing to its functional relationship with endocrine stress axes particularly with the interrenal axis. The fine-tuned mechanism that operates in fish during stressor-challenge drives the THs to play both fundamental and modulator roles in stress response by controlling osmoregulation and metabolic regulation. A major role of THs in stress response is thus evident in fish.

Effect of dietary vitamin E on growth, muscle composition, hematological and immunological parameters of sub-yearling beluga Huso huso L

This study was designed to determine the effect of dietary vitamin E on growth, some hematological and immunological parameters and muscle proximate analysis of beluga Huso huso. Experimental fish were fed practical diets supplemented with 0, 25, 50, 100, 200 and 400 mg Dl-all-rac-α-tocopherol acetate kg diet(-1) for 8 weeks. 360 fish (mean initial weight 49.7 ± 0.1 g) were distributed into eighteen 785 L circular concrete tanks and each diet was fed to triplicate groups of fish. At the end of experiment (8 weeks), growth parameters such as final weight (FW), weight gain (WG), total length (TL), feed conversion ratio (FCR), specific growth rate (SGR), protein efficiency ratio (PER), condition factor (CF), hepatosomatic index (HSI), muscle composition, and some physiological indicators, including hematological and immunological parameters, such as hematocrit (Hct), total leukocyte count (WBC), lymphocyte, neutrophil, eosinophil and monocyte, cortisol, glucose, erythrocyte fragility, lysozyme and complement activity were determined. FW, WG, SGR, PER and CF in fish fed unsupplemented vitamin E were significantly lower than those fish fed the other five diets. However FW and PER in fish fed control diet had not significant differences with fish fed at 400 mg kg(-1). FCR were significantly higher in fish fed control diet than other groups. TL and survival rate had no significant differences among fish groups. HSI in fish fed 0 and 25 mg vitamin E kg diet(-1) were significantly lower than the other treatments. Muscle composition analysis showed no significant differences among the treatments. Erythrocyte fragility, Hct, WBC, lymphocyte, neutrophil, eosinophil and monocyte, lysozyme and complement activities were not significant. Also cortisol and glucose concentrations had not significant differences between treatments. Results indicated that vitamin E had no significantly effect on muscle proximate analysis, hematological and immunological parameters of sub-yearling beluga but has a direct effect on growth performance of beluga sturgeon and this vitamin is an essential nutrient required for normal growth in this species.

Importance of environmental endocrinology in fisheries management and aquaculture of sturgeons

Less is known about the reproductive endocrinology of sturgeons compared to modern teleosts. However, tools to assess the reproductive endocrinology and effects of environmental factors on reproduction do exist. This review utilizes case studies to describe the parameters involved in environmental endocrinology and the management and recovery efforts for the phylogenetically ancient sturgeon and paddlefish (Clade Chondrostei). Specifically, we discuss the use of environmental endocrinology to determine sex and stage of maturity and identify oviposition on spawning grounds, the importance of understanding endocrine disruption pathways, the challenges and benefits of assessing stress in wild populations of sturgeon, and three major physiological events in the reproductive development of farmed sturgeon understanding of which appears to be crucial for improving sturgeon aquaculture.

Preliminary examination of oxidative stress in juvenile spring Chinook salmon Oncorhynchus tshawytscha of wild origin sampled from transport barges

Migrating juvenile wild Chinook salmon Oncorhynchus tshawytscha, collected and loaded onto transport barges at Lower Granite Dam on the Snake River, were sampled from barges at John Day Dam, 348 km downstream, at 5 day intervals beginning in late April and ending in late May. An increase in lipid peroxidation and decrease in vitamin E in liver were observed from early to late in the barge transportation season. These changes seemed unrelated to changes in plasma cortisol or corresponding glucose levels, which declined from early to late in the season, or the concentration of n-3 highly unsaturated fatty acid (HUFA) concentrations in tissue but may be related to water temperature, which increased during the transport season, or other changes associated with the parr-smolt transformation.

Central and peripheral integration of interrenal and thyroid axes signals in common carp (Cyprinus carpio L.)

In teleostean fishes the hypothalamic-pituitary-thyroid axis (HPT axis) and the hypothalamic-pituitary-interrenal axis (HPI axis) regulate the release of thyroid hormones (THs) and cortisol respectively. Since many actions of both hormones are involved in the regulation of metabolic processes, communication between both signal pathways can be anticipated. In this study, we describe central and peripheral sites for direct interaction between mediators of both neuroendocrine axes in the common carp (Cyprinus carpio). Despite suggestions in the literature that CRH is thyrotropic in some fish; we were not able to establish stimulatory effects of CRH on the expression of the pituitary TSHbeta subunit gene. In preoptic area tissue incubated with 10(-7) M thyroxine (T(4)) a 2 x 9-fold increase in the expression of CRH-binding protein (CRHBP) was observed. Thus, T(4) could reduce the bioavailable hypothalamic crh via the up regulation of crhbp expression and hence down regulate the HPI axis. At the peripheral level, cortisol (10(-6) M), ACTH (10(-7) M), and alpha-MSH (10(-7) M) stimulate the release of T(4) from kidney and head kidney fragments, which contain all functional thyroid follicles in carp, by two- to fourfold. The substantiation of three pituitary thyrotropic factors, viz. TSH, ACTH, and alpha-MSH, in common carp, allows for an integration of central thyrotropic signals. Clearly, two sites for interaction between the HPT axis, the HPI axis, and alpha-MSH are present in common carp. These interactions may be key to the proper regulation of general metabolism in this fish.

The significance of cortisol on acclimation to salinity in pejerrey Odontesthes bonariensis

The role of cortisol on the osmoregulation of pejerrey Odontesthes bonariensis at different salinities was investigated in adult fish injected with 0.7mg hydrocortisone per 100g body weight of fish, and transferred to 0, 5 and 20ppt of NaCl. Blood cortisol was 566ng/ml at the beginning of the experiment (0h) but surged to 1250ng/ml within 3h in cortisol-injected fish. Cortisol levels were influenced not only by treatment but also by time, being higher at 3h compared to 24h. Salinity level, time of exposure and their interaction, but not cortisol treatment, significantly affected plasma osmolality and the concentration of ions Cl- and Na+. This study showed that exogenous cortisol does not seem to play a significant role on the regulation of plasma osmolality and concentration of individual ions in pejerrey.

Gene expression in the liver of rainbow trout, Oncorhynchus mykiss, during the stress response

To better appreciate the mechanisms underlying the physiology of the stress response, an oligonucleotide microarray and real-time RT-PCR (QRT-PCR) were used to study gene expression in the livers of rainbow trout (Oncorhynchus mykiss). For increased confidence in the discovery of candidate genes responding to stress, we conducted two separate experiments using fish from different year classes. In both experiments, fish exposed to a 3 h stressor were compared to control (unstressed) fish. In the second experiment some additional fish were exposed to only 0.5 h of stress and others were sampled 21 h after experiencing a 3 h stressor. This 21 h post-stress treatment was a means to study gene expression during recovery from stress. The genes we report as differentially expressed are those that responded similarly in both experiments, suggesting that they are robust indicators of stress. Those genes are a major histocompatibility complex class 1 molecule (MHC1), JunB, glucose 6-phosphatase (G6Pase), and nuclear protein 1 (Nupr1). Interestingly, Nupr1 gene expression was still elevated 21 h after stress, which indicates that recovery was incomplete at that time.

Chronic administration of fluoxetine alters locomotor behavior, but does not potentiate the locomotor stimulating effects of CRH in juvenile Chinook salmon (Oncorhynchus tshawytscha)

The present study investigated: 1) the behavioral effects of chronic administration of a serotonin uptake inhibitor (fluoxetine) in juvenile Chinook salmon, Oncorhynchus tshawytscha and, 2) whether chronic administration of fluoxetine alters the behavioral effects of corticotropin-releasing hormone (CRH). Chronic (20 day) treatment with fluoxetine decreased locomotor activity when compared to fish given long-term injections of saline. An intracerebroventricular (i.c.v.) injection of CRH had no effect on locomotor activity following a 20 day intraperitoneal treatment with either saline or fluoxetine. Chronic treatment with fluoxetine also increased the amount of time fish spent near the center of the tank. A similar increase was seen in fish given a chronic intraperitoneal (i.p.) series of saline followed by an acute i.c.v. injection of CRH. However, the effect was not additive when fish were given chronic i.p. injections of fluoxetine followed by an acute i.c.v. injection of CRH. These results provide evidence to support the hypothesis that the serotonergic system is involved in mediating locomotor activity and habitat choice in teleosts.

The influence of stress on thyroid hormone production and peripheral deiodination in the Nile tilapia (Oreochromis niloticus)

The existence of an interaction between the adrenal/interrenal axis and the thyroidal axis has since long been established in vertebrates, including fish. However, in contrast to mammals, birds and amphibians, no effort was made in fish to expand these studies beyond the level of measuring plasma thyroid hormones. We therefore set out to examine the acute effects of a single dose of dexamethasone (DEX) on plasma thyroxine (T(4)) and 3,5,3'-triiodothyronine (T(3)) levels, as well as on the activity and mRNA expression of the different iodothyronine deiodinases in liver, gills, kidney and brain in Nile tilapia. To take into account the effect of handling stress, this treatment was compared both to a non-treated and to a saline injected group. In general, the observed changes were acute (3 and 6h) while values had returned to control levels by 24h post-injection. Only DEX administration caused an acute drop in circulating T(3) levels compared to non-treated animals, while none of the treatments affected plasma T(4) levels. This indicates that the DEX induced decrease in plasma T(3) levels was not due to a lowered thyroidal hormone production and secretion. DEX injection provoked a decrease in peripheral T(3) production capacity via a decrease in hepatic outer ring deiodination activity (both D1 and D2), whereas T(3) clearance increased by induction of the inner ring deiodinating D3 pathway in liver and in gills. Deiodination activities in kidney and brain were not affected. Effects of saline injection were only observed in liver, where D1 activity decreased and D3 activity increased as in the DEX group, but to a lesser extent. Real-time PCR showed that the changes in hepatic D3 were clearly regulated at the pretranslational level, while this was not confirmed for the other changes. Our results show that both handling stress and DEX injection acutely disturb peripheral deiodination activity in Nile tilapia. However, the effects of the long acting glucocorticoid analogue are more pronounced and result in a decrease in circulating T(3) availability.

Effects of acute stress on osmoregulation, feed intake, IGF-1, and cortisol in yearling steelhead trout (Oncorhynchus mykiss) during seawater adaptation

Juvenile steelhead (Oncorhynchus mykiss) acclimated to freshwater (FW) were subjected for 3 h to confinement stress in FW, and subsequently saltwater (SW, 25 ppt) was introduced to all tanks. Fish were sampled immediately after the stress treatment, and 1, 7, and 14 days after introduction of SW. Electrolytes, cortisol, glucose, and lactate showed the typical stress response expected after stress treatment in FW. Fish regained osmotic balance within 24 h. Glucose concentrations were increasing throughout the experiment and lactate levels stayed elevated during the time spent in SW. Insulin-like growth factor-1 (IGF-1) did not show an immediate response to stress but after transfer to SW we detected significantly higher concentrations for control fish at days 1 and 14. The differences in IGF-1 levels between stressed and control fish are not reflected in SW adaptability but positive correlations between IGF-1 and electrolyte levels in control fish may indicate its role for osmoregulation. Confinement stress did not impair feed intake subsequently in SW, but our results suggest that feed intake was suppressed by the change of the media from FW to SW.

Effects of ACTH and cAMP on steroidogenic acute regulatory protein and P450 11beta-hydroxylase messenger RNAs in rainbow trout interrenal cells: relationship with in vitro cortisol production

Steroidogenic acute regulatory protein (StAR) transfers cholesterol over the inner mitochondrial membrane, thereby making the molecule available for cholesterol side-chain cleavage enzyme, which carries out the first conversion in the steroidogenic pathway. In mammals, StAR controls this rate limiting step in steroidogenesis, and both StAR protein and StAR mRNA levels become rapidly elevated in response to tropic hormone stimulation. The relationship between StAR gene expression and steroid production in fish has not yet been well explored. We investigated the relationship between adrenocorticotropic hormone (ACTH)- and cAMP-stimulated cortisol production in vitro and levels of StAR transcripts in interrenal cells of rainbow trout. To assess the effect of ACTH on mRNA levels of a downstream steroidogenic enzyme, we also investigated the effects of ACTH on transcripts encoding 11beta hydroxylase (P450 11beta). In a series of experiments, juvenile rainbow trout head kidney tissue containing interrenal cells was incubated with either ACTH or dibutyryl cyclic AMP (dbcAMP). Cortisol in incubation media were measured by radioimmunoassay and total RNA was isolated from the tissue for Northern analysis or for quantitative real-time PCR. Incubation of tissue with 150 ng/mL ACTH for 1-18 h induced a progressive increase in cortisol accumulation in media, but StAR mRNA levels increased modestly and mostly insignificantly over 18 h, irrespective of treatment. Exposure of tissue for 18 h to 5, 150, 500 or 1,500 ng ACTH/mL resulted in a strong increase in cortisol production, with a peak response (15-fold increase over controls) achieved with 150 ng/mL ACTH. Although there was a trend towards a dose-response effect, mean StAR mRNA levels were only significantly affected by the highest concentration of ACTH used (1,500 ng/mL), which induced a less than 2-fold increase in StAR transcripts. However, there was a significant linear relationship between StAR mRNA levels and ACTH-induced cortisol accumulation in media (p<0.001, r(2)=0.55). Incubation of tissue with 5mM dbcAMP for 6 or 18 h induced large increases in cortisol accumulation in media over controls, but had no significant effect on StAR mRNA levels. By contrast, ACTH induced a clear dose-dependent increase in P450 11beta transcripts, with 150 ng/mL ACTH inducing an 8-fold increase in levels compared to control; nonetheless, only a weak correlation existed between transcript levels and ACTH-induced cortisol secretion (p<0.003, r(2)=0.26). Thus, despite the relatively high degree of conservation of StAR proteins in vertebrates, we have been unable to demonstrate that a rapid, acute increase in transcription of the StAR gene is the dominant mechanism supporting flow of cholesterol to the mitochondria during acute increases in cortisol production in rainbow trout. The strong stimulation of P450 11beta gene transcription by ACTH probably enhances biosynthetic capacity during longer term chronic ACTH stimulation.

Growth hormone differentially regulates muscle myostatin1 and -2 and increases circulating cortisol in rainbow trout (Oncorhynchus mykiss)

Myostatin (MSTN) negatively regulates muscle growth in vertebrates. Salmonids produce two myostatin transcripts from separate genes. Surprisingly, quantitative analyses indicate different regulatory mechanisms for the two myostatin genes in rainbow trout. MSTN1 mRNA levels were elevated 26% following recombinant bovine growth hormone (rbGH) treatment, while MSTN2 mRNA levels were reduced 74% compared to controls. MSTN precursor protein (42kDa) levels were elevated in rbGH treated fish compared to controls. In addition, circulating cortisol levels were elevated 71% following rbGH treatment compared to controls. In treated and control fish, cortisol levels were elevated 245% at day 0 compared to subsequent days. Treated fish exhibited cortisol levels 207% higher than controls at 0.5 day, and remained at least 50% higher for 7 days following treatment. This pattern of change was positively correlated to MSTN1 mRNA levels. This is the first time a direct relationship has been reported between GH, cortisol, and myostatin. In addition, following rbGH administration, myosin protein concentrations in skeletal muscle samples increased, suggesting that GH regulates expression of the most abundant muscle protein. These results indicate the two myostatin genes are differentially regulated and may possess different functions in rainbow trout muscle, and suggests a possible interaction between GH, cortisol, and muscle growth.

Effect of cortisol on some osmoregulatory parameters of the teleost, Oreochromis niloticus L., after transference from freshwater to seawater

This trial was conducted in order to determine the effects of cortisol on salt water acclimation of tilapia Oreochromis niloticus (L.). Tilapia (n=42) were injected intraperitoneally with cortisol and then were directly transferred from freshwater (FW) to 15‰ salt water (SW). Changes in plasma osmolality, chloride ion concentration (Cl-), plasma level of cortisol and gill Na+, K+-ATPase activity were measured at 6, 12, 24, 48, 72 and 168 hours after transference to 15‰ SW. Plasma osmolality and Cl- increased immediately after transference until 12-24 h. The fish injected with cortisol (F) showed higher plasma levels of cortisol than those from control group (C) that maintained the initial levels during the experiment. Gill Na+, K+-ATPase activity of C fish began to increase at first hours after transference and peak at 48h. The differences between gill Na+, K+-ATPase activity of F and C groups were significant (P<0.05) in FW, which confirm the effect of exogenous cortisol.

11beta-hydroxysteroid dehydrogenase complementary deoxyribonucleic acid in rainbow trout: cloning, sites of expression, and seasonal changes in gonads

11beta-Hydroxysteroid dehydrogenases (11beta-HSDs) are important steroidogenic enzymes for catalyzing the interconversion of active glucocorticoid (cortisol and corticosterone) and inert 11-keto forms (cortisone and 11-dehydrocorticosterone) in mammals. In teleosts, 11beta-HSD also plays a role in the production of the predominant androgen, 11-ketotestosterone, in male fish. In this study we cloned cDNAs encoding rainbow trout 11beta-HSD (rt11beta-HSD) from testes and head kidney. The predicted amino acid sequence, hydrophobicity analysis, and transient transfection assays with rt11beta-HSD in HEK293 cells showed that rt11beta-HSD is a homolog of mammalian 11beta-HSD type 2. rt11beta-HSD transcripts are present in steroidogenic tissues and in a number of other tissues. Strong in situ hybridization signals for rt11beta-HSD transcripts were found in Leydig cells of testes, in thecal cells of the early vitellogenic ovarian follicles, and in thecal and granulosa cells of the midvitellogenic and postovulatory follicles. Weaker signals were also found in head kidney interrenal cells from juvenile rainbow trout. Seasonal changes in rt11beta-HSD transcripts in testes showed a pattern similar to that of stress-induced serum cortisol levels, but not to serum androgen levels. High levels of rt11beta-HSD transcripts were found in ovarian follicles from late vitellogenesis through ovulation. These results raise the possibility of a role for rt11beta-HSD in the protection of developing gonads from the inhibitory effects of stress-induced cortisol.

The function of Atlantic salmon (Salmo salar L.) antibodies under extremes of pH and osmolarity

The ability of anti-MBP Atlantic salmon antibodies to bind to MBP was investigated using ELISA under a range of pHs (3-10) and osmolarities (100-1,000 mOsml(-1)) to determine the optimum binding conditions required for Atlantic salmon antibodies. The pH optimum was between pH 7-8 with pH 7.4 giving the highest level of antibody binding. However, the decrease in optical density was in excess of 60% at pHs 6.0 and 9.0 and in excess of 99% at pHs of 3.0 and 10.0. The optimum osmolarity required for antibody binding was in the range 100-400 mOsml(-1) with 330 mOsml(-1) giving the highest level of antibody binding. Above 400 mOsml(-1) there was a rapid decrease in antibody binding with the OD dropping by over 50% at all dilutions. This decrease was maintained at all osmolarities over 400 mOsml(-1).

Characterization and expression of steroidogenic acute regulatory protein and MLN64 cDNAs in trout

Complementary DNA-encoding proteins with high homology to steroidogenic acute regulatory proteins (StAR) of mammals were cloned from rainbow trout head kidney and a mixture of several brook trout tissues. A cDNA encoding an MLN64 homolog was also cloned from brook trout. The C-terminal domains of rainbow trout StAR and brook trout StAR were very highly conserved compared with StAR of mammals. In rainbow trout, Northern and RT-PCR analyses showed abundant StAR transcripts in head kidney, ovary, and testis, and weaker signals were found in intestine, pyloric caeca, spleen, and kidney. Brief acute stress resulted in elevated plasma cortisol levels and a 2-fold increase in rainbow trout StAR transcripts in head kidneys sampled 3 h after exposure to the stressor. In brook trout, StAR transcripts were detected only in known steroidogenic tissues. Ovarian brook trout StAR mRNA was not seen until the onset of final maturation. Its abundance increased during germinal vesicle breakdown, peaked during and just following ovulation, and decreased by 2 wk post ovulation. Brook trout MLN64 transcripts were found in all tissues tested, and transcript abundance in ovarian samples did not vary during final oocyte maturation and ovulation. Both StAR structure and function appear to be highly conserved throughout the vertebrates.

Ionoregulatory changes in the gill epithelia of coho salmon during seawater acclimation

Short-term exposure of coho salmon smolts (Oncorhynchus kisutch) to a gradual increase in salinity over 2 d (0 per thousand -32 per thousand ) resulted in a decrease in proton pump abundance, detected as changes in immunoreactivity with a polyclonal antibody against subunit A of bovine brain vacuolar H(+)-ATPase. N-ethylmaleimide (NEM)-sensitive H(+)-ATPase activities in gill homogenates remained unchanged over 8 d to coincide with a 3.5-fold increase in Na(+)/K(+)-ATPase activities. A transient increase in plasma [Na(+)] and [Cl(-)] levels over the 8-d period was preceded by a 10-fold increase in plasma cortisol levels, which peaked after 12 h. Long-term (1 mo) acclimation to seawater resulted in the loss of apical immunoreactivity for vH(+)-ATPase and band 3-like anion exchanger in the mitochondria-rich cells identified by high levels of Na(+)/K(+)-ATPase immunoreactivity. The polyclonal antibody Ab597 recognized a Na(+)/H(+) exchanger (NHE-2)-like protein in what appears to be an accessory cell (AC) type. Populations of these ACs were found associated with Na(+)/K(+)-ATPase rich chloride cells in both freshwater- and seawater-acclimated animals.

Central administration of corticotropin-releasing hormone stimulates locomotor activity in juvenile chinook salmon (Oncorhynchus tshawytscha)

This study evaluated the effect of corticotropin-releasing hormone (CRH) on locomotor activity, habitat choice, and social behavior in juvenile spring chinook salmon (Oncorhynchus tshawytscha). An intracerebroventricular (ICV) injection of CRH caused a dose-dependent increase in locomotor activity. The stimulatory effect of exogenous CRH on locomotor activity lasted for at least 24 h. Injection (ICV) of a peptide antagonist of CRH, alpha-helical CRH(9-41) (ahCRH), prevented the increase in locomotor activity when administered concurrently with CRH. Furthermore, fish administered the antagonist alone had significantly lower locomotor activity levels compared to saline-injected control fish. The effects of CRH are often dependent on the social context. However, no evidence was found that the presence of conspecifics during the testing procedure affected locomotor activity following ICV injections of CRH. Similarly, ICV injections of CRH or ahCRH did not have a significant effect on the mean time spent in contact with a conspecific. However, the position of fish in the tank was affected by the treatments. ICV injections of CRH significantly increased the amount of time that fish spent near the center of the tank. Furthermore, ICV injections of ahCRH significantly increased the mean time taken for fish to find cover in the tank. The effect of CRH and ahCRH on locomotor activity was not related to changes in plasma cortisol or thyroxine. These results support the hypothesis that endogenous CRH within the central nervous system is involved in the stimulation of locomotor activity in fish. Furthermore, CRH may also alter habitat choice in a novel environment.

Environmental salinity selectively modifies the outer-ring deiodinating activity of liver, kidney and gill in the rainbow trout

We here analyzed the effect of a mild hyperosmotic challenge on the activities of deiodinases type I (D1) and II (D2) in the trout liver, and D1 in kidney and gill, two organs involved in osmoregulation. FW-adapted immature rainbow trout were transferred to 5 per thousand SW and killed 0.5, 1, 2, 4, 8 12, 24 and 48 h post-transfer (PT). Fish maintained in FW served as controls. Hepatic, renal and branchial D1 and hepatic D2 activities were assessed as well as circulating levels of T(3), T(4) and cortisol. Hyperosmotic challenge elicited significant and sustained decreases in kidney D1 and liver D2 activities at 8 h PT, which returned to control values at 48 h PT. In contrast, liver and gill D1 activities exhibited no significant change throughout the study. Also, significant increases in circulating T(4) at 2-4 and 48 h PT were observed. Circulating T(3) remained unmodified until 24-48 h PT, when it rose sharply. Simultaneously, cortisol showed a trend towards increase during the initial 4 h PT, which attained significance at 48 h PT. The present findings demonstrate that a mild hypertonic challenge is sufficient to elicit responses in the trout thyroidal axis. Hormonal changes in the circulatory compartment are in accordance with those previously described for migratory salmonids. A novel aspect of our findings is the organ-specific differential response exhibited by ORD-enzymes when trout are exposed to a mildly different osmotic environment. Our findings further establish the uniqueness of fish thyroid physiology, and can be of value in further understanding the evolutionary aspects of this ORD family of deiodinases.