Regulation of the interrenal of fishes: non-classical control mechanisms

The regulation of the interrenal of teleostean fishes is reviewed from the perspective of non-classical control mechanisms and new evidence is presented suggesting gonadotropic control of the interrenal. Cortisol secretion by the interrenal, in addition to regulation by ACTH, appears to be mediated by other hormones. Physiologically relevant, direct control of interrenal function by hydromineral factors is unclear.In vitro experiments with interrenals of coho salmon (Oncorhynchus kisutch) indicate that salmon gonadotropin is extremely corticotropic and both ACTH and gonadotropin stimulate the secretion of large quantities of androstenedione from the interrenal.

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.

Cortisol effects on plasma electrolytes and thyroid hormones during smoltification in coho salmon Oncorhynchus kisutch

Plasma concentrations of Na+, K+, triiodothyronine (T3), and thyroxine (T4) and muscle water content were measured in yearling coho salmon. Oncorhynchus kisutch, after injection of cortisol in April, May, and June in fresh water (FW) and during acclimation to seawater (SW). Cortisol (17-21 micrograms/g), injected intraperitoneally in a melted cocoa butter suspension, suppressed the rise of plasma Na+ during SW acclimation in April but not in May or June. Muscle water content increased during SW acclimation in cortisol-treated fish in April and June. These observations suggest a hypoosmoregulatory function for cortisol during SW acclimation. Cortisol treatment also induced elevations of plasma K+ in FW (April only) and SW (April and May only). Cortisol treatment increased plasma T3 during SW acclimation in June and T4 in FW in May. The results suggest that cortisol may modify osmoregulatory processes and thyroid hormone activity during smoltification and acclimation to SW in yearling coho salmon.

Characterization of a glucocorticoid receptor in the brains of chinook salmon, Oncorhynchus tshawytscha

The effects of chronic stress on the brains of salmon may have important implications in light of the extremely high glucocorticoid levels experienced by migrating and spawning adults. The identification and the characterization of glucocorticoid receptors in salmon brains are the first steps in elucidating the effects of stress and high glucocorticoid levels on the brain. We have identified high-affinity, low capacity glucocorticoid receptors in chinook salmon (Oncorhynchus tshawytscha) brain cytosol and report the binding characteristics for the synthetic glucocorticoid triamcinolone acetonide (TA) and the naturally occurring salmonid glucocorticoid, cortisol. The binding characteristics for TA (Kd = 0.85 +/- 0.13 nM, B(max) = 22.4 +/- 2.97 fmol/mg protein, n = 7) and cortisol (Kd = 4.54 +/- 0.06 nM, B(max) = 25.40 +/- 2.20 fmol/mg protein, n = 2) demonstrated high-affinity, low capacity, and specificity for glucocorticoids. In competitive binding assays, TA, cortisol, and dexamethasone (a synthetic glucocorticoid) displaced [3H]TA most effectively, followed by RU38486. Corticosterone and RU28362 were weaker competitors. Cortisone was not a strong competitor nor were the sex steroids. Specific DNA binding was detected in DNA-cellulose chromatography assays. Receptors in nuclear extracts were not detected. These binding characteristics are consistent with published data on glucocorticoid receptors in other salmonid tissues.

Sexual dimorphism of plasma sex steroid levels in juvenile coho salmon, Oncorhynchus kisutch, during smoltification

Concentrations of plasma sex steroids, cortisol, and thyroxine were measured by radioimmunoassay in hatchery coho salmon (Oncorhynchus kisutch during winter and early spring. Mean plasma 11-ketotestosterone (11-KT) and estradiol levels fell into two distinct categories: 11-KT was 181-373% higher in males than in females, and estradiol was 109-143% higher in females than in males. No changes in plasma levels of estradiol in fish of both sexes, or in levels of 11-KT in males, were evident during spring when plasma thyroxine and cortisol were markedly elevated, indicating that the fish were undergoing smoltification. Although plasma 11-KT in females appeared to be lower in late April than in February, it showed no correlation with plasma thyroxine or cortisol in these individuals. Our finding of sexual dimorphism in 17 alpha-20 beta-dihydroxy-4-pregnen-3-one was inconsistent between stocks of fish and among sampling dates, thus making interpretation of the results difficult. However, no relationship between this steroid and plasma thyroxine or cortisol was observed. Therefore, plasma levels of sex steroids do not seem to be related to the changes in plasma thyroxine or cortisol observed during smoltification of coho salmon.

Clearance of plasma corticosteroids during smoltification of coho salmon, Oncorhynchus kisutch

The plasma clearance rate (PCR) of radioactivity after a single intracardial injection of 3H-cortisol was elevated during the spring in yearling coho salmon, Oncorhynchus kisutch. Graphical analysis suggested a seasonal correlation between PCR and gill Na/K-ATPase activity. An explanation for this correlation is suggested. The major metabolite of 3H-cortisol in plasma was 3H-cortisone. It appeared rapidly following injection of the original radiotracer.

Adenylate cyclase activators and inhibitors, cyclic nucleotide analogs, and phosphatidylinositol: effects on interrenal function of coho salmon (Oncorhynchus kisutch) in vitro

The role of cyclic AMP (cAMP) as mediator of ACTH action on interrenal steroidogenesis was evaluated in juvenile coho salmon (Oncorhynchus kisutch). Head kidneys (containing the interrenal cells) were incubated in the absence or presence of putative adenylate cyclase activators (forskolin and cholera toxin), ACTH combined with putative adenylate cyclase inhibitors (hydrolysis-resistant ATP analogs), dibutyryl cyclic (dbc) AMP, dbcGMP, or phosphatidylinositol. The cortisol content of the incubation medium was subsequently determined by radioimmunoassay. Forskolin markedly stimulated cortisol secretion by interrenal cells. Adenylate cyclase inhibitors depressed the steroidogenic response to ACTH. Dibutyryl cAMP, but not dbcGMP, enhanced steroid secretion. Thus, cAMP seems to be an important "second messenger" for ACTH action on salmon interrenal cells. In contrast to findings in mammalian adrenocortical cells, exogenous phosphatidylinositol and cholera toxin failed to stimulate corticosteroid secretion in salmon interrenal cells. However, it was unclear whether these negative findings were an artifact resulting from the use of kidney tissue fragments instead of isolated interrenal cells.

Mercury concentrations in gonad, liver, and muscle of white sturgeon Acipenser transmontanus in the lower Columbia River

This study determined the partitioning of total mercury in liver, gonad, and cheek muscle of white sturgeon (Acipenser transmonatus) in the lower Columbia River. The relationship between tissue mercury concentrations and various physiologic parameters was assessed. White sturgeon were captured in commercial fisheries in the estuary and Bonneville, The Dalles, and John Day Reservoirs. Condition factor (CF), relative weight (Wr), and gonadosomatic index (GSI) were determined for each fish (n = 57). Gonadal tissue was examined histologically to determine sex and stage of maturity. Liver (n = 49), gonad (n = 49), and cheek muscle (n = 57) were analyzed for total mercury using cold-vapor atomic fluorescence spectrophotometry. Tissue protein concentrations were measured by ultraviolet-visible spectroscopy. Plasma was analyzed for testosterone (T), 11-ketotestosterone (KT), and 17ss-estradiol (E2) using radioimmunoassay. Mean tissue mercury concentrations were higher in muscle compared with liver and gonad at all sampling locations, except Bonneville Reservoir where mean liver mercury content was the highest tissue concentration observed in the study. Significant negative correlations between plasma androgens (T and KT) and muscle mercury content and plasma E2 and liver mercury content were found. A significant positive linear relationship between white sturgeon age and liver mercury concentrations was evident. Significant negative correlations between CF and relative weight and gonad and liver mercury content were found. In addition, immature male sturgeon with increased gonad mercury content had decreased GSIs. These results suggest that mercury, in the form of methylmercury, may have an effect on the reproductive potential of white sturgeon.

Plasma androgen correlation, EROD induction, reduced condition factor, and the occurrence of organochlorine pollutants in reproductively immature white sturgeon (Acipenser transmontanus) from the Columbia River, USA

White sturgeon (Acipenser transmontanus) support an active fishery in the Columbia River, but there is poor reproductive success within the impounded sections. The poor reproductive success has been attributed to hydroelectric development; however, water pollution could be a significant factor. White sturgeon plasma, liver, and gonad samples were collected from four Columbia River locations and a California aquaculture facility. Total length and weight of the fish were measured, and plasma samples were analyzed for testosterone (T), 11-ketotestosterone (KT), 17 beta-estradiol (E2), and vitellogenin. Liver samples were analyzed for chlorinated pesticides and polychlorinated biphenyls, ethoxyresorufin-O-deethylase (EROD) activity and histopathology. Gonads were examined histologically to assess sexual maturity and characterize any lesions. Significant differences by location existed for p,p'-DDE, EROD activity, and condition factor. Plasma T was negatively correlated with p,p'-DDE in males and females, and plasma KT was negatively correlated in males. These data indicate that pollutants could be adversely affecting white sturgeon in the Columbia River basin.

Seasonal changes in cortisol sensitivity and glucocorticoid receptor affinity and number in leukocytes of coho salmon

To determine if there were organ-specific changes in immune responses or immune-endocrine interaction, we monitored in vitro immune response, cortisol sensitivity and number and affinity of glucocorticoid receptors (GR) in leukocytes from freshwater-adapted juvenile coho salmon (Oncorhynchus kisutch) during the physiological changes that prepare them to enter the marine environment. During this period, absolute immune response declined, but splenic leukocytes generated more antibody-producing cells than did cells from anterior kidney. Splenic leukocytes were initially more sensitive to the suppressive effects of cortisol and had fewer GR than leukocytes from the anterior kidney. Leukocytes from the anterior kidney were initially insensitive to cortisol but developed sensitivity at about the same time as the dissociation constant and number of GR increased. In vitro incubation of anterior kidney leukocytes in cortisol altered GR variables when experiments were conducted during March through September but not during November through February. In some years, changes in GR or immune responses were correlated with plasma cortisol titers, but in other years there was no correlation. Thus, the exact relation between cortisol, GR and immune response in anadromous salmonids is unclear and other factors are involved.

Possible Adaptive Significance of Certain Enzyme Polymorphisms in Steelhead Trout (Salmo gairdneri)

In experimentally reared winter steelhead trout (Salmo gairdneri) fry, mean weights, lengths, and condition factors of three isozyme phenotypes of lactate dehydrogenase (LDH) enzyme differed significantly. Time of emergence from the gravel was unrelated to LDH phenotype. Relative mortality of the phenotypes between eyed-egg stage and emergence was unaffected by different subgravel conditions of temperature and dissolved oxygen. Differential tolerance to acute challenges of high temperature and low dissolved oxygen was observed between phenotypes of isocitrate dehydrogenase (IDH) enzyme and LDH in juvenile trout. Parental effects may have biased the result for LDH. Differences between IDH phenotypes may be related to intrinsic properties of variant isozymes. Key words: isozymes, lactate dehydrogenase, isocitrate dehydrogenase, temperature, dissolved oxygen, adaptive significance, Salmo gairdneri

Post-mortem sporulation of Ceratomyxa shasta (Myxozoa) after death in adult Chinook salmon

Ceratomyxa shasta (Myxozoa) is a common gastrointestinal pathogen of salmonid fishes in the Pacific Northwest of the United States. We have been investigating this parasite in adult Chinook salmon ( Oncorhynchus tshawytscha ) in the Willamette River, Oregon. In prior work, we observed differences in the pattern of development of C. shasta in adult salmon compared to juvenile salmon. Adult salmon consistently had large numbers of prespore stages in many of the fish that survived to spawn in the fall. However, myxospores were rarely observed, even though they were exposed and presumably infected for months before spawning. We evaluated the ability of C. shasta to sporulate following fish death because it is reported that myxosores are common in carcasses of Chinook salmon. We collected the intestine from 30 adult salmon immediately after artificial spawning and death (T0). A total of 23 fish were infected with C. shasta based on histology, but only a few myxospores were observed in 1 fish by histology. Intestines of these fish were examined at T0 and T7 (latter held at 17 C for 7 days) using quantified wet mount preparations. An increase in myxospore concentrations was seen in 39% of these fish, ranging between a 1.5- to a 14.5-fold increase. The most heavily infected fish exhibited a 4.6-fold increase from 27,841 to 129,352 myxospores/cm. This indicates, supported by various statistical analyses, that under certain conditions presporogonic forms are viable and continue to sporulate after death in adult salmon. Considering the life cycle of C. shasta and anadromous salmon, the parasite may have evolved 2, non-mutually exclusive developmental strategies. In young fish (parr and smolts), the parasite sporulates shortly after infection and is released into freshwater from either live or dead fish before their migration to seawater, where the alternate host is absent. The second strategy occurs in adult salmon, particularly spring Chinook salmon, which become infected upon their return to freshwater in the spring or early summer. For several months throughout the summer, only prespore stages are observed in most fish, even at the time of spawning. But once the fish dies, environmental conditions experienced by C. shasta change and viable presporogonic stages are induced to sporulate. As the post-spawned fish occur in the upper reaches of rivers, the myxospores would be released in a freshwater environment that would provide a reasonable opportunity for them to encounter their freshwater polychaete hosts, which reside downstream.

Swimming Endurance in Juvenile Chinook Salmon Infected with Salmincola californiensis

Juvenile Chinook Salmon Oncorhynchus tshawytscha moving downstream through tributaries of the upper Willamette River basin can spend months in reservoirs created by dams. While residing in the reservoirs, they often obtain heavy infections of the freshwater parasitic copepod Salmincola californiensis. The physiologic effect these parasites have on salmonids is poorly understood. We developed a method to infect juvenile Chinook Salmon in a laboratory with the copepodid stage of S. californiensis. Infected and uninfected fish were subjected to a swimming challenge to ascertain swimming endurance. Severity of gill damage was assessed using a dissecting microscope. Juvenile Chinook Salmon naturally infected with S. californiensis in Cougar Reservoir, Oregon, were also challenged and compared with their lab-infected counterparts. Copepod infection greatly impaired the swimming ability of laboratory fish, and the naturally infected fish were entirely incapable of swimming at low velocity. Chinook Salmon collected in the wild were more heavily infected than the laboratory fish and had trouble surviving collection and transport to our laboratory. The intensity of infection and severity of gill damage were positively correlated with diminished swimming ability, suggesting that heavy infection with copepods impairs gas exchange and osmotic regulation, which likely results in diminished fitness and decreased survival of infected fish.

Body morphology differs in wild juvenile Chinook salmon Oncorhynchus tshawytscha that express different migratory phenotypes in the Willamette River, Oregon, U.S.A

Body morphology of juvenile Chinook salmon Oncorhynchus tshawytscha in the upper Willamette River, Oregon, U.S.A., was analysed to determine if variation in body shape is correlated with migratory life-history tactics followed by juveniles. Body shape was compared between migrating juveniles that expressed different life-history tactics, i.e. autumn migrants and yearling smolts, and among parr sampled at three sites along a longitudinal river gradient. In the upper Willamette River, the expression of life-history tactics is associated with where juveniles rear in the basin with fish rearing in downstream locations generally completing ocean ward migrations earlier in life than fish rearing in upstream locations. The morphological differences that were apparent between autumn migrants and yearling smolts were similar to differences between parr rearing in downstream and upstream reaches, indicating that body morphology is correlated with life-history tactics. Autumn migrants and parr from downstream sampling sites had deeper bodies, shorter heads and deeper caudal peduncles compared with yearling smolts and parr from the upstream sampling site. This study did not distinguish between genetic and environmental effects on morphology; however, the results suggest that downstream movement of juveniles soon after emergence is associated with differentiation in morphology and with the expression of life-history variation.

Antibody-producing cells correlated to body weight in juvenile chinook salmon (Oncorhynchus tshawytscha) acclimated to optimal and elevated temperatures

The immune response of juvenile chinook salmon (Oncorhynchus tshawytscha) ranging in weight from approximately 10 to 55 g was compared when the fish were acclimated to either 13 or 21 degrees C. A haemolytic plaque assay was conducted to determine differences in the number of antibody-producing cells (APC) among fish of a similar age but different body weights. Regression analyses revealed significant increases in the number of APC with increasing body weight when fish were acclimated to either water temperature. These results emphasise the importance of standardising fish weight in immunological studies of salmonids before exploring the possible effects of acclimation temperatures.

Spontaneous and ACTH-induced interrenal steroidogenesis in juvenile coho salmon (Oncorhynchus kisutch): effects of monovalent ions and osmolality in vitro

We determined the in vitro effects of changes in extracellular monovalent ion levels and osmotic pressure on the spontaneous and adrenocorticotropin (ACTH)-stimulated interrenal activity of coho salmon (Oncorhynchus kisutch). We used a perifusion system of incubation and monitored interrenal activity by measuring the effluent cortisol content with a radioimmunoassay. An increase in the medium osmolality with mannitol, from 206 to 290 or 353 mosmol, caused an increase in the spontaneous release of cortisol only slightly (compared with the much greater increase induced by porcine-ACTH). A similar minor increase was observed when NaCl was elevated from 130 to 180 mM. On the other hand, the spontaneous release of cortisol was not affected by increasing the KCl level from 3.2 to 9.6 mM, but was clearly increased when KCl was raised from 3.2 mM to a supraphysiological level of 27.2 mM. Ionic or osmolality changes, within the physiological range observed in coho salmon plasma, did not affect the characteristics of interrenal secretion of cortisol in response to porcine-ACTH. If our results with interrenal cells in vitro are representative of the basic functioning of the cells in vivo, then one would have to conclude that changes in concentrations of plasma monovalent ions or in osmotic pressure may not play a significant physiological role in the regulation of interrenal steroidogenesis or corticosteroid release in coho salmon.

Using blood plasma for monitoring organochlorine contaminants in juvenile white sturgeon, Acipenser transmontanus, from the lower Columbia River

Organochlorine (OC) pesticide concentrations in blood plasma samples from 88 juvenile white sturgeon collected from the lower Columbia River were measured and compared to plasma sex steroid and OC tissue levels previously measured in corresponding fish. Significant squared correlation coefficients between summation operator DDT concentrations in sturgeon plasma and gonads and livers were 0.37 and 0.32, respectively. Significant negative correlations between plasma testosterone concentration and plasma Sigma DDT concentration in male fish (r(2)=0.26), plasma 17beta estradiol concentration and plasma Sigma DDT concentration in female fish (r(2)=0.38) and condition factor and plasma Sigma DDT concentration in all fish were found (r(2)=0.17). These results suggest that blood plasma may be a suitable nondestructive method for monitoring adult sturgeon population for persistent OC contaminants.

Stress up-regulates oxidative burst in juvenile Chinook salmon leukocytes

When fish perceive stressful scenarios, their hypothalamus-pituitary-interrenal axis is activated resulting in the release of corticotropin releasing hormone, adrenocorticotropic hormone (ACTH), and finally cortisol. The physiologic stress response of fish has most often been linked to the reduced performance of the immune system, with a few exceptions where the immune system is activated. In this report, we tested the hypothesis that oxidative burst activity levels in juvenile Chinook salmon (Oncorhynchus tshawytscha) are altered when the fish is presented with a stressor. Fish were subjected to a stressor for 3 h and then allowed to recover for 20 h following the stressor. Plasma and spleens were collected from euthanized fish before the stressor, at the end of a 3 h stressor, and 23 h after the start of the experiment. Plasma was held at -80 °C until cortisol radioimmunoassay analysis was performed to confirm stress. Spleens were held in Dulbecco's Modified Eagle Medium overnight and analyzed the day following collection. Oxidative burst activity was measured in splenic leukocytes after being stimulated with phorbol 12-myristate 13-acetate. We found a significant increase in activated oxidative burst from fish subjected to the stressor as compared to unstressed fish. Speculation is given to ACTH being the leukocyte priming agent in this experiment rather than the cortisol itself.

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.

Identification of biomarkers indicative of barotrauma and recovery in black rockfish Sebastes melanops

A Sebastes-specific complementary DNA (cDNA) microarray was developed to identify potential biomarkers involved in the capture stress and recovery of Sebastes species if they are assisted in returning to their original depth of capture following barotrauma. Black rockfish Sebastes melanops were exposed to simulated decompression from 450 kPa (c. 35 m depth) (which resulted in barotrauma) and subsequent recompression. Sebastes melanops were sampled for liver tissue at days 3, 15 and 31 post-barotrauma. Potential candidate genes were identified from the microarray and then quantitative real-time PCR (qrt-PCR) was used to validate expression levels in biological replicates. Six potential biomarkers associated with the innate immune system were identified that were up-regulated in liver tissue at 3 days post-barotrauma: complement C1q-like protein 2, complement component C3, complement regulatory plasma protein, serum amyloid A-5, c-type lysozyme and hepcidin precursor type I. In addition, complement c1q was correlated to the presence of a ruptured swimbladder, providing further support that this gene may be a good biomarker of injury and recovery. Immune genes were no longer up-regulated at day 31 post-barotrauma, a good indication of recovery in S. melanops.

Growth and annual survival estimates to examine the ecology of larval lamprey and the implications of ageing error in fitting models

This study used existing western brook lamprey Lampetra richardsoni age information to fit three different growth models (i.e. von Bertalanffy, Gompertz and logistic) with and without error in age estimates. Among these growth models, there was greater support for the logistic and Gompertz models than the von Bertalanffy model, regardless of ageing error assumptions. The von Bertalanffy model, however, appeared to fit the data well enough to permit survival estimates; using length-based estimators, annual survival varied between 0·64 (95% credibility interval: 0·44-0·79) and 0·81 (0·79-0·83) depending on ageing and growth process error structure. These estimates are applicable to conservation and management of L. richardsoni and other western lampreys (e.g. Pacific lamprey Entosphenus tridentatus) and can potentially be used in the development of life-cycle models for these species. These results also suggest that estimators derived from von Bertalanffy growth models should be interpreted with caution if there is high uncertainty in age estimates.