Development of a microtitre plate indirect ELISA for measuring cortisol in teleosts, and evaluation of stress responses in rainbow trout and gilthead sea bream

A microtitre plate indirect enzyme‐linked immunoassay (ELISA) was developed for measuring plasma cortisol levels in rainbow trout Oncorhynchus mykiss, gilthead sea bream Sparus auratus sea bass Dicentrarchus labrax and Senegalese sole Solea senegalensis. Covalink microplates pretreated with disuccinimidyl suberate were coated with bovine serum albumin (BSA) conjugated to cortisol‐3‐carboxymethyl oxime. After blocking with BSA, competition was started by addition of plasma samples and anti‐cortisol antibody raised in rabbit. Goat anti‐rabbit IgG conjugated‐peroxidase was added as second antibody and then incubated with orthophenylenediamine as substrate. Reaction was stopped with 0·1 M HCl and absorbance was read at 450 nm in an automatic plate reader. The standard curve was linear from the lower limit of sensitivity of the assay (c. 0·3 ng ml^?1) to c. 3000 ng ml^?1. Dose‐response inhibition curves using serially diluted plasma samples of four species consistently showed parallelism with the standard curve using cortisol. The ELISA satisfied the strictest criteria of specificity (cross‐reactivity of anti‐cortisol antibody with testosterone, progesterone and 17ß‐oestradiol was negligible, cross‐reactivity with cortisone, corticosterone and 11‐deoxycortisol, was 1·5, 1 and 0·1%, respectively), reproducibility (interassay CV <6%), precision (intra‐assay CV <4%), and accuracy (average recovery >98%). Plasma cortisol concentration in rested fishes was in the range of 5–30 ng ml^?1. To physiologically validate the technique, changes in plasma cortisol concentrations were also measured in plasma of rainbow trout and gilthead sea bream following an acute 15 min chasing or 3 min air‐exposure stress, respectively. In both species plasma concentrations of cortisol, glucose and lactate rose significantly with respect to controls, showing concentrations similar to those reported previously for these species under similar stress conditions. Furthermore, gilthead sea bream chronically stressed by maintaining for 14 days under increased stocking density conditions also showed increased concentrations of plasma cortisol and glucose. These results validate the indirect ELISA technique developed for use in the evaluation of plasma cortisol concentration of at least four fish species.     

Relationship between stress, feeding and plasma ghrelin levels in rainbow trout, Oncorhynchus mykiss

Sexually immature rainbow trout were acclimated to small-volume (1 m³) holding tanks and then exposed to short-term stress to examine the relationship between feeding, stress, plasma ghrelin levels and other plasma stress parameters. Plasma ghrelin levels showed an increase 24 h after a single feed, plasma lactate and glucose levels decreased over the same period and plasma cortisol levels were low and constant. One hour of confinement stress resulted in elevations of plasma cortisol, glucose and lactate and depression of plasma ghrelin levels. In a separate experiment, 2 h of confinement stress also depressed feeding immediately after stress, concomitant with increases in plasma cortisol, lactate and glucose; however, in this case there was no change in plasma ghrelin concentrations. A repeat of the 2-h confinement experiment using fish that had not been acclimated to small-volume holding tanks produced a more marked elevation in plasma cortisol and a stronger suppression of feeding post-stress but in this case also, there was no change in plasma ghrelin levels. The results of this study confirm that feeding in rainbow trout is suppressed by confinement stress although the effect is transitory in this domesticated stock. Similar to that in other fishes, plasma ghrelin levels appear to be modulated by feeding status and may be influenced by stress, suggesting an orexigenic role for ghrelin in rainbow trout.     

Crowding causes prolonged leucopenia in salmonid fish, despite interrenal acclimation

Crowding for 3 weeks significantly reduced the coefficient of condition of both brown trout and rainbow trout. However, acclimation of the hypothalamic-pituitary-interrenal (HPI) axis, as assessed by changes in plasma cortisol levels, occurred within 6 days for brown trout and within 10 days for rainbow trout. Blood lactate levels were significantly reduced in the crowded fish of both species throughout the experiment. Sexual maturation of the male fish significantly elevated the number of circulating red blood cells in both species, reduced the lactate levels in brown trout and elevated cortisol levels in the rainbow trout. Despite the relatively rapid interrenal acclimation, the numbers of thrombocytes and lymphocytes in the blood of both species were significantly reduced during the period of crowding and it is concluded that changes in the composition of circulating blood cells are more reliable indicators of chronic crowding stress than are plasma cortisol levels. These findings are discussed in relation to the role of the HPI axis in suppressing the defence systems of salmonid fish during periods of chronic stress.     

Anti-Oxidative Defences Are Modulated Differentially in Three Freshwater Teleosts in Response to Ammonia-Induced Oxidative Stress

Oxidative stress and the antioxidant response induced by high environmental ammonia (HEA) were investigated in the liver and gills of three freshwater teleosts differing in their sensitivities to ammonia. The highly ammonia-sensitive salmonid Oncorhynchus mykiss (rainbow trout), the less ammonia sensitive cyprinid Cyprinus carpio (common carp) and the highly ammonia-resistant cyprinid Carassius auratus (goldfish) were exposed to 1 mM ammonia (as NH₄HCO₃) for 0 h (control), 3 h, 12 h, 24 h, 48 h, 84 h and 180 h. Results show that HEA exposure increased ammonia accumulation significantly in the liver of all the three fish species from 24 h–48 h onwards which was associated with an increment in oxidative stress, evidenced by elevation of xanthine oxidase activity and levels of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA). Unlike in trout, H₂O₂ and MDA accumulation in carp and goldfish liver was restored to control levels (84 h–180 h); which was accompanied by a concomitant increase in superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase activity and reduced ascorbate content. Many of these defence parameters remained unaffected in trout liver, while components of the glutathione redox cycle (reduced glutathione, glutathione peroxidase and glutathione reductase) enhanced to a greater extent. The present findings suggest that trout rely mainly on glutathione dependent defensive mechanism while carp utilize SOD, CAT and ascorbate as anti-oxidative sentinels. Hepatic cells of goldfish appear to utilize each of these protective systems, and showed more effective anti-oxidative compensatory responses towards HEA than carp, while trout were least effective. The present work also indicates that HEA exposure resulted in a relatively mild oxidative stress in the gills of all three species. This probably explains the almost complete lack of anti-oxidative responses in branchial tissue. This research suggests that oxidative stress, as well as the antioxidant potential clearly differ between salmonid and cyprinid species.     

Physiological stress responses of two species of coral trout (Plectropomus leopardus and Plectropomus maculatus)

The physiological responses of two species of coral trout (Plectropomus maculatus and Plectropomus leopardus) to capture, shallow water and low salinity stressors were investigated. The responses of P. maculatus and P. leopardus to capture stress were characterised by rapid and transient increases in glucose, haemoglobin, haematocrit and lactate, as well as an equally dramatic but delayed increase in cortisol levels that persisted for at least 72 h. The magnitude and duration of the response to capture stress was very similar in both species. In contrast, the levels of cortisol, glucose, lactate, haemoglobin and haematocrit were generally elevated sooner and to higher levels in P. maculatus than in P. leopardus after exposure to shallow water stress. Coral trout exposed to reduced salinity showed minimal changes in cortisol, glucose, lactate, haemoglobin and haematocrit, but such changes were not characteristic of a non-specific response to stress. Thus, the physiological stress responses of coral trouts are species-specific and dependent on the nature of the stressor. This observation probably reflects different cortical processes in the brains of P. maculatus and P. leopardus-a result that may be related to the differential variability of the respective environments in which the two species habit.     

Habitat use by Nonnative Rainbow Trout, Oncorhynchus mykiss, and Native Little Colorado spinedace, Lepidomeda vittata

We evaluated overlap in microhabitat use between nonnative rainbow trout, Oncorhynchus mykiss, and native Little Colorado spinedace, Lepidomeda vittata, a federally threatened cyprinid, in natural and experimental settings. In natural settings, we also examined occurrence and microhabitat use of two other native fishes, speckled dace, Rhinichthys osculus, and bluehead sucker, Catostomus discobolus. Native species co-occurred, as did rainbow trout and bluehead sucker. However, occurrences of Little Colorado spinedace and speckled dace were not significantly correlated with occurrence of rainbow trout. Total lengths of all three native species were significantly smaller at allopatric sites than at sites sympatric with rainbow trout. Microhabitat characteristics at sites with rainbow trout did not differ from those where the other three species were found, but did differ among the native species. In laboratory experiments with Little Colorado spinedace and rainbow trout, rainbow trout used the lower depth zone most, and spinedace increased use of the lower depth zone upon addition of rainbow trout. In addition, species tended to co-occur in zones, but used cover independently of one-another, suggesting a low level of agonistic interactions. However, after addition of a high density of rainbow trout, spinedace tended to use cover less than before. We suggest that the species can coexist at low rainbow trout densities. Potential negative effects of rainbow trout on Little Colorado spinedace likely increase with increasing densities of rainbow trout, and rainbow trout likely affect smaller size classes of Little Colorado spinedace more than larger ones.     

Substrate mobilization and hormonal changes in rainbow trout (Oncorhynchus mykiss,L.) and common carp (Cyprinus carpio,L.) during deep hypoxia and subsequent recovery

Common carp (at 20°C) and rainbow trout (at 15°C) were fitted with an indwelling cannula in the dorsal aorta. The fish were exposed to a controlled decline of waterpO₂ followed by 90 min deep hypoxia at 0.3 kPa (carp) or 4.8 kPa (trout). Thereafter, normoxic recovery was monitored in both species for 48 h. At regular intervals blood samples were analysed for glucose, lactate, free fatty acids, adrenaline, noradrenaline and cortisol. The oxygen restriction was maximal in both species and resulted in a significant increase of plasma lactate levels. In carp, adrenaline, noradrenaline and cortisol levels increased to 2, 50, and 753 ng·ml^-1 respectively during anoxia, whereas in trout these hormones increased to 12, 8 and 735 ng·ml^-1 respectively during hypoxia. In hypoxic trout, the plasma levels of glucose (3 mol·l^-1) were increased modestly whereas levels of free fatty acids (0.25 mmol·l^-1) were decreased to 0.15 mmol·l^-1. In carp, however, a marked and prolonged hyperglycaemia (from 5 to 10 mmol·l^-1) and a significant continuous depression of plasma levels of free fatty acids (from 0.4 to 0.2 mmol·l^-1) were observed indicating a difference in metabolic organization. It is suggested that hyperglycaemia is likely to be the result of hepatic glycogenolysis, stimulated by circulating catecholamines and a stimulation of gluconeogenesis by cortisol during recovery. The mechanism for the decline of plasma levels of free fatty acids is most probably a reduction of lipolytic activity, which appears to be an adaptation to hypoxia.     

Endocrine and metabolic responses to stress in a laboratory population of the tropical damselfish Acanthochromis polyacanthus

The effects of confinement and exercise on the stress response of the spiny damselfish Acanthochromis polyacanthus were investigated in a laboratory stock of fish. Cultured spiny damselfish had basal plasma cortisol values (<16 ng ml⁻¹) similar to those found in wild fish, and basal plasma glucose and lactate levels that were similar to those found in other teleosts. Plasma cortisol concentrations increased in response to stress with a latency period of 5–10 min. Removal of the stressor resulted in partial recovery of cortisol levels by 24 h. Plasma glucose levels increased in response to stress in all experiments with significant increases occurring within 15 min of the imposition of stress. Elevations in plasma glucose concentrations were not initially reflected in changes in liver or muscle glycogen content, with significant reductions in liver glycogen concentrations only occurring in response to extended periods of stress. In contrast to many temperate species, plasma lactate concentrations did not consistently increase in response to stress, suggesting that the stress response in spiny damselfish is not strongly characterized by anaerobiosis.     

Overwinter fasting and re-feeding in rainbow trout: plasma growth hormone and cortisol levels in relation to energy mobilisation

This study investigated the roles of cortisol and growth hormone (GH) during a period of fasting in overwintering salmonid fish. Indices of carbohydrate (plasma glucose, liver glycogen), lipid (plasma free fatty acids (FFAs)) and protein metabolism (plasma protein, total plasma amino acids) were determined, together with plasma GH, cortisol and somatolactin (SL) levels at intervals in three groups of rainbow trout (continuously fed; fasted for 9 weeks then fed; fasted for 17 weeks). In fasted fish, a decline in body weight and condition factor was accompanied by reduced plasma glucose and hepatic glycogen and increased plasma FFA. No consistent elevation of plasma GH occurred until after 8 weeks of fasting when plasma GH levels increased ninefold. No changes were observed in plasma total protein and AA until between weeks 13 and 17 when both were reduced significantly. When previously fasted fish resumed feeding, plasma glucose and FFA, and hepatic glycogen levels rapidly returned to control values and weight gain resumed. No significant changes in plasma cortisol levels, related to feeding regime, were evident at any point during the study and there was no evidence that SL played an active role in the response to fasting. The results suggest that overwinter fasting may not represent a significant nutritional stressor to rainbow trout and that energy mobilisation during fasting may be achieved without the involvement of GH, cortisol or SL.     

Lower sensitivity of cyprinid fishes to three acetylcholinesterase inhibitor pesticides: an evaluation based on no-effect concentrations

Researchers have suggested that cyprinid fishes are less sensitive to chemical stress than comparable fish families, yet few empirically based evaluations of this hypothesis have been conducted. In this study, we developed a generalized linear mixed model in which the no-effect concentrations (NECs; threshold concentration below which no effect on survival is predicted during prolonged exposure) of 29 fish species from 13 families exposed to an acetylcholinesterase inhibitor pesticide (carbaryl, chlorpyrifos, or malathion) were used as the response variable. The corresponding specific somatic maintenance (SSM) rates, as a size-independent proxy for fish metabolism and a categorical variable regarding whether the species is a cyprinid, were used as the predictor variables. We included SSM rates in the analysis because previous work demonstrated that they are negatively correlated with NECs. Our results indicate that the NECs for cyprinid fishes were significantly higher than those for other fishes, suggesting that cyprinids are indeed less sensitive to the three studied pesticides. Although the SSM rates were negatively related with the NECs, the actual relationship between the two was not clear, implying that the importance of SSM rates may depend on the taxonomic group tested.     

The effects of capture, handling, confinement and ectoparasite load on plasma levels of cortisol, glucose and lactate in the coral reef fish Hemigymnus melapterus

Tropical labrids Hemigymnus melapterus sampled underwater had low plasma levels of cortisol, glucose, and lactate. Plasma cortisol levels were elevated by capture stress within 5–6 min, while glucose and lactate levels were not. Plasmalevels of cortisol and glucose increased after 2–4 h of handling and transport to the laboratory. Levels of cortisol and glucose fell with laboratory acclimation back to values similar to those found in wild fish. Parasitism by gnathiid isopods across an order of magnitude of isopod numbers had no effect on plasma levels of cortisol or glucose. Thus, H. melapterus has a stress response similar to that shown by temperate species, and relatively high parasite loads are not apparently stressful to fish in the wild. This may be related to the counterproductive effects of physiological stress responses on the immune system or behaviour-modulated processes that counter parasitic invasion.     

Effects of biotic and abiotic factors on the distribution of trout and salmon along a longitudinal stream gradient

Synopsis We examined the influence of biotic and abiotic factors on the distribution, abundance, and condition of salmonid fishes along a stream gradient. We observed a longitudinal change in fish distribution with native cutthroat trout, Oncorhynchus clarki utah, and introduced brown trout, Salmo trutta, demonstrating a distinct pattern of allopatry. Cutthroat trout dominated high elevation reaches, while reaches at lower elevations were dominated by brown trout. A transition zone between these populations was associated with lower total trout abundance, consistent changes in temperature and discharge, and differences in dietary preference. Variation in cutthroat trout abundance was best explained by a model including the abundance of brown trout and diel temperature, whereas variation in brown trout abundance was best explained by a model including the abundance of cutthroat trout and discharge. These results suggest the potential for condition-mediated competition between the two species. The results from our study can aid biologists in prioritizing conservation activities and in developing robust management strategies for cutthroat trout.     

DEVELOPMENTAL INSTABILITY AND HIGH MERISTIC COUNTS IN INTERSPECIFIC HYBRIDS OF SALMONID FISHES

Interspecific hybrids have been proposed to have reduced developmental stability in comparison to their parental species because the parental genomes have not undergone selection for the maintenance of developmental stability when they occur together. We present data from four interspecific hybrids of salmonid fishes that support this view. Natural hybrids of bull trout (Salvelinus confluentus) with brook trout (Salvelinus fontinalis) and laboratory hybrids of rainbow trout (Salmo gairdneri) with Yellowstone (Salmo clarki bouvieri), westslope (S. c. lewisi), and coastal (S. c. clarki) cutthroat trout all have higher levels of fluctuating asymmetry than either of their parental species raised in the same environment. Thus, the hybrids have reduced developmental stability. The hybrids do not have meristic counts intermediate to the counts of the parental species. The hybrids usually have counts as high as the species with the higher count for those characters that differ between the parental species and often have higher counts for those characters that do not differ between the parental species. We suggest that the tendency for interspecific hybrids to have high meristic counts may be related to differences between the species in the length and timing of the developmental periods during which the counts of the characters are determined.     

Comparison of vegetable shortening and cocoa butter as vehicles for cortisol manipulation in Salmo trutta

This study demonstrates that vegetable shortening and cocoa butter are two effective vehicles for intraperitoneal cortisol implants in juvenile teleosts, specifically brown trout Salmo trutta, residing in north temperate freshwater environments. Each vehicle showed a different pattern of cortisol elevation. Vegetable shortening was found to be a more suitable vehicle for long‐term cortisol elevation [elevated at 3, 6 and 9 days post treatment (dpt)], while cocoa butter may be better suited for short‐term cortisol elevation (only elevated at 3 dpt). Additionally, plasma cortisol levels were higher with cortisol–vegetable shortening than with cortisol–cocoa butter implants. Plasma glucose levels were elevated 6 and 9 dpt for fishes injected with cortisol–vegetable shortening, but did not change relative to controls and shams in cortisol–cocoa butter fishes. In conclusion, vegetable shortening and cocoa butter are both viable techniques for cortisol manipulation in fishes in temperate climates, providing researchers with different options depending on study objectives.     

Tc1-Like Transposable Elements in the Genome of Lake Trout (Salvelinus namaycush)

This study reports on the DNA sequence of a Tc1-like transposable element Tsn1 from lake trout (Salvelinus namaycush). Tc1-like elements were amplified by PCR using an oligonucleotide primer based on the Tdr1 element of zebrafish. One full-length and two partial-length copies of the transposon were sequenced. In addition, partial Tsn1 elements were recovered from PCR reactions run with primers specific to the 3′ terminus of the 28S rDNA. However, sequence analysis of cloned fragments found that these sequences were not associated with the rDNA cistron. Sequence comparisons indicate that Tsn1 is a type A element common to both salmonid and cyprinid fishes. The consensus sequence of the full-length element (Tsn1) was 1643 nucleotides with long terminal repeats (LTRs) of 225 nucleotides. Tsn1 contains a transposase coding region corresponding to 340 amino acids that includes all of the functional elements of Tc1-like transposons. Southern analysis found a high proportion of the Tsn1 transposons in the lake trout genome to be full-length copies. Received March 7, 1998; accepted July 20, 1998     

Combined effects of environmental factors and predator–prey interactions on zooplankton assemblages in five high alpine lakes

The examination of a yearly cycle of plankton density (rotifer and microcrustacean) and of 419 stomach contents of four species of salmonid fishes, arctic charr, Salvelinus alpinus, brown trout, Salmo trutta, rainbow trout, Onchorynchus mykiss and lake trout, Salvelinus namaycush, living in five high altitude lakes in the French Alps, shows an impact of abiotic variates and the effects of predation on the composition of zooplankton assemblages. The lakes studied may be divided in two groups. The colder, Muzelle and Puy Vachier, are characterised by a low level of food resources, an important impact of predation, and the near absence of planktonic crustaceans. The second group, consisting of Lakes Les Pisses, Petarel and Palluel, is characterised by a low density rotifer assemblage and a more abundant crustacean population controlled by a low level of fish predation.     

Anadromy and the marine migrations of Pacific salmon and trout: Rounsefell revisited

Anadromy is a defining trait in salmonid fishes but it is expressed to different extents among the species in the family, as reviewed in a classic paper by Rounsefell (1958). The present paper re-examines the subject, assessing the degree of anadromy within the genus Oncorhynchus, using Rounsefell’s six criteria: extent of migrations at sea, duration of stay at sea, state of maturity attained at sea, spawning habits and habitats, post-spawning mortality, and occurrence of freshwater forms of the species. The genus ranges from pink salmon (O. gorbuscha), the most fully anadromous species in the family, to entirely non-anadromous species closely related to rainbow trout (O. mykiss), including Mexican golden trout (O. chrysogaster), Gila and Apache trout (O. gilae), and sub-species of cutthroat trout (O. clarki). This paper provides updated information on anadromy and marine migration patterns, emphasizing the iteroparous species, cutthroat (O. clarki) and rainbow (O. mykiss) trout. These two species display widely ranging patterns of anadromy, including truly “landlocked” populations and residents with easy access to the sea. Anadromous rainbow trout (known as steelhead) populations also vary greatly in their distribution at sea, incidence of repeat spawning, and associated traits. We conclude, as did Rounsefell, that anadromy is not a single trait with two conditions (anadromous or non-anadromous). Rather, it reflects a suite of life history traits that are expressed as points along continua for each species and population. Further research is needed in the marine ecology of all species but especially trout, as they are less well known but apparently more variable in patterns of anadromy and life history than salmon species.     

Effects of passive integrated transponder tagging on cortisol release,aerobic metabolism and growth of the Gulf killifish Fundulus grandis

The effects of passive integrated transponder (PIT) tagging on cortisol release, standard metabolic rate (SMR) and daily specific growth rate (G_S) were evaluated in the Gulf killifish, Fundulus grandis, a small estuarine fish native to the Gulf of Mexico. Cortisol release by individual fish was measured non-invasively prior to PIT tagging, immediately after tagging and once per week for 1 month following tagging. Within the first 2 h of tagging, cortisol release rates were significantly elevated compared with values measured prior to tagging and significantly higher than that of fish handled identically except not implanted with PIT tags. By 1 week after PIT tagging, cortisol release rates returned to control levels. SMR, determined by intermittent-flow respirometry and G_S, defined as per cent change in body mass per day, were measured prior to PIT tagging and weekly for 1 month after tagging. Neither SMR nor G_S was significantly different in tagged v. untagged fish for the duration of the study. One month after tagging, haematocrit, plasma cortisol, blood glucose and blood lactate did not differ between tagged and untagged individuals. Therefore, after a transient stress response that subsides within 1 week, PIT tagging had no significant effects on these physiological variables in F. grandis, validating its use as a method of marking this and other small fishes.     

Involvement of cortisol and sirtuin1 during the response to stress of hypothalamic circadian system and food intake-related peptides in rainbow trout,Oncorhynchus mykiss

Stress is conditioning animal welfare by negatively affecting a wide range of physiological and behavioral functions. This may be applied to circadian physiology and food intake. Cortisol, the stress-related hormone, may mediate such effect of stress, but other indirect mediators might be considered, such as sirtuin1. Then, either the independent modulatory effect or the existence of any interaction between mediators may be responsible. The circadian system is the main modulator of several integrative mechanisms at both central and peripheral levels that are rhythmically presented, thus influencing different processes such as food intake. In this way, food intake is controlled by the circadian system, as demonstrated by the persistence of such rhythms of food intake in the absence of environmental external cues. Our study aimed to evaluate the daily profile of hypothalamic mRNA abundance of circadian clock genes (clock1a, bmal1, per1 and rev-erbβ-like), and food intake regulators (crf, pomc-a1, cart, and npy) in rainbow trout (Oncorhynchus mykiss), the impact of stress on such rhythms, and the involvement of cortisol and sirtuin1 as mediators. Four cohorts of trout were subjected to 1) normal stocking density (control group), 2) high stocking density for 72 hours (stress group), 3) normal stocking density and implanted with mifepristone, a glucocorticoid receptors antagonist, and 4) mifepristone administered and stressed for 72 hours. Fish from each group were sampled every 4-h along the 24-h LD cycle, and cortisol, glucose and lactate plasma levels were evaluated. Hypothalamic mRNA abundance of clock genes, food intake regulators, glucocorticoid receptors and sirtuin1 were qPCR assayed. Our results reveal the impact of stress on most of the genes assayed, but different mechanisms appear to be involved. The rhythm of clock genes displayed decreased amplitude and averaged levels in stressed trout, with no changes of the acrophase being observed. This effect was not prevented by mifepristone. On the contrary, the effect of stress on the daily profile of crf, pomc-a1, and npy was totally prevented by mifepristone administration. Accordingly, cortisol appears to mainly mediate the effect of stress on food intake regulators through binding to specific glucocorticoid receptors within trout hypothalamus, whereas sirtuin1 is apparently mediating such effects on the circadian system in the same brain region. Further research must be performed to clarify those mechanisms through which stress influences food intake and the circadian oscillator within the same brain region, hypothalamus, in rainbow trout, and the interaction among them all.     

Variations of Some Physiological and Immunological Parameters in Siberian Sturgeon (Acipenser baerii,Brandt, 1869) Subjected to an Acute Stressor

This study was carried out to investigate the effect of an acute stressor on the variation of some physiological and immunological parameters of Siberian sturgeon (Acipenser baerii) juveniles. Fish, reared in 3 tanks for 10 weeks, were used for this study. The acute stress of fish consisted of 2 min of air exposure stress. Plasma levels of cortisol, glucose, and lactate as well as lysozyme activity in plasma were measured before stress and 1 hr, 3 hr, 6 hr, 9 hr, 12 hr, and 24 hr after stress. The plasma cortisol significantly increased in the highest level 1 hr after stress, yet it gradually declined after 3 hr. The glucose significantly increased only 1 hr after stress. There was no significant difference between plasma lactate prestress and poststress. Moreover, lysozyme activity was enhanced by stress, thus reaching the highest level 9 hr after stress. The results of this study indicate that Siberian sturgeon not only have a rapid response to acute stress, but also a great capacity for recovery from stress, thus returning physiological parameters to prestress levels after 6 hr.