Distribution of 5-hydroxytryptamine and related compounds in various brain regions of rainbow trout (Oncorhynchus mykiss)

The levels of tryptophan (Try), 5-hydroxytryptamine (serotonin, 5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in the brain regions of rainbow trout (Oncorhynchus mykiss) by high performance liquid chromatography with electrochemical detection (HPLC-EC). Brain tryptophan concentrations varied from 3.972 ± 357 ng/g cerebellum) to 8.841 ± 772 ng/g (hypothalamus). The 5-HT concentrations varied from 69 ± 7 ng/g (optic tectum) to 573 ± 34 ng/g (hypothalamus). The concentrations of 5-HIAA varied from 29 ± 3 ng/g (medulla oblongata) to 68 ± 7 ng/g (hypothalamus). Total and free serum tryptophan levels were also determined; in adult rainbow trout 92% of the serum tryptophan was observed to be free i.e., not protein-bound.     

In vitro evidence that cortisol directly modulates stress-related responses in the skin epidermis of the rainbow trout (Oncorhynchus mykiss Walbaum)

Exposure of fish to stressors leads to multiple changes in the skin epithelium. We investigated the role of the stress hormone cortisol in the control of these changes by exposure of pieces of skin from the rainbow trout Oncorhynchus mykiss with an in vitro tissue culture incubation procedure. The effects of 24 h exposure to 4 cortisol concentrations (0, 50, 500 and 1000 ng/ml) were determined. Numbers of mucous, mitotic and apoptotic cells were quantitatively assessed using immunohistochemical techniques, in situ DNA nick end labelling (TUNEL), as well as conventional light and scanning electron microscopy (SEM). The cortisol receptor blocker mifepristone was used to investigate whether the effects could be attributed to the direct action of the hormone via glucocorticoid receptors. Overall, cortisol had no effect on the mucous cell population at 24 h. Incubation with the receptor blocker reduced the number of mucous cells. Cell proliferation was stimulated by the addition of 50 and 500 ng/ml cortisol, but not at 1000 ng/ml. Incubation with the receptor blocker increased proliferation in the control group (0 ng/ml) only. An increase in apoptosis occurred at 500 and 1000 ng/ml cortisol. This increase was blocked by incubation with the receptor blocker, which resulted in lower numbers of apoptotic cells in all except the 0 ng/ml controls. SEM observations corroborated the quantitative data. The results indicated that the effects of stressors on the fish epidermis mentioned above are mediated by cortisol, with the exception of mucous cell release.     

A radioimmunoassay for N-terminal peptide of chum salmon proopiocortin

A highly specific radioimmunoassay was developed for N-terminal peptide of salmonid proopiocortin using a guinea pig antiserum to the chum salmon peptide (sNPP 1). Since sNPP I has no tyrosine residue nor free N-terminal amino group, a mixture of minor components of sNPP 1, which have extensions of H-Val-LysGly- and H-Lys-Gly- at the N-terminus, were iodinated by the lactoperoxidase method after incorporation of 3-(phydroxyphenyl)-propionate to the terminal amino groups. Plasma and pituitary extracts of several salmonid species showed parallel displacement to the standard hormone. Samples from carp, goldfish, tilapia, and eel, as well as the plasma of hypophysectomized rainbow trout, showed no crossreactivity. Proopiocortin-related hormones isolated from the chum salmon pituitary, including melanotropins, endorphins, corticotropin-like intermediate lobe peptides, and gonadotropin and prolactin showed negligible cross-reactivity. NPP contents in the pars intermedia of rainbow trout and chum salmon were 10 to 15 times greater than those in the pars distalis. Plasma levels of NPP in the mature chum salmon caught in the bay were about 50ng/ml. Plasma NPP levels in the mature chum salmon of both sexes decreased after transfer from seawater to fresh water. Plasma cortisol showed a concomitant change with NPP, thus supporting previous findings that NPP modulates corticotropin action on the trout interrenal.     

Stress responses and disease resistance in salmonid fish: Effects of chronic elevation of plasma cortisol

Basal levels of plasma cortisol in unstressed salmonid fish are normally in the range 0–5 ng ml⁻¹. An acute stress such as handling or 1 h confinement caused a temporary elevation of the plasma cortisol levels of both brown trout,Salmo trutta L., and rainbow trout,Salmo gairdneri Richardson, in the range 40–200 ng ml⁻¹ with a return to basal levels within 24–48 h. The extent of the cortisol elevation in response to an acute stress was dependent upon both the species and strain of trout. Chronic stresses, such as prolonged confinement or crowding, resulted in an elevation of plasma cortisol levels to approximately 10 ng ml⁻¹. Under these circumstances, blood cortisol levels remained elevated for periods of up to 4 weeks before acclimation finally occurred. It is shown, by means of intraperitoneal implantation of cortisol, that chronic elevation of plasma cortisol levels in the brown trout results in a dose-dependent increase in mortality due to common bacterial and fungal diseases. This effect is apparent at plasma cortisol levels as low as 10 ng ml⁻¹, levels below those often reported as being representative of ‘unstressed’ fish. These findings are discussed in relation to the known immunosuppressive effects of corticosteroids in teleost fish.     

Does oral 3,5,3 ′-triiodo-l-thyronine affect dietary glucose utilization and plasma insulin levels in rainbow trout (Salmo gairdneri)?

A factorial experiment was conducted to determine the effect and interaction of dietary carbohydrate level and triiodo-L-thyronine (T₃) supplementation on the growth, physiological response and plasma insulin and cortisol levels of rainbow trout. The oral administration of T₃ significantly increased the growth, protein efficiency ratio and feed efficiency of trout, indicating an increased protein and perhaps energy utilization in these fish. However, T, administration did not significantly increase the utilization of dietary glucose as an energy source by the trout. Similarly, the administration of T₃ did not significantly affect plasma insulin levels in either the fed or the fasted trout. Plasma insulin levels were significantly higher in fed trout reared on the non-T₃ supplemented high carbohydrate diet in comparison to trout reared on the low carbohydrate diets. This indicates that increased dietary carbohydrate stimulates increased insulin secretion in the trout. Therefore, although rainbow trout are not insulin-deficient, they can still be considered a diabetic-like animal due to their poor glucose tolerance. Plasma cortisol levels were not affected by diet composition and altered plasma glucose levels.     

Development of a protein binding assay for teleost insulin-like growth factor (IGF)-like: relationships between growth hormone (GH) and IGF-like in the blood of rainbow trout (Oncorhynchus mykiss)

Using rainbow trout plasma protein (IGF-BP) which specifically binds human insulin-like growth factor (IGF) (Niu and Le Bail 1993), we have developed an assay to measure plasma IGF-like levels in different teleost species. Before the assay and to prevent interference by IGF-BP, IGF-like was extracted from all samples, using SP Sephadex C-25 in acidic conditions. After this treatment, contamination of the IGF fraction by IGF-BP which was estimated by binding assay, was approximately 5%, and was not detectable by western ligand blot. Human IGF-I was used as standard and labelled hormone. Sensitivity of the assay was 0.15–0.40 ng/ml (ED90) and ED50 was 1–3 ng/ml. hIGF-II crossreaction was partial and no significant displacement was observed with Insulin from different species or with other hormones. Inhibition curves were obtained with plasma IGF fractions (but not with tissue extracts) from teleost and mammals and are parallel to the standard curve. These results suggest that the protein binding assay can quantify an IGF-like factor in the plasma of teleost and that the binding sites of IGF are well conserved during vertebrate evolution. Using this IGF binding assay, IGF-like was measured in parallel with growth hormone (GH) in plasma from young rainbow trout killed every 1.5h throughout one day. The daily profiles for both hormones, which appear pulsatile, are similar. A significant correlation was observed between GH levels and IGF-like levels with a 1.5h delay. Analogous observations were obtained in individual catheterized adult rainbow trout. Although plasma GH levels differ greatly between fish, less variability is found with IGF-like. In a third experiment, rainbow trout were starved or submitted to bovine GH treatment for four weeks. Starved fish, in which plasma GH levels increased, had plasma IGF-like level significantly lower than in fed fish. In bGH injected fish, plasma IGF-like level was significantly higher than in non-injected fish. These results suggest that, as in mammals, IGF-like secretion depends on plasma GH level and could be modulated by the nutritional status of fish.     

Effects of dietary ascorbic acid levels on cholesterol metabolism in rainbow trout (Oncorhynchus mykiss)

An 80‐day feeding trial was conducted to evaluate the effects of dietary ascorbic acid (AA) supplementation at different levels (0, 0.2 and 0.4 g/kg l ‐ascorbate‐2‐polyphosphate; 7.6, 77.2 and 146.7 mg/kg AA, respectively) on cholesterol metabolism in rainbow trout (Oncorhynchus mykiss). Dietary AA supplementation regardless of inclusion level increased the serum total cholesterol and low‐density lipoprotein (LDL) cholesterol levels and LDL cholesterol/high‐density lipoprotein cholesterol ratio. No significant differences were observed in the serum triiodothyronine and thyroxine levels, faecal cholesterol content, hepatic activity and mRNA expression of acyl‐coenzyme A:cholesterol acyltransferase among the dietary treatments. Dietary AA inclusion increased the faecal bile acid content, hepatic activity and mRNA expression of 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase and hepatic cholesterol 7α‐hydroxylase mRNA expression, but decreased the hepatic LDL receptor content. High level of AA supplementation (0.4 g/kg) depressed the serum cortisol levels. These results suggest that dietary supplementation with 0.2?0.4 g/kg l ‐ascorbate‐2‐polyphosphate may increase the serum total cholesterol level in rainbow trout. The cholesterol‐raising effect of AA may be due to the increased hepatic cholesterol production and the depressed cholesterol clearance from serum. In addition, dietary AA inclusion also facilitates the hepatic conversion of cholesterol to bile acids.     

Physiological Responses of Rainbow Trout Oncorhynchus mykiss to Crowding and Anesthesia with AQUI-S™

Abstract.— Following exposure to the anesthetic AQUI-S™, plasma cortisol concentration in immature rainbow trout was measured as (mean) 293 ± 48 ng/ mL, which was significantly ( P > 0.05) higher than the mean concentration in resting fish. Cortisol concentrations remained significantly ( P > 0.05) elevated for at least 24 h after treatment. This was accompanied by a significant increase and decrease in hematocrit and plasma potassium, respectively. These perturbations continued for at least 48 h following recovery from anesthesia. Plasma concentrations of total protein and sodium remained unchanged following anesthesia with AQUI-S™. Crowding stress is commonly encountered by fish during manipulation in aquaculture situations. Anesthetising fish prior to, and during, manipulation may reduce the associated stress. Changes in cortisol values resulting from crowding (30 min; 0.1 kg/L) during anesthesia with AQUI-S™ were not appreciably different from those in fish crowded without anesthesia. Thus, anesthesia with AQUI-S™ at the recommended dose of 17 mg/L did not appear to be effective for alleviating the stress of crowding under the conditions of our experiments.     

Identification of histones as endogenous antibiotics in fish and quantification in rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>) skin and gill

Antimicrobial polypeptides (AMPPs) are increasingly recognized as a critical component of innate host defense. Among the AMPPs, polypeptides related to histones have been identified from many animals. Using peptide mapping, we further confirm the identity of two histone-like proteins from fish as members of the H2B (sunshine bass) and H1 (rainbow trout) histone groups. We optimized the conditions for measuring rainbow trout HLP-1/H2B via sandwich ELISA. We used two antibodies, one to the amino terminus and one to the carboxyl terminus, of trout histone H2B, as the capture antibodies, and we used peroxidase-labeled antibody raised to calf histone H2B as the secondary antibody. Specificity of the detecting antibody was confirmed by specific reactivity with histone H2B in tissue extracts via western blotting. The test was reproducible and capable of detecting as little as 5 ng of histone H2B (0.05 μg/ml). Histone H2B levels expressed in gill tissue of juvenile, healthy rainbow trout were well within concentrations that are lethal to important fish pathogens. However, there was a significant, age (size)-dependent decline in histone H2B concentrations as fish matured, until levels became virtually undetectable in market-size fish. In contrast, levels in skin appeared to remain high and unchanged in small versus large fish. Antibacterial activity in skin and gill tissues was closely correlated with histone H2B concentration measured via ELISA, which supports our previous finding that histones are the major AMPPs in rainbow trout skin and gill.     

Stocking density and cohort sampling effects on endocrine interactions in rainbow trout

Studies were conducted to explore the effect of cohort sampling and stocking density on the interactions between plasma growth hormone (GH), thyroid hormone and cortisol concentrations in rainbow trout. Depending on the experimental design, plasma GH concentrations were either suppressed, or elevated by sequential removal of cohorts from the holding aquarium. Since plasma cortisol concentrations consistently increased during cohort sampling, regardless of experimental design, it would appear that the apparent correlation (direct or inverse) is the result of concomitant changes, i.e. not necessarily a cause-effect relationship. Plasma GH concentrations of rainbow trout were not correlated with eviscerated body weight.Trout stocked at 150 kg m^–3 exhibited a significantly lower mean growth rate, hepatosomatic index, hepatic lipid reserve, plasma triiodo-l-thyronine (T₃) concentration andin vitro hepatic T₃ production than trout stocked at 60 kg m^–3. These observations are consistent with the former group being food deprived or ration restricted. Stocking density appeared to have no effect on plasma GH or cortisol concentrations, or on the pituitary-interrenal axis response to stressor challenge, or the thyroid tissue response to exogenous TSH challenge.     

Histological changes in insulin-immunoreactive pancreatic β-cells,and suppression of insulin secretion and somatotrope activity in brook trout (Salvelinus fontinalis) maintained on reduced food intake or exposed to acidic environment

Immature brook trout (Salvelinus fontinalis) were randomly divided into a pH control, a pH and food control and an acid-stressed group. Fish in the first two groups were held at neutral pH and those in the last group were maintained at pH 4.2 for up to two months. The food supply to the pH and food control group was restricted to simulate the reduction in food intake demonstrated for acid-stressed trout. Plasma insulin levels were significantly decreased from 5–20 ng/ml to 1–2 ng/ml and plasma cortisol levels were significantly increased from 5–10 ng/ml to as high as 70 ng/ml in the acid-stressed brook trout. Concomitantly, a significant decrease of 21–39% in the proportion (volume density) of insulin immunoreactive -cells was observed within the principal pancreatic islets. Somatic growth was stunted and ultrastructural morphometry revealed the suppression of somatotrope secretory activity in the acid-stressed fish. Restriction of food supply induced a smaller but still significant decrease in circulating levels of insulin which was however not accompanied by a reduction in insulin immunoreactive -cells. The rise in plasma cortisol levels was not significant, and the plasma levels of glucose and protein were unaffected. Nevertheless, somatotrope secretory activity was suppressed and somatic growth was stunted. This study demonstrates for the first time the complexity of the endocrine response to acid stress and that some of the response to acid stress can be attributed to the lowering of food intake.     

Stress response of juvenile rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)to chemical cues released from stressed conspecifics

The objective of this study was to determine whether exposure of rainbow trout (Oncorhynchus mykiss) to water containing a stressed trout or skin extract from stressed and non-stressed trout would elicit a stress response in conspecifics. Juvenile rainbow trout were exposed for 1 hour to water containing a stressed fish, homogenized skin extracts from a non-stressed fish, skin extract from a stressed fish and water with none of these factors. The stress response was measured over a 24-h period (1, 6, 12, 24 h after exposure). Plasma cortisol levels increased at 12 h in fish exposed to water from a stressed fish and skin extract from a stressed fish. Plasma glucose and hepatic hsp70 levels were not affected by treatments. The results suggest that rainbow trout elicit a stress response when exposed to stress-related alarm cues released from conspecifics.     

Elevated serum levels of alpha foetoprotein (AFP)-like immunoreactivity in rainbow trout, Oncorhynchus mykiss (Walbaum), with aflatoxin B1 induced hepatocellular carcinoma

Abstract. Alpha foetoprotein (AFP)-like immunoreactivity was detected by double immunodiffusion in thesera of adult rainbow trout, Oncorhyachus mykiss (Walbaum) with histologically confirmed hepatocellular carcinoma experimentally induced in microinjection of embryos with aflatoxin B₁ (AFB₁). Partial characterization indicated that this AFP-like immunoreactivity gave immunologic cross-reaction of partial identity with human AFP. had alpha₁ electrophorctic mobility, and an estimated molecular weight of 72kDa. Elevated serum AFP-like immunoreactivity levels were also measured by RIA in seven out of eight adult rainbow trout with hepatocellular carcinoma, and in three out of 17 AFB₁-exposed trout without demonstrable grosws or microscopic evidence for hepatocellular neoplasms. No serum AFP-like immunoreactivity was detected or measured in normal healthy age matched DMSO-control rainbow trout. These data are consistent with the following conelusions: (1) AFP-like immunoreactivity detected and measured in the sera of rainbow trout with hepaloecllular careinoma is an analogue to human AFP; and (2) the elevated serum AFP levels measured in adult rainbow trout wilh hepatocellular careinoma resrmble those found in humans with this same malignancy. These data further suggest that serum AFP measurements might be useful to confirm the appearance of hepatocellular carcinoma in experimental fish carcinogen-assay systems, and to detect hepatocellular neoplasia in high-risk wild fish populations exposed to carcinogenie pollutants.     

Variation in semen production of farmed Atlantic salmon and rainbow trout

The variation in semen production among farmed Atlantic salmon (Salmo salar) and rainbow trout (Salmo gairdneri) has been studied. Both species were stripped at weekly intervals, the Atlantic salmon four times and the rainbow trout three times.The individual variation in volume of semen was very high, particularly in rainbow trout. The total volume of semen obtained was 137 ml (20 ml/kg body weight) in Atlantic salmon and 23 ml (5 ml/kg body weight) in rainbow trout. The intraclass correlation for volume of semen was estimated at 0.73 in Atlantic salmon and at 0.59 in rainbow trout. The correlations between volume of semen and body size (weight and length) were all positive. They were all significant and medium in Atlantic salmon whereas in rainbow trout they were all low and significant only for volume of semen at first stripping.The number of males needed to supply the Norwegian fish farming industry with semen is discussed. It is concluded that the possibility of disseminating genetic improvement throughout the whole population of farmed Atlantic salmon and rainbow trout by transport of semen from selected males is considerable.     

Effect of cortisol on the metabolism of 17-hydroxyprogesterone by Arctic charr and rainbow trout embryos

The effect of cortisol on the in vitro metabolism of [³H]17-hydroxyprogesterone ([³H]17OHP) was studied during embryonic development of Arctic charr (Salvelinus alpinus) and rainbow trout (Oncorhynchus mykiss). In the absence of cortisol, rainbow trout embryos metabolized [³H]17OHP largely to androstenedione (A₄) and androstenetrione (11-KA) with a minor conversion to 17,20ß-dihydroxy-4-pregnen-3-one (17,20P). In the presence of cortisol, this biosynthesis was inhibited. On the other hand, cortisol had no apparent inhibitory effect on the nature of metabolism of [³H]17OHP by Arctic charr embryos. In these embryos [³H]17OHP was metabolized mainly to 17,20P with a minor conversion to A₄ and without the formation of 11-KA that was seen in rainbow trout.When incubated in the presence of [³H]cortisol both Arctic charr and rainbow trout embryos produced 11ß-hydroxyandrostenedione (11ß-OHA) as the major metabolite, with a minor conversion to an unknown steroid. The catabolism of the cortisol by salmonid embryos may reflect the ability of the embryo to inactivate or detoxify cortisol to protect itself from the adverse effects of this biologically potent steroid hormone The study indicates the existence of species-specific differences in the nature of metabolism of [³H]17OHP and the inhibitory effect of cortisol on this metabolism.     

An homologous radioimmunoassay for brown trout (Salmo trutta) vitellogenin

An homologous radioimmunoassay for brown trout vitellogenin (VTG) was developed. Intact VTG, isolated from juvenile brown trout by selective precipitation and anion exchange chromatography was labelled with Na¹²⁵I, with 1,3,4,6-tetrachloro-3,6-diphenylglycoluril (Iodogen) as the oxidizing agent. Incorporation of Na¹²⁵I into VTG was higher than 75% and there was little degradation of the labelled protein. Labelled VTG eluted at the same position as unlabelled, purified brown trout VTG when analyzed by gel filtration on Sepharose 6B. Antisera with high titers, i.e. 1250 000, against brown trout VTG were raised in rabbits. The sensitivity of the assay was 5 ng VTG/ml and the standard curve was linear between 10 and 100 ng VTG/ml. Plasma from maturing female brown trout, as well as estradiol-treated and untreated juvenile brown trout diluted parallel to the standard curve, while plasma from maturing female rainbow trout and estradiol-treated arctic charr diluted non-parallel to the standard curve for brown trout VTG. Purified rainbow trout VTG and plasma from maturing female rainbow trout diluted parallel to each other, but with lower sensitivity than for brown trout VTG. Determinations of protein-bound phosphorus in the plasma of estradiol-treated juvenile brown trout correlated well with the RIA determinations of VTG. Repeated freezing and thawing of plasma samples yielded up to a hundred-fold increase in the apparent VTG level, while storage of a plasma sample for one year at –20°C did not affect the VTG level as measured by RIA.     

The non-specific activation of rainbow trout, Salmo gairdneri Richardson, complement by Aeromonas salmonicida extracellular products and the correlation of complement activity with the inactivation of lethal toxicity products

Abstract The possible mechanism of inactivation of the toxicity of Aeromonas salmonicida extracellular products (ECP) by normal rainbow trout serum was investigated using juvenile rainbow trout. ECP was prepared from culture supernatant by an acetone precipitation method. The ECP was incubated with normal rainbow trout serum at 20°C for 2 h, and the interrelationship between ECP proteolytic activity and immune complex-initiating, haemolytic complement activity (CH₅₀) of normal serum against antibody-sensitized goldfish red blood cells was evaluated. When normal serum was incubated with increasing concentrations of ECP, the CH₅₀ activity of serum decreased. The CH₅₀ activity was completely abolished in serum treated with undiluted ECP. ECP treated with serum was administered to trout intraperitoneally to determine mortality. All the fish receiving untreated ECP (0.05 ml = 0.5 mg protein) alone died within 24 h. When ECP was treated with serum at 1:1 to 4:1 (serum: ECP) in volume a similar high mortality was produced. These inocula possessed high protease activity and no or low CH₅₀ activity. However, mortality decreased and finally no mortality was recorded as ECP was treated with large volumes of serum (9:1 to 19:1). These inocula had lower protease activity and considerably higher CH₅₀ activity. Fish receiving ECP treated with heat-inactivated serum at 19:1 showed 100% mortality. A serum: ECP inoculum derived from fish which had been administered lipopolysaccharide from Salmonella enteritidis and which possessed a low CH₅₀ activity also gave a high mortality when used at 19:1. These results suggest that rainbow trout complement is implicated in the inactivation of toxicity of A. salmonicida ECP.     

Effects of hydroalcoholic extract of honeybee pollen on growth performance,flesh quality,and immune and stress response response of rainbow trout (Oncorhynchus mykiss)

The effects of dietary hydroalcoholic extract of honeybee pollen (HBPE) on growth performance, flesh quality, immunity and stress response were investigated. Two hundred fifty‐five rainbow trout (11.14 ± 1.06 g) were fed five diets containing increasing levels of HBPE: control, 0.25HBPE (0.25 g HBPE/kg), 0.5HBPE (0.5 g HBPE/kg), 1HBPE (1 g HBPE/kg) and 1.5HBPE (1.5 g HBPE/kg). After 56 days, rainbow trout fed the 0.5HBPE and 1HBPE diets displayed significantly higher weight gain (49.58 and 53.25 g) and protein efficiency (2.88 and 2.83) compared to those fed the control diet (4.89 and 2.05), respectively (p < .05). For flesh quality, higher protein content in the whole body of fish fed the 1HBPE (633.3 g/kg) and 1.5HBPE (640.9 g/kg) diets was observed when compared to other groups (p < .05). There were no significant differences in the saturated and monounsaturated fatty acid content. Individuals fed the 1HBPE (234.5 g/kg) and 1.5HBPE (234.7 g/kg) diets exhibited higher levels of n‐3 long‐chain polyunsaturated fatty acids in the muscle than the other groups (p < .05). In terms of the immune system, the serum lysozyme and alternative complement pathway haemolytic activity levels in the 0.5HBPE (47.66 and 148.00 U/ml) and 1HBPE (46.00 and 146.33 U/ml) treatments were higher than the other treatments (p < .05). When Aeromonas hydrophila was exposed to different dosages of HBPE, a higher inhibitory zone resulted from 1,000 and 1,500 mg/ml dosage. The lower levels of plasma cortisol were observed in the 1HBPE and 1.5HBPE groups after the complement stress test. Collectively, the present findings suggest that the 1HBPE diet supported superior growth, flesh quality, immunity and stress response of rainbow trout.     

Reduced water oxygen levels affect maximal feed intake, but not protein or energy utilization efficiency of rainbow trout (Oncorhynchus mykiss)

This study examined the effect of reduced water oxygen levels on the utilization efficiencies of energy and protein from a diet fed to rainbow trout. An experimental diet was fed at one of the four ration levels with an additional starved treatment also included in each oxygenation regime. Oxygen levels in each oxygenation regime varied with ration level, but averaged 9.3 ± 0.36 mg L⁻¹ for the normal regime and 5.7 ± 1.4 mg L⁻¹ for the hypoxia regime. Significant differences were observed in the apparent satietal feed intake levels in each oxygenation regime, but not at any of the pair-fed restricted levels. No significant effects of oxygenation regime were observed on the utilization of either energy or protein by the fish. Efficiency of protein use varied depending on the protein intake level, but was not significantly affected by oxygenation regime. This study demonstrates that a reduction in the oxygen levels of the water does not affect the utilization efficiency of dietary digestible protein and energy in rainbow trout, but does result in a downregulation of feed intake when the fish is fed to apparent satietal levels.     

Stress-induced changes in the affinity and abundance of cytosolic cortisol-binding sites in the liver of rainbow trout,Oncorhynchus mykiss (Walbaum), are not accompanied by changes in measurable nuclear binding

Plasma cortisol levels and the number (N_max) and affinity (K_d) of specific hepatic cortisol-binding sites were determined in rainbow trout subjected to chronic confinement stress for 14 days. Confinement significantly elevated plasma cortisol levels to 47.3 ± 13.5 ng ml^–1 within 24h and although levels declined to 8.0 ± 3.0 ng ml^–1 after 14 days, they were significantly higher throughout than levels in unstressed control fish (< 2.0 ng ml^–1). There was a 60% reduction in cytosolic N_max in stressed fish during the first 24h of confinement (35.8 ± 7.9 cf. 129.0 ± 15.2 fmol mg^–1 protein), a decline which was sustained at 7 days after the onset of stress but, although numbers of binding sites in the liver of stressed fish were still lower than in unstressed fish, the difference was no longer significant after 14 days of confinement. There was an accompanying significant rise in the K_d of cortisol binding in stressed fish during confinement, from 4.0 ± 0.6 nM at time 0 to 8.4 ± 0.8 nM after 24 h confinement. This increment in K_d was sustained at a level significantly higher than in control fish throughout the 14 day confinement period, despite marked reductions in cortisol levels and increases in N_max in stressed fish. Throughout the study, specific binding of cortisol could not be consistently detected in high-salt nuclear extracts from stressed or unstressed fish, suggesting either that high-affinity binding sites for cortisol were absent from these preparations, that receptors were present but unable to interact with ligand because they were occupied, or that receptors were present but not being extracted. These possibilities were investigated using a range of extraction procedures, by varying the temperature of incubation, by employing dexamethasone as ligand and by examining binding in purified, intact, nuclei. Estradiol was employed as a methodological control throughout and substantial amounts of specific estradiol binding were detected in all compartments and preparations. Specific cortisol-binding sites were detected in intact nuclei of both stressed and unstressed fish, at levels an order of magnitude lower than estradiol binding in the same preparations. These data demonstrate that activation of the pituitary-interrenal axis leads to significant changes in the nature of target-tissue binding of cortisol in rainbow trout, and reveal a clear difference in the subcellular distribution of binding-sites for estradiol and cortisol, which reflects the situation in mammalian tissues.