Effects of dietary nucleotides supplementation on rainbow trout (Oncorhynchus mykiss) performance and acute stress response

This experiment was conducted to examine the effect of dietary nucleotides (NT) on fish performance and acute stress response on fingerling rainbow trout (23 g ± 0.01, mean weight ± SEM). Five experimental diets according to different levels of supplemented nucleotides (0, 0.05, 0.1, 0.15, and 0.2%) were assayed on experimental fish for 8 weeks. Growth, hematological parameters (hematocrit, hemoglobin, erythrocyte, lymphocyte, and neutrophil count), serum proteins (globulin, albumin), and plasma enzymatic activity (alkaline phosphatase, ALP; aspartate transaminase, AST; lactate dehydrogenase, LDH; alanine transaminase, ALT) were assayed. At the end of feeding trial, fish fed the control and 0.2% diets were subjected to handling and crowding stress. Modulatory effects of nucleotides on acute stress response (cortisol and glucose) and plasma electrolytes (Na⁺, Cl⁻, K⁺, and Ca²⁺) were studied. The percentage of body weight gain (WG) and feed efficiency (FE) of fish were better when the fish were fed 0.15–0.2% diets. Fish fed the nucleotide-supplemented diets tended to have lower levels of serum enzymes including ALP, AST, LDH, and ALT. Plasma cortisol levels of fish fed on 0.2% diet under handling and crowding stress were significantly lower than fish fed the control diet at all post-stress time intervals. In our study, fish fed nucleotide-supplemented diet had significantly lower concentrations of glucose compared to those fed the basal diet. The concentrations of sodium, chloride, calcium, and potassium of fish fed the control diet were significantly lower than in fish fed nucleotide-supplemented diet. Dietary nucleotides administration seems to promote growth and to enhance resistance against handling and crowding stress in fingerling rainbow trout.     

Effects of dietary yeast inclusion and acute stress on post-prandial whole blood profiles of dorsal aorta-cannulated rainbow trout

Yeast is a potential alternative to fish meal in diets for farmed fish, yet replacing more than 50 % of fish meal results in reduced fish growth. In a 4-week experiment, 15 rainbow trout (Oncorhynchus mykiss) were cannulated and fed three diets each week: 30 % fish meal as a control (FM); 60 % replacement of fish meal protein, on a digestible basis, with Saccharomyces cerevisiae (SC); and 60 % replacement with Wickerhamomyces anomalus and S. cerevisiae mix (WA). Blood was collected at 0, 3, 6, 12 and 24 h after feeding. In the final week, fish were exposed to a 1-min netting stressor to evaluate possible diet–stress interactions. Significant increases in pH, TCO₂, HCO₃ and base excess were found after fish were fed the SC and WA diets compared with FM, which elevated blood alkaline tides. Yeast ingredients had lower buffering capacity and ash content than fish meal, which explained the increase in alkaline tides. In addition, fish fed the WA diet had significantly reduced erythrocyte area and fish fed SC and WA diets had increased mean corpuscular haemoglobin levels, indicating haemolytic anaemia. Higher levels of nucleic acid in yeast-based diets and potentially higher production of reactive oxygen species were suspected of damaging haemoglobin, which require replacement by smaller immature erythrocytes. Acute stress caused the expected rise in cortisol and glucose levels, but no interaction with diet was found. These results show that replacing 60 % of fish meal protein with yeasts can induce haemolytic anaemia in rainbow trout, which may limit yeast inclusion in diets for farmed fish.     

Effects of dietary β-carotene on the immune response of rainbow trout Oncorhynchus mykiss

SUMMARY: We attempt to assess the impact of different levels of dietary β-carotene on immune function in rainbow trout. Semi-purified diets containing 0, 40, 200, and 400 mg β-carotene/kg dry diet were fed for 12 weeks to fish with average weight of 45 g. In addition to the humoral and cellular immune parameters, growth and feed utilization were examined. There were no marked differences in growth and feed utilization showing that β-carotene was not particularly efficient in enhancing growth of rainbow trout. Of the immune parameters measured, total immunoglobulin was significantly highest for the 200 mg β-carotene fed group. Serum complement activity (alternate pathway) at 200 and 400 mg β-carotene supplementation was significantly higher than that of the unsupplemented group. An increasing trend in lysozyme activity was observed, however, the differences among the groups were not significant. Phagocytic activity was similar among diet groups except at the highest level of supplementation where it was the maximum. Oxygen radical production by peripheral blood leukocytes appeared to be lower at higher levels of carotenoid supplementation. Overall, dietary β-carotene clearly enhanced immune response parameters in rainbow trout such as serum complement activity and total plasma immunoglobulin but did not show a definite influence for the other factors examined in the present study.     

Effects of dietary yeast inclusion and acute stress on postprandial plasma free amino acid profiles of dorsal aorta‐cannulated rainbow trout

In a 4‐week experiment, 15 cannulated rainbow trout were fed three diets based on fish meal (FM), Saccharomyces cerevisiae yeast (SC) and Wickerhamomyces anomalus and S. cerevisiae yeast mix (WA). Fish were fed daily, and blood samples were collected on day 7 of each week at 0, 3, 6, 12 and 24 hr after feeding. In the final week, fish were exposed to a 1‐min netting stressor. All essential and non‐essential plasma amino acid levels except methionine were similar between fish fed diets FM, SC and WA. Plasma methionine and sarcosine were significantly higher in fish fed diets SC and WA, possibly due to the crystalline methionine level, form or feeding regime. Hydroxy‐proline and 3‐methyl‐histidine were higher in fish fed diet FM, which can be explained by the higher levels present in fish meal compared with yeast. In stressed fish, there were no dietary effects on plasma amino acid levels, but significant increases in taurine and cystathionine were found in stressed compared with unstressed fish. These results demonstrate that yeast‐based diets produce similar plasma amino acid profiles to fish meal and suggest that yeast may be a suitable fish meal replacement in diets for rainbow trout.     

Plasticity of the properties of mitochondria from rainbow trout red muscle with seasonal acclimatization

Cold-acclimation of rainbow trout brings only limited changes in muscle metabolic capacities, but marked modifications in membrane composition. Thus, we examined whether the functional properties of mitochondria from trout red muscle were modified by seasonal temperature acclimatization. Mitochondria from fall-acclimatized trout had higher maximal capacities (state 3 rates) for the oxidation of pyruvate and acyl carnitines at 12 and 20 °C than mitochondria isolated from summer-acclimatized trout. For these substrates, the increased oxidative capacity completely compensated for the seasonal drop in temperature. Pyruvate and palmitoyl carnitine were consistently the preferred substrates, while decanoyl and octanoyl carnitine were oxidized at higher rates than glutamine, particularly in fall trout. State 4 rates of oxygen uptake (obtained when all ADP has been converted to ATP) differed less among substrates, but varied seasonally. State 4 rates at 12 and 20 °C were higher in mitochondria isolated from fall than summer trout. At low temperatures, the Q₁₀ of both maximal and state 4 rates of substrate oxidation tended to be higher for mitochondria from fall trout. The apparent Arrhenius activation energy (E_a) for mitochondrial pyruvate oxidation was higher in fall than summer trout whereas the E_as for palmitoyl carnitine and decanoyl carnitine oxidation did not change. The fatty acids of mitochondrial phospholipids from fall trout were more polyunsaturated than those from summer trout, with 12% more double bonds occurring than in summer trout, suggesting that membrane restructuring may be involved in the observed compensatory responses.     

The effects of Spirulina platensis meal on proximate composition,fatty acid profile and lipid peroxidation of rainbow trout (Oncorhynchus mykiss) muscle

This study evaluated the effects of diets containing 0, 25, 50, 75 and 100 g kg^?1 Spirulina platensis on proximate composition, fatty acid profile and lipid peroxidation of rainbow trout (Oncorhynchus mykiss). Supplementation of S. platensis did not change moisture and protein contents, but fish fed 50 and 100 g kg^?1 S. platensis had lower muscle lipid content than those fed control diet (P < 0.05). Fish fed 100 g kg^?1 of S. platensis contained lower percentages of saturated and monounsaturated fatty acid and a higher percentage of polyunsaturated fatty acid than those fed control diet (P < 0.05). The n‐3/n‐6 ratio of the fatty acid increased and muscle atherogenic and thrombogenic indices were significantly decreased as the dietary supplement of S. platensis increased. Furthermore, lipid peroxidation of the fillet significantly decreased with increasing dietary S. platensis at 4 °C and at ?20 °C (P < 0.05). The results of this study show that supplementation of S. platensis to the diet improves muscle quality of the rainbow trout.     

Altered stress responses in rainbow trout following a dietary administration of cortisol and β-napthoflavone

Previous studies have demonstrated that fish inhabiting polluted waterways often have an impaired stress response at the organismal level. Given the possible link between the organismal (i.e. cortisol) and cellular (i.e. heat shock proteins; hsp) stress responses, we conducted this study to examine the ability of rainbow trout to respond to a 2 h, +14 °C heat stress (HS) challenge following a 28 d, sub-chronic exposure to increased concentrations of cortisol (5 mg kg⁻¹ b.w.), β-napthoflavone (bnf; 50 mg kg⁻¹ b.w.), and a combination of both (mixture), through the diet (1.5% b.w. every 48 h). While control fish responded to the HS by significantly increasing components of their organismal (cortisol, glucose, and lactate) and cellular (hepatic hsp70 protein) stress responses 6 and 24 h post HS, cortisol-, bnf-, and mixture-fed fish had impaired stress responses at both levels of organization. Additionally, hepatic hsp70 levels were significantly reduced 6 h post HS in cortisol-fed fish. While bnf-fed fish had significantly higher EROD activity, cortisol potentiated EROD activity in the mixture-fed fish. Similarly, plasma cortisol concentrations in the mixture-fed fish were significantly lower relative to cortisol-fed fish. These data are the first to indicate that sub-chronically stressed fish can have impaired stress responses at both the organismal and cellular levels. These findings raise questions regarding: (a) the universal and simple applicability of biological indicators of stress in fish; (b) the possible functional relationship between these two levels of stress responses; and (c) the importance of hsps in the generalized stress response of the whole organism. This revised version was published online in August 2006 with corrections to the Cover Date.     

急性高温胁迫对虹鳟和硬头鳟幼鱼抗氧化酶活性的影响

虹鳟(Oncorhynchus mykiss)与硬头鳟(O.mykiss)为同一种的不同生态型,都属冷水性鱼类.为探讨急性高温胁迫对虹鳟和硬头鳟抗氧化酶活性的影响,选取虹鳟[体重(22.76±2.89)g]和硬头鳟[体重(23.2±1.22)g]幼鱼,分别在不同温度梯度(16℃、20℃、22℃和24℃;16℃、19℃、...     

Socially induced stress and behavioural inhibition in response to angling exposure in rainbow trout

It is well known that fish can learn to avoid angling gear after experiencing a catch‐and‐release event, that is, after a private hooking experience. However, the possible importance of social information cues and their influence on an individual's vulnerability to angling remains largely unexplored, that is, social experience of a conspecific capture. The effects of private and social experience of hooking on the stress response of fish and subsequent catch rates were examined. Hatchery‐reared rainbow trout, Oncorhynchus mykiss (Walbaum), were implanted with heart rate loggers and experimentally subjected to private or social experience of hooking. Private and social experience of angling induced an increased heart rate in fish compared with naïve control fish. While private experience of hooking explained most of the reduced vulnerability to capture, no clear evidence was found that social experience of hooking affected angling vulnerability in fish that had never been hooked before. While both private and social experiences of angling constitute significant physiological stressors for rainbow trout, only the private experience reduces an individual's vulnerability to angling and in turn affecting population‐level catchability.     

Effects of exercise-training on cardiac performance and muscle enzymes in rainbow trout,Oncorhynchus mykiss

Rainbow trout,Oncorhynchus mykiss, were exercise-trained for 18 hours per day over 28 days at water velocities up to 60% of their measured U_crit. Anin situ perfused heart preparation was used to compare maximum cardiac performance between control and trained fish. Trained fish had a larger stroke volume at a given filling pressure, as well as an 18% higher cardiac output and a 25% greater maximum power output. These observations indicate that exercise training in rainbow trout improved maximum cardiac performance. Adrenaline produced positive inotropic and chronotropic effects on the perfused heart, but exercise training did not alter these stimulatory effects. Maximal activities of citrate synthase (CS), B-hydroxyacyl CoA dehydrogenase (HOAD), glutamate dehydrogenase (GDH) and carnitine palmitoyl transferase (CPT) were measured in cardiac and skeletal muscles. CS, HOAD and GDH increased in red and white skeletal muscle as a result of training. Training also increased GDH activity in the endocardium and epicardium, and increased HOAD in the epicardium. While the training regime did not result in a statistically significant increase in U_crit and produced a decrease in the condition factor of the fish, other training effects were clearly evident. Furthermore, significant correlations were observed between U_crit and the maximal activities of GDH and HOAD.     

Effects of seasonal temperature acclimatization on muscle metabolism in rainbow trout, Oncorhynchus mykiss

Maximal enzyme activities in cardiac and swimming muscles of rainbow trout (Oncorhynchus mykiss) were estimated during the natural progression of environmental temperature, between seasonal extremes of 4 and 18°C. Specific activity of marker enzymes were measured at a common temperature of 11°C to determine the potential for metabolic acclimatization. The results confirm an increased oxidative capacity in the cold, with little or no expansion in glycolytic capacity of slow muscle: citrate synthase (CS) activity was 23, 15 and 3 µmoles min^-1 g wet wt^-1 and pyruvate kinase (PK) 15, 23 and 17 µmoles min^-1 g wet wt^-1 from 4, 11 and 18°C acclimatized groups, respectively. Expansion of lipid metabolism was limited, with increased carnitine palmitoleoyltrasferase (CPT) seen only in the coldest group. Cardiac and fast muscle showed a similar response for CS but not PK or CPT which were greatest at 11 and 18°C, respectively. When compared with previous laboratory acclimation studies, these data suggest that environmental factors other than temperature are likely to influence the nature of metabolic acclimatization.     

Use of Chlorella vulgaris as a carotenoid source for rainbow trout: effect of dietary lipid content on pigmentation, digestibility and retention in the muscle tissue

Apparent digestibility, deposition and retention of carotenoids in the muscle of rainbow trout, Oncorhynchus mykiss, were investigated comparing the feeding of pigments from Chlorella vulgaris against commercially available pigments at two different total lipid contents (15% and 20% lipid). Algal biomass (ALG) was included in rainbow trout diets and muscle pigmentation was compared to that obtained in trout fed diets containing a 5:3 mixture of canthaxanthin and astaxanthin (MIX) (reflecting the relative concentrations of these carotenoids in the dry alga) or those fed a diet containing astaxanthin only (AST). Apparent digestibilities of pigments and nutrients were determined by the indirect method, using Cr2 O3 as indicator, and the colour intensity and pigment concentration were assessed in the muscle, using the Roche colour card for salmonids and UV-vis spectrophotometry. After 6 weeks feeding, colour intensity was similar for the various pigment sources, achieving levels 12 to 13, yet significantly higher in fish fed the diet with the higher lipid content ( 20%) (p<0.05). Pigment concentration in the muscle was also higher in the fish fed the high-fat diet. Muscle pigment concentrations were similar for fish fed diets ALG and MIX, and over 1.5 times higher than for diet AST (p<0.05) after 6 weeks. Apparent digestibility of dry matter, crude protein, lipid, total energy and specific carotenoid concentrations were also measured. Increased dietary fat content was shown to increase the deposition and the retention of carotenoids in muscle, and the difference increased with time (deposition increase of 10–20% at week 3 and 30–40% at week 6 and retention increase of 10–15% at week 3 and 30% at week 6). Pigment digestibility also apparently increases (10–20%) under those conditions despite the fact that no significant effects in terms of apparent digestibility increase were found for dry matter, protein, lipids or energy. © Rapid Science Ltd. 1998     

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.     

Effects of dietary copper and copper: Zinc ratio on rainbow trout Salmo gairdneri

Purified diets with 15 and 150 mg supplemental copper/kg with dietary copper: zinc ratios of 1:1 and 1:4 were fed for 20 weeks to rainbow trout of mean initial weight 15 g. No gross pathologies were noted in any group of fish; growth and feed conversion were the same in all groups of trout. Plasma zinc levels were positively correlated with dietary zinc intake but dietary copper level had no effect on plasma copper. Hepatic levels of copper and zinc were also related to the dietary intake of the respective minerals. The dietary copper: zinc ratio caused some small changes in the plasma and hepatic levels of a few minerals, but no evidence was found to suggest any zinc—copper antagonism in rainbow trout. The activity of the copper, zinc metalloenzyme superoxide dismutase in liver was unaffected by dietary copper or zinc intake.     

Spawning induces a shift in energy metabolism from glucose to lipid in rainbow trout white muscle

Enzymatic changes that occur in the white somatic muscle of rainbow trout (Oncorhynchus mykiss) in response to spawning were investigated, and the evenness of their distribution across the ventral-dorsal plane of this muscle was assessed. Four enzymes that are involved in energy metabolism were measured (phosphofructokinase: glycolytic capacity, 3-hydroxyacyl-CoA dehydrogenase: -oxidation, citrate synthase: citric acid cycle, cytochrome oxidase: oxidative capacity). The enzyme activities were followed in different parts of the white muscle of non-spawning female rainbow trout from May, four months after their first spawning, until December, at second spawning. Samples were taken from white epaxial muscle along the lateral line, on the dorsum, and in between. Samples were also taken from red muscle of non-spawning fish. The isoforms of myosin heavy chains (MyHC) were electrophoretically identified on 6% SDS-PAGE gel to study possible changes in contractile properties of the muscle.Transformation from the non-spawning to spawning phase was associated with dramatic changes in the activity of the enzymes studied in white muscle: glycolytic capacity decreased to less than half, whereas oxidative metabolism increased about two- to four-fold in all areas. Significant quantitative differences in enzyme activities were found between the three epaxial muscle areas: in the non-spawning fish lateral line samples differed from those taken in the other two areas, whereas in spawning fish the dorsal sample difered from the other two. No difference in the expression of MyHC-isoforms was found between spawning and non-spawning fish. Co-expression of both slow and fast isoforms was found in single fibres isolated from red muscle.The results show that the energy metabolism in white muscle of domestic rainbow trout is altered during spawning; i.e., the metabolism becomes increasingly aerobic, with an increased capacity for fatty acid utilization, concomitant with phenotypic changes associated with sexual maturation. These changes are especially pronounced in ventral, superficially located fibres.     

Effects of in vitro exposure to ozone and/or hyperoxia on superoxide dismutase, catalase, glutathione and lipid peroxidation in red blood cells and plasma of rainbow trout, Oncorhynchus mykiss (Walbaum)

In aquaculture, ozone is used as a disinfectant. In its production, extensive amounts of oxygen are formed resulting in hyperoxic conditions in culture units. Both ozone and hyperoxia have the potential to be toxic via pro‐oxidant mechanisms and to activate antioxidant defence systems in cultured species. To eliminate systemic effects, blood of rainbow trout, Oncorhynchus mykiss (Walbaum), was exposed in vitro for 5 min to ozone/hyperoxia or hyperoxia, and changes in antioxidant defences and lipid peroxidation were measured after exposure. Ozone exposure caused severe damage in red blood cells (rbc) detected as increased lipid peroxidation and oxidized glutathione (GSSG) levels in both plasma and rbc. Oxygen exposure alone increased intracellular lipid peroxidation and GSSG levels 10 min after exposure and was not evident in the plasma at any time. Ozone, but not oxygen exposure, decreased reduced glutathione (GSH) levels in plasma, and the changes were negatively correlated with increased lipid peroxidation in rbc, indicating that extracellular GSH has a dynamic role in the protection of rbc from direct oxidation by ozone. Both ozone and hyperoxic conditions increased superoxide dismutase (SOD) activity in rbc 3 and 6 h after exposure. In contrast, catalase activity was only increased 10 min after oxygen exposure, suggesting other catalase activation mechanisms rather than enzyme induction. The recovery of lipid peroxidation and GSSG levels in rbc after hyperoxia, but not ozone exposure, indicated a capacity to defend against hyperoxia‐produced oxidative damage, but an overwhelming of antioxidant defences by ozone in rainbow trout rbc in vitro.     

Effects of dietary nucleotides on the antioxidant status and serum lipids of rainbow trout (Oncorhynchus mykiss)

An 8‐week feeding experiment was conducted to evaluate the effects of dietary nucleotides (0, 0.5, 1, 1.5 and 2 g kg^?1) on serum antioxidative biomarkers and lipid contents of rainbow trout fingerlings. The serum triglycerides and low‐density lipoprotein (LDL)‐C levels were significantly decreased in fish fed diets containing 1.5 and 2 g kg^?1, whereas serum high‐density lipoprotein (HDL)‐C was higher in trout receiving diets with those levels of nucleotides. A significant decrease in thiobarbituric acid reactive substances concentration was observed in groups receiving 1.5 or 2 g kg^?1 of dietary nucleotides in comparison with control group (?32% and ?27%, respectively). A significant decrease was observed in catalase and serum glutathione peroxidase activity in trout fed 1.5 and 2 g kg^?1 dietary nucleotides compare with other groups. There were no significant changes in serum superoxide dismutase activity among the experimental groups. In conclusion, these results suggest that dietary nucleotides may reduce lipid peroxidation by increasing the levels of antioxidant lipoprotein, HDL‐C, and decreasing the LDL‐C, the main substrate of lipid peroxidation.