Tissue distribution, uptake, and requirement for alpha-tocopherol of rainbow trout (Salmo gairdneri) fed diets with a minimal content of unsaturated fatty acids

Lipid oxidation in sorted herring (Clupea harengus) filleting co-products from two seasons and its relationship to composition

Lipid oxidation in ice-stored sorted herring fractions (head, backbone, viscera + belly flap, tail, fillet) from spring and fall, and its association with endogenous prooxidants, antioxidants and lipid substrates were investigated. Peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) had increased significantly in all fractions after 1 day, but for both seasons, the most rapid PV and TBARS development occurred in head, which also had highest hemoglobin (Hb) levels and lipoxygenases (LOX) activity. Viscera + belly flap was overall the most stable part, and also had the highest α-tocopherol content. Pearson correlation analyses across all five fractions confirmed a significant impact of Hb, LOX and α-tocopherol on the lipid oxidation susceptibility, while content of total iron, copper, lipids or polyunsaturated fatty acids provided no significant correlation. Overall, the study showed which pro-oxidants that should be inhibited or removed to succeed with value adding of herring filleting co-products and the fillet itself.

Performance, feed utilization, and hepatic metabolic response of weaned juvenile Atlantic bluefin tuna (Thunnus thynnus L.): effects of dietary lipid level and source

Two trials were performed using extruded diets as on-growing feeds for weaned Atlantic bluefin tuna (Thunnus thynnus; ABT) to establish adequate dietary levels of both lipid and omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs), and impacts on lipid metabolism via liver gene expression. In trial A, ABT were fed with either a commercial feed (Magokoro®; MGK) as a reference diet or two experimental feeds differing in lipid levels (15 or 20%) using krill oil (KO) as the single lipid source in order to estimate suitable lipid content. Fish fed MGK displayed the highest growth, followed by 15KO, and therefore a dietary lipid content of 15% was considered preferable to 20% at this stage. In trial B, fish were fed MGK, 15KO, or a feed containing 15% lipid with a blend of KO and rapeseed oil (RO) (1:1, v/v; 15KORO). Fish fed 15KO and 15KORO showed no difference in weight gain, specific growth rate, and fork length. Increasing dietary lipid level or including vegetable oil, RO, in the feeds did not increase liver lipid content. Liver fatty acid compositions largely reflected dietary profiles confirming very limited endogenous LC-PUFA biosynthesis. Liver of ABT fed 15KO and 20KO displayed the highest contents of docosahexaenoic acid (DHA). The hepatic expression of genes encoding enzymes and transcription factors involved in lipid and fatty acid metabolism, as well as genes encoding antioxidant enzymes, showed that many of these genes were regulated by dietary lipid and LC-PUFA content. Results suggested that ABT juveniles can be on-grown on inert dry feeds that support good fish growth and the accumulation of DHA.

Tocopherols in Seafood and Aquaculture Products

Fish products contain various nutritionally beneficial components, namely, ω3-polyunsaturated fatty acids (ω3-PUFA), minerals, and vitamins. Particularly, tocopherols (α-, β-, γ-, and δ-tocopherol) can be provided by seafood and aquaculture products. Hence, this review shows the various aspects of tocopherols in seafood and aquaculture products. For tocopherol determination in these products, HPLC methods coupled with diode array detection in the UV area of the spectrum or fluorescence detection have been shown as sensitive and accurate. These newest methods have helped in understanding tocopherols fate upon ingestion by seafood organisms. Tocopherols pass through the intestinal mucosa mainly by the same passive diffusion mechanism as fats. After absorption, the transport mechanism is thought to consist of two loops. The first loop is dietary, including chylomicrons and fatty acids bound to carrier protein, transporting lipids mainly to the liver. The other is the transport from the liver to tissues and storage sites. Moreover, tocopherol levels in fish organisms correlate with diet levels, being adjusted in fish body depending on diet concentration. For farmed fish species, insufficient levels of tocopherols in the diet can lead to poor growth performance or to nutritional disease. The tocopherol quantity needed as a feed supplement depends on various factors, such as the vitamer mixture, the lipid level and source, the method of diet preparation, and the feed storage conditions. Other ingredients in diet may be of great importance, it has been proposed that α-tocopherol may behave as a prooxidant synergist at higher concentrations when prooxidants such as transition metals are present. However, the antioxidant action of tocopherols outweighs this prooxidant effect, provided that adequate conditions are used. In fact, muscle-based foods containing higher levels of tocopherol show, for instance, higher lipid stability. Besides, tocopherols are important not only from the nutritional point of view but also from the physiological one, since they are involved in many metabolic processes in the human organism. Moreover, synergistic interactions with selenium and ascorbic acid have been reported. It deserves attention that there is evidence tocopherols taken with food can prevent heart disease, while no such evidence was found for α-tocopherol as supplement. From this perspective, eating fish is advisable, since, for instance, a 100 g serving of salmon may provide nearly 14% of recommended dietary allowance.

Re-evaluation of the vitamin E requirements of juvenile tilapia (Oreochromis niloticus ✕ O. aureus)

A 10-week feeding trial was conducted to re-evaluate the level of dietary vitamin E (DL- α-tocopheryl acetate) that was adequate for juvenile tilapia Oreochromis niloticus ✕ O. aureus given diets containing two dietary lipid concentrations. Purified diets with eight levels of vitamin E (0, 25, 50, 75, 100, 150, 200, 400 mg/kg diet) at either 50 or 120 g lipid per kg were each given to three replicate groups of tilapia (mean weight: 0·69 (s.e.0·02) g) reared in a closed, recirculating system. Food efficiency and protein deposition were significantly (P < 0·05) higher in fish given 50 mg vitamin E per kg diet and 75 mg/kg diet in the 50 and 120 g lipid per kg groups respectively, compared with fish given the unsupplemented control diet. Mortality of fish was not affected by dietary treatment. Weight gain and liver microsomal ascorbic acid-stimulated lipid peroxidation data analysed by broken-line regression indicated that the optimum dietary vitamin E requirements in juvenile tilapia are 42 to 44 mg vitamin E per kg and 60 to 66 mg vitamin E per kg in 50 and 120 g lipid per kg diets, respectively.

Deposition of tocopherol and tocotrienol in the tissues of red hybrid tilapia, Oreochromis sp., fed vitamin E-free diets supplemented with different plant oils

Vitamin E, a potent antioxidant consisting of four isomers each (α, β, γ, δ) of tocopherol (T) and tocotrienol (T3), is found naturally in plant oils at different concentrations. In this study, four semi-purified isonitrogenous and isolipidic (10 %) diets containing canola oil, cold-pressed soybean oil, wheat germ oil, or palm fatty acid distillates (PFAD) as the sole vitamin E source were fed to triplicate groups of red hybrid tilapia (Oreochromis sp.) fingerlings (14.82 ± 0.05 g) for 45 days. Vitamin E concentrations and composition were measured in the muscle, liver, skin, and adipose tissue. Deposition of α-T (53.4-93.1 % of total vitamin E) predominated over deposition of other isomers, except in the liver of fish fed the SBO diet, where α-T and γ-T deposition was in the ratio 40:60. T3 deposition (2.6-29.4 %) was only detected in tissues of fish fed the PFAD diet; adipose tissue was the major storage depot. Fish fed the SBO diet contained significantly more (P < 0.05) muscle thiobarbituric acid-reactive substances. Muscle fatty acid composition reflected dietary fatty acid profile. This is the first study to compare the deposition in fish tissues of the naturally occurring vitamin E isomers present in plant oils. The type and concentration of endogenous vitamin E and the fatty acid composition of plant oils can affect the oxidative stability of tilapia tissues.

Vitamin C enhances vitamin E status and reduces oxidative stress indicators in sea bass larvae fed high DHA microdiets

Docosahexaenoic acid (DHA) is an essential fatty acid necessary for many biochemical, cellular and physiological functions in fish. However, high dietary levels of DHA increase free radical injury in sea bass (Dicentrarchus labrax) larvae muscle, even when vitamin E (α-tocopherol, α-TOH) is increased. Therefore, the inclusion of other nutrients with complementary antioxidant functions, such as vitamin C (ascorbic acid, vitC), could further contribute to prevent these lesions. The objective of the present study was to determine the effect of vitC inclusion (3,600 mg/kg) in high DHA (5% DW) and α-TOH (3,000 mg/kg) microdiets (diets 5/3,000 and 5/3,000 + vitC) in comparison to a control diet (1% DHA DW and 1,500 mg/kg of α-TOH; diet 1/1,500) on sea bass larvae growth, survival, whole body biochemical composition and thiobarbituric acid reactive substances (TBARS) content, muscle morphology, skeletal deformities and antioxidant enzymes, insulin-like growth factors (IGFs) and myosin expression (MyHC). Larvae fed diet 1/1,500 showed the best performance in terms of total length, incidence of muscular lesions and ossification degree. IGFs gene expression was elevated in 5/3,000 diet larvae, suggesting an increased muscle mitogenesis that was confirmed by the increase in the mRNA copies of MyHC. vitC effectively controlled oxidative damages in muscle, increased α-TOH larval contents and reduced TBARS content and the occurrence of skull deformities. The results of the present study showed the antioxidant synergism between vitamins E and C when high contents of DHA are included in sea bass larvae diets.

Selenium inclusion decreases oxidative stress indicators and muscle injuries in sea bass larvae fed high-DHA microdiets

The objective of the present study was to determine the effect of Se inclusion in high-DHA and vitamin E microdiets (5 g DHA/100 g dry weight and 300 mg vitamin E/100 g dry weight; 5 g DHA/100 g dry weight and 300 mg vitamin E/100 g dry weight supplemented with Se) in comparison with a control diet (1 g DHA/100 g dry weight and 150 mg vitamin E/100 g dry weight) on sea bass larval growth, survival, biochemical composition, malonaldehyde (MDA) content, muscle morphology and antioxidant enzymes (AOE), insulin-like growth factors (IGF) and myosin expression. For a given DHA and vitamin E dietary content, Se inclusion favoured larval total length and specific growth rate, and reduced the incidence of muscular lesions, MDA contents and AOE gene expression. In contrast, IGF gene expression was elevated in the 5/300 larvae, suggesting an increased muscle mitogenesis that was corroborated by the increase in mRNA copies of myosin heavy chain. The results of the present study denoted the beneficial effect of Se not only in preventing oxidative stress, as a glutathione peroxidase cofactor, but probably due to other as yet unknown physiological functions.

The quantitative requirement for α-tocopherol by juvenile African catfish, Clarias gariepinus Burchell

Employing practical-type diets containing graded levels of all-rac-α-tocopheryl acetate (0, 5, 15, 30, 45, 60, 75 or 100 mg/kg), the quantitative requirement for a-tocopherol by juvenile African catfish (Clarias gariepinus Burchell) was investigated. Diets, defined with respect to selenium, fatty acid and ascorbate inclusion, were offered for 12 weeks during which catfish grew from 10 g to 120 g. Dietary regime had no significant effect on growth (P > 0·05), although haematocrit values increased with increasing tocopherol dose above 15 mg/kg (assayed) (R2 = 0·71, P < 0·05). Tissue accretion of the vitamin increased concomitant with dietary dose (P < 0·001). Employing a colorimetric assay for thiobarbituric acid reactive substances (TBARS) it was evident that concentration ofTBARS in muscle and liver reflected tissue oxidation status, in that elevated dietary vitamin E resulted in decreased assayed TBARS (P < 0·05). By broken-line analysis the requirement for this species to suppress lipid peroxidation was estimated as 30 to 40 mg all-rac-a-tocopheryl acetate per kg dry diet and this agrees with published requirements of many fish species.

Effects of dietary lipid, vitamins and minerals on total amounts and redox status of glutathione and ubiquinone in tissues of Atlantic salmon (Salmo salar): a multivariate approach

The hypothesis of the present study was that Atlantic salmon (Salmo salar) would respond to large variations in supplementation of dietary pro- and antioxidants, and marine lipid, with adjustment of the endogenously synthesised antioxidants, glutathione (GSH) and ubiquinone (UQ). An experiment with 27–3 reduced factorial design (the number of cases reduced systematically from 27 (full design) to 24 (reduced design)) was conducted, where vitamins, minerals and lipid were supplemented in the diet at high and low levels. For the vitamins and minerals the high levels were chosen to be just below anticipated toxic levels and the low levels were just above the requirement (vitamin C, 30 and 1000 mg/kg; vitamin E, 70 and 430 mg/kg; Fe, 70 and 1200 mg/kg; Cu, 8 and 110 mg/kg; Mn, 12 and 200 mg/kg). For astaxanthin, the dietary levels were 10 and 50 mg/kg and for lipid, 150 and 330 g/kg. The experiment was started with post-smolts (148 (sd 17 g)) and lasted for 5 months. The only effect on GSH was a minor increase ( < 10 %) in total concentration in the liver in response to high dietary lipid. GSH redox state was not affected. UQ responded to dietary lipid, astaxanthin and vitamin E, both with regard to total concentration and redox state. Except for an effect of Fe on plasma GSH, the trace elements and vitamin C had no effect on tissue levels and oxidation state of GSH and UQ. This shows that the endogenous redox state is quite robust with regard to variation of dietary pro- and antioxidants in Atlantic salmon.

Fatty acid composition and lipid peroxidation of soft-shelled turtle, Pelodiscus sinensis, fed different dietary lipid sources

Juvenile soft-shelled turtles (Pelodiscus sinensis) were fed 7 diets containing 8% of lard, soybean oil, olive oil, menhaden fish oil, or mixtures of 1 to 1 ratio of fish oil and lard, soybean oil, olive oil for 10 weeks. Growth and muscle proximate compositions of the turtles were not affected by different dietary treatments (p>0.05). Fatty acid profiles in muscle polar lipids, muscle non-polar lipids, and liver polar lipids reflected the fatty acid composition of dietary lipid source. Turtles fed diets containing fish oil generally contained significantly higher (p<0.05) proportion of highly unsaturated fatty acids (HUFA) in both polar and non-polar lipids of muscle and polar fraction of liver lipids than those fed other oils. Non-polar fraction of liver lipids from all groups of turtles contained less than 1% of HUFA. All turtles contained relatively high proportions of oleic acid in their lipids regardless of the dietary lipid source. Further, lipid peroxidation in both muscle tissue and liver microsomes of turtles fed fish oil as the sole lipid source was greater (p<0.05) than those fed fish oil-free diets. Turtles fed olive oil as the sole lipid source had the lowest lipid peroxidation rate among all dietary groups. The results indicate that dietary n-3 HUFA may not be crucial for optimal growth of soft-shelled turtles although they may be used for metabolic purpose. Further, high level of dietary HUFA not only increases the HUFA content in turtle tissues, but also enhances the susceptibility of these tissues to lipid peroxidation.

Effect of dietary vitamin E level on growth, tissue lipid peroxidation, and erythrocyte fragility of transgenic coho salmon, Oncorhynchus kisutch

This study was conducted to investigate the effect of dietary vitamin E concentration on growth performance, iron-catalyzed lipid peroxidation in liver and muscle tissue, and erythrocyte fragility of transgenic growth hormone coho salmon (Oncorhynchus kisutch). Fish were fed one of four isoenergetic and isonitrogenous experimental diets that contained either 11, 29, 50, or 105 IU of vitamin E/kg. Following the 10-week feeding trial, no significant (P>0.05) diet-related differences were detected in growth, whole body proximate composition or erythrocyte fragility. The vitamin E contents of liver and muscle, however, were affected by the dietary treatment. Fish fed diets containing > or =50 IU of vitamin E/kg had significantly increased vitamin E concentrations in their tissues. Iron-catalyzed lipid peroxidation of liver and muscle tissue of fish fed elevated dietary vitamin E (> or =50 IU vitamin E/kg diet) was significantly lower (P<0.05) than that noted for fish fed the diet containing no supplemental vitamin E. The results indicated that changes in tissue lipid peroxidation measurements precede clinical signs of sub-optimal vitamin E intake.

Dietary vitamin C and vitamin E interact to influence growth and tissue composition of juvenile hybrid striped bass (Morone chrysops (female) x M. saxatilis (male)) but have limited effects on immune responses

Juvenile hybrid striped bass (initially 12.0 g) were fed diets containing deficient, adequate or excessive amounts of vitamin C and/or vitamin E in a factorial arrangement to investigate potential nutritional interaction and effects on immune responses. Nine semipurified diets were supplemented with 0, 25 or 2500 mg vitamin C/kg and 0, 30 or 300 mg vitamin E/kg and fed to fish in triplicate aquaria for 10 wk. Weight gain, feed efficiency, mortality and tissue vitamin levels were significantly (P < or = 0.05) affected by dietary vitamin levels. In addition, a significant interaction between vitamin C and vitamin E was observed. At inclusion levels of 25 and 2500 mg/kg, dietary vitamin C improved feed efficiency and protected fish fed vitamin E-deficient diets from growth depression and mortality. At inclusion levels of 30 and 300 mg/kg, vitamin E prevented mortality in fish fed vitamin C-deficient diets; however, 300 mg vitamin E/kg was necessary to prevent growth depression in vitamin C-deficient fish but was unable to improve feed efficiency. Lysozyme, bacterial killing ability, as well as plasma protein and total immunoglobulin levels of fish were not affected by dietary vitamin levels, whereas respiratory burst activity increased with vitamin E supplementation. Thus, interactions between vitamin C and vitamin E were observed in hybrid striped bass. These interactions may be due to the ability of vitamin C to regenerate vitamin E to its functional form but also suggest an ability of vitamin E to spare vitamin C.

Low vitamin E in diet reduces stress resistance of gilthead seabream (Sparus aurata) juveniles

This study investigates the effect of dietary vitamin E on juveniles of gilthead seabream under stressful situations, focusing on the effects on growth, haematology, some immune parameters and plasma cortisol as indicators of stress. Two sardine meal-based experimental diets, one of them supplemented with 150 mg of alpha tocopherol kg(-1) of diet (control) and another one without vitamin E supplementation (diet NE), were assayed under two different stress conditions: overcrowding as a chronic stressor (during 15 weeks) and repetitive chasing as an acute repetitive stressor. Low levels of vitamin E in the diet depleted alternative complement pathway activity [from 167.23 U ml(-1) (control fish) down to 100.99 U ml(-1)] and also nonspecific haemagglutination. Also, fish fed a non-supplemented diet showed an elevation of plasma cortisol basal levels without a stressor influence [from 3.91 ng cortisol ml(-1) plasma (control fish) up to 21.70 ng cortisol ml(-1) plasma]. Low levels of vitamin E in the diet also produced an increase of erythrocyte fragility. Under chronic stress, fish fed the vitamin E-deficient diet showed a reduction in growth and survival, and alterations in haematological parameters, such as an additional haemoconcentration in response to overcrowding when compared with control fish. Under repetitive stress, fish fed the vitamin E deficient diet showed faster elevation of plasma cortisol levels in response to stress and a lower survival rate than control fish. Production of oxygen radicals by blood neutrophils was reduced under repetitive stress in fish fed the non-supplemented diet. These results suggest that fish fed the vitamin E-deficient diet had lower stress resistance.

Effect of oral administration of high vitamin C and E dosages on the gilthead seabream (Sparus aurata L.) innate immune system

The effect of the oral administration of high dosages of vitamins C and E on the innate immune system of the seabream was investigated. Gilthead seabream (Sparus aurata L.) were fed four different diets for 45 days: a commercial diet as control, a 3g/kg vitamin C-supplemented diet, a 1.2g/kg vitamin E-supplemented diet or a diet containing both vitamin supplements. After 15, 30 and 45 days, serum ascorbic acid and alpha-tocopherol levels, growth, complement titers and head-kidney leucocyte phagocytic and respiratory burst activities were evaluated. The results showed that serum vitamin levels reflected dietary input. Fish fed the vitamin C-supplemented diet showed an enhanced respiratory burst activity, while fish fed the vitamin E-supplemented diet exhibited increased complement and phagocytic activities. All of these positive effects were found in fish fed the joint diet, as well as a synergistically enhanced respiratory burst activity at day 30. The results demonstrate that in vivo vitamins C and E exert a synergistic effect enhancing the respiratory burst activity of seabream phagocytes.

Vitamin E increases natural cytotoxic activity in seabream (Sparus aurata L.)

The natural cytotoxic activity of head-kidney leucocytes from gilthead seabream (Sparus aurata L.), after in vitro and in vivo vitamin E treatment, against tumor cells was studied by flow cytometry. Leucocytes were incubated in culture medium with different vitamin E supplementations (0.01-10 microg ml(-1)) for 6, 24 or 48 h and the results demonstrate that all the assayed vitamin E supplementations significantly enhanced the natural cytotoxic activity of leucocytes. To determine the effect of a high dietary level of vitamin E on this activity, fish were fed with 0 (control), 600, 1200 or 1800 mg of vitamin E supplementation kg(-1) diet for 2, 4 or 6 weeks. After 2 and 4 weeks of treatment, the natural cytotoxic activity was significantly enhanced at the highest (1.8 g kg(-1) diet) and lowest (600 mg kg(-1) diet) vitamin E supplement dosage, respectively. No effect of the vitamin E supplemented diet on seabream leucocyte natural cytotoxic cell activity was observed after 6 weeks of treatment.

Dietary vitamin-E modulates antioxidant defence system in giant freshwater prawn, Macrobrachium rosenbergii

The objectives of the present study were to determine the effect of supplementary vitamin-E (200, 400 and 600 mg/kg feed) on lipid peroxidation (LPX) and antioxidant defence system in gills and hepatopancreas of the freshwater prawn, Macrobrachium rosenbergii. Results indicated that vitamin-E inhibited LPX in the hepatopancreas in a comparatively lower dose than gills. Superoxide dismutase (SOD) activity was decreased significantly in gills in response to all the three supplemented diet, but in hepatopancreas decrease was observed only in response to higher doses of vitamin-E (400 and 600 mg/kg feed). Catalase (CAT) activity was reduced significantly only in gills but not in hepatopancreas. While glutathione peroxidase (GPX) activity was significantly elevated in the hepatopancreas by vitamin-E, its activity remains unaltered in gills. On the contrary, glutathione reductase (GR) activity was decreased in gills but that of hepatopancreas was constant. Glutathione (GSH) content of both gills and hepatopancreas was substantially elevated in the vitamin-E supplemented prawns. Although the ascorbic acid (ASA) content of gills was unchanged by vitamin-E, its level elevated significantly in hepatopancreas. Thus the findings of the present investigation suggest that dietary vitamin-E is capable of reducing LPX level and can modulate antioxidant defence system in gills and hepatopancreas, nevertheless, the response is highly tissue specific. It is further observed that highest dose of vitamin-E (600 mg/kg feed) could not render much additional protection in both the tissues.

Depletion of alpha-tocopherol and astaxanthin in Atlantic salmon (Salmo salar) affects autoxidative defense and fatty acid metabolism

Duplicate groups of Atlantic salmon post-smolts were fed four purified diets supplemented with both vitamin E and the carotenoid astaxanthin (Ax) (+E, +Ax), or supplemented with either vitamin E or Ax (-E, +Ax and +E, -Ax) or deficient in both vitamin E and Ax (-E, -Ax) for 22 wk. There were no effects of diet on growth rate, but an extensive lipoid liver degenerative lesion was observed in 15% of fish fed diets deficient in vitamin E. Tissue vitamin E concentrations varied in accordance with dietary vitamin E in liver, muscle, heart, plasma, brain and eye; levels were reduced to approximately 3% in liver but only to 40% in eye of fish fed diets deficient in vitamin E compared with those fed diets supplemented with vitamin E. An interactive sparing of Ax supplementation on tissue vitamin E concentration was observed, but only in brain. Dietary deficiency of both vitamin E and Ax significantly increased the recovery of desaturated and elongated products of both [1-(14)C] 18:3(n-3) and [1-(14)C] 20:5(n-3) in isolated hepatocytes, suggesting that conversion of fatty acids to their long-chain highly unsaturated products can be stimulated by a deficiency of lipid-soluble antioxidants. The antioxidant synergism of vitamin E and Ax was supported by their ability to reduce malondialdehyde formation in an in vitro stimulation of microsomal lipid peroxidation and to reduce plasma levels of 8-isoprostane. The results of this study suggest that both vitamin E and the carotenoid Ax have antioxidant functions in Atlantic salmon.

High dietary intake of alpha-tocopherol acetate enhances the non-specific immune response of gilthead seabream (Sparus aurata L.)

To determine the effects of three high levels of dietary intake of alpha-tocopherol acetate (vitamin E) on the non-specific immune response of gilthead seabream (Sparus aurata L.), specimens were fed a commercial diet (100 mg alpha-tocopherol kg-1) as control, or vitamin E supplemented diets (600, 1200 or 1800 mg alpha-tocopherol acetate kg-1) for 15, 30 or 45 days. Growth, serum alpha-tocopherol levels, natural haemolytic complement activity and head-kidney leucocyte migratory, respiratory burst and phagocytic activities were studied at each of the assay times. A positive correlation between alpha-tocopherol acetate intake and serum alpha-tocopherol levels was observed, the increase being linked to both the dosage and length of treatment. Specimens fed the diet supplemented with 600 mg vitamin E kg-1 showed no enhancement in any of their immune parameters, while those fed the diet supplemented with 1200 mg vitamin E kg-1 presented a slightly higher (but not statistically significant) specific growth rate than fish fed the other diets. In addition, serum haemolytic activity and the phagocytosis of head-kidney leucocytes were enhanced by the dietary intake of 1200 mg vitamin E kg-1 after 30 and 45 days of treatment, although leucocyte migration and respiratory burst activity remained unaffected. The highest vitamin E dietary dose used, 1800 mg kg-1, unexpectedly provoked no immunostimulation. These results indicate that a moderate level of vitamin E in the diet (1200 mg kg-1) stimulates the seabream's non-specific immune system after 30 days of administration. Lower or higher vitamin E concentrations may not be so effective, because of an imbalance in the vitamin E ratio with other antioxidants. The proposed dietary levels of vitamin together with the indicated administration time could be useful for reducing the susceptibility of farmed fish to infectious diseases.

Simultaneous determination of alpha-tocopheryl acetate and tocopherols in aquatic organisms and fish feed

In aquaculture, alpha-tocopheryl acetate (alpha-TA) is the main source of vitamin E used to fortify fish feed. alpha-TA in fish is often determined indirectly, i.e., by alkaline hydrolysis, followed by quantitation of "total alpha-tocopherol" (alpha-T) and subtraction of the natively present alpha-T. The aim of this study was to develop an HPLC method for the simultaneous quantitative determination of alpha-TA and free tocopherols in aquatic organisms and fish feed. The assay consists of a simple extraction with methanol containing butylhydroxytoluene (BHT) as an antioxidant, followed by reversed-phase chromatography with consecutive UV and fluorescence detection of alpha-TA and tocopherols, respectively. The peak of the internal standard tocol in the fluorescence trace was used for quantitation. Linearity was achieved over the range of 0.2 to 4.2 micrograms alpha-TA per ml extract of Artemia nauplii, which would correspond to 30.7 to 614.4 micrograms/g dry mass. The within-run coefficient of variation was 1.9% at a level of 310 micrograms/g dry mass. The recovery of alpha-TA ranged from 97.7 to 100.8% (concentration = 2.1 and 20.5 micrograms/ml, n = 6). The detection limit was about 7 ng and the quantification limit on spiked samples was 0.2 microgram/ml. This method was routinely applied to determine alpha-TA and alpha-, gamma- and delta-tocopherol (alpha-T, gamma-T, delta-T) simultaneously in Artemia, fish feed, shrimp eggs and various other aquatic organisms.

Effect of vitamin E on rat hepatic cytochrome P-450 activity

Hepatic cytochrome P-450 activity has been shown to be affected by various dietary factors including vitamin E. However, reports of the effect of dietary vitamin E on cytochrome P-450 activity have been inconsistent. The aim of the present study was to investigate the influence of dietary vitamin E on rat hepatic cytochrome P-450 activity. Three groups of six male weanling Sprague-Dawley rats were fed semipurified diets containing 0, 100, or 1,500 ppm vitamin E for eight weeks. Vitamin E was given in the form of alpha-tocopheryl acetate. Dietary vitamin E significantly affected liver vitamin E content (p < 0.05) but had no effect on rat hepatic total P-450 content, N-nitrosodimethylamine demethylase, and NADPH-cytochrome-P-450 reductase activities. Hepatic pentoxyresorufin O-dealkylase and glutathione S-transferase activities were significantly greater in rats fed 100 and 1,500 ppm vitamin E than in rats fed no vitamin E (p < 0.05). Dietary vitamin E induced changes in hepatic phospholipid fatty acid composition. Hepatic phospholipid linoleate was significantly greater in rats fed 0 and 1,500 ppm vitamin E than in rats fed 100 ppm vitamin E (p < 0.05). Hepatic phospholipid eicosapentaenoate was increased significantly by dietary vitamin E (p < 0.05). Hepatic thiobarbituric acid-reactive substance was significantly greater in rats fed no vitamin E than in rats fed 100 and 1,500 ppm vitamin E (p < 0.05). The results suggest that vitamin E may influence cytochrome P-450 IIB1 enzyme activity and may affect hepatic phospholipid fatty acid composition.

Distribution of alpha- and gamma-tocopherols in Atlantic salmon (Salmo salar) tissues

Groups of Atlantic salmon parr (mean initial weight 9.5 g) were fed three diets, the first containing no tocopherol supplement, the others supplemented with either all-rac-alpha-tocopherol (A-T) or RRR-gamma-tocopherol (G-T). Tocopherol concentrations in the liver, serum, testes, kidney, brain, gill, muscle, and perivisceral fat were measured after 36 wk. Despite a higher dietary intake of G-T, compared to A-T, deposition of gamma-tocopherol (gammaT) was less efficient than of alpha-tocopherol (alphaT) in most tissues except in the perivisceral fat, an adipose tissue. In fish fed the G-T diet, the gammaT/alphaT ratio was highest in the perivisceral fat and lowest in the liver, indicating that the liver is the most discriminatory organ for retaining alphaT as compared to gammaT, and the perivisceral fat is more suitable for the storage of gammaT. A negative correlation (P < 0.01) was observed between the gammaT/alphaT ratio and the corresponding tissue phospholipid content, suggesting that gammaT is less efficiently deposited compared to alphaT in the phospholipid-rich membranes which are presumed to be the functional site for lipid antioxidants in vivo. During restricted intake of alphaT, the liver and muscle exhibited the greatest reduction of this tocopherol among the tissues analyzed. The presence of minimal alphaT in the muscle from fish fed the tocopherol-unsupplemented diet led to greater susceptibility to lipid peroxidation after frozen storage than was the case for muscle containing higher concentrations of either alphaT or gammaT. However, both alphaT and gammaT were effective stabilizers of salmon muscle lipids during frozen storage.

Endogenous skeletal muscle antioxidants

Skeletal muscle is susceptible to oxidative deterioration due to a combination of lipid oxidation catalysts and membrane lipid systems that are high in unsaturated fatty acids. To prevent or delay oxidation reactions, several endogenous antioxidant systems are found in muscle tissue. These include alpha-tocopherol, histidine-containing dipeptides, and antioxidant enzymes such as glutathione peroxidase, superoxide dismutase, and catalase. The contribution of alpha-tocopherol to the oxidative stability of skeletal muscle is largely influenced by diet. Dietary supplementation of tocopherol has been shown to increase muscle alpha-tocopherol concentrations and inhibit both lipid oxidation and color deterioration. Dietary selenium supplementation has also been shown to increase the oxidative stability of muscle presumably by increasing the activity of glutathione peroxidase. The oxidative stability of skeletal muscle is also influenced by the histidine-containing dipeptides, carnosine and anserine. Whereas carnosine and anserine are affected by diet less than alpha-tocopherol and glutathione peroxidase, their concentrations vary widely with species and muscle type. In pigs, beef, and turkey muscle, carnosine concentrations are greater than anserine, while the opposite is true in rabbit, salmon, and chicken muscle. Anserine and carnosine are found in greater concentrations in muscle high in white fibers, with chicken white muscle containing over fivefold more anserine and carnosine than red muscle. Anserine and carnosine are thought to inhibit lipid oxidation by a combination of free radical scavenging and metal chelation.

Decreased concentration of hemoglobin, accumulation of lipid oxidation products and unchanged skeletal muscle in Atlantic salmon (Salmo salar) fed low dietary vitamin E

Atlantic salmon (Salmo salar) fry, initial weight 0.16 g, were fed a semipurified diet with 0, 15, 30, 60 or 120 mg dl-α-tocopheryl acetate/kg. After 24 weeks, the first two of these groups were extinct, and the fish receiving 30 mg/kg were clearly vitamin E deficient. Vitamin E deficient fish had low hemoglobin levels, characterized by a combination of reduced cellular hemoglobin concentration, red cell volume and red cell number, and an increased number and fraction of immature red blood cells. The hemoglobin concentration decreased over the decreasing range of experimental dl-ga-tocopheryl acetate levels. Therefore, even if 60 mg dl-α-tocopheryl acetate/kg gave good survival, this level was clearly physiologically suboptimal. Ceroid accumulated in the liver of fish fed 30 mg vitamin E/kg, and autofluorescent inclusions were found in the red blood cells of fish fed 30 and 60 mg vitamin E/kg. Degeneration of skeletal muscle was not observed in the present study.

Alterations in lipid peroxidation, antioxidant enzymes, and carcinogen metabolism in liver microsomes of vitamin E-deficient trout and rat

Feeding rainbow trout for 16 weeks a diet in which the levels of vitamin E were reduced 70-fold resulted in marked depletion (18-fold) of vitamin E levels in liver microsomes from these fish. The susceptibility of hepatic microsomes to lipid peroxidation in vitro and the levels of plasma and liver microsomal lipid hydroperoxides generated in vivo were markedly elevated in vitamin E-depleted trout. No appreciable alterations were observed in the liver microsomal cytochrome P450-dependent mixed-function oxidase system or in the fatty acid composition of trout liver microsomal membranes. Livers from rats fed a vitamin E-deficient diet for 10 weeks also had significantly lower levels of microsomal vitamin E. In addition, total cytochrome P450 levels were depressed (15%) and cytosolic glutathione was enhanced (40%) in livers from rats fed the vitamin E-depleted diet. Covalent binding of [3H]-(+)-benzo[a]pyrene-7,8-dihydrodiol to exogenous DNA in vitro was enhanced with liver microsomes from vitamin E-deficient trout and these fish were much more sensitive to the acute toxicity of this carcinogenic polycyclic aromatic hydrocarbon. These results indicate that trout may be a useful model for studying the significance of peroxidative pathways in carcinogenesis and their manipulation by dietary antioxidants.

Extraction of lipids and lipophilic antioxidants from fish tissues: a comparison among different methods

1. Lipids, phospholipids and lipid soluble antioxidants were extracted from Sparus auratus liver and white muscle by three different methods and the yields obtained were compared. 2. None of the three procedures can recover the above components with the same efficiency. 3. For comparison the methods were also applied to rat liver homogenates. 4. The choice of the extraction procedures depends on the tissue investigated and on specific research requirements.

Species differences in membrane susceptibility to lipid peroxidation

The susceptibility of liver microsomes to lipid peroxidation was evaluated in seven species: rat, rabbit, trout, mouse, pig, cow, and horse. Lipid peroxidation was measured as thiobarbituric acid reactive substances formed in the presence of either FeCl3-ADP/ascorbate or FeCl2/H2O2 initiating systems. For rat, rabbit, and trout microsomes, the order of susceptibility to peroxidation was rat greater than rabbit much greater than trout. The lack of peroxidation in trout microsomes could be explained by high microsomal vitamin E levels. Membrane fatty acid levels differed between species. Docosahexaenoic acid predominated in the trout, arachidonic acid in the rat, and linoleic acid in the rabbit. The contribution of individual fatty acids to lipid peroxidation reflected the degree of unsaturation with docosahexaenoic greater than arachidonic much much greater than linoleic. For all species except trout, the predicted susceptibility to peroxidation, based on the response of individual fatty acids, agreed well with directly measured microsomal peroxidation. With the exception of the trout, vitamin E content ranged from 0.083-0.311 nmol/mg microsomal protein between species, and low levels did not influence susceptibility to peroxidation. Trout microsomes peroxidized only after vitamin E depletion by prolonged incubation. The data indicate that below a vitamin E threshold, species differences in membrane susceptibility to peroxidation can be reasonably predicted based only on content of individual peroxidizable fatty acids.

The role of nutritional factors in the prevention of peroxidative damage to tissues

The multi-level defence system present in vertebrate cells to protect against chain reactions initiated by free radicals (mainly toxic metabolites of oxygen) is outlined. It comprises superoxide dismutases (Cu-Zn and Mn dependent), glutathione peroxidase (Se dependent), vitamin E and glutathione S-transferase.The protective role of superoxide dismutase (SOD) was demonstrated by studies on trout (Salmo gairdneri) retina (Desrochers and Hoffert 1983). This tissue is subject to very high O2 tensions but has a high resistance to O2 toxicity that is dependent on a high dismutating capacity. The activities of both the cytosolic Cu-Zn SOD and the mitochondrial Mn SOD in the liver of rainbow trout were significantly altered in response to changes in dietary intake of these minerals.Deficiency of Se did not affect the growth rate of rainbow trout but led to greatly reduced activities of hepatic and plasma glutathione (GSH) peroxidase. There was no evidence of a Se-independent GSH peroxidase activity. In rainbow trout depleted of Se there was a compensatory increase in hepatic GSH S-transferase activity. This enzyme in conjunction with GSH has been shown to inhibit lipid peroxidation in the Festimulated microsomal systemin vitro. A dietary synergism between vitamin E and Se in rainbow trout has been demonstrated.The vitamin E requirement of rainbow trout is related to the polyunsaturated fatty acid (PUFA) content of the diet. The molar ratio PUFA: vitamin E in rainbow trout tissues is lower than that in rats. Time course studies on the uptake of orally administered vitamin E showed rapid incorporation into biomembranes; few differences between normal and vitamin E deficient fish were evident. The ester form of vitamin E was more slowly assimilated than the alcohol.

Dietary requirements of rainbow trout for tryptophan, lysine and arginine determined by growth and biochemical measurements

Three separate studies were performed to determine the dietary requirements of rainbow troutSalmo gairdneri for tryptophan (Trp), lysine (Lys) and arginine (Arg) from both growth and biochemical data. The growth studies were carried out over a 12 week period. From graphical plots of % mean weight gain against % amino acid in diet the following requirement values were obtained, Trp 0.25% diet (0.4% dietary crude protein); Lys 1.9% diet (4.3% dietary protein); and Arg 1.6-1.8% diet (3.6-4% dietary protein). Plasma and liver amino acid concentrations measured 20h after feeding did not prove useful for determination of requirement values. Hepatic activities of Trp pyrrolase (TP), Lys α ketoglutarate reductase (LKGR) and arginase were not significantly affected by varying levels of Trp, Lys and Arg respectively in the diet. TP has a cytosolic location and a Km of 0.2 mM for Trp; LKGR is mitochondrial and the Km for Lys is 7.3 mM; arginase is also mitochondrial and has a Km of 4.9 mM for arginine. Measurements of expired(14)CO2, after injection of a tracer dose of(14)C amino acid, did allow estimates of requirement levels to be made. The values obtained from the oxidation studies reinforced the values obtained from the growth data but were not precise enough to justify using this method on its own.

Some effects of selenium deficiency on glutathione peroxidase (EC 1.11.1.9) activity and tissue pathology in rainbow trout (Salmo gairdneri)

1. Two duplicate groups of rainbow trout (Salmo gairdneri; mean weight 27 g) were given diets of differing selenium content (deficient 0.025 mg Se/kg; supplemented 1.022 mg Se/kg) for 30 weeks. 2. There were no significant differences between treatments in weight gain but packed cell volume, liver vitamin E and liver and plasma Se concentrations were all significantly lower in the Se-deficient trout. 3. Ataxia occurred in about 10% of the Se-deficient trout and histopathologies were evident in nerve cord (damage to axon sheath) and liver (loss of integrity in endoplasmic reticulum and mitochondria with appearance of increased vesiculation). 4. Glutathione peroxidase (EC 1.11.1.9) activity was significantly reduced in liver and plasma of Se-deficient fish but there was no indication, from differential assay, of any non-Se-dependent glutathione peroxidase activity. Glutathione transferase (EC 2.5.1.18) activity was significantly increased in Se-deficient trout.

Comparison of fatty acids and lipids of smolting hatchery-fed and wild Atlantic salmon Salmo salar

In Atlantic Canada the Atlantic salmon Salmo salar change from the parr stage to the smolt stage while still in fresh water, preparatory to migration to salt water. In some stocks this takes place during the second overwintering. In several hatcheries where the water temperature drops to 0-0.5 C and the ponds ice over, there is a high incidence of erosion of the dorsal and pectoral fins and sometimes of the caudal fin. No disease organism has been identified, and the lesions heal over in most cases. Dietary fatty acids were thought to be a factor. A detailed study of lipid recoveries and classes has shown that in the skins of abnormal fish the total lipid is 7.8% compared to 4.7% in control fish. Unexpectedly, an analysis of one lot of healthy smoltstage wild fish showed that whole bodies have only a quarter of the lipid of comparable hatchery fish. Comparison of fatty acids showed that wild fish lipids include a higher proportion of arachidonic acid than those of the hatchery fish. In the latter, linoleic acid is provided readily by diet but the elongation to arachidonic acid evidently does not proceed. These results suggest that the smolt lipid is involved intimately with either the cause of the dermal lesion or is a defense mechanism, possibly mediated through oxygenase activity.

Ontogenetical aspects of nutritional requirements in fish

Changes in morphology i.e. "metamorphosis", mode of respiration, allometric growth of organs, mode of swimming and efficiency of biochemical pathways are briefly reviewed. It is suggested that these processes form the basis for progressive changes in nutrient requirements involving formation and development of several organs, systems and function. Digestive tract morphology changes during ontogenesis and aspects of fish metabolism, protein synthesis rate and body growth rate are interconnected and an attempt is made to explain these processes so as to understand the specificity of larval and juvenile fish nutrient requirements as compared to subadults. Protein and amino acid requirements given the body mass perspective and the generalization of the protein maintenance requirement in protein requirements for maximum growth was estimated to amount to 5-20%. Several cases of amino acid deficiency symptoms showed strong dependence on fish weight (age), but even most numerous studies on salmonids are lacking complete research throughout the life history of one species in defined nutritional and environmental conditions. Larval and juvenile fish have reduced capacity of catabolic adaptability and this fact links them to strictly carnivorous mammals. An attempt is made, for the first time, to relate amino acid needs of fish to young and/or carnivorous mammals. Vitamin requirements of fish are reviewed, taking into account the relationship between body size and time of the first appearance of deficiency symptoms. These are virtually no studies on vitamin requirements in larval warm-water fishes and very few on first feeding salmonids. The same applies to the vitamin need in reproductory fish. Fatty acid deficiencies manifest themselves faster in juvenile fish, but larval fish might require separate classes of lipids, phosphatidylcholine, in the diet to develop and grow at all. It seems that the studies on nutrient requirements have so far not used an ontogenetical perspective, but evidence given throughout this work argues that it would be worthwhile.

Metabolic effects of feeding a high protein/low carbohydrate diet as compared to a low protein/high carbohydrate diet to rainbow troutSalmo gairdneri

Groups of trout were fed either a high protein/low carbohydrate (HP/LC) or a low protein/high carbohydrate (LP/HC) diet for 16 weeks. Fish fed the HP/LC diet had significantly higher levels of protein, ninhydrin positive material and tryptophan in plasma as well as lipid and protein in liver, but lower levels of glucose in plasma, glycogen in liver and a lower hepatosomatic index compared with fish fed the LP/HC diet. There were no differences concentrations of tryptophan or serotonin in the brain of fish fed the different diets. Fish fed the HP/LC diet had significantly lower activities of glycolytic enzymes but higher activities of gluconeogenic enzymes compared with the group fed the LP/HC diet. Those enzymes measured concerned with the TCA cycle or initiating amino acid catabolism were generally unaffected by diet although activities of threonine dehydrogenase, alanine aminotransferase and glutamate dehydrogenase were higher in those fish fed the HP/LC diet. The data suggest that rainbow trout show little adaptation in activities of amino acid catabolising enzymes to variations in dietary protein intake.

The effect of provision of the first-limiting amino acid, gastrointestinal microbial activity and the level of nitrogen intake on protein utilization and energy digestibility in rats

1. The present work with growing rats was undertaken to study the effect of protein quality, gastrointestinal microbial activity and the level of nitrogen intake on protein utilization and energy digestibility. The experiment involved a total of thirty-six dietary treatments in a 9 x 4 factorial design, with five rats per treatment. The thirty-six diets resulted from nine protein sources. Each diet was composed of a basal N-free mixture plus minerals and vitamins, with N sources added at the expense of the N-free mixture to provide 15.0 gN/kg dry matter (DM) in the first three protein-addition treatments and 30.0 gN/kg DM in the fourth protein-addition treatment. The nine protein sources were soya-bean meal, casein, wheat gluten, skim-milk powder, meat-and-bone meal, wheat bran, barley, wheat and cooked brown beans (Phaseolus vulgaris). The four formulations for each protein source incorporated the protein unsupplemented at 15.0 gN/kg DM, unsupplemented at 30.0 gN/kg DM, or supplemented at 15.0 gN/kg DM with the estimated first-limiting amino acid or the antibiotic Nebacitin. 2. With all protein sources, the inclusion of the first-limiting amino acid had no effect on either protein or energy digestibility. 3. The microbial activity in the digestive tract affected protein utilization and energy digestibility to a different degree depending primarily on the level and type of dietary fibre. True protein digestibility (TD) of skim-milk powder and brown beans, both rich in easily-fermentable energy, increased from 0.959 to 1.000 and from 0.680 to 0.777 respectively by the addition of Nebacitin. TD of the other protein sources was only marginally affected by the antibiotic treatment. Only with brown beans was the biological value (BV) markedly affected by Nebacitin with an increase from 0.482 to 0.557 by the treatment. Energy digestibility was significantly lower in rats given antibiotic with soya-bean meal, wheat bran, barley, wheat and brown beans. 4. The effect of level of N intake on protein utilization was dependent on both protein quality and the fibre concentration of the diet. Protein sources with high BV were more affected than proteins of lower BV. It was concluded that TD is not always independent of dietary protein concentration.

The glutathione S-transferases in selenium and vitamin E deficiency

Preliminary experiments confirmed the work of others showing that the total glutathione peroxidase (GSH-px) activity of rat liver supernatant fraction may be resolved into two peaks of activity (peaks I and II) by gel filtration, and that peak I is the selenium-containing enzyme and peak II is another peroxidase indistinguishable from glutathione S-transferase (GST). In selenium and vitamin E deficiency, the total activity of the GSH-px became very low, and the total activity of GST with 1-chloro-2,4-dinitrobenzene (CDNB) as substrate was enhanced. Study of the time course of these changes as deficiency progressed indicated that the stimulus for the rise in GST (CDNB) activity was the fall in GSH-px activity which preceded it. The peroxidase activity of GST was found to reside only in the GST AA, B and B2 forms of the enzyme, which were shown to be respectively a homodimer of the Yc subunit, a homodimer of the Ya subunit and a heterodimer of the YaYc subunit. As vitamin E and selenium deficiency progressed, the B2 and AA forms of the enzyme showed enhanced activity, which was interpreted as implying that the Yc subunit of the enzyme becomes enriched as a consequence of the withdrawal of selenium from the animal's diet. Densitometric measurements of the Yc and Ya subunits confirmed that the amount of the Yc subunit was nearly doubled in selenium deficiency, relative to the Ya subunit.

Some effects of vitamin E and selenium deprivation on tissue enzyme levels and indices of tissue peroxidation in rainbow trout (Salmo gairdneri)

Duplicate groups of rainbow trout (Salmo gairdneri) (mean weight 11 g) were given for 40 weeks one of four partially purified diets that were either adequate or low in selenium or vitamin E or both. Weight gains of trout given the dually deficient diet were significantly lower than those of trout given a complete diet or a diet deficient in Se. No mortalities occurred and the only pathology seen was exudative diathesis in the dually deficient trout. There was significant interaction between the two nutrients both with respect to packed cell volume and to malondialdehyde formation in the in vitro NADPH-dependent microsomal lipid peroxidation system. Tissue levels of vitamin E and Se decreased to very low levels in trout given diets lacking these nutrients. For plasma there was a significant effect of dietary vitamin E on Se concentration. Glutathione (GSH) peroxidase (EC 1.11.1.9) activity in liver and plasma was significantly lower in trout receiving low dietary Se but was independent of vitamin E intake. The ratios of hepatic GSH peroxidase activity measured with cumene hydroperoxide and hydrogen peroxide were the same for all treatments. This confirms the absence of a Se-independent GSH peroxidase activity in trout liver. Se deficiency did not lead to any compensatory increase in hepatic GSH transferase (EC 2.5.1.18) activity; values were essentially the same in all treatments. Plasma pyruvate kinase (EC 2.7.1.40) activity increased significantly in the trout deficient in both nutrients. This was thought to be due to leakage of the enzyme from the muscle and may be indicative of incipient (subclinical) muscle damage.

Rainbow trout liver microsomal lipid peroxidation. The effect of purified glutathione peroxidase, glutathione S-transferase and other factors

Glutathione peroxidase (glutathione: hydrogen-peroxide oxidoreductase, EC 1.11.1.9) was purified approximately 600-fold from rainbow trout liver soluble fraction and its activity in the NADPH microsomal lipid peroxidation system tested. The enzyme has an approximate molecular weight of 100 000, contains four subunits and four atoms of selenium per mol protein. No selenium-independent glutathione peroxidase activity could be attributed to glutathione S-transferase (EC 2.5.1.18) in trout liver. Glutathione peroxidase together with glutathione (GSH) did not provide any additional protection in the in vitro liver microsomal lipid peroxidation system over and above that provided by GSH alone. Microsomal lipid peroxidation was, however, reduced by a partially purified glutathione S-transferase together with GSH. The protection provided by dialysed liver cytosol in this system was not GSH-dependent, showing that other factors in addition to glutathione S-transferase are involved. Of other possible factors, vitamin E reduced lipid peroxidation in this system. Concentrations of vitamin E in microsomes before and after peroxidation in vitro indicated that protective cytosolic factor(s) act prior to the termination of the free radical chain reactions effected by vitamin E. A GSH-dependent protective factor was present in microsomal protein, malondialdehyde formation in the in vitro microsomal system being markedly reduced in the presence of 5 mM GSH but not significantly lowered by 1 mM GSH.

The effect of dietary lysine levels on growth and metabolism of rainbow trout (Salmo gairdneri)

Groups of rainbow trout (Salmo gairdneri; mean weight 5 g) were given diets containing 10, 12, 14, 17, 21, 24 and 26 g lysine/kg diet for 12 weeks. By analysis of the growth values the dietary requirement of lysine in this experiment was found to be 19 g/kg diet. A similar requirement value was obtained from a dose-response curve of expired 14CO2 (following an intraperitoneal injection of L-[U-14C]lysine) v. dietary lysine concentration. Liver concentrations of total lipid and carnitine and activities of lysine-alpha-ketoglutarate reductase (saccharopine dehydrogenase (NADP+, lysine-forming), EC 1.5.1.8) in the liver were not significantly different in fish from the different dietary treatments. Hepatosomatic index, however, was higher in those fish given low levels of dietary lysine.

The effect of vitamin E and oxidized fish oil on the nutrition of rainbow trout (Salmo gairdneri) grown at natural, varying water temperatures

Groups of rainbow trout (Salmo gairdneri) of approximate mean initial weight 8 g were grown in outdoor tanks over a 14-week period at water temperatures between 12 degrees (start) and 6 degrees (end). Four diets were used. Two contained non-oxidized fish oil (120 g/kg) with or without supplementary DL-alpha tocopheryl acetate and two contained moderately oxidized fish oil again with or without DL-alpha-tocopheryl acetate. The measured selenium content of the diets was 0.10 mg/kg. No significant differences occurred as a consequence of the use of moderately oxidized oil compared with the corresponding treatments using non-oxidized oil. Significant differences did occur between dietary treatments that contained supplementary DL-alpha-tocopheryl acetate and those that did not. These differences applied to weight gain, haematocrit, erythrocyte fragility, mortalities, liver and muscle tocopherol concentrations and lipid peroxidation of liver mitochondria in vitro. Liver glutathione peroxidase (EC 1.11.1.9) activity was unaffected by the dietary treatments used and the proportions of fatty acids in polar lipids of liver and muscle were little changed by the diets used. Severe muscle damage occurred in trout given diets lacking supplementary DL-alpha-tocopheryl acetate. Previous experiments carried out on rainbow trout at a constant water temperature of 15 degrees ( Hung et al. 1981; Cowey et al. 1981, 1983), using diets lacking supplementary vitamin E, did not lead to differences in weight gain, pathological changes or mortalities. Vitamin E requirement may increase as water temperature decreases; minimum dietary requirements for vitamin E measured at a constant water temperature of 15 degrees may not be valid under practical conditions where water temperatures vary over the year.

The effects of dietary tryptophan levels on growth and metabolism of rainbow trout (Salmo gairdneri)

Groups of rainbow trout (Salmo gairdneri) (mean weight 14 g) were given diets containing 0.8, 1.3, 2, 3, 4 or 6 g tryptophan/kg diet for 12 weeks. By analysis of the growth results, the dietary requirement of tryptophan was found to be 2.5 g/kg diet (equivalent to 50 mg/kg biomass per d). Carbon dioxide expired by trout following intraperitoneal injection of [14COOH]tryptophan contained little radioactivity when dietary tryptophan level was low but, above 2.0 g/kg diet, it increased rapidly with increasing dietary tryptophan level. The break point in the dose-response curve did not, however, coincide with that from the growth results. Changes in concentrations of free tryptophan in blood and liver and activity of hepatic tryptophan pyrrolase (EC 1. 13. 11. 11) in response to changes in dietary tryptophan concentration did not provide reliable indicators for quantifying dietary requirement. Unlike the situation in mammals, blood tryptophan was not protein-bound to any appreciable extent. Tryptophan pyrrolase of trout has properties which suggest it has no apoenzyme form. In fish given adequate levels of tryptophan injected intraperitoneally with a tracer dose of [14COOH]tryptophan, 60% of the dose was incorporated into body protein within 1 d. The turnover of the label in this protein is very slow. Those trout given diets deficient in tryptophan suffered from severe scoliosis and lordosis as well as having increased liver and kidney levels of calcium, magnesium, sodium and potassium.

Glutathione peroxidase (EC 1.11.1.9), glutathione-S-transferase (EC 2.5.1.13), superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6) activities in tissues of ducklings deprived of vitamin E and selenium

Vitamin E and selenium deficiencies were produced in the Pekin duckling (Anser cinerens) and were characterized by the development of lesions after 14 d in gizzard, intestine, heart and skeletal muscle. The activities of glutathione peroxidase (EC 1.11.1.9), using hydrogen peroxide and cumene hydroperoxide as substrates, glutathione-S-transferase (EC 2.5.1.13), superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6) were measured in homogenate supernatant fractions of liver, heart, intestine, gizzard and skeletal muscle of deficient ducklings and of control birds given vitamin E or Se or both. Glutathione peroxidase activities were dramatically lower in tissues of Se-deficient ducklings, and this was unaffected by vitamin E. No adaptive changes were seen in the activity of the other enzymes, even after 21 d when the deficiency was severe. It appeared likely that the variability of the enzyme activities, other than glutathione peroxidase, in the different tissues studied might explain differences among the tissues in susceptibility to peroxidative damage.