Kjartan Sandnes

Chemical and sensory evaluation of fillets from Atlantic salmon (Salmo salar) fed three levels of N-3 polyunsaturated fatty acids at two levels of vitamin E

Atlantic salmon (Salmo salar) were fed three dietary levels of n-3 polyunsaturated fatty acids (PUFA) (1.0, 2.5 and 5.0% of the diets at 17% feed lipid level), each with two levels of vitamin E supplementation (0 and 300 mg α-tocopherol acetate/kg diet). The varying dietary n-3 PUFA contents were achieved by using soybean oil, capelin oil and sardine oil, respectively. Sensory evaluation of cooked fillet from fresh, 4-days frozen, 5-weeks frozen (−18°C) and traditionally smoked fresh fish was performed. Fillet proximate composition did not differ between high-quality cultured and wild Atlantic salmon. The total lipid fatty acid composition and vitamin-E content of the fillets were highly influenced by the fish diets. The vitamin-E content of the fillets did not influence the fatty acid composition. Significant differences were found for 7 of 14 sensory parameters when comparing for homogeneity between the dietary groups. Rancid flavour was significantly higher in fish raised on a high n-3 PUFA and low vitamin-E diet. The results indicated a combined effect according to vitamin E and n-3 PUFA contents. Coloration of the fillet seemed to depend upon lipid quality and vitamin E, in addition to the feed content of pigments. The differences in fatty acid composition of the fillets caused differences in the sensory perception of fattiness, juiciness and taste intensity. Twelve of the sensory parameters showed significant differences between treatments. The freshly sampled fish was most white, tasted less intense, was most juicy and least firm. The smoked fish showed most coloration, least taste of soya, herring, rancidity and off-flavour, probably as a masking effect of the smoking procedure. Several sensory parameters were affected by freezing and storage, including decreased whiteness and increased colour strength, taste intensity, rancid flavour and off-flavour.

Growth and chemical composition of adult Atlantic salmon (Salmo salar) fed dry and silage-based diets

Abstract Atlantic salmon of 1.4 kg mean initial weight were held in four sea pens from September to May. The groups were fed one of four diets based on fish silage (A), a dry pelleted feed (B), a mixed partly defatted fish silage concentrate (C) and concentrated fish silage (D). The percentage of dietary metabolizable energy provided by protein and by lipid varied between 36 and 52%, and between 25 and 48%, respectively. The fish fed diets A and B had the highest final weights, 4.5 and 4.6 kg, respectively. Few differences were found between groups fed diets A, B and D in feed conversion, protein efficiency ratio (PER) and protein productive value (PPV). Fish fed diet C had reduced growth and slightly depressed food and protein conversion. A linear relationship was found between lipid intake and lipid retention in whole fish. The lipid content in fillets and livers reached mean levels of approximately 14 and 6%, respectively. The fillet lipids contained about 20% of ω-3 polyenoic fatty acids which reflected mainly the fatty acid composition of the dietary lipids. Alkaline phosphatase activity in serum showed a significant positive correlation with water temperature. Serum cholesterol level was reduced in the group fed the low lipid content diet (C) while triglyceride levels were not correlated with the lipid contents of the diets.

Dietary vitamin C, immunity and disease resistance in Atlantic salmon (Salmo salar)

Presmolt Atlantic salmon were fed a fish meal based experimental diet supplemented with graded levels of ascorbate-2-monophosphate (AP), equivalent to 40, 400, 2000 and 4000 mg ascorbic acid (AA)/kg for 6 months prior to a bacterial challenge experiment. The liver AA concentration reflected the dietary intake of AP, but not linearly. Growth, hematology and acid phosphatase activity in zymosan stimulated macrophages were not affected by dietary AP. Serum hemolytic complement activity was higher in fish fed the highest AP level, but the variation was not significant. Production of specific antibodies was significantly higher in fish fed the highest AP level 11 and 17 weeks after vaccination. Bacterial challenge with Aeromonas salmonicida showed increased survival in the 4000 AP group. Lysozyme activity in headkidney and serum complement activity and serum iron in fish surviving the challenge were higher in the 4000 AP group, indicating important roles of vitamin C on lysozyme, complement and iron in non-specific disease resistance. The results indicate that high dietary levels of AP favourably affect health in Atlantic salmon. Disease resistance was, however, not correlated with the AA status in the liver.

The effect of ascorbic acid supplementation in broodstock feed on reproduction of rainbow trout (Salmo gairdneri)

Abstract Two experimental diets differing in supplementation of ascorbic acid and a third commercial diet were fed to rainbow trout broodstock. A supplementation level of 115 mg ascorbic acid per kg significantly increased the number of hatching eggs compared to eggs from fish without dietary ascorbic acid supplementation. Fish reared on the commercial diet gave eggs of similar quality as from the ascorbic acid supplemented experimental feed. The results indicate that ascorbic acid is essential for reproduction in rainbow trout. Broodstock fish should be fed adequate amounts of the vitamin to provide eggs with more than 20 μg ascorbic acid/g.

The minimum dietary requirement of vitamin C in Atlantic salmon (Salmo salar) fry using Ca ascorbate-2-monophosphate as dietary source

The minimum dietary vitamin C requirement for optimal growth and normal development in Atlantic salmon (Salmo salar) fry at the onset of feeding was studied, using Ca ascorbate-2-monophosphate (AP) as dietary source. The requirement was established by means of a feeding study lasting for 23 weeks from the beginning of feeding. The practical diets used were supplemented with AP at levels of 0, 10, 20, 40, 80 and 160 mg ascorbic acid (AA) equivalents/kg. Growth, mortality, hydroxyproline content in skin and backbone, and AA in liver were recorded to evaluate the results. The results suggest that the minimum dietary requirement for optimal growth and normal development is in the range of 10–20 mg AA equivalents/kg dry diet during the period studied.

Ascorbate-2-sulfate as a dietary vitamin C source for Atlantic salmon (Salmo salar): 1. Growth, bioactivity, haematology and humoral immune response.

The present experiment shows that ascorbate-2-sulfate (AS) is not equivalent to ascorbic acid (AA) as a dietary vitamin C source for Atlantic salmon (Salmo salar). Within reasonable feed supplemental levels AS does not provide the tissues with adequate supplies of vitamin C to secure optimal physiological functions as demonstrated by biochemical and haematological analyses.AS could not be detected in the liver of fish fed either AA or AS, nor in vitamin C — deprived salmon, suggesting that AS is not the natural storage form of vitamin C in this species.There were no significant differences in antibody production against a soluble artificial antigen (NIP11-LPH) in fish fed 500 and 5000 mg AA/Kg dry diet or equivalent amounts of AS during a period of six weeks at a water temperature of 7.2°C.

Nutritional composition of rotifers following a change in diet from yeast and emulsified oil to microalgae

Rotifers, Brachionus plicatilis, fed bakers yeast and a lipid emulsion (High DNA Super Selco, INVE Aquaculture NV Systems SA, Belgium), were harvested and fed Isochrysis galbana for 72 h, the nutrient composition was analysed during this period. The enrichment effect on the rotifers following transfer to I. galbana was most pronounced for ascorbic acid and thiamin. I. galbana seemed to contribute very little as a source of the lipid-soluble vitamins. Most of the minerals and trace elements were unaffected by the transfer to I. galbana, but Fe, Mn, As and Cd increased, Cu and Ni decreased whereas the effect on Cr and Mo were uncertain. The fatty acid composition of the rotifers changed towards the composition of I. galbana during the experimental period. Intermediate glycogen levels were measured in the rotifers at all sampling times. With the exception of lysine, serine and proline, all amino acid levels seemed to be unaffected by the transfer to I. galbana. This study showed that transfer of rotifers to microalgae (I. galbana) feeding had a positive effect on nutritional value. Macronutrients were maintained at adequate levels, and algal feeding improved the nutritional quality of rotifers with respect to water-soluble vitamins. Changes in rotifer nutrient composition are discussed in relation to nutritional requirements of fish larvae.

Role of dietary ascorbic acid in vitellogenesis in rainbow trout (Salmo gairdneri)

Abstract Adult rainbow trout which were fed a diet devoid of ascorbic acid for 21 months, including the stages of gonadal development, showed no macroscopic signs of avitaminosis C and no increased mortality compared to a control group of fish with dietary supplementation of this vitamin. Fish without dietary supplementation of ascorbic acid contained more lipid in the liver and less in the ovaries than the reference fish. The lipid metabolism of the maturing fish is thus affected when the dietary intake of ascorbic acid is very low or absent. Fish without dietary ascorbic acid became anaemic (reduced levels of haemoglobin and haematocrit) towards the end of the feeding period. The serum levels of oestradiol-17β and vitellogenin were also lower in these fish. Possible modes of action of ascorbic acid in maturing rainbow trout are discussed on the basis of the presented analytical data on ascorbic acid, gross composition, blood serum levels of oestradiol-17β, vitellogenin, total protein, albumin, cholesterol, calcium, phosphorus and haematological parameters.

Ascorbate-2-sulfate as a dietary vitamin C source for Atlantic salmon (Salmo salar): 2. Effects of dietary levels and immunization on the metabolism of trace elements

Atlantic salmon fingerlings were fed a vitamin C deficient diet for four months. The fish were then provided a dry, practical fishmeal based diet supplemented with 0, 500 or 5000 mg vitamin C/kg as L-ascorbic acid or equivalent amounts of ascorbate-2-sulfate. After six weeks on these diets ten fish in each group were injected with a soluble antigen (NIP11-LPH). Six weeks thereafter blood, liver, kidney, spleen and vertebrae were examined for trace elements. The livers were also analysed for metallothionein.The vitamin C deficient fish were anemic despite the significantly elevated iron concentrations in the liver. Vitamin C had no positive effect in lowering tissue levels of cadmium. The highest level of dietary vitamin C given as ascorbic acid reduced the liver selenium concentrations. In response to antigen injection, the fish in all groups showed increased levels of hepatic metallothionein, copper, zinc and cadmium, while hepatic selenium and iron levels were less affected. The elemental composition in other organs was affected by the antigen injection to a minor extent.

Ascorbyl palmitate as a dietary vitamin C source for rainbow trout (Salmo gairdneri)

The vitamin C activity of ascorbyl palmitate was investigated for use in salmonid diets. Three groups of “swim up” rainbow trout (Salmo gairdneri) fry were fed identical basal diets for 12 weeks supplemented with no form of ascorbic acid (group A), 600 mg ascorbic acid/kg (group B) and ascorbyl palmitate in equimolar amounts to the group B supplement (group C). The fish in group C showed reduced growth for the first 8 weeks. From week 8 onwards growth rate in group C paralleled that in group B, while the fish fed the diet devoid of any form of vitamin C (group A) showed a reduced growth rate. The concentrations of ascorbic acid at the end of the experiment were < 0.5, 64 and 55 μg/g in whole fish and < 0.5, 156 and 118 μg/g in the liver for groups A, B and C, respectively. Vertebral collagen in fish fed ascorbyl palmitate contained similar levels of hydroxyproline to that in fish fed ascorbic acid as vitamin source. An in vitro assay demonstrated the presence in the rainbow trout gut of enzymatic activity hydrolyzing the ascorbyl palmitate.