title: Antioxidant nutrition in Atlantic salmon (Salmo salar) parr and post-smolt, fed diets with high inclusion of plant ingredients and graded levels of micronutrients and selected amino acids.
abstract: The shift from marine to plant-based ingredients in fish feeds affects the dietary concentrations and bioavailability of micronutrients, amino acids and lipids and consequently warrants a re-evaluation of dietary nutrient recommendations. In the present study, an Atlantic salmon diet high in plant ingredients was supplemented with graded levels of nutrient premix (NP), containing selected amino acids, taurine, cholesterol, vitamins and minerals. This article presents the results on the antioxidant nutrients vitamin C, E and selenium (Se), and effects on tissue redox status. The feed ingredients appeared to contain sufficient levels of vitamin E and Se to cover the requirements to prevent clinical deficiency symptoms. The body levels of α-tocopherol (TOH) in parr and that of Se in parr and post-smolt showed a linear relationship with dietary concentration, while α-TOH in post-smolt seemed to be saturable with a breakpoint near 140 mg kg-1. Ascorbic acid (Asc) concentration in the basal feed was below the expected minimum requirement, but the experimental period was probably too short for the fish to develop visible deficiency symptoms. Asc was saturable in both parr and post-smolt whole body at dietary concentrations of 190 and 63-89 mg kg-1, respectively. Maximum whole body Asc concentration was approximately 40 mg kg-1in parr and 14 mg kg-1in post-smolt. Retention ranged from 41 to 10% in parr and from -206 to 12% in post-smolt with increasing NP supplementation. This indicates that the post-smolts had an extraordinarily high consumption of Asc. Analyses of glutathione (GSH) and glutathione disulphide (GSSG) concentrations and the calculated GSH based redox potentials in liver and muscle tissue, indicated only minor effects of diets on redox regulation. However, the post-smolt were more oxidized than the parr. This was supported by the high consumption of Asc and high expression of gpx1 and gpx3 in liver. Based on the present trials, the recommendations for supplementation of vitamin C and E in diets for Atlantic salmon are similar to current practices, e.g. 150 mg kg-1of α-TOH and 190 mg kg-1Asc which was the saturating concentration in parr. Higher concentrations than what would prevent clinical deficiency symptoms are necessary to protect fish against incidents of oxidative stress and to improve immune and stress responses. There were no indications that the Se requirement exceeded the current recommendation of 0.3 mg kg-1.
authors.affiliation: National Institute of Nutrition and Seafood Research (NIFES), Bergen, Norway; Department of Biology, University of Bergen, Bergen, Norway.
authors.forename: Kristin
authors.identifier: 0000-0002-8302-3827
authors.initials: K
authors.lastname: Hamre
authors.affiliation: National Institute of Nutrition and Seafood Research (NIFES) , Bergen , Norway.
authors.forename: Nini H
authors.initials: NH
authors.lastname: Sissener
authors.affiliation: National Institute of Nutrition and Seafood Research (NIFES) , Bergen , Norway.
authors.forename: Erik-Jan
authors.initials: EJ
authors.lastname: Lock
authors.affiliation: National Institute of Nutrition and Seafood Research (NIFES) , Bergen , Norway.
authors.forename: Pål A
authors.initials: PA
authors.lastname: Olsvik
authors.affiliation: National Institute of Nutrition and Seafood Research (NIFES) , Bergen , Norway.
authors.forename: Marit
authors.initials: M
authors.lastname: Espe
authors.affiliation: National Institute of Nutrition and Seafood Research (NIFES) , Bergen , Norway.
authors.forename: Bente E
authors.initials: BE
authors.lastname: Torstensen
authors.affiliation: Biomar AS , Trondheim , Norway.
authors.forename: Joana
authors.initials: J
authors.lastname: Silva
authors.affiliation: GIFAS , Inndyr , Norway.
authors.forename: Johan
authors.identifier: 0000-0003-1818-5691
authors.initials: J
authors.lastname: Johansen
authors.affiliation: National Institute of Nutrition and Seafood Research (NIFES), Bergen, Norway; Department of Biology, University of Bergen, Bergen, Norway.
authors.forename: Rune
authors.initials: R
authors.lastname: Waagbø
authors.affiliation: National Institute of Nutrition and Seafood Research (NIFES) , Bergen , Norway.
authors.forename: Gro-Ingunn
authors.initials: GI
authors.lastname: Hemre
keywords: Antioxidant nutrients; Atlantic salmon; Nutrient requirement; Redox regulation; Selenium; Vitamin C; Vitamin E