Se is an essential
micronutrient required for normal growth, development and
antioxidant defence. The objective of the present study was to assess the impact of dietary Se sources and levels on the
antioxidant status of rainbow trout (Oncorhynchus mykiss) fry. First-feeding fry (initial
body weight: 91 mg) were fed either a plant- or fishmeal-based diet containing 0·5 or 1·2 mg Se/kg diet supplemented or not with 0·3 mg Se/kg diet supplied as Se-enriched yeast or
sodium selenite for 12 weeks at 17°C. Growth and survival of rainbow trout fry were not significantly affected by dietary Se sources and levels. Whole-body Se was raised by both Se sources and to a greater extent by Se-yeast. The reduced:oxidised
glutathione ratio was raised by Se-yeast, whereas other lipid peroxidation markers were not affected by dietary Se. Whole-body Se-dependent
glutathione peroxidase (GPX) activity was enhanced in fish fed Se-yeast compared to fish fed
sodium selenite or non-supplemented diets. Activity and gene expression of this
enzyme as well as gene expression of
selenoprotein P (
SelP) were reduced in fish fed the non-supplemented
plant-based diet.
Catalase,
glutamate-cysteine ligase and nuclear factor-erythroid 2-related factor 2 (Nrf2) gene expressions were reduced by Se-yeast. These results suggest the necessity to supplement
plant-based diets with Se for rainbow trout fry, and highlight the superiority of organic form of Se to fulfil the dietary Se requirement and sustain the
antioxidant status of fish. GPX and
SelP expression proved to be good markers of Se status in fish.