Abstract
Selenium (Se) deficiency is a problem widely encountered in humans and terrestrial livestock production withincreasing attention also in aquaculture. Se supports the antioxidant system, which becomes especially important during stressful conditions. In the present study, the effect of Se-supplementation in broodstock and frydiets on the performance and antioxidant metabolism of rainbow trout fry under acute hypoxia was investigated.Rainbow trout broodstock were fed plant-ingredient based diets either without any Se-supplementation (Se level:0.3 mg/kg) or supplemented with Se supplied as sodium selenite or as hydroxy-selenomethionine (Se level:0.6 mg/kg respectively) for 6 months prior to spawning. The progenies were subdivided into three triplicatefeeding groups and fed diets with similar Se levels compared to the parental diets, resulting in a 3x3 factorialdesign. After 11 weeks of feeding, the fry were either sampled or subjected to a hypoxic stress challenge. Onehundred fish were transferred to tanks containing water with a low oxygen level (1.7 ± 0.2 ppm) and monitored closely for 30 min. When a fish started to faint it was recorded and transferred back to normoxic water.Direct fry feeding of the hydroxy-selenomethionine supplemented diet improved the resistance towards thehypoxic stress. On the contrary, fry originating from parents fed Se-supplemented diets showed a lower stressresistance compared to fry originating from parents fed the control diet. Fry subjected to hypoxia showed elevated oxidative stress with reduced glutathione (GSH) levels and increased isoprostanes (IsoP) and phytoprostanes (PhytoP) levels produced by lipid peroxidation of polyunsaturated fatty acids (PUFA), arachidonic and αlinolenic acids respectively. Increased mRNA expression of transcription factors (nrf2, nfκb, keap1X2) and decreased mRNA expression of antioxidant enzymes (trxr, sod, gstπ) indicated a transcriptional regulation of theantioxidant response. In stressed fry, the mRNA expression of several antioxidant genes including gr, msr and gstπwas found to be higher when fed the control diet compared to the sodium selenite treatment, with a contraryeffect for parental and direct Se nutrition on gpx. The long-term parental effect becomes of greater importance instressed fry, where more than half of the genes were significantly higher expressed in the control compared tothe selenite supplemented group.