Effects of dietary oxidized fish oil supplementation on oxidative stress and antioxidant defense system in juvenile rainbow trout ( Oncorhynchus mykiss )

The objective of the study was to characterize the response of the antioxidant defense system against dietary prooxidant conditions in rainbow trout juveniles. Fish (initial mean weight: 62 ± 1 g) were fed three fishmeal and plant-derived protein-based diets supplemented with 15% fresh fish oil (CTL diet), 15% fresh fish oil from tuna by-products (BYP diet) or 15% autooxidized fish oil (OX diet) over a 12-week growth trial at 17.5 ± 0.5 °C. No significant differences in growth performance were recorded between dietary groups. Muscle lipid content was reduced and n-6 PUFA levels were increased in rainbow trout fed diets BYP and OX compared to CTL. After 12 weeks of feeding, the level of lipid peroxidation products in muscle was not affected whereas the 8-isoprostane content in liver was increased in fish fed diet OX as well as plasma total and oxidized glutathione contents. The hepatic and muscle contents for -tocopherol were decreased in fish fed BYP and OX. Hepatic antioxidant enzyme activities and mRNA levels were not affected after 12 weeks of feeding, except for catalase and glutathione peroxidase 1b2 mRNA levels that were decreased in trout fed diet OX. Fish fed diet OX and BYP displayed also reduced cytosolic Nrf2 and both cytosolic and nuclear NF-κB protein levels in liver. The present work indicates that feeding rainbow trout juveniles with fresh fish oil from by-products or moderately oxidized lipid appears not to be detrimental to the growth performance of fish. The mechanisms beyond the control of the antioxidant defense system by moderately oxidized lipid require further investigations in rainbow trout juveniles