Effects of dietary fish oil substitution by DHA-rich microalgae and source of astaxanthin on GSH concentrations in the muscle (fillet, A,C) and liver (B,D) of juvenile rainbow trout fed the plant meal- (PM, A,B) and fishmeal (FM, C,D)-based diets. Means labelled with different letters [lowercase (a, b), synthetic astaxanthin (SA) groups; uppercase (A, B), microalgae astaxanthin (AA) groups] are different between various fish oil substitutions (p < 0.05). Asterisks (*) indicate differences between the SA and AA groups (p < 0.05) at the same level of FO substitution. The absence of different letters (a, b or A, B) or asterisks (*) between means indicates no significant differences. GSH: glutathione. FO: fish oil. AST: astaxanthin.