Effects of 4 weeks hypoxia (dissolved oxygen, DO: 1.7 mg/L) exposure and pharmacological treatments with S-nitroso-N-acetyl-DL-penicillamine (SNAP, a donor of nitric oxide) and Nω-nitro-L-arginine methyl ester (NAME, an inhibitor of nitric oxide synthase) on endothelial nitric oxide synthase (eNOS) protein expression (A) and eNOS protein levels (B), CYP1A mRNA levels (C), CYP1A protein expression (D), CYP1A protein levels (E), and ethoxyresorufin O-dethylase (EROD) activity (F) in croaker livers. Each value represents the mean±S.E.M (N = 8–9, tissues were randomly sampled from individual fish for measurements). Significant differences identified with a multiple range test, Fisher’s PLSD, are indicated with different letters (p<0.05). Note: exposure duration only refers to period fish were exposed to target DO; fish were previously exposed to declining DO for additional 2-day adjustment period. CTL, control; HYP, hypoxia; SAL, saline.