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Abstract: Apoptotic cell ratio and mRNA expression of caspase-3, cathepsin B (CTSB), heat shock protein 70 (HSP70), manganese superoxide dismutase (MnSOD), catalase (CAT), glutathione peroxidase (GPx) and thioredoxin (TRx) in hemocytes of white shrimp Litopenaeus vannamei exposed to nitrite-N (20mg/L) was investigated at different stress time (0, 4, 8, 12, 24, 48 and 72h). The apoptotic cell ratio and mRNA expression level of CTSB were significantly increased in shrimp exposed to nitrite-N for 48 and 72h. Caspase-3 mRNA expression level significantly increased by 766.50% and 1811.16% for 24 and 48h exposure, respectively. HSP70 expression level significantly increased at 8 and 72h exposure. MnSOD mRNA expression in hemocytes up-regulated at 8 and 48h, while CAT mRNA expression level increased at 24 and 48h. GPx expression showed a trend that increased first and then decreased. Significant increases of GPx expression were observed at 8 and 12h exposure. Expression level of TRx reached its highest level after 48h exposure. These results suggest that nitrite exposure induces expression of apoptosis-related genes in hemocytes, and subsequently caused hemocyte apoptosis. Meanwhile, expression levels of HSP70 and antioxidant enzymes up-regulated to protect the hemocyte against nitrite stress. [Copyright &y& Elsevier]