Keywords: 
• deltamethrin /
• Ruditapes philippinarum /
• enzyme activity /
• organ injury

Abstract: The effects of deltamethrin on the activities of acetyl cholinesterase (AChE) and Na⁺-K⁺-adenosine triphosphatase (Na⁺-K⁺-ATPase) in lymph, the activities of glutathione S-transferase (GST) in gill and liver, and the histology of gill and digestive diverticula of Ruditapes philippinarum were studied at the present study. The results showed that, at low concentration, (0.0070 mg·L^-1) deltamethrin treatment had no significant effect on the enzymes activities (P > 0.05). In the medium concentration treatment group (0.014 mg·L^-1, 0.020 mg·L^-1), the activities of AChE and Na⁺-K⁺-ATPase in the lymph increased first and then decreased significantly (P < 0.05), the activities of GST in the gill and liver increased gradually, becoming significantly (P> < 0.05) at the end of the exposure experiment. In the high concentration treatment group (0.027 mg·L^-1), the activities of AChE and Na⁺-K⁺-ATPase in the lymph and the activities of GST in the liver decreased continuously with time (P < 0.01), while the activities of GST in the gill decreased first and then increased significantly (P < 0.05). These results indicated that, under low and medium concentration conditions, the enzymes activities exhibited a time- and dose-dependent pattern, which increased and then decreased. Under high concentration condition, the enzymes activities decreased continuously. The histological results showed that deltamethrin had a clear dose-dependent cytotoxic effect. After exposure to deltamethrin, epithelial cells of the gill filament exhibited cilia loss and disorientation, and epithelial cells of digestive diverticula exhibited expansion and inclusion body formation.