The acute effects of ammonia exposure on selected immunological and metabolic parameters in juvenile red claw crayfish,Cherax quadricarinatus as well as the post-exposure recovery were studied by using Real-time PCR technique and biochemical assays.The crayfish were first exposed to ammonia for 3 d,then half of them were sampled and the other half were moved into aerated tap water for a 7 d post-exposure recovery.The results showed that a 3 d ammonia exposure had significant impact on the activities of ACP,AKP and SOD in the muscle of juvenile C.quadricarinatus.As ammonia concentration increased,the activities of these enzymes significantly decreased.At the highest concentration(16 mg/L),they decreased to 76%,68% and 62% of the control,respectively.The mRNA expression of mitochondrial manganese superoxide dismutase(mMnSOD),cytosolic MnSOD(cMnSOD),extracellular copper/zinc SOD(exCu/ZnSOD)also showed a decreasing trend following increased ammonia concentration.In contrast,the mRNA expression of catalase(CAT),glutathione peroxidase(GPX)and glutathione transferase(GST)in muscle remained unchanged compared to the control.Dissolved protein and triglycerides in hepatopancreas significantly decreased as ammonia concentration increased.At the highest concentration,they decreased to 72% and 59% of the control.AST showed a noble elevation which was 134% of the control in 12 mg/L group.After a 7 d post-exposure recovery,ACP and AKP activities returned to the normal level in ammonia treatments.On the contrary,the activities of SOD and GPX in all ammonia treatments were significantly higher than the control.The expression of antioxidant genes was higher than the control in all ammonia treatments.Metabolic parameters showed no differences between all groups.The results indicate that high levels of ammonia might suppress activities and gene expression patterns of immune-related enzymes,leading to a loss of defence mechanism.The crayfish which had been exposed to ammonia for 3 d could not fully recover after a 7 d post-exposure recovery and oxidative stress still existed in the muscle in C.quadricarinatus.