Abstract: By decreasing water salinity gradually, the Pampus argenteus juveniles were cultured at water salinity 25, 20, 15 and 10 , for 24 h, 48 h, 96 h and 120 h, respectively, with the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione-S-transferase (GST), and glutathione reductase (GR) in liver and the activities of Na⁺/K⁺- and Ga²⁺/Mg²⁺-ATPase in gill and kidney determined. With the lowering of water salinity and the elongation of treated time, the liver SOD and GST activities had a trend of decreasing after an initial increase (P<0.05), while the CAT activity was lower than the control except that it had a slight increase at salinity 20 cultured for 24 h and at salinity 15 cultured for 48 h (P<0.05). The liver GPX activity had an increasing trend (P<0.05), while the GR activity at salinity 15 cultured for 24 h increased first and then fell down to a relatively low level (P<0.05). The Na⁺/K⁺- and Ga²⁺/Mg²⁺-ATPase activities in the gill and kidney also decreased after an initial increase (P<0.05), only the increase of ATPase activity at the thresholds of water salinity and treated time differed between the two organs. The results indicated that the decrease of water salinity could effectively stimulate and enhance the antioxidant enzyme activities in juvenile P. argenteus liver and the ATPase activities in its gill and kidney, and thereby, could effectively eliminate the excessive reactive oxygen species (ROS), sustain the intracellular homeostasis, and minimize the body damage. However, characterized by certain specificity and time sequentiality, the activation of test enzymes could also be inhibited when the salinity varied beyond the tolerance range of the body.

Key words: Pampus argenteus, juvenile fish, salinity, liver, gill, kidney, antioxidant enzyme, ATPase