A 56-day research was performed to examine the effect of water salinity (WS) on performance and some physiological responses of yellowfin seabream (Acanthopagrus latus, 12.5 g) and Asian seabass (Lates calcarifer, 33.5 g) juveniles. Fishes were reared at five WS including 6, 12, 24, 35 and 48‰. Increasing WS from 6 to 12‰ improved growth performance in A. latus juveniles; however, elevation of WS over 24‰ suppressed growth rate in this species. Increment of WS over 12‰ gradually reduced growth and feed utilization in L. calcarifer. In A. latus, fish reared at 24 and 35‰ had the greatest total protease activity, but those in 6‰ had the lowest value (P < 0.05). Lipase activity in A. latus gradually increased with enhancing WS up to 35‰ then it was decreased. The activities of total protease and lipase in L. calcarifer increased with enhancing WS form 6 up to 24‰ then their activities were gradually decreased (P < 0.05). The activity of catalase (CAT) in the liver of A. latus juveniles pronouncedly decreased with increasing WS. The glutathione peroxidase (GPX) and superoxide dismutase (SOD) activities as well as lipid peroxidation (TBARs) content were gradually increased by increment of WS in the liver of A. latus (P < 0.05). Regarding L. calcarifer, the activity of CAT and GPX remarkably decreased from 6 to 24‰, then their activity gradually increased from 35 to 48‰ (P < 0.05). However, SOD activity and TBARs content significantly increased from 6 to 24‰ then remarkably decreased in the liver of L. calcarifer. Humoral immune responses including lysozyme, alternative complement pathway activity and total immunoglubuns provoked by increment of WS in both species. Stress indices including plasma total protein, glucose, lactate, cortisol and total osmolality in both species remarkably affected by WS. According to the results of the present study the intermediate salinities (brackish water) between 6 and 12‰ are recommended for the culture of these euryhaline species.

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