This study assessed the impact of salinity on whiting (Sillaginodes punctata) in an attempt to understand the mechanisms by which salinity could potentially influence habitat selection and growth of King George whiting in southern Australia. The experiment included whiting of two age classes, young of the year (YOY) and 2+ year, at three salinities (30, 40, 50 ppt). YOY whiting showed no significant difference in length or weight gain, specific growth rate, feed intake, food conversion ratio or condition factor when exposed to the three salinities for 72day. Plasma osmolality of YOY whiting was not significantly different at any salinity, although it was significantly lower than that of 2+ year whiting. The 2+ year whiting showed significantly higher plasma osmolality than the YOY. Blood plasma potassium and chloride levels of 2+ year fish at 50 ppt were significantly higher than those at 30 ppt and 40 ppt. Blood sodium levels at 50 ppt were significantly higher than at 30 ppt but the sodium level at 40 ppt was not different from 30 ppt or 50 ppt. Haematocrit of 2+ whiting was significantly higher at 30 than at 50 ppt while haematocrit at 40 ppt was not different from 30 or 50 ppt. The 2+ year-old whiting had a more pronounced increase in plasma osmolality and plasma ions at high salinities, indicating poorer osmoregulatory capacity in older fish. This study provides physiological evidence to partially explain habitat occupancy and growth in relation to salinity of different age groups of whiting in southern Australia.