Serum osmolality was significantly higher in fish reared at 30 ppt in both trials than those reared in either 5 or 15 ppt (Table 4). Reported values for osmolality in red drum (350 mmol / kg held at 28 ppt) (Crocker el al., 1983) and for mummichog (Fundulus heteroclitus) in scawater (290-308mmol/kg ) (Marshall el al., 2000) approximate values recorded in both trials .