Physiological responses during stress and subsequent recovery at differentsalinities in adult pejerrey Odontesthes bonariensis

Mortality and physiological responses (plasma cortisol, glucose, osmolality , ions Na+ and Cl- and hematocrit values) were examined in adult pejerrey O dontesthes bonariensis subjected to transport or crowding and subsequent re covery for 1 week at 0, 5 and 20 ppt NaCl. Two experiments were conducted u sing fish from different hatcheries; the following responses were consisten t for both stocks. Mortality was observed only during post-stress recovery at 0 and 20 ppt NaCl but not at 5 ppt. During recovery, blood cortisol and glucose were generally higher, whereas osmolality and blood electrolytes (N a+ and Cl-) were lower at 0 ppt than at the other salinities. A salinity of 5 ppt NaCl could not prevent the rise in cortisol and glucose levels cause d by the stress of transport, but during recovery, it prevented further inc reases in these features and/or accelerated their return to basal levels. T his salinity also helped maintain stable blood electrolyte levels. During r ecovery at 20 ppt NaCl, osmolality and blood ions increased, whereas plasma cortisol and glucose generally decreased. Hematocrit values were lower at 20 ppt than at the other salinities. These results suggest that freshwater is not an adequate medium for post-stress recovery and that the presence of NaCl in the water either decreases the secretion of cortisol or promotes i ts clearance in O. bonariensis. (C) 2001 Elsevier Science B.V. All rights r eserved.