Mortality and physiological responses Žplasma cortisol, glucose, osmolality, ions Naq and Cly
and hematocrit values. were examined in adult pejerrey Odontesthes bonariensis subjected to
transport or crowding and subsequent recovery for 1 week at 0, 5 and 20 ppt NaCl. Two
experiments were conducted using fish from different hatcheries; the following responses were
consistent 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 ŽNaq and Cly. 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 caused by the stress
of transport, but during recovery, it prevented further increases in these features andror accelerated
their return to basal levels. This salinity also helped maintain stable blood electrolyte levels.
During recovery 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 its
clearance in O. bonariensis. q2001 Elsevier Science B.V. All rights reserved.