Physiological Responses of Juvenile Walleyes to Handling Stress with Recovery in Saline Water

Abstract

Juvenile walleyes (Stizostedion vitreum) were subjected to a 30-s net handling to determine their physiological stress responses and differential recovery in freshwater (FW) and saline water (SW; 0.5% NaCl). Plasma cortisol rose from 11 ± 4.4 ng/mL (mean ± SE) to 286 ± 40 ng/mL within 15 min of handling, and blood lymphocyte–erythrocyte (RBC) ratios decreased from 40 ± 6.0 per thousand RBCs to 13 ± 0.7 in 3 h. Plasma cortisol recovered more quickly (e.g., 123 ± 22 ng/mL in FW versus 44 ± 7.1 in SW at 3 h) and plasma osmolality was less affected (e.g., 269 ± 4.5 in FW versus 283 ± 4.7 milliosmol/kg in SW at 6 h) in fish during recovery in SW compared with those in FW. However, declines in lymphocyte–RBC ratios appeared unmodified by salt use. Confining fish during recovery evoked a second increase in plasma cortisol in both FW and SW, but the increase was less in SW (186 ± 26 and 118 ± 11 ng!mL, respectively). Plasma osmolality remained unchanged in fish held in SW, and the increase in the neutrophil–RBC ratio evident in confined fish held in FW was moderated in SW. An increase in the thrombocyte–RBC ratio occurred in handled fish during recovery in FW without confinement but not in confined fish. The use of salt in the recovery medium did not attenuate corticosteroid responses of walleyes to handling, but salt may have allowed the fish to recover more quickly and eliminated the osmoregulatory imbalance often associated with acute stress.