PHYSIOLOGICAL STRESS RESPONSES OF THE FRESH-WATER CHONDROSTEAN PADDLEFISH (POLYODON SPATHULA) TO ACUTE PHYSICAL DISTURBANCES

Juvenile paddlefish (Polyodon spathula) subjected to various physical disturbances showed significant increases in plasma cortisol and lacta te, but little or no change in plasma glucose, chloride or hematocrit. When paddlefish were given a 30 s aerial emersion handling stressor, plasma cortisol increased from 2.2 +/- 0.6 to 11 +/- 1.8 ng ml(-1) in 1 h but had returned to the prestress level by 3 h. Addition of 0.5% N aCl to the recovery tanks had no effect on plasma cortisol changes. Pl asma lactate rose from 26 +/- 2.6 to 52 +/- 4.5 mg dl(-1) within 3 h. Plasma cortisol increased to 14 +/- 4.8 ng ml(-1) and plasma lactate r ose to 67 +/- 3.7 mg dl(-1) after fish were continuously chased in the ir home tanks for 1 h; plasma lactate remained elevated for 5 h. In fi sh severely confined for 6 h in cages with intermittent handling, plas ma cortisol rose from 6.2 +/- 1.6 ng ml(-1) to its peak level of 74 +/ - 6.3 ng ml(-1) by 2 h, but approached the prestress value after 18 h of recovery. Plasma lactate levels in confined fish increased from 27 +/- 2.7 to 73 +/- 6.9 mg dl(-1) by 3 h but had returned to near-restin g levels by 24 h. The results suggest that paddlefish do not exhibit p hysiological stress responses to physical disturbances similar in magn itude to those previously documented for many teleostean fishes includ ing salmonids, although cortisol was determined to be the principle st eroid released during stress. (C) 1998 Elsevier Science Inc. All right s reserved.