PLASMA-CORTISOL AND GLUCOSE STRESS RESPONSES OF RED DRUM (SCIAENOPS-OCELLATUS) TO HANDLING AND SHALLOW-WATER STRESSORS AND ANESTHESIA WITH MS-222, QUINALDINE SULFATE AND METOMIDATE

Plasma cortisol and glucose stress responses to several common aquaculture procedures and modulation of these responses by three anesthetics (MS-222, quinaldine sulfate and metomidate) were investigated in hatchery-reared juvenile red drum (Sciaenops ocellatus). The magnitude of the cortisol and glucose stress responses to capture by dip net and transfer to another tank was related to the duration of net restraint and exposure to air. Rapid transfer of fish with only 5 s exposure to air did not elicit a cortisol stress response, whereas plasma cortisol titers increased five-fold after restraint and exposure to air for two minutes. Prior anesthesia partially blocked the response to the 2-min transfer stressor. Lowering the water level in the experimental tanks, followed by anesthetization of the fish with MS-222 or quinaldine sulfate, and then slowly refilling the tanks caused a marked increase in plasma cortisol concentrations. However, plasma cortisol titers did not increase when the anesthetic treatment was omitted from this procedure. There were dose-related increases in plasma levels of cortisol and glucose after 15 min continuous exposure to MS-222. Continuous exposure to quinaldine sulfate caused similar biochemical stress responses, whereas no changes in circulating levels of cortisol and glucose were observed after exposure to metomidate. Moreover, exposure to metomidate, but not to the other anesthetics, blocked the plasma cortisol response to ACTH administration. It is concluded from these studies that, whereas short-term anesthesia with MS-222 and quinaldine sulfate can block biochemical responses to handling stressors, longer term anesthetic exposure can itself induce a biochemical stress response. No such response occurs after exposure to metomidate, which appears to exert a direct action at the interrenal gland to block ACTH stimulation of steroidogenesis. These results suggest that the physiological disturbance of red drum during routine aquaculture procedures can be reduced by selecting appropriate handling and anesthetic treatments.