PHYSIOLOGICAL STRESS IN FISH DURING TOXICOLOGICAL PROCEDURES - A POTENTIALLY CONFOUNDING FACTOR

An increasing body of evidence suggests that stress may modulate the response of an animal to toxicological challenge. The degree of stress inherent in the procedures comprising a fish LC(50) study (OECD guidelines for the testing of chemicals, ''Fish, Acute Toxicity Test'' No. 203, adopted May 12, 1981) was assessed by measuring plasma cortisol levels (rainbow trout) and whole-body levels of immunoreactive corticasteroids, (zebra fish). Aspects of the 96 h LC(50) protocol which were found to evoke corticosteroidogenic activity in the test fish included transfer from holding tanks to test tanks, tank transfer during semistatic procedures; and disturbance associated with water quality measurement. There was evidence for acclimation of the fish to repetitive stimuli such as tank transfer, but, overall, the data suggest that the 96 h test protocols evoke a state of chronic stress in the test population. The removal of fish from test vessels during longer term studies was also found to evoke a stress response in fish remaining within the vessel, suggesting that these conditions may expose test fish to a regime of intermittent periods of acute stress. The possibility that physiological stress may interfere with the accurate estimation of toxicological end points was examined: In three independent LC(50) tests the toxicity of the arylmethane dye, malachite green, to rainbow trout was found to be markedly and consistently reduced when the degree of disturbance and handling during the test period was minimized. (C) 1995 by John Wiley and Sons, Inc.