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

An increasing body of evidence suggests that stress may modulate the r esponse of an animal to toxicological challenge. The degree of stress inherent in the procedures comprising a fish LC(50) study (OECD guidel ines for the testing of chemicals, ''Fish, Acute Toxicity Test'' No. 2 03, adopted May 12, 1981) was assessed by measuring plasma cortisol le vels (rainbow trout) and whole-body levels of immunoreactive corticast eroids, (zebra fish). Aspects of the 96 h LC(50) protocol which were f ound to evoke corticosteroidogenic activity in the test fish included transfer from holding tanks to test tanks, tank transfer during semist atic procedures; and disturbance associated with water quality measure ment. There was evidence for acclimation of the fish to repetitive sti muli such as tank transfer, but, overall, the data suggest that the 96 h test protocols evoke a state of chronic stress in the test populati on. The removal of fish from test vessels during longer term studies w as also found to evoke a stress response in fish remaining within the vessel, suggesting that these conditions may expose test fish to a reg ime of intermittent periods of acute stress. The possibility that phys iological stress may interfere with the accurate estimation of toxicol ogical 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 dist urbance and handling during the test period was minimized. (C) 1995 by John Wiley and Sons, Inc.