EFFECTS OF ACUTE STRESS ON BLOOD-CLOTTING AND YEAST KILLING BY PHAGOCYTES OF RAINBOW-TROUT

The effects of different levels of acute stress on blood parameters in rainbow trout Oncorhynchus mykiss were examined. Experimental fish we re exposed to a combination of stressors, including handling, confinem ent, and thermal shock, and were bled 30 s to 30 min later. Control fi sh were sampled quickly without intentional stress. Two activities of blood were investigated: (1) whole-blood clotting (coagulation) times and (2) the ability of heparinized plasma to influence the survival of yeast soaked in this plasma and subsequently exposed to trout phagocy tes. The speed of blood clotting increased with increasing levels of s tress, whereas blood from many resting fish failed to clot. Yeast incu bated in plasma from stressed fish before exposure to pronephric phago cytes experienced a greater reduction in colony-forming units (cfus) t han yeast incubated in plasma from resting fish. Different levels of s tress did not induce significant differences in reduction of yeast cfu s. These data support the idea that acute stress may actually stimulat e primary defense mechanisms rather than suppress them. Furthermore, w hole-blood clotting times seemed to be reliable indicators of the seve rity of stressors to which fish were exposed. We postulate that factor s appearing in blood very quickly, such as catecholamines and specific plasma proteins, play important roles in both the killing activities of phagocytes and the blood-clotting process.