Lysozyme activity in rainbow trout, Oncorhynchus mykiss (Walbaum), stressed by handling, transport and water pollution

Blood lysozyme activity was determined in rainbow trout that were stressed by handling and transport, or suffered from acute ammonia poisoning. To optimize the lysoplate assay, the pH dependence of the lysozyme activity was studied. For serum and kidney lysozyme, the pH optimum was 5.5 to 6.0. Ventilation frequency and plasma glucoseconcentration of the fish were used as stress indicators. Less severely stressful situations, such as 30 min of handling, brought about either a stimulation or a suppression of the lysozyme activity. Strong stressors, such as transport lasting 2 h or acute water pollution, reduced the lysozyme level significantly. The decrease of lysozyme activity due to handling and transport persisted for 24 h, but the activity returned to normal within 2 weeks following confrontation with the stressor.