Effects of stress on scuticociliate killing activity of olive flounder (Paralichthys olivaceus) plasma in relation to humoral immunity

Abstract

Effects of stress-induced suppression of humoral immunity on scuticociliate killing activity of olive flounder plasma were investigated. Changes in glucose level, alternative complement activity and lysozyme activity of plasma by handling stress were analysed in relation to in vitro parasiticidal activity of plasma. The plasma glucose level was about two times higher in fish after a handling stress than in control fish. Plasma lysozyme activity and natural haemolytic activity were decreased in stressed fish. The scuticociliate killing activity of plasma was significantly lower in stressed fish than in non-stressed control fish. The present results indicated that stress-induced immunodepression could be a cause of scuticociliatosis occurrence in olive flounder.