Effect of three pathogenic vibrio infections on the non-specific immunity of croaker,Pseudosciaena crocea

Ulcer disease,which caused by the pathogens such as Vibrio alginolyticus,Vibrio harveyi and Vibrio parahaemolyticus according to the researches,is the most common,wide spreading and harmful disease of cage cultured croaker,Pseudosciaena crocea.In this research,we set 3 experimental groups with injections of 0.2 cm3 Vibrio harveyi,Vibrio alginolyticus and Vibrio parahaemolyticus,respectively,besides a control group treated with a same dose of normal saline.At the intervals of 0,1,2,4,7,10,13,16 and 20 days after infection,blood leucocytes,NBT-positive cells and lysozyme level were taken and measured for the influence on the croaker's non-specific immunity function under the pressure of 3 pathogenic vibrio.The results show that the change of blood physiological signs in the croaker mainly occurred 1~7 days after infection.At the initial stage,each experimental group had a significantly increase in white blood cell and NBT positive cell number(p0.05).The percentage of lymphocyte and neutrophilic granulocyte decreased with an increasing percentage of monocyte(p0.05).Thereafter,white blood cells started to decline and the percentage of lymphocyte and neutrophilic granulocyte started to increased.Seven days after infection,the number of varied blood cells didn't change significantly any more,and the group infected by vibrio heavily had an obvious significant change of blood physiological signs and NBT positive cell number.The activity of lysozyme in serum was higher than spleen,but both of them were first increased and then decreased,at last they went to an accordant tendency.So we conclude that the activation of stress response and non-specific immunity function's happened at the early stage of infection.The pathogenic vibrio showed different influences,with a time lag,on the non-specific immunity.