Abstract: The ulcer disease of the large yellow croaker is mainly caused by Vibrio alginolyticus, V. harveyi and V. parahaemolyticus. In order to understand the immune response mechanism of resistance to pathogen infection of the large yellow croaker and provide important theoretical basis for their disease prevention, healthy croakers were divided into tree experimental groups injected with 0.2 mL V. harveyi, V. alginolyticus and V. parahaemolyticus respectively, and one control group with the same dose of sterile saline. Then samples were taken at the 0, 1st, 2nd, 4th, 7th, 10th, 13th, 16th and 20th days after infection, and the activity of 7 different immunity-related enzymes in the serum were measured and the differences of effect on large yellow croaker by the three pathogenic vibrios were compared. The results showed that from 1 to 10 days after infection, the activity of LSZ, ACP, POD and MPO in Pseudosciaena crocea's serum increased in the first few days, then decreased and increased again, and reached unanimity finally. The experiments also indicated that different pathogens had time-difference effect, and that AKP was more sensitive to V. harveyi infection, while ACP, POD and MPO were more sensitive to V. alginolyticus infection and LSZ and PO were more sensitive to V. parahaemolyticus infection.

Key words: Pseudosciaena crocea, Vibrio alginolyticus, Vibrio harveyi, Vibrio parahaemolyticus, enzymes activity