The immune response of Taiwan abalone Haliotis diversicolor supertexta and its susceptibility to Vibrio parahaemolyticus at different salinity levels

Addition of NaCl at 2.5% to 3.5% to tryptic soy broth (TSB) significantly increased the growth of Vibrio parahaemolyticus. Taiwan abalone Haliotis diversicolor supertexta held in 30‰ seawater were injected withV. parahaemolyticus grown in TSB containing NaCl at 0.5, 1.5, 2.5, 3.5 and 4.5% at a dose of 1.6×105colony-forming units (cfu) abalone−1. After 48 h, the cumulative mortality was significantly higher for the abalone challenged with V. parahaemolyticus grown in 2.5% than those grown in 0.5 and 1.5% NaCl. In other experiments, abalones held in 30‰ seawater were injected with TSB-grown V. parahaemolyticus (1.6×105cfu abalone−1), and then transferred to 20, 25, 30 and 35‰ seawater. All abalones held in 20‰ were killed in 48 h. The mortality of V. parahaemolyticus-injected abalone held in 30‰ was significantly lower over 24–120 h. Abalone held in 30‰ seawater and then transferred to 20, 25, 30 and 35‰ were examined for THC (total haemocyte count), phenoloxidase activity, respiratory burst, phagocytic activity and clearance efficiency of V. parahemolyticus after 24 and 72 h. The THC increased directly related with salinity levels. Phenoloxidase activity, respiratory burst, phagocytic activity and clearance efficiency of V. parahaemolyticus decreased significantly for the abalone in 20, 25 and 35‰. It is concluded that the abalone transferred from 30‰ to 20, 25 and 35‰ had reduced immune ability and decreased resistance against V. parahaemolyticus infection.