Ultrasonic immunization of sea bream, Pagrus major (Temminck & Schlegel), with a mixed vaccine against Vibrio alginolyticus and V-anguillarum

In order to clarify the effectiveness of ultrasonication on vaccine delivery, juvenile sea bream, Pagrus major , were treated with eight different ultrasonic methods. A mixed vaccine against Vibrio alginolyticus and V. anguillarum was used to immunize the fish. The intensity and frequency of the ultrasound were 280 mW cm(-2) and 35 kHz, respectively. The ultrasonic methods included continuous or pulsed ultrasound for 3 min, and continuous or pulsed ultrasound for 3 min before and/or after immersion for 3 min. Of all the eight ultrasonic methods tested, 'pulsed ultrasound followed by immersion' and 'immersion, pulsed ultrasound, and followed by immersion again' provided the best protection, which were comparable with protection of fish immunized by intraperitoneal injection. Moreover, the convenience of applying these two ultrasonic methods for immunization was comparable with the immersion method and was much better than intraperitoneal injection. If 2 x 10(8) CFU mL(-1) of this mixed vaccine was used for vaccination repeatedly five times by ultrasonic methods, it could still produce good protection for the immunized sea bream. Therefore, the ultrasonic method is an effective and practical approach for fish vaccination on a large scale.