The Efficacy of Inactivated Photobacterium damselae subsp. piscicida Combined with Levan/Alum as Vaccine against Photobacteriosis in Cobia, Rachycentron canadum

Photobacterium damselae subsp. piscicida ( Phdp ) is a major pathogen of cultured cobia ( Rachycentron canadum ), a primary target species for offshore cage culture in Taiwan. Serum antibody titers as well as efficiency and duration of protection against Phdp were evaluated following intraperitoneal administration of a candidate vaccine prepared with formalin‐inactivated whole cells in combination with levan/alum adjuvants. The results showed vaccinates delayed the disease onset and had significantly ( P  < 0.05) less mortality than control nonvaccinates during Days 21–105 postvaccination with highest relative percentage of survival ( RPS ) and antibody titer up to 81.4% and 1:614, respectively. There was a highly significant positive linear correlation between the RPS and antibody titer ( R 2  = 0.841). Long‐lasting and significant protection against Phdp can be achieved with inactivated Phdp plus levan/alum, a potential cobia vaccine against photobacteriosis. Levan/alum complex may represent a promising adjuvant formula for the development of a Phdp vaccine.