Diet supplementation of Pediococcus pentosaceus in cobia (Rachycentron canadum) enhances growth rate, respiratory burst and resistance against photobacteriosis

Cobia (Rachycentron canadum) is an economically important fish species for aquaculture in tropical and sub-tropical areas. Cobia aquaculture industry has severely damaged due to photobacteriosis caused by Photobacterium damselae subsp. piscicida (Pdp), especially in Taiwan. Antibiotics and vaccines have been applied to control Pdp infection, but the efficacy has been inconsistent. One species of lactic acid bacteria, Pediococcus pentosaceus strain 4012 (LAB 4012), was isolated from the intestine of adult cobia, and its culture supernatant can effectively inhibit Pdp growth in vitro. The acidic pH derived from metabolic acids in LAB culture supernatant was demonstrated to be an important factor for the suppression. After a 2-week feeding of LAB 4012, the growth rate of the fed cobia was 12% higher than that of the non-fed group, and the relative percentage of survival (RPS) of the fed cobia was found to be 74.4 in Pdp immersion challenge. In addition, the respiratory burst (RB) of peripheral blood leukocytes (PBL) in the LAB 4012-fed group was significantly higher than that of the non-fed group. Although feeding LAB 4012 did not improve specific antibody response in cobia after immunization with Pdp vaccine, it still significantly raised the survival rate by 22% over that of the non-fed group after Pdp immersion challenge. Judging by the quick induction of high protection against Pdp infection and promotion of growth in larvae, LAB 4012 was considered to be a viable probiotic for cobia aquaculture.