Vibrio proteolyticus No. 442, a potential probiotic for tiger puffer, Takifugu rubripes

The efficacy of Vibrio proteolyticus No. 442 as a probiotic in preventing opportunistic infections caused by Vibrionaceae in tiger puffer, Takifugu rubripes, was evaluated. Two strains of Listonella anguillarum, IFO 13266^T and Obama 5, were used as target bacteria. The antimicrobial activity of V. proteolyticus No. 442 peaks at approximately 25°C and is absent at temperatures at 15°C or above 35°C. This activity is also most pronounced at an oxygen concentration of 21% and is undetectable under anaerobic conditions. Using these characteristics, V. proteolyticus No. 442 and L. anguillarum IFO 13266 were co-cultured under aerobic and anaerobic conditions. The findings indicated that under aerobic conditions, L. anguillarum IFO 13266 was eradicated following a 48-hour incubation at 25°C, while under anaerobic conditions, both species maintained high bacterial densities. Consequently, the oral administration of the diets supplemented with V. proteolyticus No. 442 to juvenile tiger puffers for seven days resulted in a decrease in the density of Vibrionaceae (excluding V. proteolyticus) by two to three orders of magnitude in the gut, and by one to two orders of magnitude in the rearing water. Future research needs to investigate the long-term efficacy of V. proteolyticus as a probiotic, and its pathogenicity, fish growth, administration methods, and storage strategies.