Water-soluble adjuvants enhance the protective effect of Flavobacterium psychrophilum vaccines in ayu Plecoglossus altivelis

Bacterial coldwater disease is considered to be one of the most serious diseases in ayu Plecoglossus altivelis in Japan. We evaluated the efficacy of three highly water-soluble adjuvants (Montanidae IMS-1311, IMS-1312 and IMS-2212) combined with formalin-killed bacterin of Flavobacterium psychrophilum (FKB) in ayu, in comparison with a minimally water-soluble adjuvant (Montanidae ISA-763A). The retention period and toxicity of these adjuvants in ayu were also examined. Experimental challenge 4 wk after vaccination showed that FKB adjuvanted with IMS-1311 and IMS-1312 had higher potency than FKB alone and significantly (p < 0.05) higher potency than the control with sterile distilled water. Residues of the highly water-soluble adjuvants in ayu remained for shorter periods than that of the minimally water-soluble adjuvant, although the former adjuvants were acutely toxic at doses higher than 25 muL/fish(1.7 +/- 0.5 g). The high level of protection, short retention period and lack of toxicity indicate that a dose of 5 muL of IMS-1311 or IMS-1312 combined with 5 muL of FKB makes a promising vaccine against bacterial coldwater disease in ayu.