Immersion vaccination and water-borne challenge of ayu (Plecoglossus altivelis) against vibriosis.

Abstract

In a Vibrio anguillarum strain passaged through ayu (Plecoglossus altivelis), the LD50 value against ayu by the water-borne challenge method did not change from that of the original strain freshly isolated from diseased fish. The ayu were reproducibly infected with the passaged strain by the water-borne method in which the fish were first exposed to 5.32% NaCl solution and then to a suspension of V. anguillarum cells. The symptoms in ayu infected by this challenge method were observed to be very similar to the symptoms of a natural vibriosis infection. The LD50 value against fish exposed first to NaCl solution and then to the cell suspension was lower than that of fish exposed to only the cell suspension. This challenge method, incorporating initial exposure to a 5.32% NaCl solution followed by exposure to a Vibrio cell suspension, provided a clear difference in mortality between vaccinated and non-vaccinated fish.High level protection against vibriosis was observed in fish vaccinated by immersion in V. anguillarum cells which had been formalinized, washed, and pelleted or which had been formalinized, washed, and lyophilized.