Susceptibility and immune response to Flavobacterium psychrophilum between different stocks of ayu Plecoglossus altivelis

Abstract

Three stocks of ayu Plecoglossus altivelis, viz. an amphidromous stock, domesticated stock and hybridized stock between amphidromous and domesticated stocks, were challenged by intraperitoneal injection and by field spontaneous infection with Flavobacterium psychrophilum to compare susceptibility to bacterial coldwater disease (BCWD). Cumulative mortalities of the hybrid stock were medium between those of the amphidromous (low) and domesticated stock (high). It is possible that susceptibility to BCWD was inherited to the hybrid stock. The efficacy of immersion vaccine with the formalin-killed bacterin of F. psychrophilum and the serum aggulutinin titer of fish immunized with the formalin-killed cells of F. psychrophilum or Vibrio anguillarum were compared between these stocks. Although the mortality of the vaccinated fish was significantly lower than that of unvaccinated fish for each stock, no obvious difference was observed in the efficacy of immunization between these stocks. However, the serum aggulutinin titer of the amphidromous stock against both antigens was highest among the three stocks, possibly explaining the low susceptibility of the stock to BCWD. © 2006 The Japanese Society of Fish Pathology.