Pathogenesis of vibriosis in cultured juvenile red abalone, <i>Haliotis rufescens</i> Swainson

Abstract. Morbidity of intensively cultured red abalone, Haliotis rufescens , as well as experimentally stressed (elevated temperature and hyper‐oxygenation) abalone, was studied using clinical, histological, immunofluorescent and bacteriological techniques. Histological study showed a typical pattern of bacterial infection from all groups studied, characterized by epithelial exfoliation or rupture and systemic growth of the bacteria along vascular sinuses and along neural sheaths. Peripheral neurons degenerated rapidly and a responsive host cellular infiltrate did not appear to effectively retard the advancement of the infection. Nine bacterial isolates from the culture system water or sick animals were characterized biochemically. All were Gram‐negative, facultatively anaerobic, non‐aerogenic, oxidase‐positive rods with single polar flagella and thus appeared related to the Vibrio group. Further characterization showed that most isolates did not correspond to specifically characterized vibrios, Antiserum prepared to the isolates contained antibody both to common group antigens (from all nine strains) and to strain‐specific antigens. Selection of antiserum and subsequent absorption permitted the use of the antiserum for specific recognition of each isolate. Immunofluorescent studies clearly demonstrated that antiserum to an isolate corresponding to Vibrio alginolyticus was the predominant antiserum producing positive staining of infecting bacteria in the typical lesions in abalone tissues. The pattern of positive staining corresponded to histopathological observations of the disease. The disease can be managed in husbandry systems by both limiting the number of potentially pathogenic bacteria and by limiting the exposure of the animals to physico‐chemical stresses.