Abstract
Abstract. A disease of cultured juvenile European oyster, Ostrea edulis, and American oysters, Crassostrea virginica, was characterized by infection of conchiolinous ligament and periostracum by surface‐coating Vibrio spp. bacteria. A similar bacterium was isolated from diseased cultured hard clams, Mercenaria mercenaria, held in a facility about 300 km distance from the oyster hatcheries. The oysters demonstrated fragile, undercalcified peripheral shell and apparently excessive chalky deposits. Histological and scanning electron microscopical examination revealed that the oysters' eroded ligaments and perforated peripheral periostracum were infected with uniform rod‐shaped bacteria. The infection appeared to interfere with normal proteinaceous and calcareous shell deposition and possibly with normal ligament function. Histological examination of the digestive system organs suggested that normal digestive processes were also interrupted. Two predominant bacteria were isolated from oyster samples and one predominant bacterium was isolated from clam samples. One of the isolates from oyster culture facilities was found almost exclusively associated with oyster shell surfaces and culture tank surfaces, this isolate was similar to the one taken from clam shell surfaces. The other predominant bacterium was found in water column samples in oyster culture facilities at levels from about 105 to 107 per ml. This isolate had a DNA base ratio (moles % G + C) of 43.6; the two surface‐associated isolates had base ratios of 43.6 and 44.5%. These Gram‐negative, oxidase positive, fermentive rods have been identified as a Vibrio spp. group. Specific antibody was produced which differentiated these bacteria from each other and from other similar isolates. Practical procedures for controlling the bacteria in shellfish culture systems are described.
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