A Vibrio splendidus strain is associated with summer mortality of juvenile oysters Crassostrea gigas in the Bay of Morlaix (North Brittany, France)

• Published in: Diseases of aquatic organisms Vol. 46; no. 2; pp. 139 - 145
• Main Authors: LACOSTE, A, JALABERT, F, MALHAM, S, CUEFF, A, GELEBART, F, CORDEVANT, C, LANGE, M, POULET, S. A
• Format: Journal Article
• Language: English
• Published: Oldendorf Inter-Research 12.09.2001
• Subjects: Age Factors; Animal aquaculture; Animal productions; Animals; Biological and medical sciences; Colony Count, Microbial; Crassostrea gigas; France; Fundamental and applied biological sciences. Psychology; Gene Amplification; Genotype; Invertebrate aquaculture; Marine; Mollusca; Mortality; Norepinephrine - analysis; Ostreidae - microbiology; Phenotype; Polymerase Chain Reaction - veterinary; Seasons; Sequence Analysis, DNA; Temperature; Time Factors; Vibrio; Vibrio - classification; Vibrio - genetics; Vibrio - pathogenicity; France; Bretagne; Europe; ANE, France, Brittany, Morlaix Bay; Animal microorganism relation; Oyster farming; Mortality; Catecholamine; Young animal; Stress; Cell density; Strain; Marine environment; Pathogenicity; Bivalvia; Vibrionaceae; Bacteria; Norepinephrine; Invertebrata; Mollusca; Crassostrea gigas
• ISSN: 0177-5103; 1616-1580
• DOI: 10.3354/dao046139

Juvenile oysters Crassostrea gigas cultured in the Bay of Morlaix (France) have suffered unexplained summer mortalities for over a decade. In the present study, we tested the hypothesis that a bacterial pathogen could be responsible for this phenomenon. A first attempt failed to isolate a bacterial pathogen from moribund or weak oysters. Only non-pathogenic, probably opportunistic, bacteria were isolated. As an alternative approach, we focused on oysters presenting reduced stress-response capacities (determined by circulating noradrenaline measurements), a characteristic of juvenile oysters entering an early phase of the disease. Cultures of bacterial isolates on TCBS plates revealed that a Vibrio strain was present in diseased oysters and scarce or absent in healthy oysters. Experimental infections indicated that this Vibrio can cause mortalities of juvenile oysters when injected at concentrations ranging from 10(4) to 10(8) CFU oyster(-1). Similarly to the summer mortality disease, the Vibrio isolate caused higher mortalities at higher temperatures; apparently, it could not be transmitted horizontally, it did not affect adult oysters and it induced stress-response dysfunctions in juvenile oysters. Phenotypic and genotypic characterizations identified the pathogen as Vibrio splendidus. Taken together, the present results satisfy Koch's postulate and suggest that this bacterial strain is probably responsible for the juvenile oyster summer mortalities in the Bay of Morlaix.