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Diseases of Aquatic Organisms

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DAO 69:163-173 (2006)  -  doi:10.3354/dao069163

Immunohistochemistry of great scallop Pecten maximus larvae experimentally challenged with pathogenic bacteria

Nina Sandlund1,*, Lise Torkildsen1, Thorolf Magnesen2, Stein Mortensen1, Øivind Bergh1

1Institute of Marine Research, PO Box 1870 Nordnes, 5817 Bergen, Norway
2Centre for Studies of Environment and Resources, University of Bergen, PO Box 7800, 5020 Bergen, Norway

ABSTRACT: Three challenge experiments were carried out on larvae of the great scallop Pecten maximus. Larvae were bath-challenged with Vibrio pectenicida and 5 strains resembling Vibrio splendidus and one Pseudoalteromonas sp. Unchallenged larvae were used as negative controls. The challenge protocol was based on the use of a multidish system, where the scallop larvae (10, 13 and 15 d post-hatching in the 3 experiments, respectively) were distributed to 2 ml wells with stagnant seawater and exposed to the bacterial cultures by bath challenge. Presence of the challenge bacteria in the wells was verified by polymerase chain reaction (PCR). A significantly increased mortality was found between 24 and 48 h in most groups challenged with V. pectenicida or V. splendidus-like strains. The exception was found in larval groups challenged with a Pseudoalteromonas sp. LT 13, in which the mortality rate fell in 2 of the 3 challenge experiments. Larvae from the challenge experiments were studied by immunohistochemistry protocol. Examinations of larval groups challenged with V. pectenicida revealed no bacterial cells, despite a high degree of positive immuno-staining. In contrast, intact bacterial cells were found in larvae challenged with V. splendidus. In the case of larvae challenged with the Pseudoalteromonas sp., positive immuno-staining was limited to visible bacteria inside the digestive area and cells of the mucosa. The experiments confirm that V. splendidus and V. pectenicida are pathogenic to scallop larvae, and that the Pseudoalteromonas strain is probably not a primary pathogen, although it cannot be ruled out as a secondary pathogen.

KEY WORDS: Pecten maximus · Vibrio splendidus · Immunohistochemistry · Challenge experiments · Larvae

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