Acquired immunity to amyloodiniosis is associated with an antibody response

The dinoflagellate Amyloodinium ocellatum, which causes amyloodiniosis or ' marine velvet disease', is one of the most serious ectoparasitic diseases p laguing warmwater marine fish culture worldwide. We report that tomato clow nfish Amphiprion frenatus develop strong immunity to Amyloodinium ocellatum infection following repeated nonlethal challenges and that specific antibo dies are associated with this response. Reaction of immune fish antisera ag ainst dinospore and trophont-derived antigens in Western blots indicated bo th shared and stage-specific antibody-antigen reactions. A mannan-binding-p rotein affinity column was used to isolate IgM-like antibody from A. frenat us serum. The reduced Ig consisted of one 70 kD heavy chain and one 32 kD l ight chain with an estimated molecular weight of 816 kD for the native mole cule. Immunoglobulin (Ig) isolated from immune but not nonimmune fish serum significantly inhibited parasite infectivity in vitro. An enzyme-linked im munosorbent assay (ELISA) was developed using polyclonal rabbit antibody pr oduced against affinity-purified A. frenatus Ig. Anti-Amyloodinium serum an tibody was not always detectable in immune fish, although serum antibody ti ters in immune fish increased after repeated exposure to the parasite. Thes e results suggest that there may be a localized antibody response in skin/g ill epithelial tissue, although antibody was rarely detected in skin mucus.