The antibody response of wild striped snakehead Channa striata to thefungal pathogen, Aphanomyces invadans

摘要

The oomycete Aphanomyces invadans is the causative agent of epizootic ulcerative syndrome (EUS), which causes large-scale mortalities of fresh- and brackish-water fish in the Asia-Pacific region. The antibody response of striped snakehead, Channa striata, to A. invadans was compared between fish collected from EUS-endemic and non-endemic regions of the Philippines. All sera showed a considerable non-specific response to A. invadans and other non-pathogenic oomycetes. The highest antibody responses were found in fish recently exposed to A. invadans for the first time, but sera from fish that had been exposed for longer periods showed the strongest inhibition of germination of A. invadans in vitro, in spite of the relatively low concentrations of antibodies that recognized it. EUS-native snakeheads were passively immunized with sera from snakehead populations with various histories of exposure to EUS, then exposed to A. invadans in aquarium water. There was no difference in the prevalence of EUS between the treatment groups, but fish immunized with sera from a population that had been exposed to EUS for a long period, which strongly inhibited the germination of A. invadans, had a significantly lower mortality than fish immunized with native sera. Immunisation with sera from fish that had recovered from their first exposure to EUS also resulted in reduced mortality levels.