Effect of macrophages and serum of fish susceptible or resistant toepizootic ulcerative syndrome (EUS) on the EUS pathogen, Aphanomycesinvadans

摘要

Epizootic ulcerative syndrome (EUS) is one of the most destructive diseases of fresh and brackish water farmed and wild fish in the Asia-Pacific region. The in vitro germination and growth of the propagules of the EUS pathogen, Aphanomyces invadans (=A. piscicida), were assessed in the presence of the head-kidney macrophages, serum, and serum heated to inactivate complement proteins, of three EUS-susceptible and one resistant fish species. The susceptible species were: striped snakehead (Channa striata), giant gourami (Osphronemus gouramy) and silver barb [Barbodes (= Puntius) gonionotus], and the resistant species was Nile tilapia (Oreochromis niloticus). Fish of all species were acclimatised to either low temperature (20 degreesC +/- 1.6) at which EUS is known to occur, or to high temperature (32 degrees C +/- 5.0) at which EUS does not occur, except for giant gouramis which were only studied at low temperature. The respiratory burst of the macrophages was assessed in the presence of A. invadans or the stimulant phorbol myristate acetate (PMA), and compared to that of controls. Anti-A. invadans antibody concentrations were assessed in all species except silver barbs. All assays were carried out at the same temperature, regardless of the temperature that the fish were kept at.