Abstract
The bactericidal activity of normal sera from five species of fish, eel, rainbow trout, carp, tilapia and black sea bream, was investigated.
All sera examined indicated the bactericidal activity against Escherichia coli. After they were incubated with zymosan, the carp and black sea bream sera lost the activity completely, but the tilapia serum was not affected at all. EDTA entirely inhibited the bactericidal activity of all sera tested. While the carp and tilapia sera exhibited the bactericidal activity in the presence of EGTA, the others partially lost the activity. None of the sera used possessed antibody against E. coli. The bactericidal reaction of fish serum appeared to be owing mainly to the alternative pathway of complement, but the activation system of the alternative pathway of fish complement is probably different in each fish species.
The bactericidal activity of the sera was lower against fish pathogens, Vibrio anguillarum and Edwardsiella tarda, than against E. coli.
