Acquired immunity against Trypanosoma danilewskyi in goldfish, Carassius auratus

Two groups of goldfish maintained at 20 degrees C were experimentally infected with two different sized inocula of Trypanosoma danilewskyi. One group was inoculated with 380,000 trypanosomes/fish and the other with 3800. Forty and 90% of the fish, respectively, survived. All surviving fish challenged 190 days post-infection were protected from re-infection. The plasma of these fish when inoculated into another group of fish also protected them from infection. Finally, trypanosomes incubated in vitro in immune plasma at 20 degrees C for 2 h were not infective; however, incubations at 5 degrees C or for 1 h were not as effective.