PRODUCTION OF GILL-ASSOCIATED AND SERUM ANTIBODY BY RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) FOLLOWING IMMERSION IMMUNIZATION WITH ACETONE-KILLED FLAVOBACTERIUM-BRANCHIOPHILUM AND THE RELATIONSHIP TO PROTECTION FROM EXPERIMENTAL CHALLENGE

Rainbow trout (Oncorhynchus mykiss) were either injected twice intrape ritoneally with 0.1 ml of a 1:10 dilution from broth culture of aceton e-killed Flavobacterium branchiophilum, immersed twice for 1 h in a 1: 10, 1:100 or 1:1000 dilution from a broth culture of acetone-killed F. branchiophilum, or utilized as unexposed controls. After bath challen ge with live F. branchiophilum the percent cumulative mortality of eac h group was as follows; controls, 45.3%, i.p.-injected, 32.1%; immerse d in a 1:1000 dilution, 38.0%; immersion in a 1:100, 40.9%; and immers ion in a 1:10 dilution, 11.7%. There was no relationship between the g roup treatment and the levels of F. branchiophilum antigen detected by enzyme immunoassay following challenge. The amount of gill-associated and serum antibody to F. branchiophilum detected in the immersion imm unized groups before challenge increased with increasing concentration of antigen in the bath. The i.p.-injected group had the highest serum antibody of any group while gill-associated antibody was comparable t o those groups which were bath exposed with the lower concentrations o f F. branchiophilum antigen. A similar pattern of antibody response wa s seen with five groups of rainbow trout treated exactly as the five g roups above, in which antibody was monitored over time, but which were not challenged. Gill-associated and serum antibody were detectable fo llowing primary antigen exposure regardless of route. The serum and gi ll-associated antibody responses were present for longer following a s econd antigen exposure by the same route, and the gill-associated but not the serum antibody was increased over those following primary anti gen exposure. The greatest increase in gill-associated antibody respon se was seen in the group which received the highest concentration of a ntigen via bath.