Three geographically distinct-reared strains (Canadian, Icelandic, Norwegian) of juvenile Atlantic halibut (Hippoglossus hippoglossus L.) cultured at optimal and super-optimal growth temperatures (12 and 18degrees C respectively), were challenged with a virulent isolate of Vibrio anguillarum by injection, The halibut were injected intraperitoneally with 100 mul of the bacterial suspension (1 X 10(6) cells per fish). After challenge, temperature and strain-related differences in survival were observed. Canadian and Icelandic halibut cultured at the super-optimal temperature of IS' C were significantly more susceptible to infection than those strains cultured at 12degrees C. Total mortality at 18degrees C for the Canadian and Icelandic strains was 56(.)4 and 61(.)85% respectively, compared to 32 and 26(.)6% respectively at 12degrees C. Norwegian halibut were significantly more resistant to infection with V. anguillarum at 18degrees C compared to the other strains, with total mortality of 13(.)3%. There was no significant difference in total mortality of Norwegian halibut at 18 or 12degrees C (13(.)3, 25% respectively),The specificity of the antibodies in sera from challenged halibut cultured at 18degrees C was primarily to LPS. Immunoblots showed the presence of antibodies against O-side chain antigens. This reaction was strongest in sera from the Norwegian halibut strain compared with the Canadian and Icelandic halibut, which suggests that the difference in resistance to challenge may be ascribable to the presence of antibodies to LPS. Specific antibody levels, as measured by ELISA, increased with increasing temperature and strain differences were apparent, however these did not relate to disease resistance. (C) 2002 Elsevier Science Ltd. All rights reserved.