Location: Cool and Cold Water Aquaculture Research
2013 Annual Report
This is the second year of a project assessing whether selective breeding of rainbow trout for increased resistance against a specific agent (F. psychrophilum) has broadly enhanced immune mechanisms. Initially, efforts were focused on developing and validating an assay to accurately measure F. psychrophilum loads in infected fish. The assay detected 100% F. psychrophilum isolates (n=210) and did not amplify 23 non-target bacteria species isolated from fish farms. The assay was sensitive, with a lower detection limit of 3 genomic equivalents per reaction. This assay will be applied to future studies to characterize bacterial cold water disease pathogenesis. This year, we have made progress examining the specificity of genetic resistance by measuring post-challenge survival following exposure to common rainbow trout pathogens which included Yersinia ruckeri, Flavobacterium columnare and Weissella sp NC10. The survival of the BCWD resistant line (ARS-Fp-R), control line (ARS-Fp-C) and susceptible line (ARS-Fp-S) fish were compared following either immersion or injection challenge with Yersinia ruckeri CSF007-82. ARS-Fp-R line survival was significantly higher than ARS-Fp-S line survival following injection or waterborne challenge. Survival of the ARS-Fp-C line was not different from the ARS-Fp-S line. The results were repeated three times using different pools and year-classes of fish. Following immersion challenge with Flavobacterium columnare CSF298-10, ARS-Fp-R line survival was significantly higher than ARS-Fp-S line fish while the survival of the ARS-Fp-C line was intermediate. These studies provide evidence that selective breeding has produced measurable broad-based resistance against unrelated gram-negative pathogens. There was no survival difference between trout lines following challenge with either a gram-positive pathogen, Weissella sp. NC10, or the infectious hematopoietic necrosis virus. Studies examining the effects of breeding on the antibody response and cell populations were completed by collaborators in 2013.