HOST, PATHOGEN AND ENVIRONMENTAL INTERACTIONS IN COOL AND COLD WATER AQUACULTURE
Location: Cool and Cold Water Aquaculture Research
Title: Rainbow Trout Innate Immunity against Flavobacterium psychrophilum
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 3, 2007
Publication Date: May 2, 2007
Citation: Hadidi, S., Glenney, G.W., Welch, T.J., Silverstein, J., Blazer, V., Wiens, G.D. 2007. Rainbow Trout Innate Immunity against Flavobacterium psychrophilum. Meeting Abstract Pg 35.
Flavobacterium psychrophilum infection is associated with significant loss of rainbow trout production in the U.S. and other parts of the world. In 2005, a selective breeding program was initiated at the National Center for Cool and Cold Water Aquaculture to improve rainbow trout innate resistance to F. psychrophilum challenge (See Silverstein et al. Abstract). After an initial evaluation at 2 g size, several resistant and susceptible families were chosen for further study. Trout families were seperately reared until the average fish weight was 10g or 800 g and then naive fish were challenged with strain CSF 259-93. Six of the eight families maintained their original relative resistant or susceptible phenotypes indicating that these family traits remained stable as the fish increased ~300-fold in size. Inflammatory cytokine, IL-1beta and TNF-alpha1, mRNA levels were significantly lower in spleen tissue of resistant trout compared to susceptible trout. Interestingly, naive and challenged resistant fish had a significantly larger spleen-somatic index (spleen weight normalized to total weight) as compared to treatment-matched susceptible fish at days 1, 3 and 5 post-challenge. This observation led us to test whether spleen size would predict innate resistance in an unrelated cohort of fish from another brood year (2006). Average spleen indices were surveyed in 103 families, and fish from twelve families were pooled into groups having large (SI=1.46), medium (SI= 1.10), and small (SI= 0.73) spleen-size. Each of the three groups was challenged with F. psychrophilum or Yersinia ruckeri. Consistent with our previous observations, trout with larger spleens were significantly more resistant to F. psychrophilum challenge. However, this result was pathogen specific as there was no correlation between spleen size and survival following Y. ruckeri challenge. Histological analyses identified that there were higher hemosiderin levels, and a higher frequency of melanomacrophages in the spleens of resistant fish that survived bacterial challenge. To our knowledge, this is the first report of a positive, and pathogen-specific, association between innate immunity, spleen phenotype and cytokine response in a teleost fish. These results also suggest that selective breeding may be a promising and complementary approach to reduce loss from bacterial coldwater disease.