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Title: Spleen Size Predicts Innate Resistance of Rainbow Trout to Flavobacterium psychrophilum Challenge

item Hadidi, Sima
item Welch, Timothy - Tim
item Silverstein, Jeffrey
item Wiens, Gregory - Greg

Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: 2/16/2007
Publication Date: 5/21/2007
Citation: Hadidi, S., Glenney, G., Welch, T.J., Silverstein, J., Wiens, G.D. 2007. Spleen Size Predicts Innate Resistance of Rainbow Trout to Flavobacterium psychrophilum Challenge. American Society for Microbiology.

Interpretive Summary:

Technical Abstract: Background: Mortality attributed to Flavobacterium psychrophilum infection is a significant problem for rainbow trout producers in the US and other parts of the world. At present there is no commercial vaccine, and fish are often afflicted at a small size prior to the development of a mature immune system. In 2005, a breeding program to improve rainbow trout innate resistance to F. psychrophilum challenge was initiated at the National Center for Cool and Cold Water Aquaculture. Methods: In 2005, 75 full-sib families of rainbow trout, averaging 2.4 grams in size, were evaluated for resistance to F. psychrophilum CSF-259-93 by injection challenge. Resistance was also measured in a subset of these families after growth to an average of 10 g and 800 g size. Measurement of tissue parameters identified that resistant fish had a significantly greater, average spleen index (spleen weight/total weight) than susceptible fish. In 2006, we tested the hypothesis that spleen size is a predictor of innate resistance. Average spleen indices were surveyed in 103 families and fish from twelve families pooled into groups having large (4 families), medium (4 families), and small (4 families) spleen-sizes. Survival following F. psychrophilum and Yersinia ruckeri challenge was determined. Results: A large variability among the 75 full-sib 2005 families was observed ranging from highly susceptible (1% survival) to highly resistant (72% survival). Six of eight families maintained their original resistance/susceptibility phenotype when challenged at 10 g and 800 g size. Interestingly, naive fish from resistant families had significantly larger spleens than naïve susceptible fish. Furthermore, fish from the 2006 families selected based on spleen size predicted resistance to F. psychrophilum challenge but not to Y. ruckeri challenge. Conclusion: These results indicate that the rainbow trout broodstock at the NCCCWA displays a wide range of innate resistance against F. psychrophilum and this trait is stable throughout the growth cycle. To our knowledge, this is the first report of a positive, and pathogen-specific, association between innate immunity and spleen size in a teleost fish.