Location: Cool and Cold Water Aquaculture Research
Title: Biochemical reference intervals for Flavobacterium psychrophilum -resistant and -susceptible rainbow trout lines, and pathophysiological changes after experimental infection Authors
Submitted to: Diseases of Aquatic Organisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 12, 2014
Publication Date: N/A
Interpretive Summary: Selective breeding for disease resistance offers new opportunities for improving fish welfare in aquaculture. We have produced a line of rainbow trout that has increased resistance against bacterial cold water disease (BCWD). The biological mechanisms governing this resistance are unknown. We monitored plasma chemistry analytes and packed cell volume (PCV) to compare physiologic changes in the BCWD resistant line and a BCWD susceptible line following challenge with Flavobacterium psychrophilum, the bacteria that causes BCWD. In our experiment, we developed normal plasma biochemistry and PCV reference range intervals for resistant-line and susceptible-line fish. As there were no significant differences in biochemical analyte levels and PCV levels between the two populations, the data was combined to produce a single reference range. We then infected rainbow trout with F. psychrophilum and sampled plasma from fish on days 0, 1, 3, 6, and 9 post-infection. Packed cell volume, total protein, albumin, glucose, cholesterol, chloride, and calcium fell outside the established reference range in infected fish from both lines on at least one day post-infection. The resistant line showed significantly less change in PCV, total protein, and calcium, suggesting they have less physiologic changes occurring during infection than the susceptible line. This information is important because it describes a mechanism associated with increased survival of the resistant line and demonstrates physiologic changes associated with the BCWD, which have not yet been described.
Technical Abstract: A limitation of family-based breeding programs that select for disease resistance in aquaculture is an incomplete understanding of how artificial selection has altered disease response at the mechanistic level. The objectives of this study were to: 1) establish packed cell volume (PCV) and plasma biochemical reference range intervals in juvenile rainbow trout Oncorhynchus mykiss selectively-bred for resistance (ARS-Fp-R) and susceptibility (ARS-Fp-S) to bacterial cold water disease; and 2) observe pathophysiologic changes after intraperitoneal challenge with Flavobacterium psychrophilum and compare responses between the two genetic lines. Packed cell volume and biochemistry reference range intervals were not significantly different between genetic lines, thus samples were pooled into a single reference population (n = 86). ARS-Fp-R and ARS-Fp-S line fish challenged with F. psychrophilum demonstrated changes in mean PCV, total protein, albumin, glucose, cholesterol, chloride, and calcium that fell outside the established reference interval on at least one day post-infection through the 9 day study period. Mean PCV, total protein, and calcium significantly differed between ARS-Fp-R and ARS-Fp-S line fish on day 9 post-infection. Values in the ARS-Fp-S line deviated further from the reference interval. Packed cell volume, total protein, cholesterol and calcium negatively correlated with bacterial load, which was measured by an F.psychrophilum-specific qPCR assay. These findings demonstrate measurable divergent pathophysiologic disease responses between ARS-Fp-R and ARS-Fp-S line fish that are manifested following infection and likely associated with differential survival.