ARS | Publication request: Flavobacterium Columnare studies in rainbow trout (Oncorhynchus mykiss)

Submitted to: Aquaculture Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: September 12, 2012
Publication Date: February 25, 2013
Citation: Evenhuis, J., Wiens, G.D., Lapatra, S.E. 2013. Flavobacterium Columnare studies in rainbow trout (Oncorhynchus mykiss). Aquaculture Conference Proceedings. P0353.

Technical Abstract: Flavobacterium columnare (Fc) is the causative agent for columnaris disesase and is a problem for several fish species. Recently, columnaris has been recognized as an emerging problem in farmed trout cultured within the Hagerman valley of Idaho. The aim of this study was two-fold. First determine whether F. columnare isolates are clonal or genetically diverse. Second, investigate whether fish that have been bred for resistance to Flavobacterium psychrophilum (Fp) also have broad-based resistance against Fc in experimental challenges. In order to understand the genetic diversity of Fc in Idaho, isolates from both environmental samples and fish were collected. These isolates were obtained from water inflows and outflows, from hatch houses and raceways. Also from several different tissues in moribund fish including skin lesions, gills, spleens, kidney and brains in fish that ranged from 0.4 grams to 1 kilogram. Greater than 70 individual Fc isolates were collected. All isolates were tested by 16S HaeIII digestion, sequencing, and the SDS-PAGE protein banding pattern examined. All isolates regardless of source were genomovar I isotype by 16S HaeIII restriction enzyme digestion and had 100% sequence identity for the 16S gene. Only two of the isolates had minor protein banding pattern variations and both of those isolates were obtained from the gills of moribund fish. These results suggest that both the environmental sources and pathogenic Fc isolates from fish are genetically homogeneous and possibly clonal in orgin. A long term breeding program at the NCCCWA has produced several genetic lines of rainbow trout that have divergent resistance to Fp intraperitoneal injection challenge. The resistance of these lines to challenge with Fc has not been investigated. Four different lines were tested: ARS-Fp-R (resistant), ARS-Fp-C (control), ARS-Fp-S (Susceptible), and a cross between the resistant and control lines (ARS-Fp-RxC). A total of 200 fish per line were waterborne challenged with 4x106 CFU mL-1 Fc strain CSF298-10 for 1 h. After 28 days post-challenge, the ARS-Fp-R and the ARS-FpRxC lines exhibited the highest survival, 85 and 83% respectively. Percent survival was significantly higher (p value = 0.02) than either of the ARS-Fp-C (73%) and the ARS-Fp-S (68%) lines. The ARS-Fp-C and ARS-Fp-S lines were not significantly different (p value = 0.16). In summary, these results suggest that Fc isolates may be clonal, and while the survival difference was modest, selective breeding progress obtained within the NCCCWA population against Fp may also result in greater resistance against Fc waterborne challenge.