ARS | Publication request: Preliminary field evaluation of rainbow trout selectively bred for increased resistance to bacterial cold water disease

Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: October 19, 2010
Publication Date: February 28, 2011
Citation: Wiens, G.D., Leeds, T.D., Lapatra, S., Wilson, C., Cavendar, W., Evenhuis, J., Welch, T.J., Silverstein, J., Rexroad III, C.E. 2011. Preliminary field evaluation of rainbow trout selectively bred for increased resistance to bacterial cold water disease. Aquaculture America Conference. 308.

Technical Abstract: Bacterial cold water disease (BCWD) is one of the most frequent causes of elevated mortality in juvenile salmonids, and the development of effective control strategies is a priority. We previously reported results of a selective breeding program designed to increase rainbow trout survival following laboratory challenge with Flavobacterium psychrophilum, the causative agent of BCWD (Silverstein et al. 2009). Post-challenge survival was moderately heritable and survival of select-line families was increased 44.7% following two generations of selection (Leeds et al. 2010). In these studies, an injection challenge was employed to evaluate relative family survival and we utilized a single genome-sequenced, F. psychrophilum strain, CSF 259-93. Factors influencing BCWD resistance under production conditions remain poorly understood and optimal field-trial design has not been investigated. Studies were initiated in 2010, as part of a multi-year field evaluation process, to address: 1) egg transport and hatching under different commercial production conditions; 2) evaluation of different trial designs utilizing first-use and re-use water, 3) determine survival at locations that routinely experience natural BCWD outbreaks; and 4) determine distribution and impact of F. psychrophilum strain variants on resistance. Field evaluation was carried out at two sites in Utah in cooperation with the Utah Division of Wildlife Resources, and at one site in Idaho in cooperation with Clear Springs Foods, Inc. Eggs from resistant line fish (designated ARS-Fp-R) were produced by mating 3 year-old females (selected for two generations) with 1-year old neomales (selected for three generations). Eyed-eggs were shipped in February 2010 and hatched with 72-95% viability. In the Utah trials, survival of ARS-Fp-R line was compared to age-matched, BCWD susceptible rainbow trout (Gunnison River/Harrison Lake triploids, GHTP). Mortality in the ARS-Fp-R line over an 80 day period, post-first feeding was 2.5% (n=16,399 total fish at first feeding, FF) and 4.5% (n=32,559 at FF), while GHTP fish experienced outbreaks of BCWD with mortality of ~13% and ~19% respectively. Of note, the ARS-Fp-R fish were grown for most of the evaluation time in 100% second-use water or ~30% second-use water directly from GHTP fish experiencing BCWD. In Idaho, the ARS-Fp-R line was compared, using a blinded study design, to an NCCCWA reference control line (designated ARS-Fp-S) and all fish were cultured in first-use water. Total mortality was 2.0% (n=17,744 at FF) and 3.1% (n=17,732 at FF) respectively over an 80 day period. While several minor elevated mortality events occurred during this trial, BCWD was not diagnosed in either group. In summary, the overall survival of the ARS-Fp-R line is encouraging but the lack of an outbreak in Idaho and the lack of a contemporary randomly mated control group in the Utah study precludes us from concluding that the positive performance was due to selective breeding. We consider multi-year replication, including confirmation of F. psychrophilum exposure, and statistically significant performance difference of the ARS-Fp-R line compared to control as criteria for considering this strain improved. 2011 trial planning and preparation is underway.