Location: Cool and Cold Water Aquaculture Research
2012 Annual Report
The NCCCWA has created three lines of rainbow trout with varying resistance to bacterial cold water disease: ARS-Fp-R (resistant), ARS-Fp-C (control) and ARS-Fp-S (susceptible). In collaboration with Clear Springs Foods (CSF), Inc, field trials were initiated in 2010 and 2011 to test the relative performance of these lines in Idaho. Analyses of results from field trials continued in 2012.
In 2010, the ARS-Fp-R line and ARS-Fp-S lines were reared in adjacent raceways and evaluated over an 80 day hatch-house period starting after first feeding. While several minor elevated mortality events occurred, no bacterial cold water disease was identified in either line. As a surrogate measure of relative performance, the phenotypes of the genetic lines were measured at CSF and also at the NCCCWA using laboratory injection challenge with F. psychrophilum. There was no difference in survival between resistant and susceptible lines measured at CSF while a significant difference was observed between the resistant and susceptible lines reared at the NCCCWA. These results suggested that environmental exposure modified the relative resistance phenotype. These findings as well as insufficient egg production at the NCCCWA led us to modify 2011 field trial design.
In 2011, ARS-Fp-R, C and S line fish were cultured within a single raceway split into three sections and received third-, second-, and first-use water, respectively. During this trial, clinical BCWD was diagnosed in the ARS-Fp-S line fish at 48 days post-hatch and elevated mortality followed, resulting in greater survival of the ARS-Fp-R line (95.7%) compared to the ARS-Fp-S line (91.2%). In conjunction with monitoring raceway mortality, fish were removed at three time points (31, 70 and 97 days post-hatch) and challenged with F. psychrophilum. The phenotypes of these fish were compared to an equivalent cohort, retained at the NCCCWA, which were challenged at the same time as the CSF cohort and with an equivalent dose of pathogen. Preliminary analyses confirm that the phenotype of the resistant, control and susceptible lines are sensitive to environmental influence, although the resistant line consistently had a greater, but not always statistically significant, survival rate compared to the other lines. The greater survival of the ARS-Fp-R line provides evidence of genetic improvement through selective breeding and warrants the release of the germplasm to industry and the continued evaluation of the ARS-Fp-R genetic line in large-scale production trials.