2013 Annual Report
1a.Objectives (from AD-416):
Infectious disease is an important factor limiting trout production. Stakeholders have identified control of bacterial cold water disease (BCWD) as a high priority, and in response, the National Center for Cool Water Aquaculture initiated a breeding program to improve rainbow trout BCWD resistance. Rainbow trout have been selected for two generations for increased survival following experimental challenge with F. psychrophilum, the causative agent of BCWD. The objective of this research is to determine whether laboratory selection of trout for increased BCWD survival translates to improved performance following natural BCWD challenge in a production environment. Improved performance is defined as reduced mortality, clinical disease, and bacterial load as compared to control fish. The overall impact of this research is improved animal well-being, reduced antibiotic use and increased production efficiency.
1b.Approach (from AD-416):
Improved germplasm from ongoing ARS NCCCWA programs and breeding populations under investigation will be established in small and large scale field trials. In the small-scale trial, 25,000 eyed eggs will be produced from two NCCCWA fish lines: ARS-Fp-R (resistant) and ARS-Fp-S (reference) fish. Eyed eggs will be shipped to a Clear Springs Foods, Inc. and subsequently hatched and reared under standard production conditions. This experiment will evaluate three objectives:.
1)production and shipping of eggs;.
2)obtain baseline/comparative production and survival data; and.
3)investigate the incidence of BCWD infection. A large-scale field trial will include 70,000 fish from the ARS-Fp-R line (resistant); 35,000 fish from the ARS-Fp-C line (control line); and 35,000 fish from the ARS-Fp-S line (reference). All fish will be reared in a single production lot in order to ensure a uniform environment and equal pathogen exposure. Farm performance evaluation will consist of recording daily raceway mortality, monitoring clinical disease symptoms and kinetics including lesions and splenomegly, determining pathogen load in internal organs (by microbiological plating and quantitative PCR), and measurement of fish weight and length. Fish group will be determined by fin-clip with parental assignment made by PCR-based genotyping.
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. After a BCWD epizootic, the ARS-Fp-R line displayed significantly greater risk-adjusted survival (95.7%) than the ARS-Fp-S line (91.2%, P<0.0001) and the ARS-Fp-C line (92.4%, P<0.0001). Phenotype stability in farm-trial fish was also evaluated using laboratory challenges. The ARS-Fp-R line consistently displayed a higher, but not always statistically significant, survival percentage compared to the other lines and the data suggest that the magnitude of the survival phenotype difference is sensitive to environmental influence. In summary, the overall greater survival of the ARS-Fp-R line provides evidence of genetic improvement under production conditions. These initial findings have been published this year and were the basis for initiation of a production scale trial. This year, a total of 300,000 eyed-eggs were shipped to CSF, and survival at the initial grading (69 days post hatch) was approximately 65%. To date, growth has been within the expected range and no disease outbreaks have been observed. Growth and survival will be measured through harvest.