Genetic Basis of Cyprinid Herpes Virus-3 Resistance in Common Carp

The goal of this project was to provide scientific and technical basis for initiating the development of breeding protocols using marker assisted selection for viral disease resistance in common carp. The specific objectives were: 1) Establishing families and characterizing the phenotypic and genetic variation of viral resistance; 2) Measuring the dynamics of immune response and developing a method to measure the long term immune memory; 3) Developing markers and generating a new genetic linkage map, which will enable initial QTL mapping; and, 4) Identifying genetic linkage of markers and candidate genes (like MHC and TLRs) with resistance to CyHV-3. The common carp is an important farmed freshwater fish species in the world. Edible carp is second only to tilapia in Israeli aquaculture production and ornamental carp (koi) is an important product in both the US and Israel. Carp industries worldwide have recently suffered enormous economic damage due to a viral disease caused by Cyprinid herpes virus 3 (CyHV-3). Aside from preventative measures, a sustainable solution to this problem will be to establish a genetic improvement program of the resistance of fish to the pathogen. The aims of the project was to take the necessary first steps towards that. The differences in survival rates after infection with CyHV-3 virus among 20 families from six types of crosses between three carp lines (two commercial lines and one wild-type carp) revealed that the wild-type carp and its crosses had a much-improved survival over the crosses of the commercial lines themselves. These crosses set the starting point for breeding of commercial strains with improved resistance. Resistant fish had lower antibody titer against the virus suggesting that resistance might depend more on the innate immunity. A set of 500 microsateliite markers was developed and the markers are currently being used for generating a genetic linkage map for carp and for identifying disease resistance QTL. Fourteen candidate immune genes, some of which were duplicated, were cloned from the carp and SNP markers were identified in them. The expression of these genes varied between tissues and suggested functional divergence of some duplicated genes. Initial association between CyHV-3 resistance and one of the genes was found when SNP alleles in these genes were tested for their segregation between susceptible and resistant progeny. The results of this project have implications to the development of viral resistant commercial carp strains and effective immunization against this aggressive disease. The genetic and immunological knowledge accumulated in this project will not only promote carp and koi production but will also contribute to a broader understanding of fish immunogenetics.