Disclosed is a gene multiple insertion cassette set including rDNA NTS fragments and an auxotrophic selection marker having an incomplete promoter is developed, and a safe oral recombinant strain having no antibiotic resistant marker is constructed by multiple insertion of an optimum number of the developed gene multiple insertion cassette sets into chromosomes of a Saccharomyces cerevisiae strain, a vaccine composition including, as an active ingredient, the above strain, a culture product thereof, a cell lysate, or nodavirus capsid protein (NNVcp) isolated and purified therefrom, and a composition for feed addition including, as an active ingredient, the above strain, a culture product thereof, a cell lysate, or squalene or oxidosqualene isolated and purified therefrom.
