Causal gene identification and desirable trait recreation in goldfish

Goldfish ( Carassius auratus ) have long fascinated evolutionary biologists and geneticists because of their diverse morphological and color variations. Recent genome-wide association studies have provided a clue to uncover genomic basis underlying these phenotypic variations, but the causality between phenotypic and genotypic variations have not yet been confirmed. Here, we edited proposed candidate genes to recreate phenotypic traits and developed a rapid biotechnology approach which combines gene editing with high-efficiency breeding, artificial gynogenesis, and temperature-induced sex reversal to establish homozygous mutants within two generations (approximately eight months). We first verified that low-density lipoprotein receptor-related protein 2B ( lrp2aB ) is the causal gene for the dragon-eye variation and recreated the dragon-eye phenotype in side-view Pleated-skirt Lion-head goldfish. Subsequently, we demonstrated that the albino phenotype was determined by both homeologs of oculocutaneous albinism type II ( oca2 ), which has subfunctionalized to differentially govern melanogenesis in the goldfish body surface and pupils. Overall, we determined two causal genes for dragon-eye and albino phenotypes, and created four stable homozygous strains and more appealing goldfish with desirable traits. The developed biotechnology approach facilitates precise genetic breeding, which will accelerate re-domestication and recreation of phenotypically desirable goldfish.