Super-fast breeding of all-female giant grass carp by tiny zebrafish

Grass carp (Ctenopharyngodon idellus), a prominent species in freshwater aquaculture, boasts one of the largest body sizes and global production yields. However, the reproduction and genetic breeding of grass carp has been significantly hindered, primarily due to its protracted sexual maturation period of four to five years and the need for extensive cultivation space. In this study, we develop a super-fast strategy to breed all-female grass carp within half a year, leveraging surrogate production in a small-sized laboratory fish, zebrafish (Danio rerio). We identify and isolate female germline stem cells (GSCs) from juvenile grass carp at three months post-fertilization (mpf). The female GSCs with XX chromosomes are transplanted into germ cell-depleted zebrafish larvae at five days post-fertilization (dpf). The transplanted grass carp XX germ cells undergo rapid spermatogenesis in the zebrafish recipient. At three months after transplantation, all the zebrafish recipients develop into males capable of producing all-X sperm derived from donor grass carp. When these sperm are fertilized with wildtype grass carp eggs, a population of all-female grass carp is generated. This groundbreaking achievement highlights the feasibility of surrogate production of large-sized fish species in small laboratory fishes, and opens a new avenue for advancing genetic breeding in aquaculture.