Production of YY males through self-fertilization of an occasional hermaphrodite in Lanzhou catfish (Silurus lanzhouensis)

Lanzhou catfish (Silurus lanzhouensis), an important commercial fish in China, takes three years to be sexually mature and males display faster growth performance than females. Thus, shortening of breeding cycle and production of all-male population in Lanzhou catfish have great significance in aquaculture. Here, we first developed an optimal method for artificial gynogenesis, through which the male heterogametic XX/XY sex determination system was revealed in Lanzhou catfish. Subsequently, sex-specific markers were identified via 2b-RAD-seq and verified in artificial breeding and wild populations. Intriguingly, a hermaphrodite Lanzhou catfish with XY genotype was occasionally obtained, whose gonad contained both mature ovarian and testicular tissues. The eggs and sperm from the intersexual gonad were used for artificial fertilization to establish a self-fertilization family, which contained 21 XX females, 25 XY males, and 12 YY males in the offspring. And the YY males are able to mate with XX females to produce all-male progenies with XY genotype. Compared with the conventional way of expending two-generation time, self-fertilization of the XY hermaphrodite saved one-generation time to produce YY males. Therefore, this study not only reveals XX/XY sex determination system in Lanzhou catfish, but also directly obtains YY males for future production of all-male population in aquaculture.