Abstract
Red tilapia (Oreochromis spp.), with male growing faster and larger than female, is becoming more and more popular for aquaculture in recent years. The culture of mono-sex red tilapia is of great value. However, the lacking of convenient and accurate sex-linked marker has limited the application of sex control in the breeding process of red tilapia. In addition, red tilapias show a wide range of color variation in each generation, which makes them not as valuable as pure red individuals. These are the bottlenecks of red tilapia culture. Tyrosinase is a key enzyme in melanin biosynthesis, and mutation of tyr is one of the main causes of albinism in vertebrates. In this study, we identified a sex-linked marker by sequencing and resequencing of Wang Lab dominant red tilapia (WLDRT, the red is controlled by single dominant gene) genome, selected YY supermales and established tyrb mutant line by CRISPR/Cas9 in red tilapia. The obtained homozygous XX and YY tyrb mutants displayed normal fertility and allowed continuous production of genetically male red tilapia (GMT) without blotches. Another tyrb mutant red tilapia line was established by crossing tyrb-/- Nile tilapia (NT) (Oreochromis niloticus) female with Wang Lab recessive red tilapia (WLRRT, the red is controlled by single recessive gene) male, followed by sibling crossing of the F1 heterozygous mutants. These mutants provide useful strains with improved commercial trait for red tilapia culture and good models for analyzing the genetic basis of body color formation in tilapia.