Evaluation of an Infertile, All-Male ZZ Line Exhibiting Female-like Growth in Chinese Tongue Sole (Cynoglossus semilaevis): Growth Performance, Flesh Quality, and Muscle Metabolome

Chinese tongue sole (Cynoglossus semilaevis) is an important marine aquaculture species that exhibits pronounced female-biased sexual size dimorphism, which limits the economic value of male stocks. The F4 generation of genome-edited dmrt1−/− ZZ males carried a stable 8 bp deletion in dmrt1, developed ovarian lamella-like gonads and were completely sterile, as in vitro fertilization with their gonads produced no viable embryos. From 12 to 15 months post-hatch (mph), their growth rate was significantly higher than that of wild-type males and ultimately comparable to that of females. They weighed 3.2-fold heavier and measured 1.38-fold longer than their 15 mph wild-type male counterparts. Muscle nutritional composition and most texture traits of dmrt1−/− ZZ males did not differ from wild-type females. However, their fat content was significantly lower than that of wild-type males, while their Omega6 content was significantly higher. Metabolomic analysis identified 1262 metabolites and revealed differential enrichment of pathways related to amino acids, energy, and antioxidant and neuromuscular metabolism, without evidence of detrimental shifts. Overall, dmrt1 editing yields a fast-growing, functionally sterile male line whose flesh quality is similar to that of wild-type tongue sole, supporting its potential use in sex-control breeding in Chinese tongue sole and providing a valuable model for studying sexual size dimorphism.