# 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

## TL;DR

Scientists created a fast-growing, infertile male fish that grows like females, which could improve aquaculture and biological research.

## Contribution

A novel all-male, infertile fish line with female-like growth was developed through genome editing of the dmrt1 gene in Chinese tongue sole.

## Key findings

- dmrt1−/− ZZ males grew as large as females and were completely sterile.
- Muscle quality of edited males was comparable to wild-type females with lower fat and higher Omega6 content.
- Metabolomic analysis showed no harmful changes and enriched pathways related to amino acids and energy metabolism.

## Abstract

Chinese tongue sole is a valuable farmed fish in which females grow much larger than males, reducing the profitability of male stocks. To address this, we use genome editing to disrupt the sex-determining gene dmrt1 in male tongue sole. The edited fish grew as large as females and were completely unable to reproduce. Their muscle nutritional composition and texture were broadly comparable to those of wild-type fish, and no major abnormalities were detected in the measured parameters. These results demonstrated that dmrt1 editing can create a fast-growing, infertile all-male population, offering a useful model for biological research.

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.