Half-smooth tongue sole (Cynoglossus semilaevis) is a unique marine aquaculture fish species known for its high nutritional value and commercial potential. However, half-smooth tongue sole exhibits typical sexual dimorphism, characterized by substantially faster growth rates in females than in males, resulting in female adults being two to four times heavier than male adults. Previous studies have successfully obtained dmrt1^–/– ZZ from male half-smooth tongue sole using TALEN genome editing technology targeting dmrt1 gene. The growth rate of dmrt1^–/– ZZ males exceeds twice that of normal male fish, with weights comparable to normal female fish. This successfully addresses the issue of stunted growth in the male half-smooth tongue sole and lays the foundation for the establishment of gene editing breeding techniques for this species. Reports on the impact of transgenic organisms on the surrounding environment have raised marked concerns regarding the environmental safety of genetically-modified organisms. A pressing question is whether the edited genes could affect the environment through gut microbiota or other behavior during the rearing process. Compared to transgenic technology, gene editing has the advantage of not involving exogenous genes. Several studies on the gut microbiota of gene-edited animals have shown that no marked changes in gut microbiota composition were observed in animals after gene editing. To assess the health status and environmental safety of the gene-edited half-smooth tongue sole, this study investigated the changes in gut microbiota of the dmrt1 homozygous mutant male fish. High-throughput sequencing technology was used to compare the gut microbiota between dmrt1^–/– ZZ males and normal male and female fish kept under the same aquaculture conditions. Environmental safety risks were assessed by testing the genotypes of normal fish cohabiting with dmrt1^–/– ZZ males, as well as the eDNA from the water environment where they were raised. There were no marked differences in alpha diversity and composition of the gut microbiota between dmrt1^–/– ZZ male and normal male and female fish, and no differences were observed in the predicted functions of the gut microbiota. The differences in gut microbiota may influence growth variations. The gut microbiota composition of dmrt1 homozygous mutant male fish was similar to that of female fish, suggesting that certain microbial populations may be involved in regulating growth rates, which could play a role in enhancing the growth rate of dmrt1^–/– ZZ males. No edited genes were detected in the normal individuals cohabiting with the dmrt1^–/– Z males. Water samples taken from five sampling points along the drainage path of the aquaculture environment of the dmrt1^–/– ZZ males were amplified and sequenced indicating no presence of the edited target gene. In conclusion, dmrt1 gene editing does not lead to marked changes in the gut microbiota of dmrt1^–/– ZZ male half-smooth tongue sole and does not affect other individuals reared in the same environment, indicating no environmental risks. This study provides a reference for safety assessment methods of gene-edited aquatic animals.