Engineered exosomes were constructed by transfection with isomiR-124a and modification with PEP1 and applied for dmrt1 regulation in the testes of juvenile fish via intraperitoneal injection. After one week, the testes of fish injected with the engineered exosomes and PBS were sampled for RNA sequencing to investigate the transcriptome-wide view of the effect of engineered exosomes on testes. The role of dmrt1 in maintaining normal structure and function in determined testes were found by RNA-sequencing.