Production of all-male and sterile fish may not only substantially improve yield but also be crucial for the application of genome modified species in aquaculture. Previously, it was reported that the fish lacking primordial germ cells (PGCs) becomes infertile, and nitroreductase, an enzyme converting non-toxic metronidazole (MTZ) into toxic metabolites, induces targeted toxicity to kill the cells expressing it. In this study, we generated a transgenic zebrafish line of Tg(nanos3:nfsB-mCherry-nanos3 3′UTR) in which the NfsB nitroreductase is solely expressed in PGCs. Treating the embryos derived from the female transgenic zebrafish with MTZ from 0 through 2 dpf (days post fertilization), we found that the germ cells were completely eliminated in the ones older than 2.5 dpf. At 20 dpf, the MTZ-treated juvenile had no germ cells in their gonads. At 100 dpf, the MTZ-treated adult exhibited male-like morphology and showed normal mating behaviors although they had no germ cells but only supporting cells in their gonads. Taken together, our results demonstrated that conditional elimination of PGCs during early development make the zebrafish male-like and infertile. It may provide an alternative strategy to make sterile and all-male farmed fish that is good for increasing aquaculture yield and preventing the genome modified species from potential ecological risks.

Based on obtaining mstnb gene knockout in Pelteobagrus fulvidraco, a study on the effect of the mstn gene on skeletal morphology and growth was performed by comparing the number and length of the vertebrae of mutant and wild-type fish in a sibling group of P. fulvidraco, combined with the differences in cells at the level of vertebral skeletal tissue. It was found that mstnb gene knockdown resulted in a reduction in the number of vertebrae, the length, and the intervertebral distance in P. fulvidraco, and these changes may be the underlying cause of the shorter body length in mutant P. fulvidraco. Further, histological comparison of the same sites in the mstn mutant and wild groups of P. fulvidraco also revealed that the number and density of osteocytes were greater in mstnb knockout P. fulvidraco than in wild-type P. fulvidraco. Our results demonstrated that when using genome editing technology to breed new lines, the effects of knockout need to be analyzed comprehensively and may have some unexpected effects due to insufficient study of the function of certain genes.