Edited by Mariana F. Wolfner, Cornell University, Ithaca, NY, and approved January 26, 2021 (received for review September 17, 2020)Spermatozoon swimming performance is critical for fertilization success in fishes, yet the cellular mechanisms that regulate this vital trait are poorly understood. Here, we discovered that a water channel protein, acting as an H2O2 channel (peroxiporin) to detoxify the mitochondria, directly regulates the velocity and progressive motility of both freshwater and marine spermatozoa. The mitochondrial insertion of the peroxiporin is controlled by an increasingly...…Edited by Mariana F. Wolfner, Cornell University, Ithaca, NY, and approved January 26, 2021 (received for review September 17, 2020)Spermatozoon swimming performance is critical for fertilization success in fishes, yet the cellular mechanisms that regulate this vital trait are poorly understood. Here, we discovered that a water channel protein, acting as an H2O2 channel (peroxiporin) to detoxify the mitochondria, directly regulates the velocity and progressive motility of both freshwater and marine spermatozoa. The mitochondrial insertion of the peroxiporin is controlled by an increasingly...WW…