Many biomedical researchers use animal models to better understand diseases that occur in humans. Transplantation of testis stem cells—the foundation of sperm production and male fertility—is an established approach developed in mice, but its application to large animals (e.g., sheep, pigs, nonhuman primates) has been more challenging.

The zebrafish (Danio rerio) has been used by researchers as a model organism for human disease for decades. In recent years, however, the zebrafish has gained considerable...