In this study, the effects of selenium nanoparticles on sperm quality and reproductive performance of fish were investigated. Today, given the growing world population, providing healthy and adequate food is one of the critical issues in many countries in the world, especially in developing countries. Aquatic animals can play a vital role in providing the nutrients needed by the community. Fish reproduction control is a key issue in aquaculture. Fish quality is one of the factors limiting the reproductive success. In addition, the quality of gamet fish can be very variable and affected by a large number of external factors. The presence of minerals in the diet is essential, even minor changes in levels of these substances have significant effects on reproductive health and reproductive performance. Selenium is a negligible mineral that, as a component of enzymes such as glutathione peroxidases, as well as selenoproteins, plays an important role in various biological processes including antioxidant defense, male and female fertility, thyroid metabolism, immune function, endotracheal function, and muscle development and function Also acts as a catalytic center in the active site of the antioxidant enzyme glutathione peroxidase. Fish, and in particular free fish, may have relatively high levels of antioxidant properties in selenium to protect themselves from high levels of highly unsaturated fatty acids (PUFAs) that are susceptible to peroxidation. Selenium and selenoproteins, therefore, guarantee the survival of spermatozoa and protect against reactive oxygen species (ROS), and reproductive performance may also be increased through selenium.