Trace elements are important for improving the productivity and health of aquatic animals. Manganese (Mn) is a micronutrient that supports various physiological functions. It plays a key role in enzyme production, hormone formation, the immune response, reproductive processes, metabolic activity and antioxidant functions. Some aquafeed ingredients naturally provide Mn to meet the requirements of aquatic animals, but supplementation may be necessary for optimal growth. However, both excess and deficiency of Mn can disrupt metabolic functions and overall health. This review evaluates the role of Mn supplementation in the feed of fishes and crustaceans in improving growth performance, feed utilization, antioxidant defense, tissue accumulation, proximate composition and enzyme activity.