Fight stress - First Defense for saltwater aquaria was developed to help fish adapt to new environments by assisting the fishes’ natural immune system and First Defense promotes healing, repairs wounds and supports the immune system with vitamins and immunstimulants. Changing the environment of a fish causes stress that robs fish of essential nutrients and can weaken their immune system. First Defense is scientifically designed to provide stress relief and support the immune system, helping fish cope with stress due to bagging and shipping from the store to your tank, water changes, new fish additions, disease treatments, and other environmental changes.