Natural aquarium agent, with added vitamins, for use in the prevention of fish diseases and as supportive therapy after treatment. Enhances the immune system of fish, protects against the influence of pathogens and improves the healing process. The immunostimulatory action of Aquasan immuno makes fish more resistant to diseases and stressful conditions e.g. during transport. Recommended for use during quarantine of fish. This biodegradable agent is simple to use and does not change the chemical parameters of water.