O.S.I Spirulina Flakes are not only an excellent natural color enhancer, but the algae, spirulina, also stimulates your fish's immune system to attack gram-negative bacteria. Gram-negative bacteria are known to cause a variety of diseases in fish. By using O.S.I Spirulina Flakes, your fish are healthier, heartier and more vibrant. This diet is appropriate for all freshwater and marine species. This is especially important for marine fishes which tend to be more delicate and disease prone.