Spirulina algae, a cyanobacterium, is a superfood with a long history of use as a dietary supplement and as food for fish. It is highly nutritious, containing protein, vitamins, minerals, antioxidants, and essential fatty acids. Spirulina is a good source of protein, containing about 60% protein by weight, making it a great addition to the diet of fish, which are carnivorous. It is also a good source of vitamins, including vitamin A, vitamin B12, and vitamin K, and minerals, including iron, calcium, and magnesium. Spirulina is also a source of antioxidants, which can help protect fish from oxidative stress and disease.