daphnia magna

Quick Answer Daphnia magna is a freshwater “water flea” widely cultured as live food for koi and aquarium fish. Culture it in dechlorinated water at 64–75°F (18–24°C), pH 7.0–8.0, feeding green water, baker’s yeast, or spirulina powder — with gentle aeration only, never a strong airstone, and regular partial harvesting to keep the culture stable.