The present embodiments relate to selectively growing microalgae of a size suitable for the culturing of planktivorous finfish such as sardines, menhaden, herring, anchovy or shellfish such as oysters, clams, mussels, scallops, and sessile invertebrates such as sponges, coral, sea jellies, and other Cnidaria, or sedentary polychaete or bristle worms. A nitrogen to phosphorous content ratio of a nutrient medium may be measured. Nitrogen and/or phosphorous may be added to adjust the nitrogen to phosphorous content ratio in the nutrient medium to a ratio of 100:1 or higher. Microalgae may be grown in the adjusted nutrient medium. The environment may be controlled to produce microalgae with a predetermined diameter.
