Daphnia magna is probably the most common species in the aquarium hobby. It has been a favourite live food source since the hobby began. Daphnia magna are the largest member of the Daphnia family with males reaching 2 mm in length and females in the 3 – 5 mm range. They vary in color from a pale yellow to salmon-pink, and this is typically affected by their food source. Daphnia magna has a wide temperature tolerance, but favor cooler temperatures between 64°F / 18°C and 72°F / 22°C.
The life span of Daphnia, from the release of the egg into the brood chamber until the death of the adult, is highly variable depending on the species and environmental conditions (Pennak, 1978). Generally the life span increases as temperature decreases, due to lowered metabolic activity. The average life span of D. magna is about 40 days at 77°F / 25°C and about 56 days at 68°F / 20°C.
The nutritional content of Daphnia varies considerably depending on their age and the type of food they are receiving. Although variable, protein content usually averages 50% of the dry weight. Adults normally have a higher fat content than juveniles. The total amount of fat per dry weight is 20 – 27% for adult females and 4 – 6% for juveniles.