Lipid composition and food quality of some freshwater phytoplankton for cladoceran zooplankters

The nutritional value of several planktonic algae was tested by means of feeding trials with three cladoceran zooplankters. The algae were monocultures and included two blue-greens, four greens and four flagellates with a size range of 5-48 u,m. The specific growth rates of the zooplankters were chosen as the measure of the nutritional value of the algae. The three cladocerans showed large differences in growth rate in the different algae, but the two cryptomonads were without doubt best suited as food for all. The fatty acid composition for the cryptomonads were different from the other algae. They contained high percentages of the polyunsaturated fatty acids 20:5u)3 (EPA) and 22:6w3 (DHA), which also are common in fish. It is suggested that the lipid composition is a probable factor determining the nutritional quality of the algae.