Growth rate of Daphnia feeding on seston in a Siberian reservoir: the role of essential fatty acid

Specific growth rates (based on biomass increment in unit time) of Daphnia fed natural reservoir seston from a eutrophic Siberian reservoir were studied during four vegetation seasons in a laboratory flow-through system. Concentrations of particulate C, N, and P in reservoir seston < 115 mu m were comparatively high, 1.9, 0.2, and 0.05 mg l-1, respectively; maximum C:P ratio was 259 mol:mol. According to conventional thresholds, concentrations of elements and their stoichiometry did not limit the growth rate of Daphnia. Eicosapentaenoic acid (EPA) in seston significantly effected the growth rates at concentrations up to 13 mu g l-1(regression ANOVAR F-test value was 7.91), but not above this concentration. Thus, we consider this concentration of EPA in seston < 115 mu m to be the limiting concentration of EPA for the growth of Daphnia (longispina group), i.e., below this concentration EPA was the best single predictor of the growth of Daphnia.