Function of blue-green algae, Anabaena flos-aquae and Oscillatoria africanum on feeding behavior of Daphnia magna

The Daphnia magna is a promising candidate for feeding freshwater fish larvae in cultural media. In this research، the effect of two Cyanophycae strain (Anabaena flosaquae and Oscillatoria africanum) on ingestion، filtration rate and feeding behavioral of Daphnia magna were investigated. Exposure was down at the same condition in three replications. Rate of filtration، ingestion and feeding of Daphnia magna from two investigated Cyanophycae strain were measured according to Gauld equation (1951). The results shown that with increasing of food concentration (Cyanophycae strains)، filtration، ingestion and feeding rate of Daphnia magna significantly decreased (P<0. 05). Maximum of these indices (798±60. 2، 70861± 992 and 0. 4±0. 02 respectively) in 3 mg/lit and minimum of mentioned parameters (100±17/7، 10683±492 and 0. 2±0. 01 respectively) were observed in 12 mg/lit. It means that Daphnia not able to filtered filamentous Cyanophycae makes some difficulty in filtration system of Daphnia، especially in high concentrations. The maximum of specific growth rate (SGR) (0. 5±0. 02) was observed in feeding with Anabaena flosaquae (in 4. 25 mg/l) (P<0. 05)، and survival rate of Daphnia magna not difference among mentioned algae (P>0. 05). According to the results can conclude that it is difficult to use Daphnia magna biological control of algal bloom in fresh water.