The Effect Of Food On Growth And Reproduction Of Daphnia Hyalina From Liuxihe Reservoir, South China

A laboratory experiment was carried out to evaluate effects of foods on growth and reproduction of Daphnia hyalina from a reservoir located in the South China: Liuxihe Reservoir(E:113°46' , N:23° 45' ). The three types of food were Chlorella pyrenoidosa, cyanobacteria and natural sestons. The three organic carbon concentrations of Chlorella pyrenoidosa used in feeding culture of zooplanktons were 0.5mgC·L^-1 ,1.0mgC·L^-1 and 1.5mgC·L^-1 The four species of cyanobacteria were Microcystis sp. I , Microcystis sp. II, Microcystis sp.III and Pseudoanabaena sp., the four species of cyanobacteria mixed with Chlorella pyrenoidosa. The mixtures included 20%, 50%, 80% and 100% cyanobacteria with a total food concentration of 1.0 mgC·L^-1 in each treatment. Natural sestons from Minghu Lake and Liuxihe Reservoir were both got by filtering with 38μm and 110μm mesh, and then the two types of natural sestons from Minghu Lake diluted with water filtered with 0.45 μm mesh to get the other two kinds of food. The longest body length and lifespan decreased with increasing organic carbon concentrations of Chlorella pyrenoidosa. Under the lowest food concentration D. hyalina had the longest body length of 2.5mm, the longest lifespan of 69 days. The somatic growth rate increased with increasing cells concentrations of Chlorella pyrenoidosa, up to 0.049 mm · d^-1 at the highest food concentration. Size at maturity was not significantly affected by the organic carbon concentrations of Chlorella pyrenoidosa. The size at maturity was about 1.2mm. Hatching rate and the intrinsic rate of population increase were positively influenced by increased organic carbon concentrations of Chlorella pyrenoidosa, the hatching rate was over 80%, the intrinsic rate of increase was 0.42 at the highest food concentration. Net reproduction rate and generation time, however, decreased with increasing organic carbon concentrations of Chlorella pyrenoidosa. Under the food condition of 4 strains of cyanobacteria mixed with Chlorella pyrenoidosa, the parameters of somatic growth reduced. When D. hyalina were feed with cyanobacteria alone, the lifespan was short, the somatic growth was slow. The shortest lifespan was 9d, the somatic growth rate was 0.011 mm · d^-1 and the longest body...