Characteristic index for food(alga) concentration and the reproduction of Daphnia magna under different food concentrations in a standardization test were analyzed. The results indicated that all of the correlation coefficients r with paired comparison test within cell number, optical density and TOC of algal suspension were > 0.917(P < 0.01), and the three indexes were significantly comparable based on the linear relationship. Optical density method is more efficient in testing than the two other methods, ...