Peridinium bipes f. occultatum was able to use both orthophosphate and β-glycerophosphate as a sole source of phosphate. The maximum cell yield and the specific growth rate were saturated at 1 mgP/l in both phosphorus sources. The maximum growth rate under P-saturated condition was 0.16 d−1. The half saturation constant for the growth and the minimum cell quota were calculated to be 126 mgP/l, 50.9 pgP/cell for orthophosphate and 46 mgP/l, 28.5 pgP/cell for β-glycerophosphate, respectively. Among fresh water phytoplanktons, P. bipes f. occultatum showed a higher Ks value of phosphate for growth and lower growth rate. The optimum N:P ratio of the alga calculated from minimum cell quota was relatively low. The alga did not require B-group vitamins for the growth and the growth yield was saturated at 2.0 mgCa/l.
From these characteristics, it is difficult to explain the excessive growth of this alga and the resultant red tide.