Abstract
Nutritional effects of marine phytoplankton on population growth of the rotifer Brachionus plicatilis were investigated under sterile conditions. First-laid eggs of the rotifers were divided into two groups, and one was cultured with a species of phytoplankton and the other was cultured with Chlorella sp. (marine type) as control. They were cultured separately in many test tubes, each containing two individuals and were observed daily to obtain the survival rate and the fecundity, while food phytoplankton suspension was renewed daily. The phytoplankton suspension was adjusted at the concentration which had been decided previously as the desirable cell concentration for population growth of the rotifers. From these daily counts, intrinsic rate of population growth and net reproduction rate were calculated as the indices for evaluating the nutritional effect of phytoplankton on population growth of the rotifers.
Eight species of phytoplankton were evaluated in terms of nutritional effect on population growth of the rotifers as follows. Two species of Synechococcus elongatus and Chlorella sp. were evaluated as excellent food plankton, four species of Chlamydomonas sp, , Monochrysis lutheri, Dunaliella tertiolecta and Cyclotella cryptica as average and two species of Eutreptiella sp. and Nitzschia clostelium as deficient.
