Salinity and nutrient levels are the two most important parameters for maximum growth and reproduction of microalgae. This study investigated the instantaneous growth rates of Isochrysis galbana at different salinities (0, 5, 10, 15, 20, 25, and 30 ppt) and nutrient concentrations (100% and reduced f2 of 90%, 80%, 70%, and 60%) with three replicates each arranged in complete randomized design. Average cell density (cells/ml), and instantaneous growth rates (K’) were monitored every 24 hours. Temperature was maintained at 180 C throughout the experiment. One Way ANOVA was used to analyze the data to determine significant difference among treatments at 0.05 level of significance. Results of experiment 1 showed that ACD was significantly higher at lower salinities of 100 / 00, 50 / 00, 150 / 00 compared from salinities of 00 / 00, 250 / 00, 300 / 00. Highest average K’ occurred at same salinities but there was no significant difference detected among treatments. During the second experiment, ACD was highest at 100% f2 but not significant from other concentrations. Average K’ has no significant difference among other treatments. This means that I. galbana can be cultured at lower salinities and reduced f2 nutrients concentration and can serve as natural live food for freshwater species of fish during the larval stage.