Microalgae play a vital role in many aquaculture feed application processes. Maintaining a microalgae production facility has been estimated to account for an average of 30 % and up to 60 % of the total budget of aquaculture hatcheries, despite several research programs and global efforts to reduce production costs of algal biomass. The use of bicarbonate as carbon inorganic to produce microalgae biomass for bivalve hatcheries was proposed as an alternative to reduce this cost. The focus of this investigation is characterization of the interaction of bicarbonate-based microalgae cultivation and photoperiod on the growth rate and production of brown microalgae Isochrysis galbana. The salt was provided to the cultures at the final concentration from 0.5 to 2.5 g L^-1. Concerning photoperiod, two cycles of light:dark (6:18 and 12:12) were studied under light intensity at 160 µmol m^-2 s^-1. The growth rate of Isochrysis galbana showed values significantly higher in the culture supplemented with 0.5 and 1 g L^-1 of NaHCO₃ respectively under cycles 6L:18D and 12L:12D. Bicarbonate administration leads to a significant increase in cellular size at the stationary phase, probably related to starch or lipid accumulation. This study proved that the addition of bicarbonate is a viable strategy to enhance the production of microalgae and reduce production costs.