BACKGROUNDHigh cell density in cultures of microalgae is a key factor to recover biomass and extract metabolites of interest. A fed batch tubular reactor (FBTR) and semi-continuous reactor (SCR) with f/2 Guillard Medium (f/2GM) and algal medium (AM) were evaluated. Both modes were operated under completely defined conditions to assess their effect on cell density, and lipid, protein and carbohydrate productivity of the microalgae Nannochloropsis oculata. RESULTSResults show that the FBTR promotes the highest cell density for both culture media, achieving 525 1.84x10(6) cell mL(-1). With AM in the SCR, specific growth rate, productivities of biomass and lipids were the highest, as well as content of protein (48%), lipid (52.1%) and carbohydrates (17%). No significant differences were found in saturated fatty acids composition, whereas unsaturated fatty acids composition was affected by the operating regimen, this being higher in the FBTR. CONCLUSIONThe use of AM in both operating modes, FBTR and SCR, increased the cell density and improved the lipid content of N. oculata. A good option would be to combine both culture modes; first, use the FBTR to obtain high cell densities and then apply the SCR mode to increase lipid productivity; finally, an important quantity of high-value products could be recovered. (c) 2017 Society of Chemical Industry