en aquaculture aquaculture پژوهشي Orginal research papers This study compared the biomass production, fucoxanthin production and antioxidant capacity of the fucoxanthin from the marine haptophyte algae, <em>Isochrysis galbana </em>under different nitrogen concentrations. At first step in the salinity test, <em>I. galbana </em>could grow in 20&permil; and 35&permil; but the 35&permil; salinity was optimal. At second step, five different nitrogen concentrations (N-NO₃) of 2, 4, 8, 12 12 mM, at the salinity of 35&permil;, were investigated. Algal cell density increased as nitrogen concentrations increased<em>, </em>but a low growth rate occurred in the culture with the highest nitrogen concentration (12 mM). The maximum cell density of 72&times; <img alt="" chromakey="white" src="file:///C:UsersR8623~1.FALAppDataLocalTempmsohtmlclip1�1clip_image001.png" > &nbsp;and the maximum amount of fucoxanthin (18.1 mg g^-1) was obtained in<em> I. galbana </em>cultured in media containing four mM nitrogen (N-NO₃). The purified fucoxanthin exhibited strong antioxidant properties, with the effective concentration for 50% scavenging (EC50) of 1, 1-dihpenyl-2-picrylhydrazyl (DPPH) radical, being 0.2 mg/ml. This study suggests that the production and fucoxanthin concentration of <em>I. galbana </em>can be improved using nitrogen-replete culture in 35&permil; salinity. Also under this condition this microalgaecan be a commercial source of fucoxanthin for human health and nutrition. Isochrysis galbana, Culture, Nitrogen replete, Salinity, Fucoxanthin. 2901 2908 http://jifro.ir/browse.php?a_code=A-10-2437-3&slc_lang=en&sid=1 R. Mousavi Nadushan mousavi.nadushan@gmail.com 100319475328460038311 100319475328460038311 Yes Department of Marine Biology, Tehran North Branch, Islamic Azad University, Tehran, Iran. I. Hosseinzade ima_hb@yahoo.com 100319475328460038312 100319475328460038312 No Department of Marine Biology, Tehran North Branch, Islamic Azad University, Tehran, Iran.