Nitrogen is one of the most critical nutrients affecting cell growth and the biochemical composition of microalgae. The Effect of different nitrogen sources on the growth and biochemical composition of Nannochloropsis oculata sp. (N. oculata sp.) was investigated in this study. Five different forms of nitrogen at 0.88 mmol L-1 each: ammonium bicarbonate (NH4HCO3), ammonium sulfate ((NH4)2SO4), ammonium nitrate (NH4NO3), ammonium chloride (NH4CL), urea were all compared to F/2 media which has sodium nitrate (NaNO3) as a control. The experiment lasted for 15 days under the conditions of 100 μmol photons m2s light intensity (L/D= 24:0), salinity 25 ppt, 23± 1 °C , pH 7.5 ±0.3. Ammonium bicarbonate promoted cell density and specific growth rate (µ) achieving the highest cell density 25.27×106 cell/ml and 0.41 div./day after nine days while urea achieved the lowest cell density 13.58 ×106 and ammonium sulphate achieved the lowest specific growth rate 0.25 div./day. Total protein content increased significantly (P≤0.05) by 38.28% in urea medium however, it had the lowest total lipid, carbohydrate, and ash 30.11%, 12.22 %, and 1.32% by dry weight, respectively. Ammonium nitrate had the highest total lipid content of 43.67%, as well as the highest total ash content of 3.77 %, total carbohydrate content increased by 19.09 % in sodium nitrate (control), whereas ammonium chloride had the lowest total protein content 19.28 %. The major fatty acids detected in different treatments were (C14:0), (C15:1), (C16:0), (C16:1n 7), (C17:1), (C18:0), (C18:1 n9), (C18:2 n6), (C20:3 n6), (C20: 4 n6), (C22:2), (C20:5 n3). N. oculata sp., which was cultured by the media supplemented with NH4HCO3, NaNO3, NH4NO3 and urea had higher content of Eicosapentaenoic acid (C20:5 ω3) EPA, Decosahexaenoic acid (C22: 6 ω3) DHA, while Arachidonic acid (C20: 4 ω6) increased with urea and Linoleic acid (C18:2 ω6c) increased with ((NH4)2SO4).
Overall, our findings demonstrate that nitrogen sources can strongly influence growth and biochemical composition in N. oculata sp. which represent potentially interesting microalgae for aquaculture purposes.