The Growth and Biochemical Composition of Nannochloropsis oculata Under Influence of Different Phosphorus Sources for Aquaculture Live food

: Phosphorus is one of the most important nutritional factors that regulates cell growth and plays a significant role in most cellular processes. The effect of different phosphorus sources on the growth and biochemical composition of Nannochloropsis oculata ( N. oculata ) was investigated in this study. Four treatments: mono potassium phosphate (KH ₂ PO4), potassium di phosphate (K 2 HPO 4 ), calcium super phosphate (CaH 6 O 9 P 2 ), and media without any phosphorus sources were all compared to F/2 media, which has sodium di hydrogen phosphate (NaH 2 PO 4 ) as a control at a concentration of 36 µmol -1. The experiment lasted for 15 days under the conditions of 100 μmol photons per m2s of light intensity, with a light-to-dark (L/D) ratio of 24:0, a salinity of 25 g/L, temperature maintained at 23± 1 °C, and a pH value of pH 7.5 ±0.3. The growth of N. oculata based on cell density was inhibited in the medium without any phosphorus sources (5.3×106 cell/ mL) and increased significantly in the medium with NaH 2 PO 4 (16.4×106 cell/ mL). All phosphorus sources showed that there were significant differences ( P ≤ 0.05 ) between all treatment media in chlorophyll content; KH ₂ PO 4 achieved the highest significant chlorophyll a content (Chl a) with 4.25 mg/l, followed by K 2 HPO 4 4.12 mg/l. Cells treated with NaH 2 PO 4 produced the highest total protein and lipid content (31.14% and 46.63% by dry weight, respectively). Media without phosphorus had the highest total carbohydrate (22.48%), while the lowest total lipids and total carbohydrate achieved by KH ₂ PO 4 and CaH 6 O 9 P 2 had the lowest total protein (25.90%). Arachidonic acid (C20:4 ω6) recorded its highest value (0.83%) with K 2 HPO 4 . While γ-Linolenic acid (C18:3 ω6) recorded its highest value (1.43%) with NaH2PO4. Whereas eicosapentaenoic acid (C20:5 ω3) was achieved the highest level in NaH 2 PO 4 (9.53%) and CaH 6 O 9 P 2 (0.37%). In conclusion, this study demonstrated the variation of growth, fatty acid profile, and biochemical composition in N. oculata , benefiting the production of microalgae for aquaculture live food.