Evaluation of agricultural fertilizers as cost-effective alternatives to Guillard’s f/2 medium for the growth and biochemical composition of Nannochloropsis sp

The high cost of laboratory-grade Guillard's F/2 medium presents a significant barrier to the mass production of Nannochloropsis sp., a microalga of considerable value in aquaculture as a feed source rich in protein, lipids, and essential fatty acids. This study evaluated three agricultural fertilizers, namely NPK, Urea, and Diammonium Phosphate (DAP) as cost-effective alternatives to F/2 medium for outdoor cultivation of Nannochloropsis sp. in transparent 35 L PVC containers. Specific growth rate (µ) and doubling time (Td) were determined via cell counts every four days using hemocytometer and a compound light microscope. Chlorophyll-a was quantified spectrophotometrically following 90% acetone extraction. Proximate composition was assessed using the Kjeldahl method (crude protein), Bligh and Dyer's method (total lipids), and the phenol-sulfuric acid method (carbohydrates). Data were analyzed using one-way ANOVA with Tukey's post-hoc test. F/2 yielded the highest specific growth rate (µ = 0.805 day⁻¹); however, NPK (µ = 0.723 day⁻¹) showed no statistically significant difference (p > 0.05), demonstrating comparable growth performance. Urea and DAP produced significantly lower growth rates (p < 0.05). Notably, Urea supported the highest crude protein content (42.1% DW), while NPK and DAP promoted enhanced lipid accumulation (>31% DW), consistent with nitrogen limitation-induced lipid biosynthesis reported in related species. These results indicate that NPK fertilizer is a statistically viable and economically practical substitute for Guillard's F/2 in large-scale Nannochloropsis cultivation, with implications for reducing production costs in aquaculture hatchery and algal biomass industries.