Humic Acid Stimulation of Growth and Optimization of Biochemical Profiles on Two Microalgal Species Proposed as Live Feeds in Aquaculture

A series of batch culture experiments on two marine microalgae species, Dunaliella salina Teodoresco and Nannochloropsis salina Hibberd, was conducted at various humic acid (HA) concentrations (0.0, 0.1, 0.2, 0.3, 0.4, 0.5 mgL-1), in order to evaluate the stimulatory potential of HA on microalgae growth (expressed as a biomass concentration), pigment production (chlorophyll a and carotenoids) and carbon to nitrogen (C:N) ratio. The impact of HA on the proximate composition (moisture, ash, dietary fiber, crude lipid, available carbohydrates, crude protein, and energy content) was also considered. Results demonstrated a highly significant positive effect of HA on growth, pigment production, and proximate analysis (P≤ 0.01). The excellent response of the two investigated microalgae to HA recommends it as a low-cost, high-yield investment, despite the finding that the C:N ratio in D. salina showed a gradual decrease upon addition of HA. A slight increase in the C:N ratio was observed upon addition of HA in N. salina.