Fatty acid composition of different microalgae strains (Nannochloropsis sp., Nannochloropsis oculata (Droop) Hibberd, Nannochloris atomus Butcher and Isochrysis sp.) according to the culture phase and the carbon dioxide concentration.

This study aimed to evaluate the influence of different volumes of supplemented carbon dioxide, which is a potential donator of carbon atom, on the fatty acid profile of four microalgae strains (Nannochloropsis sp., Nannochloropsis oculata (Droop) Hibberd, Nannochloris atomus Butcher and Isochrysis sp.) currently used to enrich rotifers fed to marine fish larvae during two different phases of growth (logarithmic and stationary). Half of the microalgae were cultured at a low CO2 concentration (0.5 L/min), corresponding to 1% the air volume (0.038 L/min per L of culture) and the other half of microalgae were cultured at a high concentration of CO2 (1.1 L/min), corresponding to 2% the air volume (0.086 L/min per L of culture). The resulting fatty acid profile was species-specific and Nannochloris atomus appeared less suitable for marine organism feeding because of its high percentage of alpha-linolenic acid which represents the only n-3 PUFA of this alga (28.7%). On the contrary, Isochrysis sp. showed the largest proportions of n-3 PUFA also when maintained in the stationary phase (36.46%). Algae cultures contained higher percentages of n-3 PUFA during the logarithmic phase than in the stationary phase when the proportions of short-chain fatty acids increased. High levels of concentrated CO2 generally increased the content of long chain fatty acids from 17 carbon atoms onwards. The percentages of total n-3 and n-6 were higher than those recorded at low CO2 concentration. Similarly, the n-3/n-6 ratio was higher at the maximum CO2 concentration (logarithmic phase). During stationary phase the difference between the two groups was less apparent than that observed in the logarithmic one. The high CO2 addition exerted a significant and more favourable influence than the low supplementation on the C18:1, C20:0, C20:4n-6, and C22:6n-3 concentrations in both phases, in all four microalgae strains studied.