Heterotrophic growth and nutritional aspects of the diatom Cyclotella cryptica (Bacillariophyceae): effect of nitrogen source and concentration

To investigate the nutritional value of the diatom Cyclotella cryptica Reimann, Lewin, and Guillard as an alternative feed for the use in the aquaculture industry, the heterotrophic growth characteristics, total fatty acids, and the resultant fatty acid profile of the microalga were studied when cultivated with sodium nitrate, ammonium chloride, or urea. All three nitrogen sources supported growth under heterotrophic conditions, and their uptake affected the pH of the cultivation medium, even when buffered. The use of sodium nitrate or urea resulted in a significant increase in the pH of the cultivation media, whereas the use of ammonium chloride caused a minor decrease in the pH of the cultivation media. The maximum specific growth rate was highest when urea and ammonium chloride were supplied at a low concentration; however, the total fatty acid content was not significantly affected (P = 0.101) by the nitrogen source when supplied at 10.7 mM nitrogen. The total fatty acid content and fatty acid profile of C. cryptica was more affected by the growth phase (predominately influenced by the initial nitrogen concentration) than by the source of nitrogen.