Effects of different nitrogen sources on the growth and biochemical profile of 10 marine microalgae in batch culture: an evaluation for aquaculture

Growth responses and biochemical composition were investigted ill 10 species of marine microalgae Of potential use in aquaculture. The algae were grown in Walne's medium and supplied with nitrate, ammonium or urea as a nitrogen (N) source at a high concentration (1.18 mM). Growth was monitored by daily cell counts. and samples for biochemical analysis were taken near the end of the exponential growth phase. when N nutrient and phosphate still remained in the medium. Two species. Hillea sp. and Prorocentrum minimum, failed to grow with ammonium-N because of the toxic effect of ammonia in high concentration. Hillea sp. and Nannochloropsis oculata on urea-N, and Isochrysis galbana, Phaeodactylum tricornutum and Synechococcus subsalsus on ammoniumn-N, showed significantly lower final yield than with the other-N sources. Greater percentages of protein and chlorophyll (dry matter) occurred in the treatment (N source) that produced higher final cell yield. Treatments producing lower final yields tended to give a larger relative content of carbohydrate and lipid in the Cells, and in some cases greater cellular volumes. Seven species tended to produce lower percentages of polyunsaturated fatty acids (FAs) with urea-N. Hillea sp., a microalga not yet used in aquaculture. seems to be a promising food-species because of its fast growth rate with nitrate-N and its large relative content of protein and lipids, and because it produces all essential FAs. Differences in chemical profiles resulted from the use of different nitrogen Sources in most cases. but few general trends were identified, even within the same taxonmic group (diatoms, green algae).