Abstract
The protein and polyunsaturated fatty acid (PUFA) enrichment of microalgae can improve their nutritional value for larvae of various reared organisms. Protein enrichment can be achieved by increasing nitrogen concentration and selecting nitrogen sources that are easy to assimilate during microalga culture. Nitrogen-rich cultures can increase organism growth, biomass, and protein content, but their lipid content tends to stall. Since the diatom Thalassiosira weissflogii is usually provided to feed shrimp larvae, this study evaluated its digestibility and biochemical composition, culturing it with two nitrogen sources (NaNO3 and NH4Cl) at different concentrations (111.25, 222.50, 445 and 890 µM). The cell abundance, dry-weight biomass, Chl a, proteins, carbohydrates, total lipids and essential fatty acids were determined. The cell density and biomass peaked faster (day 12) with treatment < 890 µM than with 890 µM (day 15) in both nitrogen sources. However, the highest cell density, biomass and peak protein yield were not significantly different among treatments, suggesting the need to compare maintenance costs for a given production. After nine days of culture, concentrations ≤ 222.5 µM increased lipid content irrespective of the nitrogen source and decreased by 10–20% afterwards. With higher lipid production, the dominant PUFA were eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). One gram of NH4Cl provides ~60% more nitrogen than 1 g of NaNO3. In conclusion, based on time and growth rate, T. weissflogii cultivated with NH4Cl at 222.50 µM produced EPA and DHA at a better yield–cost ratio for biomass and lipid production. Furthermore, its nutritional value as enriched live-food for the reared larvae of marine organisms suggests potential biotechnological applications for aquaculture.
Highlights
In the last few years, interest in aquaculture has increased worldwide because of the growing market demand and high commercial value created by these products [1]
Their biochemical composition is important for their nutritional value because of their ability to synthesize and accumulate essential fatty acids and other nutrients [8,9]
The estimated time to reach half of the maximum cell density occurred 33 h earlier for C4 compared with N4
Summary
In the last few years, interest in aquaculture has increased worldwide because of the growing market demand and high commercial value created by these products [1]. As a consequence of their nutritional value, diatom species, such as Skeletonema costatum, Thalassiosira sp., Phaeodactylum sp., Chaetoceros gracilis, C. calcitrans and the flagellates Pavlova lutheri, Isochrysis galbana, Tetraselmis chuii and T. suecica are all grown as food for rearing marine organisms of commercial value [6,7]. Their biochemical composition is important for their nutritional value because of their ability to synthesize and accumulate essential fatty acids and other nutrients [8,9]
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