Abstract
Microalgae are the principal producers of long-chain polyunsaturated fatty acids (LC-PUFAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in marine ecosystems. Algae are used in aquaculture systems as direct or indirect feed for zooplankton, filter-feeding mollusks and larval stages of crustaceans and fish. Therefore, it is necessary to select nutrient-rich strains, with high levels of EPA and/or DHA, preferably during the stage of rapid growth. During the course of algal growth (exponential to stationary phase), many microalgal species accumulate lipids, especially triacylglycerols. However, relatively little is known about the effect of growth phase on LC-PUFA accumulation. In the present study, absolute and relative EPA and DHA levels of seven representative species of marine microalgae were determined during different growth phases in batch culture. Four species (Phaeodactylum tricornutum, Thalassiosira weissflogii, Thalassiosira pseudonana and Rhodomonas salina) accumulated fatty acids during growth. In all these species, intracellular EPA levels were higher during the late stationary growth phase than during exponential growth. In contrast, an increase in DHA content was not observed and therefore the DHA-to-EPA ratio was significantly lower in late stationary phase cultures. These results can be used to improve the nutritional value of microalgae cultivated for application in marine aquaculture systems.
Highlights
Due to their high nutritional value, microalgae are important feed sources in aquaculture systems (Patil et al 2005)
eicosapentaenoic acid (EPA) percentages in S. costatum were comparable with the other diatoms (9 % of total fatty acids on average), absolute levels of EPA normalized to biovolume were low (\1 fg lm-3)
docosahexaenoic acid (DHA) percentages were highest in E. huxleyi, while absolute levels were of total fatty acids), absolute EPA and DHA content, total fatty acid content, maximum quantum efficiency of photosystem II (PSII) (Fv/Fm) and DHA-to-EPA ratio
Summary
Due to their high nutritional value, microalgae are important feed sources in aquaculture systems (Patil et al 2005). Marine algae are key organisms in the production of essential long-chain polyunsaturated fatty acids (LC-PUFAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These n-3 PUFAs are necessary for optimal nutrition and stress tolerance of marine fish, especially at the larval and juvenile stages (Khozin-Goldberg et al 2011, and references therein). During the course of batch growth or when grown under stress, many microalgal species accumulate lipids, especially TAGs (Hu et al 2008). Tonon et al (2002) reported accumulation of DHA in T. pseudonana and P. lutheri, the incorporation into TAGs was significantly lower and accumulation started later during the course of batch growth. EPA or DHA content per algal biomass was reduced or not significantly affected by culture age or nutrient limitation (Klein Breteler et al 2005; Hsiao and Blanch 2006; Gong et al 2013; Nalder et al 2015)
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