Assessment of microalga Tisochrysis lutea in the deceleration growth phase as a n-3 HUFA source for Brachionus plicatilis rotifers in Japanese flounder larviculture

For fish oil-free aquafeed development, a photoautotrophic microalga Tisochrysis lutea is believed to be the candidate source of n-3 highly unsaturated fatty acid (n-3 HUFA) because of its docosahexaenoic acid (DHA) biosynthesis. While DHA contents of T. lutea vary during the cultivation periods depending on algal growth phase, little is mentioned about how this dependence should be taken into consideration when evaluating the suitability of microalgae as an alternative to fish oil-formulated diets. Here, we compared nutritionally maximized cells of deceleration growth phase T. lutea and fish oils-formulated product (n-3 HUFA-enriched Chlorella) as a rotifer enrichment diet for enhancement in Japanese flounder Paralichthys olivaceus larviculture. T. lutea had higher concentrations of DHA in the polar lipids than those for enriched Chlorella. Such higher concentrations of T. lutea were estimated only in the deceleration growth phase (not in the logarithmic growth or stationary phase). When deceleration growth phase T. lutea were fed to Brachionus plicatilis rotifers previously cultured on unenriched Chlorella, the DHA of the rotifers was boosted up to the level in those fed with enriched Chlorella. Furthermore, use of T. lutea-fed rotifers for initial feeding of fish larvae enhanced the growth, survival, n-3 HUFA levels, and final juvenile productivity of the larvae as much as feeding the larvae with enriched Chlorella-fed rotifers. We propose that T. lutea in the deceleration growth phase are efficacious, fish oil-free sources of n-3 HUFA for marine fish larviculture.