Effect of oil enrichment on Brachionus plicatilis rotifer and first feeding red sea bream (Pagrus major) and Japanese flounder (Paralichthys olivaceus)

Euryhaline rotifer belonging to the genera Brachionus are often used as live feed for first feeding marine finfish larviculture. Two common rotifer enrichments, a single usage of docosahexaenoic acid (DHA)-enriched Chlorella vulgaris and a combination of DHA-enriched C. vulgaris and salmon roe emulsion oil were used to assess: (i) nutritional status of rotifers and, (ii) performance when rotifers were fed to Pagrus major and Paralichthys olivaceus larvae from 2 to 15 days after hatching (DAH). Both rotifer enrichment treatments were found to be nutritionally effective with high unsaturated fatty acid (HUFA) content, especially in the combined treatment with significantly higher eicosapentaenoic acid (EPA). Despite deficient levels of EPA, DHA-enriched C. vulgaris was found to be a suitable enrichment for rotifer and also had positive response in survival, growth and trypsin activity in both P. major and P. olivaceus. DHA-enriched C. vulgaris only treatment had higher rotifer population growth (13% higher), egg bearing capacity (7% higher), almost double the soluble protein content and generally higher free amino acid content. Oxidation of lipids in the combined diet due to its high-saturated fatty acid content could be a possible cause to the inferior performance of the combined treatment. Both P. major (20.1 ± 10.1%) and P. olivaceus (12.3 ± 3.87%) suffered low survival and lower gut content in the combined treatment especially during periods of significant growth in both species (7–11 DAH). Despite high HUFA content in the combined treatment, this study revealed that consideration of free amino acids and soluble protein content as parameters of nutritional indicators for first feeding P. major and P. olivaceus should not be discounted.