Effect of docosahexaenoic acid enrichment in Artemia on growth of Pacific bluefin tuna Thunnus orientalis larvae

Feeding enriched Artemia induces growth failure in Pacific bluefin tuna (PBT) Thunnus orientalis larvae; however, feeding of yolk-sac larvae of marine fish promotes larval growth. It is considered that this growth failure partly results from dietary docosahexaenoic acid (22:6n-3, DHA) deficiency. Therefore, we examined the effect of DHA contents in enriched Artemia on the growth of PBT larvae. Artemia nauplii were enriched with graded levels of DHA ethyl ester, and fed to PBT larvae for 9 days. Yolk-sac larvae of Japanese parrotfish Oplegnathus fasciatus were used as a reference diet. The DHA contents in Artemia increased with the enrichment from 0 mg g^? 1 dry weight basis (DW) to 25 mg g^? 1 DW, while the content in the reference diet was 21 mg g^? 1 DW. Feeding of enriched Artemia significantly improved the growth of PBT larvae. However, this improvement was negligible when compared with the excellent growth of the larvae that were fed the reference diet. PBT larvae that were fed the reference diet accumulated approximately twice or much higher levels of DHA in the neutral and polar lipids in the body when compared with the larvae that were fed enriched Artemia. These results show that PBT larval growth cannot be promoted by feeding enriched Artemia even if the DHA contents in Artemia are elevated to the same levels as those of yolk-sac larvae. The incorporation of dietary DHA into phospholipids in the fish body may be desirable for the normal growth of PBT larvae.