Dietary value of marine rotifer Brachionus plicatilis at different population growth stages for larval Japanese flounder Paralichthys olivaceus

This study assessed the dietary value of rotifers at different population growth stages for larvae of Japanese flounder (Paralichthys olivaceus). Rotifer cultures were prepared daily and continued for up to eight days. Rotifers were taken out on the 2nd, 4th and 8th day from the batch culture and equally enriched with freshwater Chlorella containing n-3 HUFA oil. The flounder larvae were reared in 500-L tanks for 16 days and supplied with different rotifers as above-mentioned. Population after 17-hr enrichment, which reflected their initial physiological status (low daily growth rate and egg rate), decreased in the 8th day rotifer. Feeding group moreover, the flounder larvae fed on those rotifers significantly showed the lowest. growth and morphological development on the 16th day after hatching. Despite no marked difference in essential fatty acid (EFA) levels in rotifers among all groups, the EPA and n-3 HUFA contents in flounder larvae were significantly the lowest in the 8th day rotifer feeding group. These results show that the dietary value of rotifers was poor after the logarithmic growth phase of batch culture, in spite of enrichment with n-3 HUFA, similar to the results of larviculture of red seabream.