Preliminary results in improving essential fatty acids enrichment of rotifer cultured in high density

Abstract

High density cultured marine rotifer (Brachionus rotundiformis) fed on freshwater Chlorella was cultured secondarily with an emulsion of ethyl esters (65% DHA, 15% EPA) for EFA-enrichment, with or without freshwater Chlorella. Culture tanks (30 1, 20 1 working volume) set in a water bath (24 °C) were continuously supplied with air (2.501 m⁻¹) or high-purity oxygen gas (1.25 1 nn⁻¹). Samples for fatty acid composition analysis were collected at 0, 6, 12, and 24 hours after the inoculation of rotifer, followed by the monitoring of rotifer density, DO, NH₄-N and pH.

The n-3 HUFA content plateaued at 6 hours after the onset of the secondary culture and no significant differences were observed afterwards, regardless of the aeration methods. The HUFA content increased with decreasing amounts of Chlorella added. The highest content (ca 3.5% on a dry basis) was noted in non-Chlorella feeding groups. When large amounts of Chlorella were fed, the DO of culture water drastically decreased and the NH₄-N concentration increased. The results from the experiment indicate that the presence of Chlorella cells greatly affect the HUFA intake of rotifers during the secondary culture process. Also the supply of high-purity oxygen gas was effective for preventing a culture crash of rotifers during EFA enrichment.

Contribution from Fish. Res. Lab., Kyushu University, No. 220.