Research On Feeding And Fatty Acid Composition Of Brachionus Plicatilis Enriched With Microalgae

The rotifer Brachionus plicatilis can be mass cultivated and is commonly used for first feeding of altricial larvae in mariculture. But it is low in the HUFAs such as ARA(C20:4n-6), EPA(C20:5n-3) and DHA(C22:6n-3) which are essential fatty acids for larviculture of fish and crustaceans. Chlorella sp., Chaetoceros muelleri and Isochrysis galbana were cultured as foods of the rotifers. The rotifer Brachionus plicatilis were enriched with single or mixed microalgal species to learn how to enhance the nutritional value of rotifer efficiently. The main results are presented as follows:1. The dynamics of filtration and ingestion rates of Brachionus plicatilis fed on single or mixed microalgal species was recorded. The filtration and ingestion rates of the rotifers were influenced significantly by the microalgal concentration, microalgal quality and cultural duration. The filtration and ingestion rates of the rotifers decreased with their increasing cultural duration. Under the experimental condition, within 6 hours, the sequence of the filtration rates of the rotifers on the three types of microalgae as follows: Chlorella sp. >Isochrysis galbana >Chaetoceros muelleri; while within the whole experimental times (12 hours), the sequence of the filtration rates of the rotifers on the three types of microalgae as follows: Isochrysis galbana >Chlorella sp. >Chaetoceros muelleri. The sequence of the selectivity of rotifers fed on the mixed microalgae as follows: Isochrysis galbana >Chlorella sp. >Chaetoceros muelleri.2. The fatty acid composition of three types of microalgae and the rotifers fed with single and mixed microalgal species were examined using gas chromatography (GC) technique. The composition and the content of short-chain and low unsaturated fatty acids were steady comparatively, while the composition and the content of long-chain and highly unsaturated fatty acids in rotifers were greatly affected by that in the diet. The result indicated that Chlorella sp., Chaetoceros muelleri and Isochrysis galbana are all suitable to enrich rotifers, which contain high level of EPA and DHA respectively. In addition, the contents of the three types of essential fatty acids (ARA, EPA and DHA) in rotifers enriched by mixed diet of Isochrysis galbana and Chlorella sp. was 1.0509% of dry weight, and the ratio of DHA/EPA and EPA/ARA of rotifers was about 0.7/1 and 5.4/1, respectively. On the basis of these results, the rotifers enriched by mixed diet of Isochrysis galbana and Chlorella sp. were more suitable as first feeding for marine larvae than the other diet.3. The fatty acid composition of four types of algae powder and the rotifers fed with these algal powders were examined. The result indicated that the Chlorella powder and the Spirulina powder are not suitable to enrich rotifers to improve the content of HUFAs. The Schizochytrium powder and the Crypthecodinium powder contain high level of DHA, however they should mixed with other diet that contain high level of EPA when they were used for enriching rotifers cultured only by yeast.