The Effect Of Lipid Nutrients In Feed Microalgae On The Growth Of Juvenile Ark Shell (Tegillarca Gransa Linnaeus)

Polyunsaturated fatty acids such as docosahexaenoic acid (DHA) and eicosapcntaenoic acid (EPA) have been proved as important nutritious component for bivalves. However, another type of lipid, sterols is also considered very crucial because of the low ability of biosynthesis and biotransformation of sterols, the only source is from its feed, namely microalgac. It has been pointed out in the previous literature that different microalgal species has different lipid compositions, while different shellfish could need different lipid requirement owing to their different ecological conditions and biological habits.Ark shell (Tegillarca grama Linnaeus) is one of the most important aquacultured economic shellfish species in China eastern-southern coast, with delicious taste and high nutrition, as well as wide adaptation to temperature and salinity. However, little information is available on the requirement and accumulation of lipid nutrients for ark shell.In this present study, by applying a novel two step derivation method and devising the temperature program, simultaneous analysis of fatty acids and sterols have been achieved on SPB-5 capillary chromatographic column using Shimadzu QP2010 gas chromatography mass spectrometer.The fatty acid and sterol compositions of twenty nine microalgae were analyzed using GC-MS simultaneous determination method. Fifty six fatty acids and thirty seven sterols were identified.According to the result, six microalgae were choiced to feed the juvenile shellfish .The feeding effects of six different microalgae on the growth of juvenile ark shell were studied. The results indicated that the best feed effects found in Chaetoceros calcitrans, followed with Isochrysis galbana and Pavlova viridis, worse effects found in Chlorella sp. and Nannochloropsis oculata.The results indicated that the close correlation of sterol compositions between algal species and juvenile ark shell is existed, but not significant in fatty acids.In the juvenile shellfish after feeding, the ratio of total saturated fatty acids (SFA) increases rapidly while the ratio of total polyunsaturated fatty acids (PUFA) decrease considerably. The species of sterols in the ark shell also decreases, however, with much more increasing content, implying the high capacity of sterol accumulation.The results obtained from statistics analysis in this paper give out important results, which is very different from usual impression and not mentioned in the existing reference: the content of total PUFA cannot explain the different feeding effects of microalgal species on the development of juvenile ark shell. EPA is actually no obvious nutritious effects, and arachidonic acid (AA) has significant positive effects. DHA is possibly the limited nutrition factor, that means it should be very essential to be above a threshold value. If DHA is higher than that value, the content of DHA will affect very little. Among the sterols, cholesterol is the best one, with strong selective absorption, accumulation and biotransformalion in the juvenile ark shell, whereas brassicasterol and 24-ethyl-5-cne-stcroid are beneficial to enhance the growth of juvenile ark shell in the condition of scarcity of cholesterol..