The Nutrition Of Size-fractioned Plankton In The Yellow Sea And Analysis Of The Diet Transformation Of Juvenile Anchovy(Engraulis Japonicus)

Fatty acid and amino acid for growth of marine larval and juvenile fish are almost obtained from plankton. The variation of food species reflects the variation of nutrition need in marine larval and juvenile fish. In this paper, fatty acid and amino acid composition of plankton in different fraction size in the Yellow Sea were analyzed, the diet compositon and ontogenetic variation of juvenile anchovy(Engraulis japonicus) at body length of 32~52 mm were examined, aimed to provide a reference for studying the fatty acid and amino acid of plankton which can provide us a basic data of nutrition of plankton in natural, help us to explore the potential capacity of providing nutrition in plankton and the feed transformation of marine fish researches.For better understanding on the nutritional quality of planktonic food for the marine fish, the fatty acid composition of size fractioned plankton was investigated and compared between the seasons of winter and spring in the Yellow Sea. The plankton individuals were size fractioned into six groups of 100 μm, 200 μm, 300 μm, 500 μm, 1000 μm and 2000 μm at once after they collected on the sea, and then preserved in liquid nitrogen. Fatty acid contents of the plankton were determined using capillary column gas chromatography in lab. Compared between two seasons, the plankton of all size groups in winter had higher content of total saturated fatty acid(SFA), but lower content of total monounsaturated fatty acids(MUFA), total polyunsaturated fatty acids(PUFA), fatty acid 16:1ω7, EPA, DHA, 20:1+22:1 than in spring. Of the size groups in both winter and spring, the contents of ω3 PUFA, EPA, DHA, and 20:1+22:1 were higher in large plankton individuals with above 500 μm than those small size groups of < 500 μm, but those of fatty acid 16:0, 18:0 were on the contrary higher in small size groups. With regard to nutritional quality indicators of DHA/EPA, 16:1/16:0 and ∑16/∑18, only the ratios of ∑16/∑18 were higher in winter than in spring, but the other two had higher values in spring. Moreover, the ratios DHA/EPA only reached up to 2 in the plankton size groups of 500 μm and1000 μm in winter, while in spring they showed over or close to 2 among all size groups. By multiple analyses, the seawater temperature had the main effects on the compositions of fatty acids in the plankton of the Yellow Sea, especially positively on the content of MUFA and PUFA in the plankton of 100~1000 μm. From the results of this study, in winter only plankton of > 500 μm could meet the nutritional requirement by marine fish, especially the larvae and juveniles, whereas in spring those of size groups from 100 μm to 2000 μm were relative proper as the food sources of marine fish with high DHA/EPA and ω3 PUFA. It may be inferred that size spectrum of planktonic food resources with high fatty acids nutrition quality is more wide for marine fishes or fish larvae in spring than in winter in the Yellow Sea.The fatty acid compositions of several zooplankton species of was studied in the Yellow Sea in the spring of 2015, which included on copepod(Calanus sinicus), one krill(Euphausia sp.), one chaetognath(Sagitta sp.) and one amphipod(Themisto sp.). The result showed that, Calanus sinicus provided more fatty acids to zooplanktivorous fish than Euphausia sp. and Themisto sp., while Sagitta sp. had lower value of fatty acid nutrition.The amino acid content of size fractioned plankton was investigated and compared between the seasons of winter and spring in the Yellow Sea. The results were as follows: The content of total amino acid and essential amino acid increased with the fraction size increased in the winter and spring; compared between two seasons, the plankton of all size in spring had higher content of the total amino acid and essential amino acid, the percentages of them and the percentages of Arg and Met were higher in the spring; while in winter, fraction size above 500 μm had higher percentages of each amino acids than the fraction size below 500 μm. It may be inferred that each size fractioned plankton in spring had higher nutrition value of protein, while only fraction size that above 500 μm had higher nutrition value in winter.The stomach contents of juvenile anchovy(Engraulis japonicus) collected in the southern waters of the Yellow Sea during the period of 2014 were analyzed. The main food in the stomach of juvenile anchovy were copepoda, ostracoda, amphipoda, chaetognatha and eggs of them. The food preference of anchovy changed with fish sizes, while the Levin’s standardized index showed that all anchovy were stenophagic and the food composition were basically consistent. Cluster analysis revealed that anchovy that body length below 46 mm preferred plankton of small size fraction, while above 46 mm began to capture larger size fraction in plankton.