The mechanism of polyunsaturated fatty acid synthesis by pond snail and application for conservation of biodiversity.

必需脂肪酸包括20：5n3、20：4n6和22：6n3，是动物的重要营养物质。通常，这些脂肪酸被认为是由水生生态系统中的藻类物种产生的。在本研究中，我们发现淡水蜗牛和鱼类的饲料中含有这些必需脂肪酸，即使这些脂肪酸在它们的食物来源中不存在。实验中还发现，在饲料上有原生动物聚集，而在饲料来源的食物上几乎没有发现原生动物。粪便中必需脂肪酸含量与原虫密度呈显著正相关。这表明饲料中必需脂肪酸的存在可能与原生动物有关。在碎屑食物网中，饲料上原生动物的群集似乎提高了饲料的营养质量。

Essential fatty acids including 20:5n3, 20:4n6 and 22:6n3 have been widely known as important nutrient for animals. Generally, these fatty acids have been considered to be produced by algal species in aquatic ecosystems. In this study, we found that feaces from freshwater snail and fish included these essential fatty acids even these fatty acids were absent in their food sources. We also found that protozoa swarmed on the feaces but almost no protozoa were detected on the food sources which was original of the feaces in the laboratory experiments. Moreover, significant positive relationship between density of protozoa and concentration of essential fatty acid in the feaces were confirmed. It indicate that essential fatty acid in feaces would be attributed to the presence of protozoa. Swarm of protozoa on the feaces seemed to enhance the nutritional quality of feaces in detrital food web.