Fatty acid (FA) is used as an indicator of food source quality for animals. However it is not cleared whether FA composition of food source is a good indicator of abundance and richness of animals in ecosystems.

In this study, field surveys of paddy fields were conducted to clarify the relationship between benthic animals and FA composition of sediment as a potential food source for those animals. A field experiment was also conducted to evaluate the effect of pond snail Bellamya chinensis on FA composition of sediment and other animals.

We found a positive relationship (p<0.05) between the concentration of 20:5ω3 (EPA) in sediment and the number of families of benthic animals. On the other hand, there were no significant relationships between other FAs (DHA and PUFA) and benthic animals.

In the field experiment, the total biomass of loach was higher in a B. chinensis co-existent site than in nonexistent site, though there was no difference in FA composition of sediment between them. We also found EPA content in feces of B.chinensis was higher than that of sediment. Therefore, it was considered loach ate the feces of B. chinensis as a better quality food source.