We studied feeding, egestion and digestion of Corbicula japonica in the laboratory. Clams were collected from an artificial shallow pond(20-60 cm deep)near the brackish Lake Jinzai in 2001. Pond water was supplied continuously from Lake Jinzai using a pump. Feces and pseudo-feces of the clams were observed by microscope.
Clam pseudo-feces were irregular, wooly, and brown in color when clam fed phytoplankton. These were mainly composed of living micro-algae, detritus, cf. amoebocytes and protozoa. When clams were placed in filtrated water, they mainly egested inorganic particles and detritus. Clam fecal pellets were clearly divided into two types, namely, undigested feces and digested feces. Undigested feces consisted of many living cells of benthic and planktonic micro-algae(diatoms, chlorophytes, dinoflagellates, cyanobacteria)and detritus. These were rod or ribbon shaped, opaque, dark brown in color. Digested feces consisted of many brown particles(ca. 0.5-3μm), mucilage, bacteria, and a small number of micro-algae and protozoa. These were ribbon or intestine shaped, translucent or opaque, brown or dark brown in color.
From small particle sizes and almost absence of micro-algae in digested feces, and from presence of many living cells of micro-algae in undigested feces, C. japonica seems to feed and digest detritus, small living planktonic and benthic micro-algae which could pass through mouth to midgut gland of the clams. Foods ingested from mouth which could not pass to midgut gland egested as undigested feces.