The particle size distribution of suspended solids of pearl fam in Ohmura Bay was investigated to elucidate food environment of Japanese pearl oysters, Pinctada facata martensii, from May to December in 1989. The particles of suspended solids were divided into the sizes, >300, 100-300, 50-100, 10-50 and l. 2-10/μm With various mesh sizes plankton net. And in each fractionated particle, the dry weights and phytopigment contents (chlorophyll a + phaeopigment) were measured. Dry weights and phytopigment contents of the fine particles (1. 2-10 μm) indicated always high value more than those of other size particles every month. The rate of dry weight and phytopigment contents of the fine particles (1. 2-10μm) were ranged 27-61% with experimental period mean of 42% and 31-77% with experimental period mean of 55%, respectively. These results suggest that the fine particles, e. g. nano-phytoplankton, predominate in the suspended solids at the pearl farm. It was reported that pearl oyster ingested the fine particles. Therefore it is considered these fine particles in the pearl farm are important as food environment of pearl oysters.

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