Efficiency of the retention of small particles by the gills of the Japanese oyster was investigated. From the results thus obtained and measurements of the size distribution of particulate material suspended in sea water, estimation of the quantity of particulate matter as food for oysters was also discussed.
Particle filtration by the oyster was studied in the 1.5 to 6.0μ size range in relation to naturally occurring particles. The oyster usually retained particles larger than 3μ. but could retain particles of sizes down to 2.0 or smaller when larger particles became scarce. There was a sharp increase in removal efficiency as particle size increased from 1.5 to 3.0μ. Larger sizes showed no evidence of further change in efficiency. The particulate matter in Hiroshima Bay consisted mainly of particles smaller than 40* in diameter and this portion accounted for more than 90% (dry basis) of all particulate matter.
Therefore. the particulate matter measured by filters such as Whatman GF/C and Ultra fine filter that could retain particles larger than 1μ is estimated to be quantity of food for oysters, but for more precise measurements Nuclepore or metal filter of 3μ pore size would be preferable.