Long-term fluctuation of the yield and ash content of muscle dissected from marine organisms were investigated for establishing a standard of pretreatment procedure based on the data on radioactivity analyses of various biological samples such as fish and shellfish which were collected from 15 sea areas adjacent to nuclear power stations in Japan. The muscle yield in terms of the percentage of muscle weight to the whole raw weight as well as ash content were obtained for 53 species during the period from 1983 to 2007 and subjected to a statistical scrutiny. There was no significant change in general in the muscle yield and ash content, with the exception of some species due to modification of pretreatment method. However those exceptions would not have resulted in a critical change of the level of 137Cs concentration in marine organisms as a whole in the sea areas of concern, because it was usually expressed as the average for three different species in the present study. The ash content would be useful, nevertheless, as an index to assure the comparability of sample preparation technique. The 137Cs radioactivity concentration in muscle of marine organisms gradually decreased year by year from 1990 after the Chernobyl nuclear accident, and would not be more than 0.24 Bq/kg-wet, the maximum level during 2003 to 2007, in the future from the viewpoint of fail-safe approaching.
