According to the research of Ministry of the environment from December to February, freshwater fish accumulate more cesium than marine products.
MOE compared the contamination of aquatic organisms taken at 8 points of river, lake and sea.
Comparing result is like this below,
<Sea> (Offshore Iwaki city)
Slime flounder, Suzuki : 260 Bq/Kg
<Fresh water> (Iidatemura ~ Minamisoma)
Goby : 2,600 Bq/Kg
Plecoptera (Aquatic insects) : 330 ~ 670 Bq/Kg
Iori Mochizuki