The Food and Drug Administration (FDA) is the agency responsible for monitoring food safety. You can find information about their import alerts and other measures related to the Fukushima incident on their website at: http://www.fda.gov/newsevents/publichealthfocus/ucm247403.htm.
FDA has systems in place to help assure that our food supply is wholesome, safe to eat, and produced under sanitary conditions. You can find additional information on FDA's radiation safety initiatives at: http://www.fda.gov/Food/RecallsOutbreaksEmergencies/Emergencies/ucm253893.htm.
The National Academies of Science (NAS) has published a research report about seafood safety and radiation released from Fukushima. The report, "Evaluation of Radiation Doses And Associated Risk From The Fukushima Nuclear Accident To Marine Biota And Human Consumers of Seafood," can be viewed at: http://www.pnas.org/content/early/2013/05/30/1221834110.full.pdf
Woods Hole Oceanographic Institution answers frequently asked questions about the impact of radiation from Fukushima on seafood safety and the state of fisheries along the western coast of the United States on its website. You can view this information at: http://www.whoi.edu/page.do?pid=83397&tid=3622&cid=94989