Professor Nicholas Fisher of Stony Brook University was 'stunned' to find the radioactive signal in bluefin tuna. All the fish examined in the study showed elevated levels of radioactive caesium - the isotopes 134 and 137. Caesium-137 is present in seawater anyway as a result of the fallout from atomic weapons testing, but the short, two-year half-life of caesium-134 means the contamination can be