According to the rules of 20th century science fiction, Fukushima nuclear reactors' radiation leaks should lead to massive genetic mutations in local animals, and spawn giant monsters that will soon be rampaging through Tokyo. Or perhaps the Hulk or original Spiderman premise will play out, with a cleanup worker there being magically mutated into a superhuman of some kind. Or not. Probably not, actually.

The reason is that nuclear radiation is not magical, but particulate. It consists of lots of tiny bits of matter shooting out of unstable atoms. Those bits can sometimes have enough mass and energy to penetrate our skin and enter living cells where it can randomly damage genetic material. Expecting a high dose of radiation to improve an animal -- to give it any big advantageous changes all of a sudden -- is a bit like opening fire with an assault rifle on a block of marble and expecting Michelangelo's statue of David to be the result. It's not impossible, but very unlikely.

So what will likely happen to the fish and other animals in the waters closest to the damaged nuclear power plant?

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"I don't know that it's known," said Nicolas Fisher, a researcher at SUNY Stony Brook who specializes in studying radioactivity in fish -- including those taking up the radioactive cesium leaked from Fukushima. "It doesn't appear to outright kill them."

Certainly there is a danger to wildlife very close to the site, Fisher said. It's also a good idea not to eat the fish and other marine animals from that area. But on the other hand, you don't have to go very far from the site before the levels drop to well below the natural levels of radioactivity in sea water.

"I'm not in favor (of radiation leaks) and I wish it hadn't happened, but we should respond in a measured way," said Fisher.

And that means keeping the radiation levels in perspective. While the Fukushima cesium has been found in blue fin tuna that have crossed the Pacific, the radiation from that cesium is far less than that of the naturally occurring polonium in the oceans and in fish.

In fact, a person who eats a lot of tuna is in far more danger of getting sick from mercury poisoning than the radionuclides in the fish, said Fisher.

Meanwhile, studies of animals on land around Fukushima and around the world's only other comparable nuclear disaster -- Chernobyl -- suggest that it may take years for the effects of the radiation to play out on animals.

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"The mean the level of radiation was higher and less variable at Fukushima than at Chernobyl, implying that we should expect more negative effects on the abundance of animals at Fukushima if immediate effects of radiation were important," wrote Anders Pape Møller and colleagues in a paper in the January 2013 issue of the journal Ecological Indicators.

They counted spiders, grasshoppers, dragonflies, butterflies, bumblebees, cicadas and birds at 1,198 sites in Chernobyl and Fukushima. Surprisingly, Fukushima didn't follow the expected pattern.

"While (groups of animals) showed significant declines in abundance with increasing levels of background radiation in Chernobyl, only three out of seven taxa showed such an effect at Fukushima," they wrote.

The difference, say the researchers, is that drops in any animals populations in Fukushima are probably due to sudden, lethal doses of radiation, while those at Chernobyl are probably due to years of accumulated genetic mutations that cause a drop in the reproduction levels of animals.

In other words, maybe a giant city-eating bumblebee is still in Fukushima's future. But since none has appeared at Chernobyl, despite almost three decades of irradiation, you shouldn't hold your breath.