When a new video of catfish patrolling the cooling pond of the Chernobyl power plant surfaced online earlier this month, it didn't take long for the usual cries of "monster fish!" to follow. Yes, the animals are certainly impressive – but despite the hyped-up headlines, radiation is not the reason for their oversize stature. 

We repeat: these fish were not made massive by radiation. Let's discuss.

For a start, your first clue when determining if a fish has been negatively impacted by radiation is the animal's overall fitness. Being large and in charge takes a lot of energy, which is why we almost never see sick fish reaching their full growth potential. 

"Very, very few mutations lead to extra-large size," explains University of South Carolina radiation specialist Dr Timothy Mousseau. "[Instead], they grow less efficiently, they're less capable of catching food and they tend to not live as long." This is also the reason (among many others) why we must rule out radiation as a possible explanation for the size of this "Fukushima mutant" wolffish.

Among the hefty residents of the Chernobyl pond are wels catfish (Silurus glanis), a species known to reach gargantuan proportions across much of its range. As for the maximum size of these aquatic giants, a quick Google search will turn up stories of 800 pound (362kg) record-breakers – and while these are typically exaggerations (or misidentified beluga sturgeon), it's entirely feasible for a wels to reach 350 pounds (158kg) under the right conditions. 

Italian fisherman Dino Ferrari managed to catch and release this colossal wels back in May, and as you can see, its size far surpasses that of the "radioactive monsters" filmed in Chernobyl: 

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Image:Sportex Italia/Facebook
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Image:Sportex Italia/Facebook
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Image: Sportex Italia/Facebook

Chernobyl's cooling pond offers the catfish populations an isolated habitat, one that's free from predators and packed with ample prey. Catfish are both active predators and scavengers, known to feed on fish, amphibians, worms, birds and even small mammals. In fact, the fish will eat just about anything – alive or dead – that can fit into their very large mouths, and here at Chernobyl, they have virtually no competition for food. 

This brings us to our next point: catfish have been cruising Chernobyl's cooling pond for years. Over time, they've become a tourist attraction, and though some specimens are thought to be up to ten years old, that's positively youthful for fish that can live to over 50. 

The animals even drew the attention of Jeremy Wade, host of Animal Planet's River Monsters (cue dramatic editing, pulse-pounding music, ominous voiceover and, oh, some fishing.) The Chernobyl fish caught by Wade, we're told, were "16 times more radioactive than normal" – and although that sounds pretty alarming, detectable does not always mean dangerous, as we've explained before

Three decades after the worst nuclear accident in history, experts are still working to unravel just how the region's increasingly abundant wildlife is being affected by the radiation – but the fish swimming in Chernobyl's pond seem to be feeding, reproducing ... and growing! (We just wouldn't recommend snacking on them.)

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Top header image: Joachim S. Müller, Flickr