Whether it's two-headed sharks or see-through frogs, we've come to learn that when a strange-looking creature confounds the internet, it's not long before someone reaches for explanations of the radioactive kind. And the latest poster animal for "radiation mutants" comes our way in fishy form: 

Holy Mother of Carp

Just minutes after Imgur user StuffyUnicorn posted this short clip of a deformed fish online last week, references to Fukushima and Chernobyl were flooding social media, from Twitter and Facebook, to Reddit and Instagram.


The jump from freaky fish to Fukushima is understandable: six years on, misleading and often scaremongering stories about the disaster and its effects continue to circulate. And let's face it: this specimen does bring to mind "Blinky" – the three-eyed wonder from "The Simpsons" Old Fishin' Hole.

The details surrounding the video are sparse (if you own the source clip, let us know!), but before you classify this guy as a two-headed Blinky brethren, let's get a few things straight about those "mutant" features. 

First off, the "duplicate" peepers. The fish in the video is an Asian carp – likely a bighead carp (Hypophthalmichthys molitrix) or close relative – which belongs to a group of freshwater fishes known for their low-set eyes. Our strange specimen might seem overcompensated in the ocular department, but that second (top) set of eyes is actually a pair of olfactory openings (think fish nostrils).

You can see those same structures in this healthy Asian carp, which was found in North America's Great Lakes, or this one, caught by the US Geological Survey in the Illinois River:

Image: USGS/Flickr

As for the fish's "second" mouth, the most likely explanation is not a deformity but rather a healed injury. Look closely at the clip and you'll notice that both openings feed the same throat structure: there is only one set of teeth and gills. At some point in this fish's life, a puncture wound may have separated the tissue that connects the jaw with the tongue and gill-arch structures. This same kind of hooking disfiguration has been seen before in trout and other popular game fishes. 

Post-hooking deformities of this kind are not uncommon in carp either: just last year, a fishermen in South Australia hauled up this stunner, complete with a similar-looking "extra" mouth.

However, we can't rule out a double-mouth defect that may have been with this fish throughout its development. If that was the case, any number of environmental factors – like runoff, algal blooms, or changes in salinity and temperature – could be to blame. In situations where contaminated environments play a part, however, we expect to see multiple sightings of funky fish. When runoff in California caused a harmful algal bloom earlier this year, for example, dozens of leopard sharks turned up with meningitis

University of South Carolina biologist Dr Timothy Mousseau notes that with so little information available about the clip – and a sample size of just one – it's difficult to say whether the abnormalities seen in this fish can be linked to any environmental factors.

And what about radioactive contamination? Having spent decades studying the impact of radiation in Chernobyl, and later Fukushima, Mousseau is uniquely qualified to weigh in on the subject – and he's careful to emphasise that the effects of radioactivity mostly do not manifest in the monstrous mutations that horror movies have taught us to expect. For one thing, contaminated fish don't grow to freakishly massive proportions; in fact, many die before reaching maturity, and are never discovered.

(Aside from its obvious defects, meanwhile, the fish in StuffyUnicorn's upload looks relatively strong and healthy.)

"Most radiation-induced mutations lead to lower growth, survival and fertility," explains Mousseau, who is currently in the field at Chernobyl. "Most such 'mutants' do not live long enough to get so large. Most are slower, less capable and thus more likely to be eaten or die than 'normal' individuals." 

The idea that the catfish in Chernobyl's cooling ponds have reached their impressive size thanks to a radioactive boost, for example, has been widely debunked (we've covered this in detail here) – yet stories of these mutant catfish persist.

In reality, assessing radiation's impact on wildlife is a subtly complex and difficult process.

"In our studies we look at hundreds, often thousands, of individuals before we can suggest that radiation was the cause," says Mousseau. "Without properly controlled experiments it is almost impossible to say for sure what the cause might be unless such a mutation has been observed before in other radioactive places. This is one reason we look at both Chernobyl and Fukushima."

And problems certainly persist in these contaminated regions. At certain levels, extended radiation exposure does cause damage to DNA molecules, and can cause mutations. Mousseau and his team have found tumours, cataracts and damaged sperm in birds from high-radiation areas in Chernobyl, and impacts on biodiversity in Fukushima. Studies conducted on carp near Fukushima found some individuals with abnormal growth of spleen, kidney and liver structures (and scientists are still investigating those cases).

Beyond such areas, however, most of us will never encounter dangerous radiation levels, and misguided radiation-related panic only serves to detract from other – very real and very serious – environmental threats (more on this here, here and here). 

"There are all sorts of oddities in nature that arise just by chance," says Mousseau. "As stated above, most [radiation-affected individuals] are less 'fit' and so we rarely see them because they tend not to survive."