This is Fugu, or Japanese pufferfish.

Fugu is partly famous for being highly poisonous.

Here in Japan it's also a delicacy.

However, climate change is making Fugu riskier, both for adventurous eaters and the fisherman that catch them.

Normally, some of the fish's organs carry a neurotoxin.

If they aren't removed in the right way, the toxins can kill a person in just 20 minutes.

Death by fugu is extremely rare.

That taste of danger, though, means the fish can sell for more than 200 dollars per kilogram at markets like this.

Normally, the toxins aren't a problem for expert chefs, who are specially trained and licensed.

But lately, warming waters have changed the fugu.

(SOUDNBITE)(Japanese) ASSOCIATE PROFESSOR AT THE NATIONAL FISHERIES UNIVERSITY, HIROSHI TAKAHASHI, SAYING: "Due to climate change, the pufferfish which usually swim around the Sea of Japan, escaped their gradually warming habitat and crossed into the Pacific Ocean.

There, they inter-bred with their sibling species that triggered an increase in the number of hybrid fish." The hybrids are sometimes very hard to tell apart from their pure-bred cousins.

While the freaky fugu used to be rare, experts say hybrid fish are now much more common.

They've gone from one in a thousand, to more than 20 percent of some catches today.

(SOUDNBITE)(Japanese) ASSOCIATE PROFESSOR AT THE NATIONAL FISHERIES UNIVERSITY, HIROSHI TAKAHASHI, SAYING: "From a fisheries industry perspective, fishermen are forced to get rid of hybrids because you're not allowed to sell these fish to consumers.

I believe they're seeing big losses.

From a biodiversity and purely scientific standpoint, if these two pure species continue to mix and lead to just one large group of hybrids that means a loss of biodiversity so that is problematic." Japan's health ministry says it's still collecting information about the hybrids But so far there's no official word on exactly what to do - about the changing nature of one of Japan's culinary traditions in the face of a changing climate.