A dangerous new species of pufferfish has appeared in the Pacific Ocean off Japan due to global warming, researchers have found.

The danger is that it is difficult to know where the toxic poison is inside the edible fish, making it impossible for a chef to safely remove it before serving the delicacy on the dinner table.

Global warming is probably why the fish has been caught in large numbers since five years ago.

These risky pufferfish are released or disposed of after they are visually examined by experienced fishermen and are not packed off to the fish market.

The blowfish is the hybrid of the spottyback puffer, which can be found mainly in the Sea of Japan, and the vermiculated puffer, a species that inhabits waters around Japan, according to Hiroshi Takahashi, an associate professor of fishery science at National Fisheries University in Yamaguchi Prefecture.

The university, the Yamaguchi prefectural government, Shimonoseki city in the prefecture and other parties are conducting joint research to develop a science-based system to distinguish crossbred pufferfish to ensure food safety.

The DNA type of the fish will be analyzed, so that the physical characteristics of pufferfish identified as crossbred, such as their color, pattern and shape of fins, as well as the touch of their skin, where they are caught and other data can be registered on a database.

When images of caught fish taken with smartphones and other devices are sent, the system will determine whether the pufferfish are crossbred based on the database.

Global warming has likely led to an increase in the seawater temperature and changed the marine ecosystem off Japan, according to the researchers.

Takahashi and other scientists were informed in 2012 that “unknown pufferfish was caught in large numbers” off Ibaraki Prefecture, and they then conducted genetic analysis of about 250 blowfish caught in the Pacific near Ibaraki, Fukushima and Iwate prefectures.

The results showed 149 of the 187 fish that were not identified based on their appearance alone seemed to be a hybrid of the spottyback puffer and the vermiculated puffer.

Although the two types of pufferfish are able to mate with each other, such crossbreeding rarely occurs in the natural world.

Takahashi pointed out the possibility that global warming enabled the spottyback puffer on the Sea of Japan side to inhabit northern waters and to move to the Pacific side through the Tsugaru Strait in large numbers, resulting in more frequent crossbreeding of the two species.

If global warming continues, a wider variety of pufferfish could live in the same waters and different species could more easily mate with one another in the future.

(This article was written by Tatsuyuki Kobori and Nanoka Yamada.)