The International Union for Conservation of Nature unveiled an updated Red List of species at risk of extinction on Thursday that includes the ocean sunfish, which are popular in aquariums in Japan and elsewhere.
The Switzerland-based body classified ocean sunfish as "vulnerable," the lowest of three levels within its threatened category, meaning the species is facing a high risk of extinction in the wild.
The IUCN also put the kissing loach, a Japanese freshwater fish, on its list, classifying it as "critically endangered," or facing an extremely high risk of extinction in the wild.
While the IUCN's list is not legally binding, fisheries and aquariums are likely to come under pressure to limit their catch of the species.
Ocean sunfish have disc-shaped bodies and can grow over 3 meters long and weigh over 2 metric tons. They are found throughout warm and temperate oceans.
The IUCN said it suspected a global decline in the population of ocean sunfish, due mainly to bycatch in fisheries using long lines and midwater trawls.
In Japan, the fish are often captured along the Pacific coast in eastern and northeastern Japan.
Regarding kissing loach, the IUCN warned that a construction project in Kameoka, Kyoto Prefecture, would threaten the species' existence as the area is one of its few habitats.
Other species added to the list as threatened species included Ishikawa's frog, which is endemic to Amami-Oshima Island in Kagoshima Prefecture, and the Yanbaru long-armed scarab beetle, which inhabits the northern part of Okinawa Prefecture.
The list assessed 79,837 species and designated 23,250 of them as threatened species.
The IUCN said many species, such as polar bears, face a higher risk of extinction due to the effects of global warming, highlighting the need to step up efforts against climate change.