A giant sunfish weighing more than 6,000 lbs is the heaviest bony fish ever found, researchers say

A 6,000-pound sunfish was discovered off the coast of Portugal last year – and scientists now say it is the heaviest bony fish in the world. Researchers with Atlantic Naturalist Association were studying stranded large animals in the Azores, a region of Portugal, when they found a giant sunfish dead and floating near Faial Island.

The fish was weighed with a crane scale, by raising it with a forklift truck for a few minutes in order to allow the exact measurements to stabilize, the researchers write in their study, published in the Journal of Fish Biology last week. The scientists also measured its length with a tape measure and it came in at 10 feet long and nearly 6,050 pounds. 

The scientists also took a tissue sample to determine the DNA of the specimen, and determined it to be a giant sunfish – or Mola alexandrini. These sunfish are often confused with ocean sunfish, Mola mola, but their differences were recently clarified. Sunfish are often found in temperate and tropical seas. 

There are two types of fish – bony and cartilaginous. The great majority of fish are bony fish, meaning they have skeletons. This group includes swordfish, trout and, of course, sunfish. Fish with cartilage, part of the chondrichthyan group, include sharks, skates, rays and chimaera.

The heaviest sunfish previously recorded was also a Mola alexandrini, weighing 5,070 pounds, discovered in 1996 in Japan, the researchers say. 

This new finding "shows the oceans are still healthy enough to sustain the heaviest fish in world," Jose Nuno Gomes Pereira, the study's lead author, told CBS News. However, international cargo traffic and some ocean fishing must be better regulated to sustain this, he said. 

In 2021, a paddle boarder spotted a sunfish off the coast of Southern California and the photo of the giant sea creature went viral.

A sunfish was also captured by a crew on a tuna fishing boat off the coast of the Mediterranean coast of Ceuta, Spain. It was 10.5 feet long and 9.5 feet long, but it was too heavy for their scale, which only held up to about 2200 pounds.

In 2019, a New Jersey man spotted a sunfish in his own backyard. The giant fish, estimated to be about 300 pounds, was seen swimming in the bay behind his house in Ortley Beach.