Researchers find the world’s first known warm-blooded fish

Researchers have discovered the first known warm-blooded fish — the opah, a deep-water predator that looks like a giant’s Frisbee with fins.

Scientists from the National Oceanic and Atmospheric Administration (NOAA) described the unique mechanism that lets the opah keep itself warm in the journal Science on Thursday.

The warm-blooded advantage turns the opah into a high-performance predator that swims faster, reacts more quickly and sees more sharply, said the lead author of the paper, fisheries biologist Nicholas Wegner of NOAA Fisheries’ Southwest Fisheries Science Center in La Jolla, California.

The researchers documented that opah are warm-blooded by tagging and tracking them off California’s coast, measuring their body temperature, water temperature and the depths at which they swam.

Tuna and certain sharks can warm specific regions of their body such as swimming muscles, the brain and the eyes in order to forage in chilly depths but must return closer to the surface to protect vital organs such as the heart from the effects of the cold.

The opah, also called the moonfish, internally generates heat through constant flapping of winglike pectoral fins, with an average muscle temperature about 7 to 9 degrees Fahrenheit higher than the surrounding water.

The opah, which has an orange-red and silver body and darker fins, boasts a unique structure that prevents this heat from being lost to the environment.

Warm-blooded animals, such as birds and mammals, known as endotherms, generate their own heat and maintain a body temperature independent of the environment. Cold-blooded animals, or ectotherms, include amphibians, reptiles, invertebrates and most fish.

“With a more whole-body form of endothermy, opah don’t need to return to surface waters to warm and can thus stay deep near their food source continually,” said Wegner.

The opah weighs up to 200 pounds and is about the size of a car tire, with an oval body shape. Found in oceans worldwide, it spends most of its time at depths of 165 to 1,300 feet, hunting fish and squid.

A unique structure in its gills lets warm blood that leaves the body core help heat up cold blood returning from the gills’ surface, said fisheries biologist Owyn Snodgrass of NOAA and Ocean Associates.

Al Jazeera with Reuters