Move over, mammals and birds, and make room for a fish called the opah in the warm-blooded club.
said in the journal Science on Thursday that this deepwater denizen is
the first fish known to be fully warm-blooded, circulating heated blood
throughout its body, enabling it to be a vigorous predator in frigid
certain sharks can warm specific regions of their body such as swimming
muscles, brain and eyes in order to forage in chilly depths but must
return 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 wing-like pectoral fins, with an average
muscle temperature about 7 degrees to 9 degrees Fahrenheit (4-5 degrees
Celsius) above the surrounding water temperature at the time.
The opah boasts a unique structure
that prevents this heat from being lost to the environment.
animals, such as birds and mammals, and known as endotherms, generate
their own heat and maintain a body temperature independent of the
environment. Cold-blooded animals, known as 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 fisheries
biologist Nicholas Wegner of the U.S. National Oceanic and Atmospheric
Administration's National Marine Fisheries Service.
is a rusty reddish color, has white spots and bright red fins. It weighs
up to 200 pounds (90 kg) 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 165-1,300 feet (50-400 meters), hunting fish and squid.
A unique structure within its
gills lets warm blood that leaves the body core help heat up cold blood
returning from the gills' respiratory surface, said fisheries biologist
Owyn Snodgrass of NOAA and Ocean Associates Inc.
Being warm-blooded gives it
distinct advantages over its cold-bodied prey and competitors including
faster swimming speeds and reaction times, better eye and brain function
and the ability to withstand the effects of cold on vital organs.
dwelling at such depths typically are slow and sluggish, ambushing
rather than pursuing prey.
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.