Move over, mammals and birds, and make room for a fish called the opah in the warm-blooded club.
Researchers 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 ocean depths.
Tuna and certain sharks can warm specific regions of their bodies 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.
Photo: Reuters
The opah, also called the moonfish, internally generates heat through constant flapping of wing-like pectoral fins, with an average muscle temperature about 4°C to 5°C above the surrounding water temperature at the time.
The opah boasts a unique structure that prevents this heat from being lost to the environment.
Warm-blooded 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 US National Oceanic and Atmospheric Administration’s National Marine Fisheries Service (NOAA).
The opah weighs up to 90kg and has an oval body shape. Found in oceans worldwide, it spends most of its time at depths of 50m to 400m 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, NOAA and Ocean Associates Inc fisheries biologist Owyn Snodgrass said.
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.
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