Unlike his fellow animals known to be “cold-blooded”, the Opah, or kingfish moon, is able to regulate its internal temperature throughout his body, making him the first fish to “warm-blooded” discovered scientists.
This feature gives it advantages in the cold waters of the ocean depths where it moves and hunt prey.
According to scientists from the US National Oceanic and Atmospheric Administration (NOAA), who publish their findings in the journal Science , the Opah generates heat in his muscles by beating its side fins. This heat is then transmitted to the whole body.
This fish joins the birds and mammals in the category of vertebrates capable of maintaining a body temperature higher than that of their environment for long periods.
Scientists already knew that fish like tuna or sharks occasionally manage to warm up certain muscles or their head, but this is not comparable nor as effective as the strategy put in place by the Opah.
A heat exchanger
The Opah is equipped at its gills real heat exchangers against the current – a system called rete mirabile . The composure that comes from loading oxygen in the gills flows in the veins surrounded by other vessels filled them warm blood that reaches muscles fins. The oxygenated blood then heats and dives inside the body where it can maintain the internal organs warm.
Some species of birds have webbed similar heat exchange mechanism to warm their feet.
In addition, the Opah has layers of fat around the gills, heart and muscle tissue.
Ultimately, this system allows the Opah keep his brain warm, efficiency, and maintain its assets muscles to swim faster and catch prey. It does not to rise to the surface frequently to warm up.
The researchers calculated that the Opah, which weighs about 90 kg (some specimens reach even 270 kg) and is about the size of a car tire, and gets to keep his body temperature by 4 or 5 degrees above the temperature of the water – in average of 8 to 11 degrees Celsius in the 50 to 300 meters deep area where the fish lives.
“We have never seen anything like the gills of other fish before,” explained Nicholas Wegner, a researcher at NOAA and lead author of the research. “This is an interesting innovation of these animals that gives them a competitive advantage.”
“Before this discovery, I thought it was a slow fish, as many fish swimming in cold environments,” says Nicholas Wegner. “But since it can warm the body, it is a very active predator that hunts agile prey such as squid, and can migrate long distances,” he adds.
This discovery provides new avenues to scientists now have to compare different species across the globe in order to study their evolution in colder waters.
The animals in “hot blood”, or endothermic, such as birds and mammals, generate their own heat and most keep their body temperature constant. Animals “cold-blooded”, or ectothermic, whose body temperature is the same as the external environment include amphibians, reptiles, invertebrates and most fish.
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