No Cold Fish Here
May 19, 2015
Can a fish really be warm-blooded? Researchers from the National Oceanic and Atmospheric Administration (NOAA) seem to think so. A study published this week in Science describes this extraordinary fish, the opah (Lampris guttatus), and its unique mechanism for keeping its body consistently warm. The secret to being warm-blooded lies in its gills.
The opah is a large, brilliantly colored, deep-sea fish. It is found in the warmer regions of the Atlantic Ocean. The opah can grow as large as 6.5 feet (2 meters) long. Deep-water fish are usually slow-moving and sluggish, but not this one. It is a very fast and active predator. Opah migrate long distances.
Most fish have body temperatures that are the same as the water in which they swim. But tuna and a few sharks, including the great white, can keep their bodies warmer than the water. In these animals, warm blood flows in and around the muscles, a strategy known as regional endothermy. This helps the fish swim faster. It also enables it to achieve sudden bursts of speed that are useful in chasing prey. However, these animals lose the majority of their body heat to the surrounding cold water. They cannot heat their entire bodies. The opah can warm its entire body thanks to a unique gill design.
A fish’s gills take in oxygen from the surrounding water. But close contact with water leaves blood coming from the gills cold. In the opah, however, blood vessels coming from the gills pass close to other blood vessels in the body. This enables blood in those vessels to warm the blood coming from the gills. This adaptation, along with thick layers of fat, enables the opah to keep its body 9 Fahrenheit degrees (5 Celsius degrees) warmer than the surrounding water, making the opah the world’s first, and so far only, truly warm-blooded fish.
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