The First Warm Blooded Fish Discovered By Scientists

According to researchers from the Southwest Fisheries Science Center, which is run by the US National Oceanic and Atmospheric Administration, new studies show that the opah, sometimes called a moonfish or sunfish, has an advantage over other fish in the sea – it warms its own blood by flapping its thick fins. The warm blooded fish, a round-shaped, orange and speckled colored, flat fish in the Lampridae family, can grow as large as 200 pounds or 90 kg. It lives in all of the world’s seas and is usually seen between about 165 and 1,300 feet or about 50 to 400 meters down. Its ability to keep itself warm makes it a fast and agile predator that can speedily travel around catching squid and other types of fish.

Warm Blooded Fish Increases Its Own Blood Temperature

The opha can warm its own blood to a temperature of 7 and 9 degrees Fahrenheit or 4 to 5 degrees Celsius above the surrounding ocean. Additionally, its makeup keeps it from losing this increased body heat, allowing for the warm blooded fish to travel longer distances than other fish living in such a cold environment.

This body heat protects the fish’s brain, heart and other organs while it swims deep down into the cold parts of the ocean. While some other fish, for instance the tuna, is able to warm up certain parts of its body for bursts of speed, the  moonfish warms its own blood to heat up its entire body, making it the first “warm blooded” fish.

Study Highlights Differences in Opha Fish Compared To Others

The study, which took place in California waters, was conducted by putting thermometers inside the warm blooded fish in order to take measurements when it dived down into the ocean. In addition, researchers also took the temperature of various parts of its body.

According to the results, researchers found that the fish has a sponge-like apparatus in its gills called the rete mirabile (“wonderful net” in Latin), that warms the water after it enters the fish’s gills. This has never been seen before.

Another unique thing about the warm blooded fish is that it doesn’t undulate its body to travel and swim through the waters like the majority of fish species. The moonfish flaps its thick pectoral fins, which is also how it warms its own blood while it swims. It is an ability that has never before been seen in a fish, according to the scientists in the study.

Up until now, the only warm-blooded creatures were thought to be mammals and birds. The majority of fish are called ectotherms, which are cold blooded like amphibians, reptiles and invertebrates. However, since the opha fish warms its own blood, it can no longer be put into that category.