Posted in Wildlife

Animal of the Week: The Moonfish (“Opah”)

The reclusive moonfish, seen off the coast of Southern California. Photo by Ralph Pace via National Geographic.
After coming across this article published on National Geographic this week, I knew I needed to learn more about this intriguing creature. Little is known about them and it is rarely photographed in its natural habitat, but recently scientists are coming to know what makes the moonfish, also known as the opah, characteristically significant.
First off, the size of these creatures is nothing short of impressive. These fish are about 100 pounds in weight (the one pictured above is estimated to be closer to 130), and can span to about seven feet in diameter.
Just for size-estimation–a moonfish caught off the coast of California. (FYI: This little guy was released back into the ocean after research) Photo via Southwest Fisheries Science Center, NOAA Fisheries Service.

As you might have noticed, the color of the opah can vary. It can be silvery gray and also reddish, and has red and white spots toward the belly area. Its fins and mouth are red, while their eyes have gold outline. It’s unusual because their bodies are flat and round (which might explain the origin of its name).

Their primary habitat is in the deep ocean, which explains why scientists know relatively little about them. The verdict’s still out on their exact life span, their growth patterns, their anatomy and diet. Estimates show they grow pretty fast, can live for about six years and have a gill arch structure otherwise unseen in the deep blue sea.

The moonfish mostly lives on its alone, but has been seen schooling with tuna and swordfish. They spend much of their time at deep ocean depths, and can maintain the temperature of their eyes and brains 2°C warmer than the rest of their bodies (something known as cranial endothermy). Why is this important? When diving at depths of up to 500 meters, where the water temperature is near freezing, opahs can maintain the functioning of their eyes and brains. And keep swimming.

It’s also useful since opahs span nearly every major ocean and seaway in the world, from the Pacific to the Western Atlantic, and from the Mediterranean to the Indian Ocean.

Basically, this fish is fearless. Endowed with biological prowess to discover the seven seas, the moonfish continues to baffle scientists because of its unique characteristics and fishy character.

Stay inspired,


Sources: National Geographic, FishWatch.Gov, Hawaii Seafood

2 thoughts on “Animal of the Week: The Moonfish (“Opah”)

    1. Thank you! I found both its name and its qualities so unique for fish, and yes you’re right about its flesh having three different colors and tastes. Apparently, it’s considered a delicacy in Hawaii.

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