New Species Of Opah Fish Discovered In Hawaiian Fish Market

Posted: Jun 27 2018, 2:11am CDT | by , Updated: Oct 12 2019, 12:34am CDT , in Latest Science News

 

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New Species of Opah Fish Discovered in Hawaiian Fish Market

Opahs are the mysterious warmblooded fish.

A buyer at a Honolulu auction house recently noticed something curious about some fish he was interested in: colorful, disc-shaped opah. One specimen had a much larger eye than its neighbor. This instigated some DNA testing. The outcome? This casual observation in a Hawaiian market eventually led to notification of three new species of opah.

According to Karen Underkoffler, author of a paper recently published in Zootaxa (the peer-reviewed taxonomy journal): "The more we looked, the more differences we could pull out." As well as those oversized eyes, her report outlined other anatomical anomalies, such as one fish having a purple tongue. This research has compounded other findings by National Oceanic and Atmospheric Administration (NOAA) scientists, who have now identified five distinct species of opah, contrary to previous suppositions about one global species. There has been a call to acknowledge the separate species for some time, and now these clear anatomical differences and DNA sampling have confirmed the true picture.

Identifying these differences are critical in terms of ensuring separate populations are protected. Although not commercially harvested, opah are often trapped as a byproduct of tuna or swordfish fishing off the Hawaiian and Californian coasts. Opah are also caught by anglers and can weigh in at 100 pounds. They are popular in seafood restaurants in Hawaii.

But what is particularly remarkable about opah, all five species of them, is they are the only known example of warm-blooded fish. Until detailed examination of their anatomies several years ago, science had long assumed the only endothermic (warm-blooded) aquatic creatures were seafaring mammals.

Biologist Nicholas Wegner of the NOAA examined an opah's gills and found the tissue had a unique design feature, allowing it to maintain endothermy. The journal Science published Wegner's paper. He summarized his findings in a statement: "Nature has a way of surprising us with clever strategies where you least expect them. Before this discovery, I was under the impression the opah was a slow-moving fish, like most other fish in cold environments. But because it can warm its body, it turns out to be a very active predator that chases down agile prey like squid and can migrate long distances."

As Wegner's team performed a dissection they noticed the gills contained an intricate network of red and blue blood vessels. Known by the Latin expression retia mirabilia (translating as "wonderful net"), these veins and arteries are seen in other highly adaptable ocean-going predators, such as sharks and tunas. But unlike these cold-blooded hunters, opah retain their internal heat, generating this directly from the movement of their muscles – but only around specific areas of their anatomy.

The scientists also took the opportunity to plant small thermometer devices in several opah before releasing them back into the wild. These revealed temperatures consistently higher than the surrounding waters. The opah's average muscle temperature was around 5 degrees Celsius above the mean ocean temperature while swimming between 150-1,000 feet below it.

In conclusion, the researchers remarked the opah's unique properties - its ability to raise the internal temperature of its brain and muscles, but most notably the heart - gave it a distinct advantage within its ecosystem. Opah have become highly-specialized for living in deep water and catching their prey.

Of course, the waters in the southern hemisphere where opah are to be found in abundance are renowned for a dazzling array of species, warm and cold-blooded. Exploring the Great Barrier Reef is a hugely popular pastime. Whether you join a sub-aqua club or meet with diving companions in a chat room setting, the ocean never ceases to throw up fascinating new discoveries.

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The Author

<a href="/latest_stories/all/all/2" rel="author">Luigi Lugmayr</a>
Manfred "Luigi" Lugmayr () is the founding Chief Editor of I4U News and brings over 25 years experience in the technology field to the ever evolving and exciting world of gadgets, tech and online shopping. He started I4U News back in 2000 and evolved it into vibrant technology news and tech and toy shopping hub.
Luigi can be contacted directly at ml[@]i4u.com.

 

 

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