Sleuths solve mystery of opah
THE fish buyer noticed something different about the large, colourful disc-shaped opah waiting to be sold at the auction house in Honolulu.
Among the differences: one fish had a bigger eye than the other. His curiosity set in motion DNA testing and more sleuthing that led to the identification of three new species of opah – a peculiar deep-diving fish recently found to be the first fully warm-blooded fish.
“The more we looked, the more differences we could pull out,” said Karen Underkoffler, lead author of a recently published paper in the peer-reviewed journal Zootaxa that describes the anatomical characteristics of the different species of opah, including one marked by its big eyes and a purple tongue.
In all, scientists with NOAA Fisheries identified five distinct species of opah, revealing that there isn’t a single global species. Three are newly identified, one was already named and researchers better identified another that had been previously described.
“We have known for quite some time that opahs in different parts of the world look different,” Misty Paig-Tran, assistant professor of marine biology and biomechanics at Cal State Fullerton who was not involved in the paper, said in an email.
People were calling them all the same thing, and the paper clearly shows their differences, she wrote, adding that it’s great to finally have anatomical descriptions and DNA to back those descriptions.
The researchers say knowing the population of opah – which has a silvery grey body, red fins and mouths, and white spots – is important to make sure they don’t get overfished.
Sport anglers frequently catch the colourful fish, which on average weigh about 45kg and can be as big as a car tyre.