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What can fish skeletons teach us about life in the deep sea?

By Jessie Perelman, Safina Center “Kalpana Chawla Launchpad Fellow”

From long fangs to massive eyes, expandable jaws to bioluminescent lures, fishes of the ocean’s ‘twilight zone’ are peculiar, to say the least. The twilight (mesopelagic) zone lies at a depth between 200-1,000 meters in the ocean, where the last rays of sunlight begin to disappear and darkness encroaches. It’s no surprise that the animals living in this environment have some pretty amazing adaptations that allow them to survive here.

Finding food in this expansive and borderless habitat can be a challenge, as a fish may only encounter a meal on rare occasions. So, the seemingly odd adaptations are actually quite effective for capturing prey and making use of what minimal light exists at these depths. But it’s not just the external features of mesopelagic fish that are so unique. The bones of these animals might actually tell us a more detailed story about how they function and behave, and this is valuable for animals that live too deep to observe alive.

The loosejaw (Malacosteus niger) and threadfin dragonfish (Echiostoma barbatum) are just two of the 90 mesopelagic fish species that were scanned using micro-CT at FHL. With expandable jaws and razor sharp teeth, these creatures are well equipped to catch prey in this deep, dark habitat. Photos courtesy: Jessie Perelman

I am on a mission to see what we can learn from studying the bones of mesopelagic fish, and recently travelled to Friday Harbor Laboratories (FHL) in Washington State to begin this endeavor- one that I hope will provide a new perspective on deep-sea biodiversity.

Friday Harbor Laboratories (FHL), a field station for the University of Washington, sits on the beautiful shores of Friday Harbor on San Juan Island- an ideal and inspirational place to conduct marine research! Photo: Jessie Perelman

Using FHL’s high-resolution micro-CT scanner in collaboration with a campaign called oVert, I generated 3D images of nearly 300 preserved museum specimens spanning 90 species of fishes. Because these organisms are difficult to collect and many are rare in museum collections, CT scanning is a great way to study their internal anatomy nondestructively. Plus, it provides stunning images of these crazy creatures!

To prepare fish specimens for scanning, they were rolled gently in gauze and secured tightly in a plastic can so as not to move during the 4-8 hour scanning process. After scanning was complete, all specimens were sent back intact to the museum collection from which they came. Photo courtesy: Jessie Perelman
Micro-CT scanning is a powerful tool to study the anatomy of vertebrates. This nondestructive technique highlights the amazing biodiversity among deep-sea creatures, and it is providing new insights about the behaviors they might display in their natural habitat. (From left: Polyipnus lynchus, Malacosteus niger, and Chauliodus sloani). Photos courtesy: Jessie Perelman

The oVert project is a four-year campaign to provide open-source, 3D digital models of more than 80% of all vertebrate genera on Earth to scientists, educators, and the public. Fishes, reptiles, birds, you name it. The ambitious movement is constructing a game-changing database of biodiversity, and I am honored to contribute to the efforts with a broad range of mesopelagic fishes. These CT scans will be explored over the next few years, answering questions about form and function in the deep sea, and adding to the mysterious story of the ocean’s twilight zone.

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