One Man’s Quest to CT Scan All the World’s Fishes
On the island of San Juan, just off the coast of Washington, a mad scientist is building fish burritos. He takes a handful of specimens, wraps them in ethanol-soaked cheesecloth, and bundles them together. Then he gently piles the things into a cylinder and pops the “burrito” into a mini CT scanner. In go the fish and out comes an image you wouldn’t believe: a precise three-dimensional rendering of each specimen’s skeleton.
Adam Summers is on a quest to scan all 33,000 species of ray-finned fish—that’d be the ones like bass and tuna you’d find in the supermarket. He also wants to upload all of that data for anyone to tinker with. With every scanned specimen, science gets a better understanding of a species in the precarious age of human-induced mass extinction.
But first, Summers has to get his hands on thousands of specimens. Instead of plucking them from the sea, he’s lifting them from museum collections. “Some of these fish populations are already extinct,” he says. “Some of them are critically endangered. So this is a record of what was there.” He also welcomes grad students and professors who are interested in particular groups of fishes to bring by their own specimens and give the scanner a whirl.
Once he has a specimen in hand, Summers photographs it with its museum tag. Then he rolls it up in the cheesecloth soaked in ethanol, which keeps the fish from drying out and curling and shrinking. By packaging multiple fish in a single burrito, Summers can image them all at once—which, considering the scan can last five or six hours, saves a lot of time. “That’s really the innovation here,” he says, “is that instead of having one scan for one fish, what we’re doing is having one scan that covers 10 to 20 species of fish.”
Now, this CT scanner doesn’t work like the donut-shaped one you may have been through. It’s more like an oven that bombards the fish with X-rays instead of heat. These rays pass through the specimens and cast shadows when they hit certain tissues. Each image the scanner makes is actually a cross-section—only when Summers processes the individual images does a cohesive form emerge.
By this point you may be thinking that not every fish can fit in a burrito, and that’s certainly a shortcoming of a miniature CT scanner. But Summers won’t always go after adults. “All fish start out really small, so we can scan small examples, young examples of everything,” he says.
Eventually, that everything will include more than fishes: Summers wants to scan every vertebrate on Earth. And vertebrates, with their sturdy skeletons of bone, can grow to outlandish sizes (the blue whale, at 100 feet long, is the biggest creature to ever live). To tackle those, Summers says, you need a laser scanner. And indeed, scientists have already laser-scanned a blue whale.
Why go through all that trouble? For one, using this data, scientists can 3-D print their own specimens anywhere on Earth. And by enlarging a tiny thumb-sized fish into one the size of your hand, researchers can get a better look at, say, a particular bone. “So you can actually really hold the morphology in your hand,” Summers says.
Plus, with the digital-only approach, scientists can put the knives away. “This is not only fabulous for showing us what we have had, because this works on museum specimens that may have been collected hundreds of years ago, but it also is a way of non-destructively sampling important specimens that have just been collected,” Summers says.
All told, Summers so far has scans of over 700 ray-finned fishes, plus a steady stream of other researchers visiting to scan their own specimens. Not a bad start, and certainly not a terrible use of a burrito.
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