In recent years, SCUBA technology has advanced, making it possible for researchers to dive into the twilight-like mesophotic zone 200 to 500 feet underwater. There, they can get hands-on with hundreds of little-studied coral and fish species. But then what? Fish transported from these depths, which can have about 15 times the pressure of the ocean's surface, can experience barotrauma (human divers call this "the bends") if they ascend too quickly. Their air-filled swim bladders expand, pushing their stomachs out of their mouths and even popping out their eyes. In the past, collectors would sometimes pierce the fishes' swim bladders to relieve the pressure, an invasive and risky procedure. Now, reports Maddie Stone at Earther, researchers have developed a new device that SCUBA-diving scientists can use to safely bring these mysterious creatures up to the lab.

The technology is called the Submersible Chamber for Ascending Specimens or SubCAS. The two-foot long gadget was put together by researchers from the California Academy of Sciences and Monterey Bay Aquarium. To use the device, which is essentially a long, clear tube, researchers place any fish they hope to bring to the surface in a collecting cylinder. When the diver and their finned friends reach 180 feet, the cylinder is placed inside another tube. Then a bubble is blown into the lid, creating an air gap between the two cylinders. “The air bubble is critical as it expands during ascent and helps maintain the pressure inside the chamber,” Matt Wandell, aquatic biologist at the Monterey Bay Aquarium who built the chamber says in a press release.

When the diver reaches 100 feet, they hand the samples off to biologists who, slowly, over the course of two or three days, release the pressurized bubble, allowing the fish to acclimate to surface pressure. The chamber is described in the journal Frontiers in Marine Science.

According to JoAnna Klein at The New York Times, the SubCAS team put the device through its paces between 2014 and 2017, collecting 174 fish from the mesophotic zone in the Philippines and the Pacific islands of Vanuatu, Palau and the Micronesian island of Pohnpei. The SubCAS proved to be remarkably successful. While not all the fish survived, the unlucky ones died because of problems like predation between species, not because of issues with pressure. Survival rate using the gadget is otherwise almost 100 percent.

Once the fish were successfully brought to the surface and depressurized, they were sent to the California Academy of Sciences, where most have become part of a first-of-its-kind exhibit at the Academy’s Steinhart Aquarium called Twilight Zone: Deep Reefs Revealed.

“When we started doing these deep dives, seeing whole ecosystems nobody’s ever seen....I wanted to bring those to the public floor,” Bart Shepherd, senior director of the Steinhart Aquarium tells Stone. “We’re showing a million-plus people a year these things nobody else will have the opportunity to see, and [using] that as a way to have a conservation about coral reef decline.”

“I want to shine a light into the twilight zone and show people that these ecosystems exist, are under threat, and there’s something we can do about it,” he tells Klein.

SubCAS isn’t just about stocking aquariums either. Stone reports that the researchers are using the newly collected fish to figure out the evolutionary relationships between various mesophotic species. Then, in 2019 the team will head to the little-explored twilight reefs in the Indian Ocean where Shepherd says they believe they’ll find “a ton of new species” that they can bring into the lab using SubCAS.