There's a challenge in bringing live deep-sea fish up to the surface. Unless divers use a needle to poke a hole in the animal's swim bladder, that organ could rupture due to the gas within it expanding as the water pressure lowers upon ascent. A new device, however, is designed to make such poking unnecessary.

Known as the SubCAS (Submersible Chamber for Ascending Specimens), the gadget was created by aquatic biologist Matt Wandell, working with a team at the California Academy of Sciences and the Monterey Bay Aquarium. It's intended for use in the "twilight zone," a region of the ocean located 200 to 500 feet (61 to 152 m) beneath the surface. Although divers can reach such depths, they typically need to use closed-circuit rebreathers in order to do so.

The SubCAS consists of two main parts: a hinge-lidded inner transparent collection jar that is perforated in order for water to flow through it, and a larger transparent chamber housing which the jar fits snugly inside of.

Divers start by gathering live fish in the twilight zone, placing them inside the collection jar, and then beginning their carefully-controlled ascent. Once they've reached a depth of about 180 ft (55 m), they stop and put the jar into the chamber housing, blow a bubble of air into the housing, and seal it up. As they subsequently continue to ascend, that bubble expands, maintaining the water pressure within the chamber.

Upon reaching a depth of 100 ft (30 m), the SubCAS is handed off to a team of support divers dispatched from the surface, who proceed to take the device back to facilities on the shore. There, over the next two to three days, the pressure within the chamber is gradually lowered via a release valve, allowing the fish within to acclimatize. After that, the animals are able to be released into a regular aquarium for scientific study or public display.

In tests of the system, it maintained a survival rate of almost 100 percent. Some of the fish collected with it can now be seen in the Academy's "Twilight Zone: Deep Reefs Revealed" exhibit. A paper on the technology was published this week in the journal Frontiers in Marine Science.

"The SubCAS is an important innovation," says co-author Dr. Hudson Pinheiro. "It allows for detailed study of new-to-science species while they're thriving outside of their natural habitat. We can gain important insights about fish biology and behavior that we couldn't obtain otherwise, helping us better understand what it takes to survive in a region as mysterious as the twilight zone."

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