Fish elevator reveals mysterious fish from the Twilight Zone

06 June 2018

Pseudanthias_fasciatus

colourful fish in deep sea

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A "fish elevator" to safely transport newly-discovered fish from the ocean’s depths to the surface has been developed by researchers in the US.

Dubbed SubCAS, short for Submersible Chamber for Ascending Specimens, the new system works like an aquatic lift, with a capsule that can keep deep-dwelling species at the water pressures they're accustomed to so that they make it to the surface unharmed. 

It is often said that we know more about outer space than we do about our own oceans. Now Bart Shepherd and his team at the California Academy of Sciences aim to change this by exploring the "Twilight Zone".

Many know it as a television show, but in fact, the Twilight Zone is the layer of ocean that exists between 200-500 feet below the surface. This region earned its name due to the extremely low levels of sunlight that penetrate to this depth.

The Twilight Zone exists between two popular ocean layers of marine research. The shallowest layer, the Sunlight Zone, spans from the ocean’s surface down to the Twilight Zone. The Sunlight Zone is easily accessible to researchers via boats and scuba divers.

Below the Twilight Zone is the Midnight Zone, then the Abyss, and finally the Trenches. Such deep layers of the ocean are only accessible to researchers via submarines or unmanned ocean vehicles.

The development of closed-circuit rebreathers has allowed for longer and deeper scuba dives, making the Twilight Zone more accessible than ever. Shepherd argues that the Twilight Zone is often overlooked on the way to deeper ocean layers, but there is much to be learned from the sea creatures that reside there.

“We can closely explore these environments without relying on large submarines or remotely operated vehicles, so we needed a similarly agile way to collect important fishes and bring them back alive," says Shepherd.

Fish that live in the Twilight Zone are accustomed to swimming at pressures of up to 1470 pounds per square inch. To put that into perspective, that is over 100 times the pressure our bodies experience swimming at the ocean surface.

Fish maintain buoyancy in the water thanks to an organ called a swim bladder. The swim bladder is filled with gas, much like the air in your favourite inflatable pool toys.

When a fish is brought closer to the surface, its swim bladder reacts to the change in pressure. If the pressure outside of the fish’s body decreases, the gas inside of the swim bladder will expand.

If the pressure changes too rapidly, the swim bladder can rupture, killing the fish. It's preferable to study specimens that are still alive, so Shepherd and his team developed the SubCAS as a way to bring fish from the Twilight Zone to the surface unharmed.

The SubCAS is a custom-built housing that consists of two chambers. The inner chamber, called the collection jar,  has a hinged door that opens to the specimen and then closes around it. The collection jar is perforated, which allows water to flow in through the jar and around the fish.

The collection jar fits snugly inside another chamber, called the hyperbaric chamber. When the collection jar is placed inside of the hyperbaric chamber, the operator blows an air bubble into the housing alongside it before sealing the hyperbaric chamber door.

During the ascent to the ocean surface, the air bubble inside of the hyperbaric chamber expands as the surrounding water pressure drops. The expansion of the air bubble creates pressure against the water that flows inside of the housing and through the collection jar. This keeps the fish under relatively higher pressures and prevents the animal's swim bladder from bursting.

The SubCAS has proven to be crucial in accessing and researching specimen from a region of the Ocean that we know little about. "In a time of global crisis for coral reefs, discovering strange and beautiful fishes from unexplored reef habitats is critical to our understanding of how to protect them," says Shepherd.

"These species are ambassadors of important environments that are rarely included in marine protected areas or sanctuaries. Our goal is to remind the public of the ocean's vast and unexplored wonders and to inspire its conservation for future generations."

So far, the SubCAS has aided Shepherd and his team in discovering many new specimens including a new butterflyfish from the Phillipines called Roa rumsfeldi, as well as the Pseudanthias fasciatus (pictured above).

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