The problem of studying the living world in the so-called twilight zone of the ocean, at depths from 50 to 200 m, is that the creatures living there are adapted for life at a pressure that is much higher than atmospheric. Scientists have long been forced to pull to the surface only corpses deformed from pressure drops, but the only alternative before were only bulky pressure chambers in which the fish survived - however, it was difficult to study them. And so the California Academy of Sciences presented an elegant solution to the problem.
The device for fishing deep-sea fish looks like a transparent container made of durable plastic with a secure lid, which has a built-in mechanism for connecting to a water filter. Fish are caught at depth in any convenient way, placed in a container, then the diver launches an air bubble from his scuba into the filter and mounts the filter on the container, sealing it. The air is at the pressure that exists at a particular depth, but as it rises, the gas will begin to expand, exerting a proportional pressure on the water in the system.
The result is a simple, self-regulating pressure chamber that does not need energy sources and provides partial safety of the environment familiar to fish. If you solve the issue of feeding food through a filter with an air bubble, and then collecting waste, the container can serve as an aquarium for a very long time. As a last resort - to act as a transport module for the transport of exotic fish from the place of catch to laboratories on the mainland.