About coelacanth, it,s impossible to keep one in captivity. The conditions needed for it (specially water pressure) cannot be recreated artificially.
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I believe that those found at 100 meters depth are just warrants and the species is found usually much deeper.
An aquarium wouldn't need a pressurized tank to keep a coelacanth. Species kept from within its depth range, to 2-300 meter, generally do perfectly fine in cold and dark aquariums if brought up slowly to allow them to release pressure from their swim bladder. The limit is still being pushed, too. Both coelacanth species regularly occurs shallower than 200 m and at least the African species is regular close to 100 m, as evident by the population off Sodwana Bay in South Africa.
Quite some years ago a large Japanese aquarium made a serious attempt of getting the African species for display, which would have been in their deep sea tank (cold and dark, but no pressure). After failing for a long period they stopped, citing both their initial lack of success in catching one and the ethics of bringing up a species that was pretty rare. Since then Japanese aquariums have been heavily involved in wild coelacanth research, but none have attempted to catch one for an aquarium.
It's not clear where the "pressure limit" (fish requiring pressurized tank) begins, but it's much deeper the 1-200 meter depth limit for the coelacanth. Additionally, when aquariums start getting to the really deep water, much deeper than coelacanth, oxygen may be a big problem. Some years ago Monterey Bay failed at keeping certain very deep water invertebrates, speculating that they were particularly vulnerable to high oxygen levels (deep ocean generally contains much less oxygen than the ocean close to the surface).
Vancouver has build an aquarium which recreates the pressure at 2000 meters (yes it is very small but still it has to create a pressure of 200 bar).
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I just found out it is actually a travelling exhibition and it is currently at the Oceanopolis in Brest.
Just for the record, this tank was built by French researches for Oceanopolis in France. Although the exhibit is "travelling" in theory, so far it hasn't been put up anywhere else. There are no immediate plans of changing that, but it would definitely be cool if this sort of tanks started spreading.