I'm assuming this is a brackish or marine crab and thus needs a brackish or marine setup. With that said I doubt it will last long in captivity. It seems like it has a parasitic relationship with oysters and thus needs them to survive. To keep oysters id think a stable tank with lots of micro life, e.g. Phytoplankton, zooplankton is necessary. Even if the crab lives, keeping the oysters alive long term would be a hassle.
Any idea the temp. Of the water or salinity these guys are found at?
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