The Red Claw Crab is a semi-aquatic freshwater and brackish water crab. While it will benefit from the addition of some salt to the aquarium water, we have maintained these individuals long term in soft, acidic water, and they are often found in similar swampy conditions. The Red Claw Crab generally will not bother fish in the aquarium, though care should be taken when placing it with slow moving or bottom dwelling fish. It needs a place to emerge from the water, and may escape the aquarium without a tight fitting lid.