The Crayfish is a freshwater crustacean commonly found in the aquarium hobby. The average Crayfish reaches 3 in size and should be housed in a minimum of 30 gallons. There are not many fish you can put with your Crayfish, but if you wish to keep more than one Crayfish together, you will need a larger aquarium to avoid aggression. You should provide your Crayfish with hiding spots and caves.