Although my first batch of fiddler crab only managed to survive for only 5 months, part of the reasons why it was short-lived has got to do with myself being inexperienced and having the wrong notion as stated above. My previous understanding was that it was totally freshwater and it can stay fully submerged all the while with other aquarium fish. Later after I found out about the truth, I’ve decided to mix in some aquarium salt to create the natural condition for it to live in.
The enclosure setup should be made up of rocks and sands at the base bottom with one part slightly sloped to contain the brackish water. Usually one tablespoonful mix of aquarium salt to every 1 gallon of water is enough to create the salinity level ideal for your fiddler crabs. You can even consider adding aquatic plants to create the natural condition and to provide hiding place. When it comes to food, the crabs are not picky and they will enjoy sinking fish food pellets and every dried shrimp. Their usual activity includes sifting through layers of sands looking for food and climbing on top of rocks to rest.
Another characteristic, which you should be aware of, is that the crabs will molt meaning that they will shed the exoskeleton behind and later consume it to recover the lost calcium. So far, attempts to breed this little creature in captivity have not been successful due to my inability to provide perfect living condition. Nevertheless, it was still exciting to have them around and just remember, they are not supposed to be mixed into your aquarium tank and swim around like the fish. Nowadays, the latest craze has been the Red Claw Crabs, which are offered for sale in aquarium stores and online pet sites.
For easy and fast setup, you can even consider getting a starter fish tank to house them. Other invertebrates for your fish setup: Freshwater Clams and Crayfish (Yabbie)