How long can a fiddler crab survive in freshwater?

The fiddler found in pet stores are most likely semi-terrestrial brackish , which means they need some salt in their water as well as access to air and dry land. Unfortunately, many pet stores keep fiddlers in a freshwater aquatic set up, and recommend the same to new owners. They may do fine in a fresh water and fully aquatic set up for weeks, but will eventually become weak and die. If possible, find a store that keeps them in brackish water, or wait for a new shipment so their time spent in fresh water is minimal. Look for that are active and have all their legs and claws.