Rawriie: fiddler crabs live in brackish waters. Bettas live in fresh water. Brackish water is a mix of salt water and fresh water. Being as salty as it is, it is not good for bettas. If you read thread BettaFishCrazy posted, you will see that someone else got one, and listed reasons why not to get them as in they are messy, prefer land over water, need brackish water, etc. Also, bettas do not necessarily like or need shallow water.