I decided to make a Fiddler Crab Care tip post for the Uca sp. since I know a lot of people who are getting them and are having troubles finding a lot of helpful information. So this is in no way a complete or official care sheet for the fiddler crabs, just what I have learned either on the internet or thru trial and error with my little guys. I hope this provides a bit of help!
Crabitat/Habitat: No smaller than a 2 gallon tank if housing 1 fiddler crab. No smaller than a 5 gallon tank if housing 2 fiddler crabs. The more crabs you have the larger amount of space you will need. I plan on having my two fiddlers in a 20 gallon tank, this will give me room to add 2 more if I wish. The tank needs to be 1/2 water and 1/2 land (sloped out of the water)--there needs to be a pool and a shore, they need to be able to get out of the water. If you do not want to create a shore, you can also place several rocks that comeout of the water for areas they can sit.
Substrate: You can use playsand or aquarium rock, although sand is a favorite as they sift thru it to find small particles to eat. Some also like to dig and sand provides a good substrate to do this in. I use a turkey baster once a week to clean the poop off the substrate, as well as pick up any uneaten food they many have dragged into the water.
Temp/Humidity: My fiddlers like temps that range from 78-82 degrees on a regular basis, they also like to bask under a heat lamp (75 watt DayGlo and a 75 watt NightGlo) where the temperatures rise to around 95 degrees. I try and maintain a tank humidity of at least 70% (relative) because they are from shore/beach they need a humid environment.
Water: Needs to be salt water, between brakish and the recommended mixing insturctions onthe salt container. I use Oceanic Sea Salt with the mixing instructions on the bag. The water also needs to be dechlorinated (use a dechlorinator without a slime coat). The water also needs to be filtered and cycled like a fish tank. I use the small worlds filters on my 5 gallon tank, and will be moving to a DUETTO 50 when I move them to a larger tank. Cycling of the tank will take at least 2 weeks I have found. I keep an ammonia monitor strip in my tank during this time. When the strip reads normal after the ammonia peak, Iknow the water is now cycled and has the appropriate amount of good bacterias to keep the water healthy and clean (on top of the filtration).
Diet: They need a dish of fresh dechlorinated water on land, this is so they can regulate their body salt content. Fiddler crabs are mostly vegetarian but will eat rotting meats, fruits, flowers, and vegetables. I keep algae wafers in their tank because they mostly eat algae and sea veggies. I usually feed one wafer broken into 6 or 7 bits about twice a week, or less depending on what else I offer them to eat. Mine also like the blister packs of frozen fish foods, black banana, grapes, rose petals, dried krill and brine shrimp, and scrambled eggs (no milk, scrambled in either extra virgin olive oil or coconut oil). They are very clean eaters, in that if you offer them a rock they will pick it clean of any algae growth.
Molting: They molt about once every two months. They do so underwater. They usually arent interested in their exo, but I leave it in for them to munch on. They seem to like to molt in protected areas of the tank, such as under leaves from their silk and plastic plants. If your fiddler is missing legs or claws they will be regrown at this time.
Male vs Female: The males will have one large claw and one small/feeder claw. The females claws will both be small and relatively the same size.
If I have left out anything out please feel free to leave a comment and I will try and add to this to answer your question. I have other posts in my blog with photos of my tank as well as my fiddler crabs, feel free to take a look!
