The incorporation of invertebrates into traditional tank communities of fish is becoming ever more popular for aquarists.
It’s easy to see why some types like small shrimp species and snails are used. They are excellent processors of algae and keep your tank clean.
But for something different, why not try a crab that spends part of its time in the water and partly terrestrial?
The Fiddler Crab (Family Ocypodidae) family has around 100 different species in the group, so there should be something for everyone. They are also commonly referred to as the Florida Crab (most stockists get them from Florida, where they are sourced for the hobby), Uca Crab, Signal Crab, or Calling Crab.
Distinctive with their one overtly large claw, fiddler crabs are easily identified and are found all over the world, particularly in brackish waters.
If you’re only familiar with keeping fish, there are some distinctly different things to be aware of when it comes to keeping crabs.
Resist the urge to keep them as freshwater creatures because it will significantly reduce their lifespan despite what suppliers might tell you.
Small, energetic, and industrious, the Fiddler Crab family is hardy when basic needs are met.
Let’s dig into what’s under the shell of these fascinating creatures that offer something a little more unique for the at-home aquarium and beyond.
Fiddler Crab Behavior
Fiddler Crabs, in all of their iterations, are fun and active little things. Most owners will tell you that you never get tired of watching these guys as they go about their business.
They can often be found creating burrows and digging into the sand. They will scurry across the sand like lightning and can often be seen crawling around under the waterline.
Fiddlers will scavenge for food as they traipse around the tank. They can often be seen testing out mouthfuls of the substrate and then eliminating sand in little balls that have yielded nothing tasty.
Because the males have only one useful claw to feed with, they spend twice as much time eating as females do
These crabs also do a fun display with their dominant and extra-large claw and wave it to communicate. It’s a signal to other crabs that they are present. An extra-large hello wave, if you will!
For the most part, these crabs will get along with others and aren’t aggressive, except, of course, when it comes to breeding season. Males can get into fisticuffs over females, and if things escalate, legs can be lost! Best to keep an eye on them at these times and separate any aggressors.
Females, on the other hand, are not aggressive at all.
Molting will also occur every 8 weeks or so, leaving behind an old exoskeleton in exchange for a fresh one that was growing beneath. They can replace lost limbs this way too!
Fiddlers like to spend a lot of time in the water and in the wild will retreat to burrows when tides go out. Burrow construction is essential to keeping the crab from desiccating and to protect them from predators.
They don’t readily go too far from their burrow, and males can also be observed fighting over prime burrow territory. In the wild, when the tide comes in, they plug their burrow entrance with mud.
They can get stressed with handling, so this should be avoided as much as possible. In addition, they can clamp down with that oversized claw when stressed, so they may grasp onto a wayward finger of yours if they get frightened.
Fiddler Crab Lifespan
If you cater to the needs of your Fiddler Crab, you could expect them to live for around 2 – 3 years. The quality of their tank conditions will impact their lifespan, as always, so you can expect a longer life if you meet their requirements meticulously.
We will discuss more on tank requirements a little later in this article.
Fiddler Crab Appearance
Since most pictures are close-ups of these crabs, people are often surprised to discover that they rarely grow beyond 2 inches across their leg span. So they truly are quite tiny and not as daunting as you may have previously thought.
They are usually brown and orange, although it is possible to see some species with grey, black, violet, and red present.
Fiddler crabs have both gills for underwater breathing and also a primitive lung so they can handle both water and air conditions as needed, although they won’t want to be far from water for long.
Males have one wildly larger claw than the other, and because of how it is held up by the crab, they gained the moniker Fiddler Crab as it resembles how a fiddler would hold up the instrument.
Males are also usually more vibrant in their coloring also, in addition to being larger.
It’s easy to tell the sexes apart!
They have large expressive eyes that sit on stalks, as well as antennae and a rostrum at the front of their carapace (the hard shell).
Fiddler Crab Habitat And Tank Requirements
Since these crabs are coastal inhabitants, they are used to changeable conditions and dealing with tidal fluctuations.
They naturally gravitate to sandy substrates that enable them to construct burrows easily.
Brackish waters are where they are most often found, and they enjoy well-oxygenated water that is slightly alkaline.
Tank Conditions
Getting a tank ready for Fiddlers is straightforward but not the same as what is required for a fish tank.
As these critters like brackish water, you’ll need to keep an eye on salinity levels by using a hydrometer.
Start off with a sandy substrate that replicates a shoreline. They spend plenty of time in the sand burrowing, so you can’t have the tank substrate submerged. Aragonite sand is ideal as it will provide essential minerals for your Fiddlers.
Keep water levels shallow as you need to have a sloping sandy bar at one end of the tank for them to get busy burrowing into.
Vegetation can be added into the water along with rocks or driftwood.
Avoid using hang-on-back filters since crabs are handy climbers. Internal filtration is best to prevent this misstep. It’s essential to have a mesh lid or a ventilated lid to prevent any escapees.
As these crabs like a warm temperature, you may need a reptile lamp to assist with a steady temperature. Keep a thermometer in the tank to ensure it’s always warm enough.
Airstones or air bladders will help keep the water well oxygenated despite the shallow depth.
Water changes need to be done every few weeks of at least 20% to keep optimum water quality. Keep the filter cleaned out regularly.
Water conditions should be noted and maintained as follows:
- pH of 7.2 – 8.2
- Water hardness between 8 – 25G dH
- Temperature between 75 – 88ºF (25 – 31ºC)
- Specific gravity 1.005 to 1.08
- Lighting conditions should be natural or standard, avoid bright lighting
Tank Size
The minimum tank size for 1 – 4 Fiddler Crabs would be a 10 gallon one, and for every additional one, you should add 3 – 5 more gallons.
Crabs can be stressed by overcrowding, though, so don’t push to have too many at once and see how they settle in. You should also only include one male in the mix, which is easily observed since they are so easy to spot.
Choosing Tank Mates For Fiddler Crabs
It’s possible to have fish included in tanks with Fiddler Crabs provided that they are suited for brackish water, and there is ample room for them to escape a crab attack!
Only larger tank sizes upwards of 30 gallons should be considered if you want to have tank mates with your crabs.
Some species to try include:
Avoid anything aggressive or too large like Cichlids, as they will attack your crabs in all likelihood and make a meal of them.
How To Feed Fiddler Crabs
Fiddler Crabs are known as Detritivore/Omnivores in the animal kingdom. Detritus means that they will eat the dead plant and decomposing matter in the sand.
Normally Fiddler Crabs will use their claws to bring substrate to their mouths in the wild. So they will put the sand into their mouths, scrape off organic matter and then spit out the remainder in little balls. It’s an entertaining watch!
Things that are great to feed your Fiddler Crabs include shrimp pellets or granules, flaked fish food, frozen blood worms, and shrimp feed.
They are omnivores, so they will require plant matter like veggies, so consider spinach, leafy greens, or peas to supplement their diet.
Remove any uneaten foods within 24 hours of presenting them to your crabs to avoid fouling the water.
Fiddler Crabs will happily eat most foods you add to their tank but ensure you include things that have calcium which helps them build new exoskeletons before molting. Leave any molted exoskeletons in the tank as they may consume some of it for additional calcium supply.
Ideally, you should feed your crabs once a day and keep varying your food sources to give them an enriched diet.
Common Diseases And Illnesses
Like any species we decide to include in our setups, we should aim for great water conditions. When water condition turns poor, it is often the reason behind disease and afflictions that can cause real problems for your crabs.
Crabs are susceptible to things like shell disease. Any variety of viruses, fungi, and bacteria can create lesions on their shell.
The beauty of crabs, though, is the molting process. This allows most to rid themselves of health issues quite quickly. This includes loss of limbs which can be reformed!
Once they have molted, it’s important to keep an eye on them because it takes a few days for the new exoskeleton to harden and be protective.
Breeding Fiddler Crabs
Breeding Fiddler Crabs isn’t possible in captivity, no matter how you slice it. Even commercial fisheries that regularly breed hard-to-breed fish can’t accomplish this.
This is because after the female lays her eggs in a burrow and gets fertilized, the larvae go into the open ocean known as planktonic larvae.
They then feed in the ocean and then go back to shore.
Although you may see the male doing a courtship dance with your females waving his large claw for attention and becoming aggressive if any other males are present, you should not expect any fertilized eggs to develop.
Are Fiddler Crabs The Right Choice For Your Aquarium
Fiddler Crabs make an exceptional proposition for someone looking for a relatively easy aquarium project.
Their entertaining behavior gives them an enduring appeal to newbies in the hobby. Even if they are a gateway species to eventually having fish in a tank or a side tank for someone who is experienced with fish already and wants something extra, they are remarkably easy to care for.
They are constantly on the move and make exceptionally rewarding pets for the hobbyist without too much trouble and fuss in terms of water conditions. Just don’t let yourself get slack in terms of ensuring their water is well aerated and does get cleaned as often as it needs to be!
Fiddler Crabs are a nice alternative to keeping fish if you want a short break from a true aquarium. They are much easier to maintain and offer a completely different vibe from a fish tank.
Consider these diminutively sized crabs if you want to try your hand at something new.
Get your claws into something completely different with a Fiddler Crab!
