Caring For Your Pet Fiddler Crabs: Everything You Need To Know

Although hardly a pet to be cuddled or played with, fiddler crabs can be very entertaining. Their behaviors, such as waving the claws, scavenging, and climbing, are interesting and, if properly maintained, fiddler crabs are inexpensive and easy-to-handle pets.

How To Choose A Healthy Fiddler Crab

Since pet stores frequently sell fiddler crabs as “freshwater” creatures, try to buy your crabs as close to their delivery date at the store as possible. The less time they have spent in freshwater, the better.

Fiddler crabs are happiest in pairs. Always keep equal numbers of males and females, and don’t overcrowd. Remember that this species is highly territorial.

Try to pick fiddler crabs that are active, moving about the tank, and climbing. Note that crabs that are kept in overcrowded tanks in pet stores will be more docile since these conditions seem to have an almost sedative effect.

Estimated Costs To Keep Fiddler Crabs As Pets

  • Fiddler Crabs – $4 / £2.55 per crab
  • Tank: minimum 10 gallon / 37.85 liter – $20 / £13 will hold four crabs $16 / £10.23
  • One bag Instant Ocean $15 / £9.77
  • Submersible power filter sufficient to handle up to 20 gallons / 75.7 liters $15 / £9.77
  • 20 lbs / 9kg play or aquarium sand $15 / £9.77
  • 2 thermometers $10 / £6.50
  • Decorative items like rocks or standard aquarium structures vary widely budget $10-$25 / £6.50-£15.98
  • Plants vary by species budget $5$15 / £3.19-£9.77
  • Estimated Total: $100-$130 / £63.95£83.14
  • If you live in a cooler climate, your tank may require a heat mat. These units are frequently used with reptiles and are inexpensive. Expect to pay roughly $15 / £9.77. It is also possible to use an underwater aquarium heater, at a cost of approximately $30-$40 / £19-£26.

Once you have purchased your fiddler crabs, the following are the items you will need and the parameters to be followed to establish a suitable aquarium environment for them.

Minimum Tank Size

At a minimum, buy a 10 gallon / 37.85-liter tank to hold no more than four fiddler crabs. The general rule is that a fiddler crab requires a square foot / 0.092903m2 of space.

The tank will need a solid lid to preserve the correct temperature and humidity. Small tanks of this size are extremely economical and can be purchased for only $20 / £13.

The ideal conditions are 75-85 F / 24-29 C with a relative humidity of 75% – 85%.

Creating Brackish Water For Fiddler Crabs

Fiddler crabs require brackish water, which in nature occurs at points where freshwater and saltwater meet as lagoons, estuaries, coastal streams and mangrove swamps. The salinity of brackish water changes daily in relation to the tides so that species that thrive in such environments tend to have a high level of adaptability. Fiddler crabs cannot, however, survive in completely freshwater.

If you plan to keep only fiddler crabs, it doesn’t have to be as precise about the specific gravity or salinity of the water as you would be with fish. The recommended specific gravity, however, is 1.005 to 1.010.

A good recipe for beginners is to mix 2 gallons / 7.57 liters of de-chlorinated water with 2-3 tablespoons / 1.97 – 2.95 UK tablespoons of Instant Ocean marine salt (considered by enthusiasts as the leading product). Shake the water until the salt is completely dissolved.

A bag of Instant Ocean suitable to mix 50 gallons of water costs only $15 / £9 and will obviously last a very long time.

Use a submersible filter for aeration. A suitable unit would be a Duetto Submersible Power Filter, which can handle tanks of up to 20 gallons / 75.7 liters and can be purchased for as little as $15 / £9.

Physical Tank Elements

When raising fiddler crabs it’s important to arrange the sand or substrate in the tank to create a “beach.” The slope needs to run from approximately 1 inch / 2.54 cm at one end of the tank to 8 inches / 30.32 cm at the other. The water level should come about halfway up the slope and no farther.

Fiddler crabs cannot survive unless they can climb out of the water. The sloping arrangement will also allow you to bury a plastic box or similar container in the substrate that the crabs can use as a burrow. They will need plenty of places to hide.

This arrangement will take more sand than you might think. Purchase about 20 lbs./ 9 kg to achieve the correct arrangement. The cost will be approximate $15 / £9.

It’s a good idea to use large rocks at the foot of the slope to keep the sand in place. Note that when you first add the sand and water, the quality will be very murky and dirty. The tank may need a full day for the sediment to settle appropriately. Don’t put the filter in the water until it is clear.

Provide A Heat Or Sun Lamp

Fiddler crabs enjoy both light and heat. Even a simple plant lamp will suffice, so long as the creatures feel they are getting “sunlight.” It’s not necessary to buy an actual heat lamp unless you have difficulty maintaining the correct temperature in the aquarium.

Purchase two small thermometers or temperature gauges to keep an eye on tank conditions. Put one on the “land” side of the tank and the second in the water. Maintain both at a level of 75-85 F/ 24-29 C.

It’s a good idea, however, to spend $10 / £6.50 for at least one combined unit that reads both temperature and humidity to keep an eye on that reading as well. If you choose to use a combined gauge, plan to put it at the “land” end of the tank.

To Cycle or Not To Cycle?

It is a sad fact that some people regard fiddler crabs as “throwaway” pets. Regardless of their short lifespan in captivity, that attitude is cruel. Any companion animal deserves the best level of care you can provide.

Most people who keep fiddler crabs don’t cycle the tank first to condition the water and prevent dangerous levels of ammonia from developing in the tank. This can be a serious mistake.

Crabs literally graze on the small organisms and plant life that lives in the sand of the beaches and tide pools they call home. That microbial life takes time to develop in an artificial environment like an aquarium.

The process of cycling a tank can be lengthy, however, which is why many people don’t do it. The following is an overview of basic water chemistry and the nitrogen cycle, which you will need to understand if you are planning on trying to house fiddler crabs and fish together.

Water Chemistry And The Nitrogen Cycle

Water chemistry can be an endlessly complicated topic among those who are passionate about aquaculture. Whether you are keeping tropical fish or fiddler crabs, you do have the considerable responsibility of maintaining the atmosphere in which they live. While crabs are not entirely aquatic, poor water quality will kill them.

For the beginner, there are three basic measurements with which you should be familiar.

Acidity Or Per Hydrogen (pH)

Typically when anyone sees the chemical sign pH they think of the associated measurement as an expression of acidity.

The actual meaning of the pH, however, is that low numbers represent more acidic water, high numbers mean more “basic” or alkaline water.

The scale runs from pH 5, which is slightly acidic to a relative neutral pH7 on to alkaline water at pH 8.

The measurement is based on the balance between hydrogen (H+) and hydroxide (OH) ions in the water.

  • Saltwater has a pH range of 7.5 to 8.4
  • Freshwater has a pH range of 6.5 to 7.5
  • Brackish water has a pH of 7.5 or greater

Carbonate Hardness (KH)

Confusion over this measurement stems from the fact that it refers to the alkalinity of water, which is not the same measurement as “alkaline.”

Alkalinity describes how well water can serve as a “buffer” to absorb and neutralize the acid. High KH, water with more alkalinity, won’t be subject to as many changes in pH level. In its most simplistic explanation then, high KH water is more chemically stable.

Specific Gravity (sg)

This measurement quantifies the relative salinity of the water. It is taken with a hydrometer or a refractometer.

The specific gravity of natural seawater varies by location. In a saltwater aquarium, for instance, the target level would be 1.022. Once a level of specific gravity is attained in a tank, the goal is to not allow it to vary too widely.

Tanks that seek to recreate brackish waters where rivers and estuaries meet the ocean typically have an sg range of 1.002 to 1.005 sg.

Understanding The Nitrogen Cycle

Establishing the nitrogen cycle in any kind of aquarium environment is a process that cultivates bacteria in the water to keep marine species alive and healthy. Any marine animal, including fiddler crabs, will produce waste materials that create toxic levels of ammonia in the water.

Nitrifying bacteria, however, eat ammonia, and in time produce nitrite, which, when eaten by the second set of bacteria, becomes relatively harmless nitrate.

Without this cycle, the very water that is supposed to keep your fiddler crabs and fish alive will kill them.

There are many ways to establish the nitrogen cycle in a new tank. For a beginner who intends to house only fiddler crabs, the simplest approach is to set up the tank and then introduce household ammonia to the water.

Using an ammonia test kit, bring the water up to an ammonia level of 2-4 ppm. Then, put in a large handful of fish food. Test the water at 24 hours intervals until the ammonia levels begin to drop, signaling the presence of nitrite.

Add more ammonia to return to the water to the target range, and begin testing for both ammonia and nitrite. Add ammonia as needed and watch for a drop in nitrite.

When you have achieved 0 ppm of ammonia, 0 ppm nitrite, and get a nitrate reading, the water is ready to support life forms. Change out 70-90% of the water, and try to achieve a nitrate level of less than 40 ppm.

(This material is only a general overview of establishing the nitrogen cycle in a new tank. If you are attempting to introduce fiddler crabs into an existing aquarium, the cycle will already be in place.)

Some people do not cycle their tank before introducing fiddler crabs, but if you opt for that route, keep the tank clean and use test strips daily to watch for toxic ammonia build-up.

Daily Care and Feeding

Fiddler crabs will basically eat anything you put in the tank. The crabs spend most of their time “grazing.” Over time, the sand or substrate in your aquarium will be home to the microbes your pets need, but you will still have to supplement their diet daily.

The biggest consequence of overfeeding is murky, ammonia-filled water, so feed sparingly. A good daily diet would be a brine or baby shrimp or a few tropical fish flakes, alternating every few days with freeze-dried blood worms, freeze-dried plankton, and a few pieces of seaweed or algae disks.

It’s perfectly fine to experiment with what you feed your fiddler crabs as long as you keep an eye on the quality of the water in the tank.

Cleaning The Tank

Maintaining proper water quality is the most important part of maintaining a fiddler crab environment if the creatures are housed alone.

Since the crabs are often referred to as “beach cleaners” and provided you don’t overfeed, the creatures themselves will be very helpful in keeping their tank in good shape, even obligingly eating any algae growth.

Every six months plan on doing a total water change. As water evaporates, do not add more salt. Test the water to maintain proper salinity and only add pre-mixed water when the levels drop.

Never introduce salt directly into the tank. Remember, you can always add more salt to the water, but you can’t take it out.

Also, only use dechlorinated water with your pets. If the crabs have left food in the tank and it is not consumed in a few hours, remove the debris.

Typically crabs will eat their own shells after molting as a source of calcium, but if they do not, take the old exoskeleton out of the tank as well.

If your fiddler crabs have been introduced into an existing aquarium, follow your typical maintenance routine.