Freshwater Crabs

In freshwater crabs, you’ll discover the perfect pet for your home. While they may not be as popular as dogs and cats, freshwater crabs are just as fun and easy to take care of, and can provide years of enjoyment.

There are a number of different types of crabs available in the United States, and they all have different sizes, shapes, colors, and activity levels. There is a type for every family.  These pets are ideal for kids, and parents will love that they only need to be fed once a day, and that they can clean up after themselves.

Freshwater crabs are a great addition to any aquarium! They are almost completely harmless to other tank mates, and are not too aggressive with other crabs. They are also a great way to introduce children to the world of pet ownership, as they can handle most food without the need of additional prep work. They are also quite easy to care for, and most of their needs can be met with a minimum amount of effort.

fiddler crab

What they lack in looks they make up for in personality.  Freshwater crabs are active little creatures that will scuttle around the floor of your tank, looking for things to scavenge. This is usually food that others in the tank didn’t eat. A freshwater crab is just one of the many unique animals that make a great addition to your families aquarium.

Freshwater Crab Information

    • Average Length: 1 – 4 inches depending on type
    • Scale Colors: Brown, Orange, Red, Gray and Blue
    • Attention Needs: Low
    • Good tolerance to Heat and Cold: No
    • Good Pet: Yes!
    • Good with Other Crabs: Depends on the specific crab species
    • Good with Other fish species: Only with non-aggressive species
    • Suitable for First-Time fish Owners: Yes
    • Health Concerns: They tend to have Shell Disease and Loss of Appendage.

Physical Appearance of Freshwater Crab

Freshwater Crabs are crustaceans (invertebrate organisms with a thick exoskeleton)  with 10 legs. In terms of body structure they are closely related to lobsters, shrimp and crayfish. Like these creatures, Freshwater Crabs also do not have a backbone or a bony skeleton. Instead they have a hard exoskeleton that provides support to their delicate body and also protects them from predators. They shed this exoskeleton several times during their lifetime through a process called molting.

Freshwater Crabs have a flat, short and somewhat circular-shaped body. They have 5 rows of legs with the first row called the claws. The claws are not used for movement but help them to burrow and catch prey. The legs have multiple joints and are stiff. The way their legs are designed makes it hard for them to move forward or backwards with any speed. This is why Crabs usually only move sideways to get around.

There are over 9 different species of Freshwater Crabs that are commonly kept in aquariums. Even with the smaller selection, there still is a huge choice in colors, size and textures. 

One of the most popular Freshwater Crabs is the Thai Micro Crabs. These grow up to a maximum of 1 inch. They have a gray-colored body with white and brown markings. Thai Micro Crabs are also known as “false spider crabs” because of the spider-like long legs they have. 

Similar to Thai Micro Crabs are the Pom Pom Crabs. These are also considered a popular choice for freshwater tanks. They have light brown color with white, gray and black markings. Their legs are not as long as the Thai Micro Crabs and are almost equal to the length of their carapace. They derive their name from the fluffy, hair-like cluster on both their claws as it looks similar to Pom Poms.

Fiddler Crabs are another crab species that is quite popular in freshwater aquariums. They come in light brown or orange color and can grow up to 2 inches. There are several varieties of Fiddler Crabs with some like the Gold Fiddler Crab having a bright yellow color on their claws. They have lungs as well as gills that allow them to live both on land and water. One unique thing about their appearance is that male Fiddler Crabs have a giant claw that has a lighter color than the rest of the body. The giant claws help them to communicate and also court females.

Temperament of Freshwater Crabs

Freshwater Crabs are nocturnal and mostly active during the night. They are scavengers who will look for leftover food and any other organic waste inside the tank that can be eaten. They will climb on anything that they find like sticks, rocks, caves, plants or air tubing, which makes securing the tank lid extremely important.

When introducing them to a new tank you may find them spend most of their time in hiding. As they become used to the new living environment the Crabs will gradually come out in the open. 

The temperament of Freshwater Crabs also varies depending upon the species. While most are peaceful some like the Red Claw Crabs tend to be extremely territorial and aggressive. The male Fiddler Crabs are also known to get aggressive with other male Crabs.

Best Habitat for Freshwater Crabs

Not all Freshwater Crabs are fully aquatic. Freshwater Crabs like Fiddler Crabs live in a land and water environment. To replicate this an area of dry land should be created inside the tank for these types of Crab species. 

pom pom crab

This can be done a few different ways depending on the size of your aquarium, or if you plan on keeping fish in the aquarium.

If you don’t plan to keep any fish in the aquarium with your Fiddler Crabs the easiest thing you can do is pour in the sand so that you build a gradual incline higher than the water level you intend to have for the tank. In this case the wider the aquarium the better as it will let you build a more gradual incline.

A method people tend to do when they want to have fish with the crabs is they will place stairs in the tank that leads to a “dry zone platform”. Most of these don’t take up too much space and it lets you be able to keep Freshwater Crabs and fish together.

In cases where you have a large fish tank where stairs are not practical, creating an underwater dry zone becomes your best option. For this method you will want a large glass jar that you can fill with sand. Run an air hose into the jar so that you keep fresh air in the jar for your little crabs and now you can keep both crabs and fish in the same tank without any trouble.

Crabs can climb almost anything which makes them amazing escape artists. To prevent this from happening the tank lid should be tightly secured. You can also add a tank net to prevent them from escaping.

Tank size

For a tank that is going to house only Freshwater Crabs, a minimum size of 5 gallons is recommended. If you plan to build a community fish tank and want to add a large number of Freshwater Crabs or fish then a larger tank will be needed.


The ideal water temperature for Crabs is in the range of 72 to 82°F. Depending on the specific Crab types this can slightly vary.

Water Hardness and PH

The pH should be in the range of 7.5 to 8.5 and water hardness between 8 to 12 dKH.


The lighting conditions of Freshwater Crabs will depend upon the type. Standard lighting conditions will do for most but some like Thai Micro Crabs prefer a darker environment. Adding floating plants and lots of hiding places can help to replicate the dark lighting conditions for That Micro Crabs.

Tank Substrate 

For Freshwater Crabs a sand substrate is recommended. Sand allows the Crabs to burrow and hide. Using gravel is not recommended as it is hard and will prevent the Crabs from burrowing and hiding. Gravel can damage their legs and claws.


Crabs need a lot of hiding places inside the tank. You can create hiding places by adding decorations like plants, rocks, caves, treated driftwood or seashells. 

Before adding plants make sure to check the compatibility of your Crab type with plants. Some like the Red Clawed Crab are known to destroy living plants. Tanks that have Red Clawed Crabs should not have living plants, but plastic ones seem to be fine.

Tank conditions

Before introducing any Freshwater Crabs to a new tank, make sure to properly cycle the water as it will help to promote the growth of beneficial bacteria.

A few Crab types like Fiddler Crabs need brackish water. Brackish water is referred to water that has a higher salinity level than freshwater but less than seawater. To get the correct salinity level in your tank, you will need to add a teaspoon of marine salt for every gallon of water.

Tank Maintenance 

The water temperature, pH and the level of dissolved organic compounds should be measured daily. Crabs cannot tolerate rapid changes in water conditions, so maintaining consistent water conditions is important.

A 10 to 25 percent water change should be performed once every month. The filter media should be cleaned once every month to ensure they work efficiently. 

Any new inhabitants should be introduced gradually to the tank. New inhabitants can feel stressed which can cause diseases that can affect existing aquatic organisms inside the tank, including Freshwater Crabs.

thai micro crab
Freshwater Crab

Best Tank Mates for Freshwater Crab

The tank mates that you can keep will depend upon the type of Freshwater Crab and the water conditions the Crab needs. Most crabs need freshwater, but Fiddler Crabs need brackish water which most freshwater fish cannot live in. 

The only tank mates that can handle brackish water for Fiddler Crabs are:

For Pom Pom Crabs ideal tank mates are: 

Pom Pom Crabs should only be kept with fish species that are not aggressive and will not eat them. These Crabs are also opportunistic eaters and should not be kept with very small fish, crabs or shrimp as they will eat them.

For Thai Micro Crab ideal tank mates are:

Avoid keeping Crabs with larger aggressive fish species like Cichlids, Goldfish, Angelfish and larger Catfish.

Many Freshwater Crabs are also known to eat snails so avoid adding snails to your tank.

Health Issues

A healthy Freshwater Crab will be active and have bright coloration on their exoskeleton. While crustaceans like Crabs are less prone to getting infected with diseases, some commonly found diseases are:

Loss of Appendage

Loss of Appendage is a disease in which the Crab loses its foot or claws. There can be several reasons for this, the most common being fighting between crabs or with aggressive fish. The disease is not fatal as the Crabs will normally regrow the lost foot or claws when they molt. You can add iodine supplements when the Crabs are molting as it will help them in the process.

Shell Disease

The disease causes degradation of the exoskeleton of the Crabs which leads to lesions of different sizes. Shell disease is common in all species of crustaceans and is mainly caused by bacteria or fungi. In the initial stages, the disease is not fatal but if it continues growing, the disease can cause problems like difficulty in molting and sometimes can even result in death. The rate of the disease in Crabs is low but poor water conditions can act as a catalyst to increase the likelihood of the disease.

Freshwater Crab - pom pom crab
fish flakes

Feeding Freshwater Crab 

Freshwater Crabs are omnivores and should be fed a mixture of plant and animal-based diets. In the wild they will generally graze feed all day, but in your aquarium you only need to feed them once a day. In the wild they generally feed on smaller crustaceans, insects, fish and plant matter. Some also occasionally snack on algae.

In a captive environment they should be given freeze-dried, low-grain/no grain pellets or flakes. You can also give them frozen foods or live food like bloodworms and brine fish.  Plant-based food like algae wafers, blanched peas and zucchini should also be given to them. As mentioned before, Freshwater Crabs love to snack on snails so you can occasionally feed them snails as well. 

Feeding a well-balanced combination of plant and freeze-dried foods will keep your crab healthy. When giving them food, ensure that the food sinks to the bottom of the tank. This will prevent the food from being eaten by fish and other freshwater organisms in your tank. If you have a larger tank you can use a Shrimp Feeding tube. This will ensure the food reaches the bottom of the tank without being eaten by others in the tank. 

If you use a feeding tube the crabs will know where their food is, and you will be able to see how much they are eating. You can feed them more or less, depending on how much food you see where the tube drops the food.

One more important thing to remember is to thaw any frozen food, before giving it to them.

Most Freshwater Crabs also need calcium supplements. You can make sure they get enough by adding cuttlebone (a mineral bar typically used for birds) inside the tank. It’s best if you break it up into smaller pieces or even grind it up for them. You can also add calcium supplements directly to their food. The calcium supplement helps them in molting and also in the formation of their exoskeleton. If you want them to have a healthy shell and be able to molt easily, make sure they have all the calcium they want.

Related Questions:

How do Freshwater Crabs molt?

Molting is the process of shedding the exoskeleton and almost all crustaceans molt. Crabs molt by cracking open the shell from the back and come out in a soft shell covering. While molting the Crabs may sometimes lie still on their back. Many fish tank owners can get concerned about this behavior but it is normal for them to do this when they are molting. If you find your Crabs lying on their back, make sure to check if they are molting before thinking they are sick. Crabs generally burrow or hide when they are going to molt. They are most vulnerable during their molting period. After molting it takes some time for them to grow back their hard exoskeleton which can make them an easy target for predators.

My Crab has missing legs and claws, what should I do?

There is no need to worry because the Crabs are capable of regenerating their missing claws and legs when they molt. If you have purchased a Crab with a missing leg or claw, wait for a few molting periods. The claws or missing legs should grow back fully after they molt a few times. To help them in the process you can add iodine supplements to your tank as it will help them in molting.

Can Crabs Swim?

For most Crabs, walking sideways is the main way for them to get around but some crabs, like the Blue Crabs can swim. These belong to a category called “swimming crabs.” They have their last row of legs modified into a paddle, which aids them in swimming through water.

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