Keeping crab

Aquarium crabs can be kept for various reasons. Many species are great scavengers and can help you to keep up the water quality, since they will consume dead and dying organic matter, e.g. left over fish food and decaying plants. Others are kept chiefly for their good looks and fascination behaviors, such as the Red-clawed crab and the Fiddler crab.

The term aquarium crabs is often used to describe a wide range of different aquatic creatures, but it is actually only the members of the infraorder Brachyura in the order Decapoda that is considered true crabs by biologists. The true crabs have five pairs of walking legs, but the first pair has developed into a pair of claws. Most true crab species have flattened shells, and the abdomen is usually folded under the cephalothorax (the first major body section).

As mentioned above, a lot of species that do not belong to the infraorder Brachyura is still sold as aquarium crabs, since they resemble crabs by being short crustaceans with thick exoskeletons and ten legs. In this group of “un-true” aquatic crabs you will for instance find King crabs, Porcelain crabs and Hermit crabs. King crabs, Porcelain crabs and Hermit crabs are all examples of specimens found in the infraorder Anomura. Just like the infraorder Brachyura, the infraorder Anomurabelongs to the order Decapoda. Unlike the true crabs found in Decapoda, the Anomura species do however have their last pair of legs hidden inside the gill chamber, where they are used to clean the gills.

Another species that is often counted among the aquarium crabs is the Horseshoe crab, even though it is actually more closely related to spiders than crabs. It belongs to the family Limulidae and the genus Limulus. Provide your Horseshoe crab with a water temperature between 72 and 78° F, a pH between 8.1-8.4 and a dKH between 8 and 12. It is a peaceful saltwater crab and is therefore popular in reef aquariums.

As mentioned earlier, one of the most popular aquarium crabs among the species kept for their beauty is the Red-clawed crab. If you want to keep this crab, you must provide it with surface access. It will prefer a half-filled aquarium with brackish water and can be kept with other brackish species, as long as the crab won’t consider them as food or vice versa. It will survive in freshwater, but brackish water is a better choice. The water quality should be hard and alkaline. Make sure that the lid is tight-fitting, since the Red-clawed crab will otherwise escape from the aquarium. Feed your Red-clawed crab dry food and vegetable matter. You don’t need a huge aquarium to house this crab, since it grows no larger than 7 centimeters (2.7 inches).

If you have problems with extensive algae growth in your aquarium, you add some of the smaller aquarium crabs to combat the problem. Two popular species used for algae control are the Scarlet Hermit Crab, the Dwarf Red Tip Hermit crab and the Dwarf Zebra Hawaiian Hermit crab. Such aquarium crabs are often sold combined with snails that will consume algae as well.