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InvertebrateBrackishFreshwaterIntermediate

Rainbow Crab

Cardisoma armatum

The Rainbow Crab is a strikingly colorful, semi-terrestrial crab from West Africa. It requires a spacious paludarium with deep burrowing substrate and fresh to brackish water access for survival.

Taxonomy

Class:Malacostraca

Order:Decapoda

Family:Gecarcinidae

Genus:Cardisoma

Species:Cardisoma armatum

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Water Temperature

22 - 28 °C

pH Value

7.2 - 8.2

Water type

Brackish / Freshwater

Invertebrate type

Marine crab

Adult size

15 cm

Minimum group

>= 1

15 - 25 dGH

8 - 12 dKH

TDS

305 - 495 ppm

Ecological role

Scavenger

Species description

Geographical Origin and Habitat: This species is native to the coastal regions of West Africa, ranging from Angola to Senegal. It inhabits mangrove swamps, muddy estuaries, and coastal forests. It digs deep burrows in moist soil near the shoreline, requiring access to fresh or brackish water to moisten its gills, while spending most of its time on land.

Taxonomy: Belongs to the family Gecarcinidae and the genus Cardisoma. Cardisoma armatum is a terrestrial crab that has adapted to breathe air using modified gill chambers, which must be kept moist. It features a robust exoskeleton designed for land locomotion and foraging.

Social Behavior: Highly territorial and aggressive toward conspecifics and other crabs. They defend their burrows aggressively using their large claws. It is a nocturnal digger, spending daylight hours inside its burrow. If threatened, it will quickly retreat or display its open claws in a defensive posture.

Coloration and Sexual Dimorphism: Exhibits striking coloration: a dark purple to blue carapace, red or orange walking legs, and whitish-yellow claws. Males possess one claw that is significantly larger than the other (heterochely). Females can be identified by their wide, rounded abdominal flap used to carry eggs.

Care, breeding and tankmates

Tank Setup: Requires a paludarium or terrarium measuring at least 80x40 cm (32x16 inches) for a single crab. The enclosure must be split into a land area (60-70%) and a water area. The land area should have a deep substrate of at least 15 cm of damp sand or coconut fiber to allow for burrowing. Secure lid is mandatory.

Diet and Feeding: Omnivorous and detritivorous. Offer a varied diet including fresh vegetables (carrots, peas, zucchini), fruits (apples, bananas), dried leaves, shrimp pellets, and protein sources like crickets, mealworms, or small pieces of fish. Calcium supplements are crucial for successful molting.

Water Quality: The water section can be fresh or brackish (recommended, specific gravity 1.002-1.005). Keep air and water temperatures between 24°C and 28°C (75-82°F). Install a small filter in the water portion to manage waste, as they frequently carry food into the water and pollute it.

Compatibility and Tankmates: Must be housed alone. Keeping multiple rainbow crabs together in a standard aquarium will lead to territorial fights, limb loss, and mortality. Do not keep fish in the water section, as the crab is an opportunistic predator and will catch them at night.

Aquarium Breeding: Captive breeding is extremely difficult and virtually impossible in home setups. In nature, females carry eggs to the ocean to release them into saltwater. The larvae undergo several planktonic marine stages before metamorphosing into terrestrial crablets.

Risks and Diseases: The primary health risk is a failed molt (ecdysis), which is often caused by low humidity, lack of dietary calcium, or stress. Provide a secure, undisturbed hiding place during the molting process. Mold or bacterial infections can occur if the substrate is allowed to become swampy.

Geographic Origin and Distribution

This species is native to the coastal regions of West Africa, ranging from Angola to Senegal. It inhabits mangrove swamps, muddy estuaries, and coastal forests. It digs deep burrows in moist soil near the shoreline, requiring access to fresh or brackish water to moisten its gills, while spending most of its time on land.

Origin

North AmericaAfrica and Madagascar

Invertebrate profile

Diet: Omnivore
Ecological role: Scavenger
Shock sensitivity: Medium
Calcium and minerals: Medium
Molting: Yes
Reproduction: Oviparous
Compatibility & tankmates: Species only

SeaLifeBase

Window to the official scientific data of the species

Data synced on: 06/15/2026

Scientific Parameters & Models

Resilience: High (less than 15 months)

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Species description

Care, breeding and tankmates