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Marine Crab Care Sheet

Marine Crab Care Sheet

Developed with and approved by a qualified veterinarian.

marine crab

This care sheet covers a variety of marine crab species, including:

  • Emerald crabs
  • Decorator crabs
  • Sally lightfoot crabs
  • Arrow crabs
  • Blue leg hermit crabs
  • Red leg hermit crabs
  • Porcelain crabs
  • Pom pom crabs
  • Electric blue hermit crabs
  • Halloween hermit crab



Scientific name: Mithraculus sculptus, Camposcia retusa, Percnon gibbesi, Stenorhynchus sp., Clibanarius tricolor, Paguristes cadenati, Petrolisthes galathinus, Neopetrolisthes ohshimai, Lybia sp., Calcinus elegans, Ciliopagurus strigatus

Found all across the globe, marine crabs are crustaceans that can add a whole new element of interest and beauty to an aquarium. Some marine crabs have a joined outer shell while others reside in abandoned snail shells. Coming in various sizes and colors, some crabs can fit into tight crevices searching for detritus while others help rid aquariums of pests such as bristle worms or nuisance algae. Many shed or molt their hard exoskeleton or change shells as they grow. With their ability to walk sideways, diagonally, forwards and backwards, some marine crabs can reach speeds of up to 12 mph!  With a wide variety of species, there is sure to be a marine crab that benefits just about every aquarium.


Typical appearance and behavior 

  • Small blue leg and red leg hermit crabs make excellent first crustaceans for the home aquarium
  • Because they love to eat, they will spend a lot of their time looking for food
  • While some species are carnivores, most are omnivorous and will eat a variety of meat-based and plant-based foods Some crustaceans are known to eat small fish and invertebrates
  • Some crab species may become aggressive toward other species in smaller aquariums
  • Many species provide great natural algae, cyanobacteria and pest control
  • Some crabs can be escape artists 



Care Difficuty Beginner to intermediate, depending on species
Average Life Span Up to 8+ years with proper care, depending on species
Average Adult Size 1 to 12+ inches long, depending on species
Diet Omnivore and carnivore, depending on species
Minimum Habitat Size 10+ gallons, depending on species
Water Temperature 74-80°F
Specific Gravity 1.023-1.025



Habitat size

A minimum of 10+ gallons is recommended; however, water conditions can change rapidly in smaller water volumes. A larger aquarium is recommended for groups of marine crabs.

Building your habitat

  • Water health - Provide proper filtration to ensure optimal water quality to help maintain health. Slow to strong water circulation, based on species, should be provided to mimic water currents found in the marine crab's natural habitat. Stable water quality (pH, ammonia, nitrate, nitrite) and water temperature are critical to the health of aquatic life. If you are unsure of your water quality, bring a sample to Petco for free testing. The addition of a protein skimmer can aid with maintaining great water quality and high dissolved oxygen levels. An aquatic heater should be used to stabilize water temperature, ensuring it does not fluctuate more than 2 degrees in either direction in a 24-hour period. The specific gravity should remain stable. Do not allow specific gravity to fluctuate more than 0.001 in either direction in a 24-hour period 
  • Décor - Provide hiding places or caves, appropriate depth of substrate based on species and plenty of décor for marine crustaceans to protect themselves
  • Live rock can provide a natural food source while also enhancing biological filtration



A well-balanced marine crab diet consists of:

  • Sinking pellets, dry seaweed, algae wafers,  freeze-dried and frozen foods

Things to remember when feeding your marine crab:

  • Most crabs will feed off algae and excess food and debris in the aquarium but will also benefit from small daily supplemental feedings
  • Thaw frozen food before feeding


Marine crab care

  • Water care: Maintaining great water quality with regular water changes and adequate filtration is important to help keep your marine crab healthy
    • Daily: Check filter, water temperature and other equipment
    • Weekly: Test water quality at least once a week
    • Weekly to monthly: Change 10–25% of the total volume of water every 2–4 weeks, or as needed; change filter media monthly
  • Use of copper-based medications is toxic to crustaceans
  • The use of an iodine supplement can be beneficial during a crustacean's molting process
  • Crabs need adequate calcium levels to build their exoskeleton; ensure proper calcium levels are provided 
  • Avoid overcrowded conditions, which are a major cause of stress and disease 


Where to buy marine crab

Marine crabs are available for purchase at Petco online and in-store; availability varies by location. If visiting your local location, please call ahead to check availability.




Tank mates 

  • Clownfish
  • Damsels
  • Angelfish 
  • Blennies
  • Cardinals
  • Gobies
  • Butterflyfish
  • Tangs
  • Dragonets 
  • Dartfish 
  • Dottybacks 
  • Jawfish
  • Basslets
  • Foxface & Rabbitfish 
  • Reef-safe wrasses
  • Introduce new inhabitants to the aquarium gradually
  • Marine crabs are usually not compatible with mollusks, squid and octopuses 
  • Caution should be used when adding crustaceans to a tank that contains slow-moving aquatic life or aquatic life known to eat crustaceans



Signs of a healthy marine crab

  • Healthy appetite
  • Even coloring
  • Sleek, non-pitted shell and legs (applicable to certain species)
  • Free of parasites or disease

Red flags (If you notice any of these signs, contact your local aquatic specialist or aquatic veterinarian)

  • Loss of color or appetite
  • Spots or fungus on body
  • Erratic movements
  • Disfigurement
  • Missing limbs or antennae
  • Hermit crab not retreating into shell 
  • Hermit crab without a shell


Common marine crab health issues

Little is known about diseases that affect crabs. As long as environmental conditions and food supplies are adequate, marine crabs are fairly resistant to disease.

Health Issue Symptoms or Causes Suggested Action
Health IssueBody or surface erosion Symptoms or CausesPoor water quality; nutrient deficiency. Suggested ActionTest and treat water or perform a water change immediately; maintain proper diet; contact your local aquatic specialist or aquatic veterinarian.
Health IssueLoss of appendage or antennae Symptoms or CausesFighting between crabs or due to an aggressive fish. Suggested ActionWill usually regenerate; an iodine supplement can help with the molting process; contact your local aquatic specialist or aquatic veterinarian.



  • What do emerald crabs eat? Emerald crabs are opportunistic feeders and can be offered dried seaweed, sinking pellets, freeze-dried and frozen foods. 
  • How big do emerald crabs get? Emerald crabs can grow to 2.5 inches. 
  • How many emerald crabs can you house per gallon? Emerald crabs should be housed one individual per 10 gallons, as they can become aggressive with one another if adequate space and food are not provided.  
  • How long do emerald crabs live? Emerald crabs can live 4+ years with proper care.
  • What do decorator crabs eat? Decorator crabs are carnivores and should be provided meaty foods such as krill, shrimp and protein-based pellets. 
  • How big do decorator crabs get? Decorator crabs' size will vary based on species, but most kept in the home aquarium can grow 4–5 inches. 


Additional care sheets

Notes and resources

Ask a Pet Care Center partner about Petco's selection of products available for the care and happiness of your new pet. All products carry a 100% money-back guarantee.

Because all aquatic life are potential carriers of infectious diseases, such as atypical mycobacterium and salmonella, always wash your hands before and after handling your aquatic life or habitat contents to help prevent the potential spread of disease.

Pregnant women, children under the age of 5, senior citizens and people with weakened immune systems should contact their physician before purchasing or caring for aquatic life and should consider not having aquatic life as a pet.

Go to the Centers for Disease Control at for more information about aquatic life and disease.

The information on this care sheet is not a substitute for veterinary care. If you need additional information, please contact your veterinarian as appropriate.