Emerald Crab Care And Breeding Guide

When looking for an aquarium cleaner, the Emerald Crab is one of the best sea animals to shop for. Considered a superb algae eater, this crab is also well known for eating up any remnants after feeding the tank fish.

Appearance of Emerald Crab

Emerald Crab

The emerald crab is named after its colorful yet distinct appearance. The overall body color is a shiny emerald green. It is a few inches in diameter (1.5-2inches) and has hairy legs punctuated with powerful claws. The body is almost flat. A quick glance would give one the impression that it is the bubble algae. On the contrary, the later is a favorite delicacy of the emerald crab.


The crab is an original inhabitant of the Caribbean Sea, with some found in The Gulf of Mexico. Notoriously known for clearing an algae formation, this sea animal is a darling after fish have fed. Most hobbyists who have issues with cleaning up a tank after fish have had their meal are likely to find it an ideal choice. It literally cleans the tank and one may not be obliged to clear any leftovers that are likely to make the aquarium smelly.

In its native habitat, Mithraculus Sculptus, as it is scientifically referred to, is known to be nocturnal. At daytime it prefers to hide in caves and crevices. It comes out at night to scavenge for leftovers and grab any algae it is likely to chance upon. When it gets used to a tank however, it may outlive its shyness and come out of its hiding during the day.

Tank Requirements

Being a tank cleaner with minimal special needs, it often survives most tank conditions. However, the following conditions may make its existence more comfortable.

A small sized animal like the emerald crab will survive in a big, medium or small tank. Naturally, it is a cleaner that is stocked with other fish. Disclaimer though; there are some fish that are likely to gobble it up and these should not share a tank with it.

Temperatures of about 75-80 Fahrenheit would be very ideal. A pH of 8.4- 8.4. Calcium 420-440 PPM, Magnesium of 1260-1350, Alkaline of 8-9.5 DKH, Nitrates below 10 PPM, Phosphates below 10 PPM . The water chemistry may be raised gradually as it helps create ideal conditions for algae growth. When phosphate levels go up to 10, it is time to make a water change.

Provide live rock so that they find a suitable condition for them to forage into. As a way of ensuring the environment remains friendly to it, dosing pumps may be provided. This will ensure the levels of dosing in the tank are kept constant. Of course some hobbyists do this manually but it is hectic. The pump makes this work easier. Sand and gravel are another necessary addition to fulfill all the tank requirements.


Crabs are by nature scavengers that feed on leftovers. They eat anything from meaty foods to bubble algae in the aquarium. They also enjoy leafy foods. To get rid of algae formation in the aquarium, emerald crab will be of great service. Other foods to help supplement its diet include:

  • Live micro algae
  • Nori or sea-weed could also be a delicious dish to the crab
  • Mysis shrimp is another delicacy that can be added to its diet
  • Formula one fish pellets. Small ones for a start. They are kept in nitrogen bags. This ensures they are soft and easy to digest. If garlic is added to them, the crabs are able to be disease resistant.
  • Krill could be added to the diet too. It enhances the green shiny color.
  • Spirulina and plankton could be added as well.

Most hobbyists assume that since the crab is a cleaner, it does not need a special diet. This is not so. Apart from the remnants after the other tank-mates have fed, supplement diet is a necessity. This way, the crab does not seriously interfere with the corals. As a matter of fact, the crab has an affinity for small fish. When keeping it with tank-mates, do not keep the very tiny fish with it. The powerful claws can disrupt the body make-up of most types of fish.

Other important information for a hobbyist:

One crab is enough to take care of a tank. There is no need to stock many of them in a single tank. As much as they feed on algae, a big formation of it may not be eaten up successfully. In case there is a huge build up, it will call for manual removal and setting right water conditions that will not favor lots of algae growth.

Crabs shed off their exoskeleton as they age. Once the outer skin is shed off, the remnant is a picture of the real crab. One may think the crab is dead while it will be hiding under rocks or crevices in the tank. It is important to remove whatever is left behind as it may prevent the build-up of nutrients in the aquarium. Remember they are scavengers and will gladly feed on the dead fish as well. This should not appear strange to a first time hobbyist.

Larger fish find them delicious and may pry on them. When selecting tank-mates, be sure only small friendly ones are in the tank. When kept with other fish, keep a close eye on the tank because they may attempt to claw away part of some fish. While they often attack fish when hungry, there are times when supervising their movements around other fish for a few weeks is necessary.


Not much is recorded about breeding the emerald crab in captivity, but there are always first times. Differentiating males from females is difficult. When planning to spawn them, collecting a variety of the crabs and placing them in the same tank can create an opportunity for breeding.

Some hobbyists have reported observing two crabs locked in something like a tight embrace. This means that even in captivity, there is a likelihood of mating.

Emerald crabs are a necessity for keeping the tank clean. Taking care of them can be a beautiful experience because they have simple needs.

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