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Emerald crab reproduction

Emerald crab reproduction

(mithraculus sculptus or mithraculus forceps)

I present to you an excellent candidate to introduce you to marine reproduction. The size of the crab does not matter, as they start breeding around six months of age. So normally all the emerald crabs you see on the market can breed.

 First step: the breeding tank

Immediately forgot the reproduction in your main tank. The emerald crabs available on the market are small and do not produce hundreds, even thousands of larvae. A few dozen at best! If you do not want the larvae to be eaten by your fish, it is better to isolate the breeding pair in a small aquarium, a 5 gallons tank does very well with a few live rocks.

Second step: obtaining a breeding pair

Fortunately, it is extremely easy to determine the sex of crabs in this family without having to observe the shape of the tail. The female has small claw and the male has large claw. As simple as that! Only one breeding pair per aquarium.

If you want to determine the sex from the tail, here is a photo of a male:




And here is the photo of a female:


Third step: reproduction.

In summary: wait, feed the adults well and if you are lucky you will have the chance to observe the mating. Once a week, capture the female and check for eggs. To do so, raise the tail. If there are eggs, there will be a black mass under the tail. If the female has eggs, I suggest isolating her in a small container of about 1 gallon. I use a small air pump and a small live rock in the container. Hatching takes place about 4 to 5 days after the eggs are laid.


Fourth step: Collect of the larvae.

Now that the female is isolated in a small tank, it will be easier to collect the larvae. The birth takes place at night, about 1 to 2 hours after the lights are closed. The larvae look like little balls hopping in the tank and for good reason, the body is spherical with a tail that folds under the body. The larvae are about 1 mm wide no more.  So every night I close the air pump. Every 15 minutes, I check the eggs for hatching. If the hatching takes place, I remove the small piece of live rock as well as the female. But before removing the female, I check that all the eggs have hatched.

Then, using a small pipette, I remove the larvae, one by one.

 Fifth step: The growing tank.

As the larvae are very small, I recommend taking a round bowl like for ice cream and ideally white to see the larvae well, which is very important. Ideally, have two identical container. I will explain why later! No need to fill up with water, half a gallon is enough. Then an air pump with a rigid tip, no air stone. About 1 to 1.5 bubbles / second. When the larvae are born, you have 24 hours to add freshly hatched artemia. The ideal is to add them from birth, but not everyone hatches artemia every day.

Sixth step: Maintenance and metamorphosis.

Now that the larvae are in a tank with artemia, 24 hours after hatching, with a pipette, count the larvae by placing them in the second tank. The larvae have a lot of black such as the eyes and the digestive system. If the container used is white, it is easier to see the larvae. Inspect the debris at the bottom. Using a microscope helps a lot. Sometimes the larvae land on the bottom, but are not dead. Only a microscope can confirm this. When all the larvae are removed, collect the artemia to feed your fish tanks, empty and rinse the tank well to remove all the detritus. The washed tank can be used the next day. Added freshly hatched artemia to the tank containing the crab larvae. This step must be repeated every day. This step removes dead larvae, rotting nauplia, uses clean water, and most importantly reduces bacteria and other unwanted material that could have been picked up by mistake with crab larvae.

5-7 days after hatching, a small pair of claw will appear. This stage is what we call "megalope".

This is the final stage before the metamorphosis. This stage lasts approximately 2 days and during this stage, the larva does not feed. It is therefore essential that the larva has eaten well during the first days.

At this stage, I use a third tank to contain only the megalopes. If the megalopes are not isolated, when the larva metamorphoses, the crab will hide in the debris. So by removing the debris every day you will make your life easier to find the crabs which are a little less than 1 mm wide for the shell. Using a microscope becomes essential to find the crabs.


Seventh step:

Place the small crabs in a new container with live rock. One day, you will have the chance to see them again, about 3 months post metamorphosis. Ideally, use live rock that only contains bacteria to filter water. Crabs are extremely small, so you don't want predators such as small worms, amphipods, etc..

After several trials I temporarily stopped this species because the adults are very ferocious during reproduction and death is often expected.