Unidentified crab

Nitheesh H N · Nov 18, 2017

I recently got live rock into my aquarium. There was no activity or any sign of any critter for the first few days. On the 6th day, I noticed a random crab hiding under my rock. See pics attached.

Is this guy of any danger to my system? The tank is a FOWLR with 2 hermit crabs and 3 anemones . But I intend to add corals eventually.

aKlevans · Nov 18, 2017

Not sure, but black claws are not usually a good sign. Do you think that you could get it out for a better id?

kireek · Nov 18, 2017

aKlevans said:
Not sure, but black claws are not usually a good sign. Do you think that you could get it out for a better id?

I agree.That is probably a Xanthid crab of some sort.You could try matching it up with one of the pictures in this link.
http://www.wildsingapore.com/wildfacts/crustacea/crab/xanthidae/xanthidae.htm

Nitheesh H N · Nov 18, 2017

aKlevans said:
Not sure, but black claws are not usually a good sign. Do you think that you could get it out for a better id?

It was hiding under a large rock when I spotted it. In the time since I uploaded this thread, it's moved to another spot and I can't find it anymore.
It clearly did have black claws though.

kireek said:
I agree.That is probably a Xanthid crab of some sort.You could try matching it up with one of the pictures in this link.
http://www.wildsingapore.com/wildfacts/crustacea/crab/xanthidae/xanthidae.htm

It does look like the rock crab in the link you shared. Same body colour and claw colour.

Does this crab attack fish? I ask because three of my clowns have had their tail fins damaged in the week since the rock was added. There's been no sign of fighting among the clowns.

Nitheesh H N · Nov 19, 2017

Update:

Spotted the crab once more in between the rock structure. I think kireek was right. It looks very similar to the rock crab mentioned in the article shared.

I think I'll have to remove it the next time it shows up out of the rock.

Pics are not of the best quality but you can see it there.

DSC reef · Nov 19, 2017

If the crab hides in a rock then try to remove it and leave it out of the water for a bit. That should get him to come out. Good luck., he needs to go.

Nitheesh H N · Nov 19, 2017

I tried to reach in. The problem is that he's in between the rock structure and I cannot think of any way to remove him without the entire structure falling apart, which I'm trying to avoid as my carpet anemone has made itself comfortable on the rocks.

The crab seems to prefer the dark a bit more. So going to turn off the lights and wait for him to show up outside the rock structure. Should hopefully be able to catch him then.

aKlevans · Nov 19, 2017

Nitheesh H N said:
I tried to reach in. The problem is that he's in between the rock structure and I cannot think of any way to remove him without the entire structure falling apart, which I'm trying to avoid as my carpet anemone has made itself comfortable on the rocks.

The crab seems to prefer the dark a bit more. So going to turn off the lights and wait for him to show up outside the rock structure. Should hopefully be able to catch him then.

Also, you can use a red flashligh to see in the dark., they cannot see red light o it will not scare them.

sagee · Nov 19, 2017

Nitheesh H N said:
I tried to reach in. The problem is that he's in between the rock structure and I cannot think of any way to remove him without the entire structure falling apart, which I'm trying to avoid as my carpet anemone has made itself comfortable on the rocks.

The crab seems to prefer the dark a bit more. So going to turn off the lights and wait for him to show up outside the rock structure. Should hopefully be able to catch him then.

You might have to get some kind of skewer or something thin like that you can fit in the rocks to stab and kill it unfortunately.

Nitheesh H N · Nov 20, 2017

He's a small critter (about the size of a small coin). Gonna wait for him to come out of the rock. Will probable skewer him then. Don't want to risk having my rocks fall down on my anemones.

Really grateful for the help though.

kireek · Nov 21, 2017

I wish I could take him off your hands for you.To be realistic, the rocks will probably need to be removed in order to catch it.On another note you may want to get a picture of your clown fish and create a post in the fish disease forum. https://www.reef2reef.com/forums/fish-disease-treatment-and-diagnosis.771/ .Just to be certain that they are well and not suffering from a ailment.

Jl330 · Nov 21, 2017

You could build a coke bottle trap and try to catch him that way.

flsalty · Nov 21, 2017

Personally, I wouldn't sweat something like that in a FOWLR. I had a decent sized mud crab in one of mine. The only thing he ate was a small blue crab I put in there. Other than that he just kept the tank clean. He never bothered the gobies.

Oldsalt01 · Nov 21, 2017

Wait until dark, take a small hunk of shrimp, tie it with a piece of monofilament or thread, drop it into the tank near where u think it lives, and ...... wait. When he comes out, and he will, he'll glom onto the shrimp and you can gently (slowly) lift him out of the tank without disturbing the rock. This has worked for me several times over the years to catch small rock crabs, gorillas, and even a mantis shrimp. I gently bring a net in under the crab as I lift JUST in case he lets go, but they usually hang right on. And yes, a red light will let you see it with freaking it out.