Bad Experience with Emerald Crabs

[gbose]

I recently re-built my saltwater tank, with Live Sand, Regular Black Sand, Liverock. I transplanted my 3 tube anemones, Rock Flowers and Coral plus a Serpent Star. I added an Emerald Crab; bad move!

The tank looked and measured fine. But as I added fish, they each disappeared in a couple of days. I tried re-cycling the tank and still lost fish. I removed the Serpent Star - no good. Then I realized it was the Emerald Crab; this was confirmed when I saw him attacking a Duncan and (amazingly) Zoas. It took quite a while to find him, hiding in a rock, but I get him and re-homed him.

I've got a firefish goby in there and (fingers crossed) he's still alive on the fifth day.

No more crabs, ever!!

 

[exnisstech]

I've kept emerald crabs for years and have never lost a fish to one.

 

[MajorDad74]

This is an odd circumstance. Maybe it had rabies……….

 

[Thales]

They are fine, unless they aren't.

 

[Ef4life]

Emerald crab are kind of known to mess with zoas and other corals, usually they don’t hurt or bother them too much, but thy could. But killing fish that’s a first for me, not saying it’s not possible, but seems unlikely unless it’s a huge crab or not an emerald

 

[revhtree]

I’ve never had issues with emerald crabs that I’ve confirmed at least. Mostly good!

 

[slingfox]

I have had multiple emerald and pithos crabs. Zero issues with each. They help keep the tank clean and fun to spot.

 

[Bryman]

IME the male emeralds start going rogue once they get to a certain size. I had one that took up toppling live rock as a hobby. I couldn't believe he was able to move such big rocks until I saw him do it. Another male took a liking to my healthy frogspawn out of the blue one day and started going to town. Never had any issues with the smaller clawed females though.

 

[BryanM]

My emerald nipped at corals, and had to go.

Almost every thing I've read says crabs generally only feast on fish that are already on their way out.

 

[D'sreef]

Make sure it's an emerald crab. Alot of places sell emerald crabs, but that's not what they are. If it's has brown or black tips on its claws get rid of it.

 

[BonnieB]

I recently re-built my saltwater tank, with Live Sand, Regular Black Sand, Liverock. I transplanted my 3 tube anemones, Rock Flowers and Coral plus a Serpent Star. I added an Emerald Crab; bad move!

The tank looked and measured fine. But as I added fish, they each disappeared in a couple of days. I tried re-cycling the tank and still lost fish. I removed the Serpent Star - no good. Then I realized it was the Emerald Crab; this was confirmed when I saw him attacking a Duncan and (amazingly) Zoas. It took quite a while to find him, hiding in a rock, but I get him and re-homed him.

I've got a firefish goby in there and (fingers crossed) he's still alive on the fifth day.

No more crabs, ever!!

Send the murderer to sump prison like I did!

 

[Gumbies R Us]

I’m curious, do you have photos of the crab?

 

[Mr. Mojo Rising]

Its not the crab IMO, fish can easily swim away from crabs, crabs can't swim.

The comment that you tried to "re-cycle" the tank is a red flag to me, what would prompt you to think this and how did you re-cycle the tank? Are you testing your water?

Fish dying while inverts are fine often points to fish disease, or poor acclimation for the fish. LFS keeps salinity of fish much lower than we do, invert tanks are maintained at the proper salinity. So I think either disease or acclimation issue, but the crab is not one of my suspects.

 

[gbose]

Emerald crab are kind of known to mess with zoas and other corals, usually they don’t hurt or bother them too much, but thy could. But killing fish that’s a first for me, not saying it’s not possible, but seems unlikely unless it’s a huge crab or not an emerald

It was big, but not huge. I wondered if it was not a real Emerald; are there similar species?

 

[gbose]

IME the male emeralds start going rogue once they get to a certain size. I had one that took up toppling live rock as a hobby. I couldn't believe he was able to move such big rocks until I saw him do it. Another male took a liking to my healthy frogspawn out of the blue one day and started going to town. Never had any issues with the smaller clawed females though.

How do you tell the females from the males?

 

[BZOFIQ]

It was big, but not huge. I wondered if it was not a real Emerald; are there similar species?

Snap a pic, there was a thread few days back with same issue - turned out it was NOT an emerald crab.

 

[gbose]

Make sure it's an emerald crab. Alot of places sell emerald crabs, but that's not what they are. If it's has brown or black tips on its claws get rid of it.

Interesting. What are the ones with Brown or black claws?

 

[BZOFIQ]

Interesting. What are the ones with Brown or black claws?

Let's just say emerald crabs done have brown or black claws.

Here is what the emerald looks like

 

[BZOFIQ]

I have had multiple emerald and pithos crabs. Zero issues with each. They help keep the tank clean and fun to spot.

That's spot on the experience I have. Bring them from FL every time I go.

 

[gbose]

Its not the crab IMO, fish can easily swim away from crabs, crabs can't swim.

The comment that you tried to "re-cycle" the tank is a red flag to me, what would prompt you to think this and how did you re-cycle the tank? Are you testing your water?

Fish dying while inverts are fine often points to fish disease, or poor acclimation for the fish. LFS keeps salinity of fish much lower than we do, invert tanks are maintained at the proper salinity. So I think either disease or acclimation issue, but the crab is not one of my suspects.

Mojo,

I lost each fish within 2-3 days of putting it in. I had my water tested, and it was 0% on Ammonia, Nitrites and 2 PPM Nitrates; I wondered about the low Nitrates, as I'd expect more from a cycled tank. But my coral and inverts (crab, snails, serpent star) seemed fine. I noticed I was getting lots of brown gunk on the sides of the tank; I wondered whether the problem was that my tank had not properly cycled. So I put in bottled bacteria, plus filter material from my LFS. That's what I mean by 're-cycled'. It did not work.

The fish I got all went into the rocks at night. The crab lived there; I suspect he ambushed them in their sleep.

Additional reason to blame him: I never found any traces of the missing fish. Almost like something ate them up....