My emerald crab - fish killer??

I have 2 emerald crabs in my tank. One male, one female. And yes I'm positive on that...they had "some fun" about a week ago.

Yesterday all was good in my tank of 4 green chromis, 2 emerald crabs and some snails. Today total war broke out. Or at least it seems so.

Casualaties:
1 snail - KIA
1 green chromis - KIA
1 green chromis - MIA

I found the larger of the emerald crabs munching on one of the green chromis. And he devoured him. Every bit of him as near as I can tell. I watched the whole thing...it was quite sad. Now I never saw the crab attack the fish but his claws were all uummm...if it was land, he'd have blood on his claws.

The snail had his slimy part of body all gone but the the body part inside his shell was still there when I pulled him out.

I moved the live rock away from where one of the chromis liked to stay at times and he is nowhere to be found. I'm guessing he's also become a meal of the large crab.

Now the smaller of the 2 crabs is just doing her normal thing of munching algae on the one piece of live rock that she likes.

Now I have to decide if I should take male back to the LFS since he's obviously become so aggressive.

 

Do you have any pictures? Emerald crabs are not supposed to be aggressive at all, it's possible you may have a different type of crab or a hidden critter in your live rock.

 

Ever see crabs in the wild? They will eat anything!....lol
Is it possible that your fish died and the crabs being scavengers are eating the dead and may not have killed the fish at all? Or is the battle something you witnessed and are sure that the crabs killed the fish?

~ kate

 

I have a pic of him on my home computer. I'll post it when I get home from work. I didn't see any actual battle, just the crab with claws on a dead fish.

I am bit surprised to see him being this aggressive. It maybe that there isn't much algae left to eat.

 

The crabs will eat anything dead so that is what you are seeing there. They are quite the clean up crew. eeuuuu....

Must have been an awful sight to see. Are you sure the fish didnt die for other apparent reasons such as water conditions?

~ kate

 

The crabs will eat anything dead so that is what you are seeing there. They are quite the clean up crew. eeuuuu....

Must have been an awful sight to see. Are you sure the fish didnt die for other apparent reasons such as water conditions?

~ kate

I checked all my readings last night to verify my water is in good shape. Ammonia, nitrites and nitrates are all 0. PH is 8.4. Everything looks to be good. I even got my phosphates back down to 0 and the diatoms that I was dealing with last week are just about all gone.

 

You should check your liverock or whatever else you have in your tank. You probably have an unwanted guest hiding somewhere, possibly a mantis shrimp. I would agree with capekate they are just finding food. I used to drop a small part of a veggie wafter once in awhile when I had my emerald crab, so if you think they are not getting enough food you can always add some.

 

You should check your liverock or whatever else you have in your tank. You probably have an unwanted guest hiding somewhere, possibly a mantis shrimp. I would agree with capekate they are just finding food. I used to drop a small part of a veggie wafter once in awhile when I had my emerald crab, so if you think they are not getting enough food you can always add some.

I've been looking for anything like that but haven't seen one yet. I did see a video last night on Youtube of a mantis shrimp taking out an emerald crab. It was quite the site to see!!

 

Yes I couldn't imagine an emerald crab fast or skiled enough to take down a chromis anyways. I'm thinking there is something in your tank. Could be interesting as to what it is. Mantis shrimp are quite cool, lucky I didn't get any in my tank.

 

For crying out loud. There has to be something else in the tank. My wife just called me and she can only find one fish now. It's looking like I may have lost another. That's 3 fish and one snail in 2 days.

 

Good chance there is since a snail and fish died, if it was just fish then maybe a disease but as far as I know I don't think snails transfer diseases to fish and vice versa. If you check your tank tonight don't forget to wear gloves and hopefully it's not a mantis shrimp, they can break glass.

 

Oh ya...I've reading up on them. Their striking ability is quite amazing.

 

yeah ouch.

 

Sorry to hear about all the probs you're having. BTW, I used to live in Acworth, GA. near Lake Allatoona off 41. Where bouts are ya if you don't mind sharing?

 

Sorry to hear about all the probs you're having. BTW, I used to live in Acworth, GA. near Lake Allatoona off 41. Where bouts are ya if you don't mind sharing?

I'm just off of Cedarcrest Rd in the Bentwater subdivision.

An update on what's going on. I talked to the LFS that I deal with and they brought up an important little fact. If it was a mantis shrimp, I'd be hearing a tapping sound as the work on the live rock. And I'm not hearing anything like that. And I didn't loose another fish. It just turns out he was hiding. Both of them were swimming around normally when I got home from work yesterday.

What the guys at the fish store think is that the temp is dropping too low at night. We've had a nice cold spell the last few days here in Atlanta. Last night it dropped down to 16F. I turned up the heater last night and the temp in the tank was 75.5 this morning. Normally it's around 76.

We'll see. So no more deaths since Tuesday.

 

Yeah it's always great to hear good news. That's reaaallyy cold for Atlanta I'm in Michigan and it's 16F this am. Sounds like you have a good LFS which is also good to hear. Standing by for pics

 

No more deaths. I just added a second heater and that appears to be helping in keeping the heat up where it needs to be.

Here is a picture of my crab. My son named him Mr. Crabs from Spongebob.

 

arent crabs known for eating fish? couldve swore that's kinda what they do. hence the reason why I would never get one...

 

arent crabs known for eating fish? couldve swore that's kinda what they do. hence the reason why I would never get one...

From what I'm told and can read, they're scavengers by nature. I did see a video of one on YouTube attempting to grab a passing fish but couldn't grab him/her.

Though this one did quite the job in devouring on of my fishes that I assume he found at the bottom of the tank.

 

That could be it, I usually keep my tank at a nice 80F year round.