Will an Emerald crab kill fish?

inigomontoya · 02/14/2012, 02:14 PM

I have 3 emerald crabs in my 260- one of which I have had for over a year in various tanks. He has been a good guy- eating away at algae even when in a frag tank I set up while transitioning to my new bigger tank, never bugged the coral. He has just gotten rather large for an emerald and similarly cocky.
We noticed him sitting on a rock a couple of weeks ago, picking little bits of algae off the rock, which always looks funny due to his size, picture a sumo wrestler with a bowl of sunflower seeds eating one at a time quickly with both hands. He was near our clownfishes' host coral and she started to buzz him. He stood up on his back legs and started waving his claws at her-actually chasing her off (hence, his nickname-Kong

).
I was moving a rock in the tank yesterday and noticed him doing the same to me- standing on back legs and both arms out waving them at me to chase me off. This made me wonder- I had recently put in a few new fish and two of the wrasses are missing. I know emeralds don't eat fish per se, but would they take one out if they felt threatened? Especially considering wrasses sleep in the sand. I have a decent amount of Lr and fish will just as likely disappear if they die versus being found floating, but I have nothing in there which would create foul play, made me wonder if he was a possibility or not.

RtReef · 02/14/2012, 02:21 PM

I don't think they do. I've had a few in my tank and never really saw any aggression, except for their territory.

sporto0 · 02/14/2012, 02:25 PM

Don't eat fish per se? Oh they can & will eat anything that is food, including fish, usually what happens is the crab gets a hold of the fish at night when they are hiding/resting. It may not happen for a while, but rest assured it will. I have a nasty Coral Banded Shrimp that has eaten several of my smaller fish. Good luck.

cbm369 · 02/14/2012, 02:32 PM

Crabs in general are opportunistic feeders. If the opportunity presents itself, they won't turn it down....

inigomontoya · 02/15/2012, 02:48 PM

Anyone actually seen an emerald get this aggressive? I know they can be territorial, but big difference in shooing something off and ambushing them in their sleep. The crab is wife's favorite and does add some personality to the tank. However, hate missing fish and can send him to sump if it looks like he is the most likely culprit. Just never seen anything more than a defensive wave off move. And like RTReef had only heard of them as being mellow (versus CBS which I have avoided for exact reason SportOO mentions)

Mr. Demeanor · 02/15/2012, 03:19 PM

It seems all crabs do the claw wave when they get bigger. I thinks its their version of giving you the finger. I had a good sized hermit that would backhand(claw) the fish when they tried to pick food away from him but he never went after one even though he was perfectly capable.

cjk76 · 02/15/2012, 03:42 PM

I would keep the crab and wait to see if the wrasses turn up. I had an emerald that I loved, but it started eating corals. Seriously, I saw it ripping apart an acan and picking at a leather. I never had a problem with emeralds and fish.

Even if the crab did eat the fish, they were likely dead before it got to them. Do you have anything else that would account for the wrasses being dead? A spike in Ammonia? an agressive fish?

ryeguyy84 · 02/15/2012, 03:54 PM

I've caught my emerald crab feeding on a fish but to his defense I think the fish died and he was doing his job of cleaning up. it was a flame angel that wasn't doing well for a few days.

davocean · 02/15/2012, 03:55 PM

Emerald crabs are fairly slow and don't have very big or strong claws.
If one got a fish I would be very surprised, and would guess that fish was very weak or sick.
Some say they suspect them at picking at corals, but I have had nothing but good luck w/ them, and I've had them take care of some pretty big valonia outbreaks.

insomniac2k2 · 02/15/2012, 04:01 PM

I cant imagine that an emerald would kill anything. Mine have always been very docile. Would it eat an already dead fish? Absolutely. It's doing you a favor!

insomniac2k2 · 02/15/2012, 04:03 PM

I have a big patch of pulsing Xenia that my emerald like to pick at now and then when its time to remind me to give him some seaweed. I find it very amusing. He's getting a lot of character these days.

When he's really hungry, he comes to the front of the tank and holds his claws out like he's trying to give me a hug. When i give him food, he snatches it up and dissapears back into the Xenia patch.

Quote:

Originally Posted by davocean

Emerald crabs are fairly slow and don't have very big or strong claws.
If one got a fish I would be very surprised, and would guess that fish was very weak or sick.
Some say they suspect them at picking at corals, but I have had nothing but good luck w/ them, and I've had them take care of some pretty big valonia outbreaks.

dadnjesse · 02/15/2012, 04:59 PM

Quote:

Originally Posted by davocean

Emerald crabs are fairly slow and don't have very big or strong claws.
If one got a fish I would be very surprised, and would guess that fish was very weak or sick.
Some say they suspect them at picking at corals, but I have had nothing but good luck w/ them, and I've had them take care of some pretty big valonia outbreaks.

Im not sue about weak claws, I had one fall on the floor when I removed a rock and when I picked him up he grabed a hold of my finger and I was bleading when he finally let go.

davocean · 02/15/2012, 06:15 PM

Quote:

Originally Posted by dadnjesse

Im not sue about weak claws, I had one fall on the floor when I removed a rock and when I picked him up he grabed a hold of my finger and I was bleading when he finally let go.

Well, I guess it depends on what you are comparing to, my hands are pretty callased, so I've handled them often w/out injury of any kind.
If OP were talking about a Coral banded shrimp or sally lightfoot or something of that nature, then I would suspect them in the event of fish losses, but generally speaking I would not suspect an emerald to take out a healthy fish.

inigomontoya · 02/16/2012, 11:01 AM

Thanks guys, this ties more into what I had read before on them- having not seen any truly suspect activity (just waving one off) I didn't think it likely, but I don't have anything aggressive in there nor any ammonia spikes or other water parameters. These wrasses were brand new additions so I will lean towards something pre-existing or other acclimation issues. I have 7 scissor tail gobys that sleep in the rock and if anyone was to be caught by an aggressive critter I would expect it to be them and they are all fine. To be clear I never saw him touch a fish dead or alive- just have a couple missing and with the aggression wanted to see if it was a possibility. Will keep an eye on him though.

cdsmith · 11/29/2013, 07:52 AM

I recently purchased a pistol shrimp watchman goby pair. They were doing fine until the pistol shrimp decided to make a tunnel under the rock where a large emerald was. Pistol shrimp gone soon after. Then last night my watchman decided to hide in that same rock for the night, this am I found the goby where he was last night but in the claws of the emerald, with his head gone.

Crna · 11/29/2013, 08:08 AM

We had an emerald in a BC14 that got pretty big really quickly. At least, he seemed really big in that little tank. He started getting cocky, and would reach out at the fish if they got too close. I started to get concerned that we were going to find him munching on my yellow clown goby, so back to the LFS he went. As too the claws, they are pretty tough to pull off of a rock!

devimik · 11/29/2013, 09:10 AM

I've had one Emerald in my 90g for almost a year. I've seen him do the waving thing and his claws are strong. I feed him nori using some long tweezers - he usually grabs the tweezers and it is hard to get him to let go. I don't think he could catch and kill a healthy fish and even if one was sleeping, he'd wake it up and it would swim away. Something in my tank has eaten a frogspawn coral and a torch coral. I believe it was the Peppermint shrimp, but I suppose it could have been the crab. My opinion is that the Emerald won't get your healthy fish, but I do agree that if the opportunity presented itself, it would eat anything.

Art13 · 11/29/2013, 09:55 AM

i've had 3 and all three of them went after my sps coral.

d2mini · 11/29/2013, 10:18 AM

Jeff, I've had lots of red mithrax which is basically the same thing. They do get big and brave for sure. But IME, they won't go after anything that isn't already dead/sick. I do end up removing mine once they get too big because they just annoy my corals too much. They pick at stuff and inadvertently remove polyps, knock stuff over, etc.

Trock577 · 01/15/2014, 12:22 PM

Quote:

Originally Posted by sporto0

Don't eat fish per se? Oh they can & will eat anything that is food, including fish, usually what happens is the crab gets a hold of the fish at night when they are hiding/resting. It may not happen for a while, but rest assured it will. I have a nasty Coral Banded Shrimp that has eaten several of my smaller fish. Good luck.

Coral banded shrimp go after fish. I had no idea. I was looking for my scooter blenny but could
Find him. Now i guess
I know what happened

mayjong · 01/15/2014, 01:21 PM

i think there may be a difference of experience due to the sex of the crab. males tend to get bigger and seem more aggressive to me.
females seem more passive...my .02

JB63 · 01/16/2014, 11:38 AM

I had an emerald with 3 chromis in a 12g once ... one minute the 3 chromis were swimming, the next, suddenly he's holding one and tearing it apart, one bite at a time.

Reeferz412 · 01/16/2014, 12:32 PM

No they are far too slow. I have owned emerald crabs for about 4 years and they eat anything that comes their way (algae, pellets, frozen food, flake, freeze dried) so I would assume that if you keep them well fed, they really have no need to go after fish. I have had a wrasse jump out and I placed it back but he was gone in the morning, emerald was on top of it and it was a pile of bones lol.

MellowReefer · 01/16/2014, 12:38 PM

Quote:

Originally Posted by mayjong

i think there may be a difference of experience due to the sex of the crab. males tend to get bigger and seem more aggressive to me.
females seem more passive...my .02

That's what I've heard on forums and from two LFS owners who gave me females. So far no problems and my bubble algae is under control (foxface probably helps a lot too though).

malcojo · 01/16/2014, 02:57 PM

I had banned mine to a 10 gallon remote fuge. I also had a Yellow Watchman Goby in there becaue he kept going into the overflow in my DT. I found the goby with a bloody face twice and now he is missing. I checked the foor and he didnt jump out, but I cant rule out going into the sump and through the pump...

My emrald got big and cranky quickly.

02/14/2012, 02:14 PM	#1
inigomontoya Registered Member Join Date: Sep 2010 Location: Houston Posts: 241	Will an Emerald crab kill fish? I have 3 emerald crabs in my 260- one of which I have had for over a year in various tanks. He has been a good guy- eating away at algae even when in a frag tank I set up while transitioning to my new bigger tank, never bugged the coral. He has just gotten rather large for an emerald and similarly cocky. We noticed him sitting on a rock a couple of weeks ago, picking little bits of algae off the rock, which always looks funny due to his size, picture a sumo wrestler with a bowl of sunflower seeds eating one at a time quickly with both hands. He was near our clownfishes' host coral and she started to buzz him. He stood up on his back legs and started waving his claws at her-actually chasing her off (hence, his nickname-Kong ). I was moving a rock in the tank yesterday and noticed him doing the same to me- standing on back legs and both arms out waving them at me to chase me off. This made me wonder- I had recently put in a few new fish and two of the wrasses are missing. I know emeralds don't eat fish per se, but would they take one out if they felt threatened? Especially considering wrasses sleep in the sand. I have a decent amount of Lr and fish will just as likely disappear if they die versus being found floating, but I have nothing in there which would create foul play, made me wonder if he was a possibility or not.

02/14/2012, 02:32 PM	#4
cbm369 Registered Member Join Date: Dec 2011 Location: South Carolina Posts: 242	Crabs in general are opportunistic feeders. If the opportunity presents itself, they won't turn it down.... __________________ 125g Fowlr - Basement 55g sump/fuge

02/15/2012, 03:55 PM	#9
davocean Registered Member Join Date: Nov 2005 Location: San Diego, CA Posts: 14,655	Emerald crabs are fairly slow and don't have very big or strong claws. If one got a fish I would be very surprised, and would guess that fish was very weak or sick. Some say they suspect them at picking at corals, but I have had nothing but good luck w/ them, and I've had them take care of some pretty big valonia outbreaks. __________________ There's a fine line between owning your tank and your tank owning you! Current Tank Info: SCA 120g RR Starfire, Tunze silence 1073.02 return, 40g sump w/ fuge, SWC Extreme 160 cone skimmer,Geismann reflexx 4xT5, 2x Panorama Pro LED strips, Vortech MP40QD

11/29/2013, 07:52 AM	#15
cdsmith Registered Member Join Date: Dec 2012 Posts: 2	Yes they will if given opportunity I recently purchased a pistol shrimp watchman goby pair. They were doing fine until the pistol shrimp decided to make a tunnel under the rock where a large emerald was. Pistol shrimp gone soon after. Then last night my watchman decided to hide in that same rock for the night, this am I found the goby where he was last night but in the claws of the emerald, with his head gone. Last edited by cdsmith; 11/29/2013 at 07:53 AM. Reason: Typo

11/29/2013, 09:10 AM	#17
devimik Registered Member Join Date: Dec 2012 Location: KC, KS Posts: 637	I've had one Emerald in my 90g for almost a year. I've seen him do the waving thing and his claws are strong. I feed him nori using some long tweezers - he usually grabs the tweezers and it is hard to get him to let go. I don't think he could catch and kill a healthy fish and even if one was sleeping, he'd wake it up and it would swim away. Something in my tank has eaten a frogspawn coral and a torch coral. I believe it was the Peppermint shrimp, but I suppose it could have been the crab. My opinion is that the Emerald won't get your healthy fish, but I do agree that if the opportunity presented itself, it would eat anything. __________________ Mike D Coral Beauty, Green Filefish, One Spot Foxface, Springeri Dottyback, 2 Ocellaris Clowns, Yellow Watchman Goby, Flame Hawkfish, Spotted Mandarin Current Tank Info: 90g Softie Reef, 150# live rock, 30g sump w/refugium, Tunze Osmolator 3155 ATO, Octopus NWB 150 Skimmer, Mag 950 return, Maxspect 120w Razor 10K LED light X2, BRS Phosphate Reactor; Apex Lite

02/14/2012, 02:21 PM	#2
RtReef Registered Member Join Date: Dec 2011 Location: Ft. Lauderdale Posts: 603	I don't think they do. I've had a few in my tank and never really saw any aggression, except for their territory.

02/14/2012, 02:25 PM	#3
sporto0 Moved On Join Date: Apr 2010 Location: Pittsburgh, Pa. Posts: 2,924	Don't eat fish per se? Oh they can & will eat anything that is food, including fish, usually what happens is the crab gets a hold of the fish at night when they are hiding/resting. It may not happen for a while, but rest assured it will. I have a nasty Coral Banded Shrimp that has eaten several of my smaller fish. Good luck.

02/15/2012, 02:48 PM	#5
inigomontoya Registered Member Join Date: Sep 2010 Location: Houston Posts: 241	Anyone actually seen an emerald get this aggressive? I know they can be territorial, but big difference in shooing something off and ambushing them in their sleep. The crab is wife's favorite and does add some personality to the tank. However, hate missing fish and can send him to sump if it looks like he is the most likely culprit. Just never seen anything more than a defensive wave off move. And like RTReef had only heard of them as being mellow (versus CBS which I have avoided for exact reason SportOO mentions)

02/15/2012, 03:19 PM	#6
Mr. Demeanor Registered Member Join Date: Jan 2012 Posts: 298	It seems all crabs do the claw wave when they get bigger. I thinks its their version of giving you the finger. I had a good sized hermit that would backhand(claw) the fish when they tried to pick food away from him but he never went after one even though he was perfectly capable.

02/15/2012, 03:42 PM	#7
cjk76 Registered Member Join Date: Dec 2011 Location: Kansas City, KS Posts: 358	I would keep the crab and wait to see if the wrasses turn up. I had an emerald that I loved, but it started eating corals. Seriously, I saw it ripping apart an acan and picking at a leather. I never had a problem with emeralds and fish. Even if the crab did eat the fish, they were likely dead before it got to them. Do you have anything else that would account for the wrasses being dead? A spike in Ammonia? an agressive fish?

02/15/2012, 03:54 PM	#8
ryeguyy84 Registered Member Join Date: Mar 2011 Location: New Jersey Posts: 2,753	I've caught my emerald crab feeding on a fish but to his defense I think the fish died and he was doing his job of cleaning up. it was a flame angel that wasn't doing well for a few days.

02/15/2012, 04:01 PM	#10
insomniac2k2 Registered Member Join Date: Apr 2011 Location: concord Posts: 1,280	I cant imagine that an emerald would kill anything. Mine have always been very docile. Would it eat an already dead fish? Absolutely. It's doing you a favor!

02/16/2012, 11:01 AM	#14
inigomontoya Registered Member Join Date: Sep 2010 Location: Houston Posts: 241	Thanks guys, this ties more into what I had read before on them- having not seen any truly suspect activity (just waving one off) I didn't think it likely, but I don't have anything aggressive in there nor any ammonia spikes or other water parameters. These wrasses were brand new additions so I will lean towards something pre-existing or other acclimation issues. I have 7 scissor tail gobys that sleep in the rock and if anyone was to be caught by an aggressive critter I would expect it to be them and they are all fine. To be clear I never saw him touch a fish dead or alive- just have a couple missing and with the aggression wanted to see if it was a possibility. Will keep an eye on him though.

11/29/2013, 08:08 AM	#16
Crna Registered Member Join Date: Oct 2013 Location: Columbia, SC Posts: 246	We had an emerald in a BC14 that got pretty big really quickly. At least, he seemed really big in that little tank. He started getting cocky, and would reach out at the fish if they got too close. I started to get concerned that we were going to find him munching on my yellow clown goby, so back to the LFS he went. As too the claws, they are pretty tough to pull off of a rock!

11/29/2013, 09:55 AM	#18
Art13 Registered Member Join Date: Sep 2013 Location: South Jersey Posts: 1,444	i've had 3 and all three of them went after my sps coral.

11/29/2013, 10:18 AM	#19
d2mini Registered Member Join Date: Nov 2008 Location: Houston, TX Posts: 10,344	Jeff, I've had lots of red mithrax which is basically the same thing. They do get big and brave for sure. But IME, they won't go after anything that isn't already dead/sick. I do end up removing mine once they get too big because they just annoy my corals too much. They pick at stuff and inadvertently remove polyps, knock stuff over, etc. __________________ -dennis Elos Diamond 120xl \| Elos Stand \| Radion G4 Pros \| GHL Profilux Controller \| LifeReef Skimmer \| LifeReef Sump Photos taken with a Nikon D750 or Leica M.

01/15/2014, 01:21 PM	#21
mayjong Registered Member Join Date: Oct 2009 Location: Sacramento CA Posts: 2,426	i think there may be a difference of experience due to the sex of the crab. males tend to get bigger and seem more aggressive to me. females seem more passive...my .02 __________________ No Tanks... I'm out! still lurking, though...

01/16/2014, 11:38 AM	#22
JB63 Registered Member Join Date: Apr 2007 Location: Chicago, USA Posts: 401	I had an emerald with 3 chromis in a 12g once ... one minute the 3 chromis were swimming, the next, suddenly he's holding one and tearing it apart, one bite at a time.

01/16/2014, 12:32 PM	#23
Reeferz412 Coral Hoarder Join Date: Mar 2011 Location: Miami, FL Posts: 2,247	No they are far too slow. I have owned emerald crabs for about 4 years and they eat anything that comes their way (algae, pellets, frozen food, flake, freeze dried) so I would assume that if you keep them well fed, they really have no need to go after fish. I have had a wrasse jump out and I placed it back but he was gone in the morning, emerald was on top of it and it was a pile of bones lol. __________________ Alex FMAS Member Current Tank Info: 400 Gallons of frags... 30 gallon Deep Blue mixed reef ... 70 other tanks throughout south FL

01/16/2014, 02:57 PM	#25
malcojo Registered Member Join Date: May 2009 Location: Fort Wayne Indiana Posts: 62	I had banned mine to a 10 gallon remote fuge. I also had a Yellow Watchman Goby in there becaue he kept going into the overflow in my DT. I found the goby with a bloody face twice and now he is missing. I checked the foor and he didnt jump out, but I cant rule out going into the sump and through the pump... My emrald got big and cranky quickly.