Who dunnit? Prime suspect emerald crab???

awall · 07/06/2014, 05:05 PM

About 10 days ago I added a royal gramma to my reef tank. After that first day I never saw it again. I figured it had either died upon introduction or was hiding in a live rock cave, I had read that they can sometimes hide for long periods.

Yesterday I found half of it floating in my tank. Looked to me like it had been alive until recently and that something in my tank had perhaps attacked and killed it.

Currently the tank is stocked with the following:
Snails, hermit crabs, 3 emerald crabs (1 male, 2 female), spiny urchin, salmacis urchin, 2 percula clown fish, 4 benji cardinalfish, 1 starry blenny, 1 firefish goby, 1 dragon goby, 2 peppermint shrimp, 2 skunk shrimp, and 1 blood shrimp.

None of the other livestock in the tank seems like it would kill a royal gramma, I am beginning to suspect the male emerald crab, he was introduced to the tank to control the initial algae bloom and has gotten quite large since then. I have also seen him hanging around my galaxy coral at night which make me suspicious he may start eating it as well. I do feed algae pellets and waffers into the tank and had hoped this would keep him feed and prevent him from eating corals or fish.

Just wondering if anyone could confirm that the royal gramma appears to have died recently and had been attacked from the photo attached. I have been told the eyes of the fish can indicate how long it was dead for.

Also wondering if anyone could confirm the emerald crab is the most likely suspect if the royal gramma had been killed recently.

I currently have the male emerald crab removed from the tank, I don't really want to get rid of him, however I don't want to loose any more fish or coral. Should I keep him out now that he has been removed?

Odysi · 07/06/2014, 05:14 PM

Crabs are opportunistic eaters the gramma could have died and the crab just found a free meal, but unless you seen him grab the fish it's hard to say.

HumbleFish · 07/06/2014, 05:19 PM

How did you acclimate the RG to your DT, and was he QT'd beforehand? IME; RGs are a lot more sensitive to changing water chemistry and diseases than most people realize. If he didn't adjust to your tank properly, was weak or dying somewhere; then yeah, I can see an opportunistic emerald crab turning him into a midnight snack. It also doesn't help that RGs usually live/sleep in little hidey holes, and emerald crabs like to scavenge through those rocks at night. Ambushes are bound to happen.

Gunsnroses · 07/06/2014, 05:22 PM

I have two large Emeralds in my tank with 10 other fish, including a Royal Gramma. My Emeralds don't even notice the other fish. I have Wrasses that sleep under some of the same rocks the Emeralds scavenge around.
So I would have to go with them eating the fish after it had perished based on how mine interact with other fish.

AZBigJohn · 07/06/2014, 06:01 PM

I have heard of larger emeralds taking smaller fish, but never seen it, and I would think the fish would need to have been quite weakened for it to have happened.

I second the theory that the RG may have perished, and been fed upon afterward... That is, after all, why we have the Clean up crew...

Mcgeezer · 07/06/2014, 07:36 PM

The gramma could have already died. Because dead fish = dinner bells to all crabs

Being that he's chopped in half is a good sign he was already dead. Your emerald doesn't look big enough to latch on without the fish putting up a fight to get away.

awall · 07/06/2014, 09:48 PM

Thanks all for the replies,

I did think it was most likely the case that the fish got ate after it died. However the fact I didn't find it for 10 days and the lack of decomposition lead me to believe that the royal gramma had survived the initial introduction into the tank. Perhaps the fact I didn't see it at all might indicate that it could have starved to death as well.

That combined with how fast the male emerald crab has grown and the issues I have heard some people have with them made me nervous, as well as seeing him hanging around the coral.

Guess he'll get a second chance and go back in the tank, under very close watch.

07/06/2014, 05:22 PM	#4
Gunsnroses Registered Member Join Date: Nov 2013 Location: Pleasant View TN Posts: 421	I have two large Emeralds in my tank with 10 other fish, including a Royal Gramma. My Emeralds don't even notice the other fish. I have Wrasses that sleep under some of the same rocks the Emeralds scavenge around. So I would have to go with them eating the fish after it had perished based on how mine interact with other fish. __________________ He who gets frustrated with freshwater tank, Never owned a Reef tank Current Tank Info: 180 gallon RR-75 gallon sump-50 gallon Refugium-RO Diablo DCS 200 Skimmer-Diablo 10500 and 5500 return pumps-Spectrapure MaxCap 90gpd

07/06/2014, 06:01 PM	#5
AZBigJohn Usually confused... Join Date: Jun 2012 Location: Phoenix, AZ Posts: 1,091	I have heard of larger emeralds taking smaller fish, but never seen it, and I would think the fish would need to have been quite weakened for it to have happened. I second the theory that the RG may have perished, and been fed upon afterward... That is, after all, why we have the Clean up crew... __________________ John Current Tank Info: Currently a 29 gallon all-in-one frag tank and a 210 gallon tank slowly becoming my dream system!

07/06/2014, 05:14 PM	#2
Odysi Registered Member Join Date: Jan 2014 Location: Brooklyn, NY Posts: 401	Crabs are opportunistic eaters the gramma could have died and the crab just found a free meal, but unless you seen him grab the fish it's hard to say.

07/06/2014, 05:19 PM	#3
HumbleFish Moved On Join Date: Feb 2013 Posts: 4,757	How did you acclimate the RG to your DT, and was he QT'd beforehand? IME; RGs are a lot more sensitive to changing water chemistry and diseases than most people realize. If he didn't adjust to your tank properly, was weak or dying somewhere; then yeah, I can see an opportunistic emerald crab turning him into a midnight snack. It also doesn't help that RGs usually live/sleep in little hidey holes, and emerald crabs like to scavenge through those rocks at night. Ambushes are bound to happen.

07/06/2014, 07:36 PM	#6
Mcgeezer Reef gardener Join Date: Jan 2014 Location: DeLand, Florida Posts: 1,205	The gramma could have already died. Because dead fish = dinner bells to all crabs Being that he's chopped in half is a good sign he was already dead. Your emerald doesn't look big enough to latch on without the fish putting up a fight to get away.

07/06/2014, 09:48 PM	#7
awall Registered Member Join Date: Apr 2014 Posts: 14	Thanks all for the replies, I did think it was most likely the case that the fish got ate after it died. However the fact I didn't find it for 10 days and the lack of decomposition lead me to believe that the royal gramma had survived the initial introduction into the tank. Perhaps the fact I didn't see it at all might indicate that it could have starved to death as well. That combined with how fast the male emerald crab has grown and the issues I have heard some people have with them made me nervous, as well as seeing him hanging around the coral. Guess he'll get a second chance and go back in the tank, under very close watch.