# Other Aquarium Forums > Marine Tanks >  Are crabs reef-safe?

## setiardi

Me saw more than 10 crabs from 1cm - 2cm size in my reef tank (2x2x1.5ft).Most probably got them from my liverocks. At night can hear them clicking frequently and when I use my flashlight I can see them. Don't know species but if not safe for my corals and fishes I got no problem removing them. Maybe no wonder my cleaner shrimp disappear the next day - that was last month.No courage to introduce the shrimps since.

----------


## LiveRock

Me also have crabs inside my pico-tank. I think I counted 2 brown-spotted crabs and 1 hairy white crab, and 2 porcelain blue spotted crabs. So far, they are harmless to all my fishes. These crabs have grown by molting a few times as I see their discarded shells quite often.
Unfortunately, recently my cleaner shrimp also disappear after a few days...
when it came, it was very shy and stayed at the top of the tank. It molted the 3rd day with new shell and antenna. Maybe it became more confident and went down behind the rocks to venture. That was the last time I saw it. I thought it might be hiding to wait for its shell to harden but its been 4 days and I still have no sight of him.. I guess the crabs decided to have him for supper ( a lobster supper perhaps)

----------


## kelstorm

well.. for me, whenever i see crabs.. i usually take them out if possible, if not, i use a pincer to crush them in their hideout.. to me, a good crab is one that is on my dinner plate.. done in chilli or pepper... [ :Grin: ] yes.. they are very safe when they are young.. but as they grow.. they tend to get destructive and will prey on your fishes....

----------


## Tigger

Reminds me of black pepper crab......Yummy!

----------


## Killerwhale

Few days ago, I witnessed one of the crab (about 20 cents size) ambush my samll hermit crab (zebra hermit) and dragged it into his hole. Luckily I managed to distract the crab and my hermit was free. 

Can anyone suggest a 100% safe way to catch them out of the tank without disturbing the infrastructure of the landscape ?

----------


## Spiff

off all the lights. wait for 1 hour or 2. use a red light can check for the crabs.they cant c the red light(tts wat the US ppl say). then can jus use a forceps to pluck them out.

----------


## kelstorm

what i do is off the lights, then wait for a while.. try to see where they located and pierce them.. unless they are hiding under the corals.. if so, remove the rock to catch them.. i dun know abt the red lights though...[ :Grin: ]

----------


## nivlac

I removed almost all the crabs from my system. Crabs are not 100% reef safe. They will eat the critters from your sand bed (bad if you're running a DSB), ambush your fishes (bad for fishes that retreat into crevices- a royal gramma of mine got buggered this way).


One way to trap them is you could use a purpose built trap (I bought a $30 Mantis shrimp trap from Hong Leong that could be used for this purpose). Alternatively, use a brands' chicken essense bottle or Heinz baby food glass bottle (can buy at about $1.30 each). Bait it with some prawn or fish meat and leave the bottle next to some rock the crab can access. It can enter, but then cannot escape and all you need to do is to scoop up the bottle and dispose of the crab

----------


## kelstorm

that is an excellent idea, alvin.. [ :Grin: ]

----------


## LiveRock

hello

would u explain how the crabs are able to get IN the bottle and UNABLE to get OUT?
Is there some kind of trap door, etc.

thank you very much...

----------


## nivlac

Liverock- good question. The are able to get into the bottle cos they can slide down the bottle from the rock....but unable to climb out cos the glass wall of the bottle prevents them from getting traction to climb up. Somemore, the walls of a brand's chicken essense bottle is quite high for a normal stone crab found in liverock. Unless you got a monster sized crab  :Smile: .....

----------


## LiveRock

oic! So you put the bottle standing up; letting the fellow slide in but can't climb up.
very clever!

----------


## yazid

I got lots of crabs when I first started my reef. It came through the live rocks. After a few fish dissappear, I got really frustrated and started to do crab hunting. Basically, removing the live rocks one by one and removing all the crabs from it. I got around 40 plus small and big.

After almost a year, yesterday I saw one SUPER WHITE VERY HAIRY BIG crab. [:0] So far no missing fish, so I'll let that crab free.

Someone could have told me about the bottle trap, or I wouldn't have redecorated the tank. [ :Grin: ] 

Regards

----------


## LiveRock

I also got the white hairy crab... I named it 'Ting Hai' in Cantonese; which was the name of a popular HK movie abt stock markets...  :Smile:

----------


## kelstorm

After almost a year, yesterday I saw one SUPER WHITE VERY HAIRY BIG crab. 
*hairy crabs.. yum yum.. the hongkongers love it.. []*

----------


## coelacanth

If u wanna remove crabs from a reef tank, use octopus. very effective. :Smile:

----------


## Mez

Wouldn't an octopus eat all the fish too?
Mez

----------


## kelstorm

IMO, i dun think octopus is a good idea.. for small crabs.. u can consider using bird wrasse.. octopus will not prey on crabs alone.. fishes too.. so.. pls ponder on that..

----------


## coelacanth

True, octopus eat ornamental shrimps too... but seldom fish, wat i do is to place the liverock and octopus together in the quarantine tank for a week, then the LR in the display tank. 

Bird wrasses are some destroyer of reef tank, equally dangerous to shrimp as well as other fishes...must consider. :Smile:

----------


## LiveRock

Hello

IMO, I find using one animal to consume another in order to get rid of the latter is not entirely a good idea.... 

I will worry abt what is going to happen to the predator when all its prey are eaten up?
Will the predator starve? Must I supply it with its natural food (prey)? Thus, the cycle begins...

One exception I think are the algae grazers; algae are nuisance and their food are light and unwanted nutrients..

 :Smile:

----------


## kelstorm

coelacanth,
hahah.. i do agree that bird wrasse can be destructive when adult size.. but as i dun have reef.. so, it still pretty ok.. using octopus is fine.. just make sure that it is not blue-ring.. very dangerous.. and the holding tank is escape-proof...


Liverock,
_IMO, I find using one animal to consume another in order to get rid of the latter is not entirely a good idea.... 

I will worry abt what is going to happen to the predator when all its prey are eaten up? 
Will the predator starve? Must I supply it with its natural food (prey)? Thus, the cycle begins..._ 
*yes.. i agree that using another animal to consume another is not really a good idea.. in my case, when i had the bird wrasse, it did the removal job for me and strive on tetra bits too.. they will consume anything.. but u have to consider the bio-load increase.. the alternative method would be to manually remove the crabs.. tedious..*

----------


## coelacanth

but sad to say, manual removal is not possible as they'll somehow hide somewhere.

i quite agree with you that meddling with food chains are not appropriate, but thats life. fish keeping by itself is a chain breaking activity... [ :Embarassed: ]

----------


## coelacanth

sorry for that multiple posting. something wrong with my computer.

----------


## kelstorm

what multiple post??? [:0]

----------


## coelacanth

i posted the same reply few times but i tink its deleted.

----------

