Please advise: Crabs dying in my tank

[ckpeh]

Hi all,

Need some advise here, my tank (2ft) is up for abt 3 weeks and I found some dead crabs (previously hiding in the live rocks) at the bottom of the tank. the 2 fishes are ok happy swimming. So what's the possible reason(s)for the crabs to die off? Is it the protein skimmer that I install recently (over the weekend)? I only have some star polyps attached with the live rock.

Thanks.

Rgds,

Tom

[X_Japan]

Hi Tom,

to ask ....

did u have a look at the shell??

take a closer look, the eyes may be transparent...

if it is, then the crabs are not dead, it is just that they changed their outer carapace.

that's all

anyway,these crabs are not what u would want to have in your tank.

they will cause an early demise to your fishes if they are rather big in size.......... just a word of warning....

[Stenopus Hispidus]

Alternatively, if they are really dead and not just an empty carapace, then it could be a signal to bigger problems with your water.

Crustaceans are normally the first to react to chemical imbalances present in your water like medication, toxicity from metals, nitrite, etc. Their lives in a way helps you preempt problems. Maybe your water is not matured enough (3 weeks) but definitely their death has got nothing to do with your newly installed skimmer.

Finally, it could also be your fishies who love to savour a delicacy of raw crab beat in brine.

[Phang]

Or to add on,

MANTIS SHRIMPS....

I find dead bodies of crabs once in a while on my sand bed... many times mutilated.....

Well, at least there some use to having a Mantis in my tank.....

[hongqixian]

Since you had live rock, the hitchhiking crabs along on it probably died during the cycling period, because you said that your tank was only 3 weeks old. A guess of mine.

[Bluebeard]

actually i find those crabs nice! i like to keep crabs you see.

yes i agree that if those crabs are dying, something might be wrong with the water. mostly likely is not cycle enough.

[ckpeh]

Thanks people for the prompt reply.

justy saw them climbing the day before. They are really small and I don't think they harm the few fishes I have thus I kept them.

I check the Ammonia, Nitrite and PH. All seems ok.

How about Nitrate? Any impact? I need a test kit for that.

Rgds,

Tom

[derf]

from wat i understand, crustaceans are v sensitive to high nitrates. do a test on ur nitrate levels.

[ckpeh]

Any way to control or reduce nitrate level? Bio or mechanical? ...

Tks.

[Tanzy]

Bio = Deep sand bed or plenum by Natural Nitrate Reduction(NNR); or macroalgae refugium; or less livestock; or less feeding.

Mechanical = Good protein skimmer; maintenance of system to prevent buildup of detritus.

[Norvin Ng]

Crabs when small are cute, but not when they grow from 1 cm to 5 cm in a few months!!! I have lost a couple of smaller fishes over a few days after buying them!! Have been trying to catch it but its always hiding within the rocks. Actually hoping it will die off suddenly!!

[ckpeh]

Hi people, thanks for the reply.

Tested the nitrate, level not high at all. Still wondering what kill the two crabs.

[hongqixian]

Your tank can't have high nitrates, its 3 weeks old!! When your tank cycled with Live rock, the ammonia and nitrite levels must have peaked, right? So that killed off the crabs because they have been sitting there all the while. But I think you're lucky because I'm a rock crab murderer too.

[Achilles Tang]

I consider all crabs as not reefsafe.... KILL THEM ALL!!!!

j/k.

Actually, there are only two species of crabs with are reef-safe... they truly are vegetarian... one is the Emerald crab, the other I forgot!

Even some species of hermits eat tubeworms and disturb coral polyps.

[hongqixian]

Some emeralds take a fancy to Xenia. The other crab is the sally lightfoot- atlantic and the pom-pom/boxing crab is also reef safe.

[Norvin Ng]

Spent two hours catching my crab yesterday and found two instead. The bigger bugger (was a cute one when its was 1 cent size) is my suspect that was eating one of my coral (and a few smaller fishes). It was also trying to drag one of my coral branch into the rocks when I got home yesterday!!!!

Rock arrangement was completely "re-arranged" in the process!!!

The only crab I like now is the black pepper crab that my in-laws will be buying for dinner tonight!!!

Trust me, keep your crabs and a few months later, you will be posting - how to catch my crabs"!!