Strange fish death

[sigshane]

So I had a recent cycled 90-gallon FOWLR, with the following residents:

1 maroon clown
1 keyhole angel
1 convict tang
1 orchid dottyback
1 chocolate chip star
Several small snails

So I added, at the same time, 4 green chromis, and a decorator crab.

Within two days, tang was dead, Angel dead, one chromis dead, one missing, dottyback dead, and the remaining chromis and clown hiding like Hell!!

Checked water parameters, everything seems perfect.

So on a hunch, I removed the crab to the sump, and after only a couple hours, the remaining fish were back out and around, like normal.

Did the decorator crab go on a terror spree in the tank, do you think?

I want to start replacing the (allegedly) murdered livestock, and an wondering if the crab should ever go back in the display tank, or just back to the store.

Thanks in advance,

 

[porpoiseaquatics]

This should probably answer your question:


Quick Facts :: Spider Decorator Crab
Care Level: Easy
<span style="color: SandyBrown">Temperament: Semi-Aggressive</span>
Maximum Size: 4"
<span style="color: Red">Diet: Carnivore</span>
Aquarium Level: Substrate & Rocks
Minimum Tank Size: 12 Gallons
Reef Compatible: No
Water Conditions: 72-78&#65533; F, dKH 8-12, sg 1.020-1.025, pH 8.1-8.4
Supplements: None
Coloration: Brown, Tan, Orange
Origin: Indo-Pacific
Family: Majidae

 

[jennm]

How long did you have the fishes that died? And when you retrieved the bodies, did they have any symptoms? (Either before or after..)

If the missing chromis died, the crab OR the sea star would have eaten them - or so would worms or other small fauna.

How large is the decorator crab? In a 90, usually fishes could stay well away from even a fairly large crab.

I think the crab *may* be a victim of circumstance. Yes it's possible for it to pick off sleeping fishes, but usually with bigger specimens like an angel or tang, you will see fin damage where the crab picks at the fish while it's hiding/sleeping but usually the fish can get away.

Were the bodies you did find, chewed up?

Edit: If it's one of those decorator Arrow crabs (per Jeff's post above) it's quite possible that it went on a killing spree.

I had a regular Arrow crab pick about 5 chromis out of the water column and stack them up in a pile once. I intervened when he was reaching for another as the dwindling school swam by it again.

Jenn

 

[sigshane]

For the most part, no signs of a struggle, I'm just dumbfounded as to what could have caused this. Nothing surely points to the crab, except the way the surviving fishes seemed to relax when I took the crab out...

 

[jennm]

I can see the fish being nervous about the presence of the crab but if they weren't tattered at all, then he likely didn't kill them. There would be damage - touching them doesn't kill them, impaling/pinching them etc., kills them.

How long did you have the fishes that died?

And what are your parameters?

 

[stacy22]

Did you QT the newcomers?

 

[miami dolfan]

I once had a similar situation. I bought an unknown crab and fish started dying. I was anle to determine that it was the crab because the fish bellies were always gutted out and the fins were chopped off.

 

[jennm]

Right - and there are the telltale signs of predation - gutted fish. Predators will usually eat the gut first.

If the fish died but had no signs of trauma, it's likely for some other reason.

Jenn

 

[jp30338]

Had this haapen to me when I setup my 90 in October last year. Turned out to be stray voltage from a powerhead. One night the gfi kept tripping and narrowed it down to a powerhead. I immediately replaced it and no deaths since.