Emerald Crab Kill Our Small Fish ?

[427HISS]

We've had three fish die in our 14g quarantine tank in a week.

The last today, which was our blue damsel. He was swimming very well and ate about 3 hrs ago, then just found him dead.
We added a Emerald Crab three weeks ago.

The detrimental water parameters are fine.

Ammonia, Nitrite are 0
Nitrate 15 (no skimmer or media)
PH 7.9

With years of experience behind us, I failed to understand what has happened.
The only thought is the crab killed them, even the tough damsel.

 

[Tahoe61]

I would have suspected a large emerald but I sure would not rule it out. Remove the emerald, you may not have enough of the right types of algae to keep it well feed.

 

[427HISS]

He's actually pretty small, maybe a dime size, and we really enjoy feeding him, so I don't know if that's the reason ?
The damsel was apx 1.5".

 

[Ozzy]

In my experience the only trusted crab I will keep in my reef are very small hermits and anemone crabs. I had an emerald crab at one point start trying to catch fish..wish I would have caught it on camera..but that was before these fancy smartphones lol. My favorite crabs are the sally lightfoots...but man..they are terrors as well.

I would say remove him, do a few water changes to get those nitrates down as well, depending on how you acclimate..that could possibly be an issue? Never really have had to deal with nitrates all that often (OCD sometimes on waterchanges haha). Good luck with whatever you do!

 

[427HISS]

Yep, he's gone tomorrow to a local fish store !
The nitrates are pretty low for this fish only quarantine tank, as it's not a reef with corals. It is possible that the damsel killed the two other small fish last week, but we never seen any aggression out of him and they were killed during the day, not at night, but with Damsels, you never know. Maybe the crab killed him today ?

 

[wrasseluver]

What time of water flow do you for gas exchange? I find it hard to believe that crab killed a healthy fish. I would say low O2 levels would cause a fish to die that fast.

 

[427HISS]

The tank is the Oceanic BioCube 14g. Good flow with the return pump and a new Jebeo WP-10 for circulation. If it was bad gas exchange the fish would show signs. I don't have a oxygen test, but out of curiosity I may buy one, but very doubtful it's the cause.

 

[wrasseluver]

Well I had this happen to me. Fish looked fine and eating came back a few hours later they were died. Found that the skimmer was off and had a few fish that died. The remaining fish were hiding and as soon as I turned on the skimmer they came out.

 

[wrasseluver]

Oh I did have 2 MP40 that were moving water in the tank plus a 1200 gph return pump.