Help me figure out what's eating my fish?

[MichelleRay]

I have come to the conclusion that something nasty hitchhiked in on my Florida live rock. The pieces were only a max of 6 inches across so it may have come in as a baby, but either way I'm down 2 fish now. First was a 4" tang, now a diamond goby. My two clowns are still fine and my tailspot blenny is fine. Note that the blenny sleeps in a 'treehouse' of a little hidey hole I hung off the side of the tank that sits about 3 incches below the top. I suspect that is why he is still alive. That small amount of live rock is the only thing wild I have put into my tank.

Total missing things:
1 4" tang
1 3" diamond goby
multiple large snails (shell and operculum all that remained)
multiple small snails
multiple hermit crabs
1 brittle star ~hand sized

Urchins have not been touched. Clowns have not been touched. Peppermint shrimp have not been touched. Coral may have been bothered but that may have been the microalgae and shrimp harassing them. I'm not certain.

In both cases when the fish went missing they vanished completely. Not a trace has been found on the floor or in the filters/tank. No scales, no bones, absolutely nothing. It's like they jumped out and walked away. Whatever is killing them is either swallowing them whole or burying them.

Of note, I ordered from the same website once before about 2 years ago and got a bobbit worm that subsequently destroyed my tank. I have a suspicion I may have gotten a second one. I refuse to just tear down my tank this time though. If I have to I will throw out every piece of rock in the tank and buy more, but I would really rather not have it come to that. Any suggestions on how to confirm the worm or ideas on what else it might be?

 

[*K&AreeFers*]

Might also be a mantis shrimp they have been known to eat fish. Do you hear any noise like clicking if so could be your culprit. Taking out the rock and closely inspecting it might be the only option to save further fish

 

[MichelleRay]

I haven't heard any clicking but I have an air filter running in the same room that would mask softer sounds. Is it possible for them to hide for 6 months? That's about how long I've had the rock I think.

 

[cracker]

Maybe set out a bait of some sort & peek every so often after lights out? Iv'e gotten rock form tbs several times ,both I got a pretty small reddish Mantis. Is there a lot of rock for it to hide. would it have to be a pretty good size to devour a 3 inch goby let alone a tang also. I'd think the snails an various crabs would point to a mantis. A Bobbit worm? How much of a sand bed do you have?
Very interesting !

 

[ThunderGoose]

Yes, a mantis can hide for months, especially if she was small when you first got the rock. I got two mantis from my TBS live rock and the first showed up after about 4 months, the second one was around 6 months. Neither was the kind that go after fish, though.

Are the snail and hermit shells damaged or whole? If they're whole I'd look elsewhere for a culprit. Are you sure it's not something other than a predator? A good clean up crew will clean up dead fish before you even notice they're missing.

 

[Fishfinder]

How big of a tank is it?
How much sand and rock do you have?
How many snails and crabs do you have and how many are dead?

 

[MichelleRay]

It's a 55g rectangular. Sand bed is about 1.5 inches on one side tapering down to about a half inch on the other side. Not many crabs, maybe 10 or so surviving. One porcelain and one emerald used to live in there but I haven't seen them in a while so I've no idea if they're around. The rest are white, red, and blue legged hermits. Also 2 mysis shrimp that came in with some pods and apparently like it in there. snails wise its hard to say. I'd guess about 10 - 15 mediums. I bought 100 tiny guys but I've no idea how many are still alive. I know some have died so I'd guess maybe 75 living but its just a guess. I had a very big snail in there too but I founds its shell and operculum recently. When the tang vanished I had 5 peppermint shrimp living in the tank but they've since been relocated to an external 'fuge' type thing because some of them were jerks.

The shells have all been intact. No holes or nicks in them.

I've tried checking the tank after the lights have been out a few hours and so far haven't seen anything amiss.