unknown fin nipper

[chemman1]

I have had two experiences with fish getting their fins nipped off. The tank is a AGA 29g with about 40lbs of carribean LR from live aquaria. All that is in the tank (that I know of) is some hermits, snails and a cleaner shrimp. Twice fish have gotten their fins nipped pretty badly. I dont think the hermits would be doing this. Could it be a crab or what else is known to do this? How come my cleaner shrimp has never had any problems? Any ideas are welcome.

Thanks.

[JimKelly12203]

WHat types of fish do you have in there? I think it's likely that these are fish on fish crimes :)

[chemman1]

Cant be fish on fish. First there was a royal gramma (only fish in at that time) its fin got nipped bad and within a day it was gone. Now I have a lawnmower blenny and I just noticed his fin, he is the only fish atm.

[uscharalph]

Sounds like you've got a hitchhiker.

[masonicman]

Yup you might have an invader that came in on your live rock. CRAB that is

[OliverM3]

What about just stress/water quality?
Fish loose their fins when the water quality is bad.
It would have to be a pretty big/fast crab to catch a fish's fins.

[chemman1]

"Sounds like you've got a hitchhiker."

I agree. I have picked over all my live rock and dont know where anything too big could be hiding. As for water quality I am pretty sure thats not the problem as everyhting else in the tank looks great, hermits, snails, shrimp, zoas, softies and sps.

My guess is some kind of crab but if he can get the fins of fish how does my cleaner shrimp escape him? I have never seen anything wrong with the shrimp.

[OliverM3]

What happened to the royal gramma?
Since you say the lawnmower is the only one in the tank.
I still thinking something is off.

then again could be where the fish was purchased.
I've had a fish go in to a pristine stable tank that was running forever. start loosing his fins because of the shipping stress.

[JimKelly12203]

you should build a trap. I know i've seen such devices described on these forums before.

[chemman1]

I noticed the fin nipped on the royal gramma one day but it wasnt terrible, the next day the fish was gone, never seen again. It was some time after that that i got the lawnmower. Both fish were purchased from a LFS and were in great condition for three weeks before anything happened to either of them. It was not an issue of stress, at least not stress from acclimation or shipping, maybe stress of the hitchhiker variety.

[kawicivic]

does anyone think this could be an mantis?