Mystery fish killer?

[spanky]

I have a month-old 150 gallon tank. I started with good water and Kent's salt complex. I have a wet/dry filter in sump. After the system was up and running for a few days I started adding cured live rock from a reputable lfs. I now have about 40 pounds of live sand and 100 pounds of live rock, about 30 pounds of which came aout of a healthy five year old tank. I seeded the system with bacteria as I added a clener crew and fish.
I have added:
20 hermits
30 snails
3 yellow tail damsels
2 domino damsels
2 striped damsels
3 blue green chromis
2 dotty backs
1 small patch, 2"x 3", of coral
I feed frozen every other day - just enough so they feed vigorously for 2-3 minutes, then it's gone.
Water parameters seem perfect:
no amonia, no nitrates, no nitrites
phosphates very low
Ph 8.2
water temp 82 degrees
The diatom bloom came and went last week.
The two domino damsels died - don't know what happened to them. They looked great...then one was missing. Two days later, the other didn't show for chow.

Then, a week later, one of the stripped Damsels was missing in the morning. The same thing happened with a chromis a few days after that. If I didn'y know better I think they were getting eaten at night...
Then, yesterday, I saw my last stripped Damsel looking rough. It looks like he has been bitten... There is a small, round patch of flesh visible on his side and he's having trouble swimming. He seems prone to float...he'll rise up, then struggle to swim back down...then the cycle repeats. There is also a 2.5 inch filament trailing behind him. It's the thickness of a hair.
Any ideas?

 

[tthemadd1]

The dreaded, although, pretty cool, mantis shrimp?

 

[bigarn]

Did you find any remains of these fish or were they just gone? If no remains were found, or any remains looked chopped up, there's a very good chance you have a mantis. Do you ever hear a clicking noise in the tank at night?

 

[mr_bill]

Originally Posted by tthemadd1
The dreaded, although, pretty cool, mantis shrimp?
I've actually caught a few of these in the wild while fishing for sea bass drifting across a sandy bottom. They are one mean critter and before I knew what they were my friends and I just called them devil shrimp. About 1 foot long and very colorful when full grown.

 

[trainfever]

What is killing your fish is your fish. 10 of your 12 fish are damsels. It is OK to have Damsels of the same family in the same tank but when you start mixing them, they are going to fight. Damsels are very territorial and extremely aggressive. You should stick with one family of Damsels and return the others. You're not finding dead fish because the clean up crew is doing its' job.

 

[mr_bill]

Originally Posted by Spanky
There is a small, round patch of flesh visible on his side and he's having trouble swimming. He seems prone to float...he'll rise up, then struggle to swim back down...then the cycle repeats. There is also a 2.5 inch filament trailing behind him. It's the thickness of a hair.
Another damsel can do this? sounds like a predator to me.

 

[trainfever]

Yes, they can do it. I put a Royal Gramma in my tank the other day and in less than two hours, my yellow tail damsel had bitten off better than half of the Grammas' tail fin.
Needless to say, one of them has to go. So for the time being I was able to catch the Gramma and he is residing in my refugium until I can catch the damsel.

 

[tthemadd1]

Good luck catching that Damsel. I have had the same yellow tail in my tank since i set it up. The LFS said they were peaceful and arent aggresive. Ill never catch that fish...... :hilarious

 

[teen]

u might have a bacterial infection which is causing ur fishes flesh to decay, and that looks like the fish has been bitten. ur clean up crew may be taking care of the dead fish by dragging them under rocks and then eating them.

 

[spanky]

Thanks gang.
There is no clicking noise, so I guess that rules out the mantis. (I looked them up here. They're a pretty cool looking customer - and a pretty scary critter to have in your tank.)
I got a chance to speak to the experienced guy at the LFS today, and he guessed aggression too, although a parasitic or bacterial problem remains a possibility. He suggested a "wait and see" attitude, since the remaining fish look healthy. If it's bacterial or parasitic, can I expect the other fish to start showing symptoms quickly?
Removing the Damsels would be impossible with all the rock in place. They're incredibly fast little guys.
I want to start adding inverts, but I am nervous about doing that in case the tank needs to be treated. I guess I'll just sit tight for a week or two.

 

[slock]

I had a mantis for 3 weeks, never heard any clicking. I happened to briefly catch glimpses of his eyes pearing out from a whole a couple times. I put a raw shrimp on a fishing line down on the sand in the bottom, shut off the lights, and checked a couple of times. finally saw him, catching killing was another story. just happened to see him go under a piece of rock that had fallen and was laying in the sand bed, took a huge net and scooped the rock and 2 inches of sand, must have weighed 5 lbs, brought it to the sink, and behold...Mantis.

 

[ophiura]

IMO, you have few fish in a very large tank. Sure, you don't have a lot of LR - are they all hanging around it? But that makes aggression, IMO, a little less likely unless you are seeing blatant aggression during the day with lights on. Is there lots of chasing and nipping going on? Do the current fish have intact fins? Are any hiding up in the corners of the tank?